Yellow spots on pumpkin leaves

Diseases Of Pumpkins: Learn About Pumpkin Diseases And Treatments

Whether you are planting pumpkins for eventual carving with the kids or one of the delicious varieties for use in baking or canning, you’re bound to encounter problems with growing pumpkins. It might be an insect invasion or some other critter munching on the pumpkins, or it may be any one of a number of diseases of pumpkins threatening your crop. Pumpkin disease identification is of primary importance when treating pumpkin diseases. The following article contains information on pumpkin diseases and treatments.

Pumpkin Disease Identification

It is important to identify as soon as possible any diseases affecting the pumpkin crop. Early detection will enable you to treat the symptoms early on and, hopefully, save the crop. It is helpful to not only recognize the symptoms of infectious diseases but also to know how they spread and survive. Diseases afflicting pumpkins may be foliar in nature or diseases of the fruit. Foliar disease often opens the plant up to other infectious diseases as well as sunscald.

Pumpkin Diseases and Treatments

Foliar diseases of pumpkins commonly afflict pumpkin crops. Powdery mildew, downy mildew, white speck (Plectosporium), gummy stem blight and anthracnose are the most common foliar disease culprits.

Powdery mildew

Powdery mildew looks exactly like what it sounds like. First seen on the lower leaf surface, powdery mildew is a white “powdery” covering of spores that move from the lower leaf surface to the upper, eventually defoliating the pumpkin plants. Spores survive among the soil and crop residue, and are dispersed via wind.

It is one of the easiest diseases to identify and unlike other foliar diseases, tends to increase in severity during periods of dry weather. To combat powdery mildew, rotate with non-cucurbit crops and treat with fungicide at the first sign.

Downy mildew

Downy mildew is seen as lesions on the upper surface of the foliage. Initially, the lesions are yellow spots or angular water soaked areas. The lesions become necrotic as the disease progresses. Cool, wet conditions foster this disease. Again, the spores are dispersed via wind.

Broad spectrum fungicides are somewhat effective against downy mildew. Planting early season varieties can also reduce the chances of downy mildew infiltrating the crop, as the disease is generally more common late in the growing season when conditions are cool and rains are more likely.

Anthracnose, White speck, Gummy stem blight

Anthracnose begins as small, light brown spots outlined with a darker margin that expands as it progresses. Eventually, the leaves develop small holes and fruit may show lesions as well.

White speck, or Plectosporium, also appears as tan spindle shaped lesions on the surface of the leaves. Fruit can become afflicted, showing tiny white spots that are more circular in shape than the diamond shaped leaf lesions.

Gummy stem blight affects most cucurbits and is caused by both Didymella bryoniae and Phoma cucurbitacearum. This disease is most common in the southern United States.

Fungicide applications at the first sign of any of these diseases will aid in reducing and combating them.

Additional Disease Problems with Growing Pumpkins

Black rot

Black rot caused by Didymella bryoniae, the same fungus that causes gummy stem blight, and results in large gray blotches on the fruit that become black rotted areas. Warm, humid summer nights favor black rot. Spores are dispersed through water and wind.

There are no disease resistant varieties. Treating this pumpkin disease with cultural control alone is insufficient. Combine crop rotation, planting of non-susceptible crops, fall tillage and fallowing areas with a history of the disease with chemical control. Fungicides should be applied in 10- to 14-day intervals beginning when the vines have a heavy canopy of leaves.

Fusarium crown rot

Although the names are similar, fusarium crown rot is unrelated to fusarium wilt. Wilting is a sign of crown rot along with yellowing of the entire plant. Over a 2- to 4-week period, the plant eventually decays. Leaves will be marked with water soaked or necrotic areas while fruit symptoms vary, depending upon the fusarium pathogen.

Yet again, the spores survive in the soil for long periods of time and are spread through the use of farm equipment. There are no disease resistant varieties. Crop rotation will slow the fusarium pathogen population. There are no chemical controls for this disease.

Sclerotinia rot

Sclerotinia rot is a cool season disease that affects many types of vegetables. The pathogen produces sclerotia that can survive in the soil indefinitely. Cool temps and high relative humidity foster the development of a white, cottony mold around water soaked infected areas. Black sclerotia grow among the mold and are the size of watermelon seeds.

The whole plant, including the fruit, rots. Spores are spread through wind. There are no disease resistant pumpkin varieties. Fungicides can be effective if applied to young plants.

Phytophthora blight

Phytophthora blight is a serious disease caused by a fungal pathogen that can reside in the soil indefinitely and spread rapidly. Primary symptoms can be viewed on the fruit and spreads to the vines. A soft rot combined with an expanding area of white, cottony mold is seen. It also afflicts many other crops.

Phytophthora blight is most severe when late summer is cool and wet. Spores are dispersed through water splash, wind, and equipment use. There are no disease resistant varieties of pumpkin. Crop rotation may reduce the severity of the disease for future crops as well as avoiding planting in soil that drains poorly or tends towards standing water. Fungicide applications can reduce losses.

Bacterial fruit spot

Bacterial fruit spot is common amongst pumpkins and other fall squash. It presents as small lesions on the fruit. The foliage does have small, dark, angular lesions but they are difficult to detect. Fruit lesions occur in clusters and are scab like. They enlarge, becoming blisters that eventually flatten.

Bacteria are spread in infested crop residue, contaminated seed and water splash. Rotate crops with non-cucurbit crops. Apply copper spray during early formation of the fruit to reduce the incidence of bacterial fruit spot.


There are also a number of viral diseases such as cucumber mosaic virus, papaya ring spot virus, squash mosaic virus and zucchini yellow mosaic virus that can afflict pumpkins.

Foliage of virus infected plants tend to be mottled and distorted. Plants that are infected early in development or near or before the bloom time are most seriously affected and produce fewer fruit. Fruit that does develop is often misshapen. If the plant is infected once the pumpkins have attained full size, there is rarely any effect on the quality of the fruit.

Viruses survive in weed hosts or are spread via insect vectors, usually aphids. Late pumpkins have a greater chance of becoming infected with a virus, so plant early maturing varieties. Keep the area weeded to reduce the chance of infection.

Bacterial diseases of pumpkins: An old enemy and an emerging bacterial disease

Bacterial diseases were present in pumpkin fields in the 2014 growing season. In Michigan, the most common bacterial disease in pumpkins is angular leaf spot. However, bacterial leaf spot, a different disease, is emerging in the Midwestern United States. Understanding the similarities and differences between angular leaf spot and bacterial leaf spot can help you manage them better and prepare for the 2015 growing season starting this fall.

Angular leaf spot (ALS)

Most growers are familiar with the symptoms of angular leaf spot caused by Pseudomonas syringae pv. lachrymans. Characteristic symptoms of ALS in cucurbit foliage (cucumber, melons, squash and pumpkin) are irregularly-shaped lesions that are water soaked when young, and bleach to gray as lesions expand. The center of the lesion becomes brittle and breaks, leaving a “shot hole” on the leaf surface. Early lesions on the fruit are water soaked and oval to circular (0.04-0.2 inches) in shape. Under humid conditions, bacterial exudates can ooze from the lesions in leaves and fruits and when dry the exudate looks like a whitish residue.

Angular leaf spot symptoms in pumpkin leaf. Photo by Lina Rodriguez Salamanca, MSU Extension

Pseudomonas syringae pv. lachrymans is seedborne, specifically associated with the seed coat, therefore infection occurs as early as early as cotyledons emerge. This pathogen is dispersed by rain. Insects, machinery, labor clothing and hands can also aid plant-to-plant dispersal.

This bacterial pathogen can be found in irrigation water. Overhead irrigation represents not only a high risk for the potential introduction of the pathogen in the fields, but also can create extended humidity periods conducive to disease development. The bacterium can survive winter associated with plant debris.

Bacterial leaf spot (BLS)

Bacterial leaf spot is caused by Xanthomonas cucurbitae (syn=X. campestris pv. cucurbitae). Lesions appear first on the underside of the leaves as small, water soaked dots that look yellow from the upper side of the leaf. Lesions are especially small (0.07 inches) in pumpkin, winter squash and gourd leaves. As lesions enlarge (0.07-0.15 inches), they can coalesce and look like ALS. Fruit lesions start as sunken, circular spots (0.04-0.1 inches) that enlarge and can reach up to 0.6 inches in diameter. These openings allow the colonization of the fruit by saprobes or secondary microorganisms that can cause fruit rot in the field or post-harvest.

Ongoing field research by Mohammad Babadoost, University of Illinois at Urban-Champaign, and collaborators has found that X. cucurbitae can survive in the soil for 24 months when associated with plant tissue.

Pumpkin leaves infected with Xanthomonas cucurbitae. A, a leaf with translucent lesions; B, a leaf with angular spots; C, a leaf with dark lesions with yellow margins; D, a severely infected old leaf. Photo by Mohammad Babadoost, University of Illinois at Urbana-Champaign

Xanthomonas cucurbitae is a seedborne pathogen, favored by high precipitation or overhead irrigation. Before 2005, outbreaks were considered sporadic in the Midwestern United States. According to recent research by Ravanlou, et. al, the occurrence of this disease in the Midwest has increased over the last eight years. The disease was observed in more than 85 percent of the fields sampled across eight states, including Illinois, Indiana, Iowa, Kansas, Missouri, Nebraska, Ohio, Wisconsin and Michigan, causing as much as 90 percent yield loss in severely affected fields. In the last three years, bacterial leaf spot outbreaks have had a significant impact on the pumpkin industry in Illinois. The Michigan fields sampled during 2011 and 2012 (five fields each year) by Ravanlou and collaborators had a lower percentage of bacterial leaf spot-infected fruit per field when compared to other Midwestern states sampled.

Bacterial leaf spot symptoms in pumpkin fruit. Photo by Mohammad Babadoost, University of Illinois at Urbana-Champaign

What does ALS and BLS management have in common?

Since both bacterial pathogens are seedborne, disease management starts with the use of pathogen-free seed. Seed treatments (dry heat, hot water, sodium hypochlorite, etc.) can reduce the bacterial numbers in the seed, but will not eliminate it completely.

When ALS or BLS have been confirmed in a specific field, rotate away from cucurbits for two years or longer. Avoid working fields when plants are wet (morning dew or after rain) as this minimizes bacterial spread from diseased to healthy plants. If irrigation is needed, avoid using overhead irrigation to minimize bacterial pathogen dispersal. Avoid using surface water for irrigation as several species of Pseudomonas and Xanthomonas have been documented in surface water.

Frequent foliar application of preventative sprays can help decrease the bacterial population in the field to some extent.

Preventative sprays considerations

The efficacy of copper products and other materials to manage ALS and BLS is limited. Preventive application of copper can reduce the number or plants infected and the severity of disease development in the field, but has limited efficacy on years with high rainfall. Preventative application of copper formulations is considered more efficacious compared with sprays after the symptoms have developed.

Different copper formulations are available. However, it is important to tank-mix or alternate with other products such EBDC, Manzate, Actigard, Tanos or Serenade. Michigan State University Extension reminds growers to always read the labels. The development of copper resistance is a growing concern; alternating different modes of action is a tool to prevent and manage copper resistance.

Keep in mind that copper formulations should not be applied in solutions having a pH below 6.5. As pH decreases, more copper ions become available and can cause damage in leaves or fruits. However, the efficacy of copper formulations can be impacted at basic pH. A pH range of 6.5 to 8 allows for available copper ions while decreasing the risk of phytotoxicity.

For more information, see “Bacterial Spot of Cucurbits” from University of Illinois Extension.

For more information on Midwest survey and treatments tested to manage BLS:

  • “Occurrence of bacterial spot (Xanthomonas cucurbitae) in cucurbit fields in the Midwestern of the United states” by Ravanlou, A., Liu, Q., Thapa, S., Zhang, X., and Babadoost, M.
  • “Outbreak of Bacterial Spot (Xanthomonas cucurbitae) in Pumpkin Fields in Illinois” by M. Babadoost and A. Ravanlou

For more information on seed treatments:

  • “Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens” by Ohio State University
  • “Evaluation of the efficacy of chemical and physical seed treatments in reducing the incidence of bacterial spot on pumpkin seedlings” by X. Xu, S.A. Miller and M.L. Lewis Ivey

Downy mildew on a cucumber leaf.
Photo: Christian Hummert

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Here is a brief overview of the main diseases and pests that can threaten pumpkins, squash, calabash, marrow, watermelons and cucumbers and other cucurbits.

Caused by Sphaerotheca fuliginea. It starts as a white, powdery growth on the upper surface of leaves, and leads to reduced yield and poor fruit quality.
Control: Chemical control is essential; plant tolerant cultivars; control weeds.

Caused by Pseudoperonospora cubensis. The disease appears as yellow or brown spots on the upper leaf surface, with a grey/ purple fungal growth on the lower surface.
Control: Chemical control essential; plant tolerant cultivars; avoid over-irrigation; plant in well-drained soils.

Fusarium wilt

Caused by Fusarium oxysporum. This disease favours warm soil temperatures. Plants wilt and die. When the lower stem is cut open, stem tissues are light brown in colour.
Control: Plant disease-free seed; plant tolerant varieties; adjust soil pH to 6,5 using nitrate nitrogen; control nematodes.

Phytophthora crown/root rot

Caused by Phytophthora capsici. The lower stem and roots become brown and rot, causing plants to wilt and die.
Control: Chemical control; avoid over-irrigating plants; use well-drained soil; use clean water (borehole or municipal water); crop rotation.

Viral diseases

May be caused by cucumber mosaic virus (CMV), squash mosaic virus (SqMV), watermelon mosaic virus (WMV), and zucchini yellow mosaic virus (ZYMV). Symptoms include a mosaic pattern on leaves that, in severe cases, result in a shoestring effect. Fruits can be malformed and bumpy, and seeds can also be malformed.

The viruses are transported mainly by infected seed or insects such as aphids or cucumber beetles.
Control: Remove virus-infected plants from the land and destroy. Buy disease-free seeds from certified seed companies.


These soft-bodied insects often appear in clusters. They are very small and may be green, red, brown, or black. They suck plant juices and transmit viral diseases.
Control: Aphids can be controlled with registered chemicals. On smaller plots, spray with light liquid soap or repellent mixes, such as onion and garlic extracts.

Pumpkin fly

This pest stings young fruit (usually smaller than 10cm) and lays eggs in a cluster under the peel. Infected fruit rots.
Control: Put out bait consisting of Dipterex, sugar and water when flowering starts. Control with pesticide every seven to 10 days.

Cucurbit leaf beetles

At least three common cucurbit leaf beetles attack pumpkins in South Africa. They are all black and orange and damage flowers and leaves.
Control: Cucurbit beetles must be controlled when they are first noticed in the spring. Daily scouting is essential during the emergence and early life of the crop while the plants are small and susceptible.

Source: Production Guideline for Summer Vegetables, ARC.

Diagnosing and Curing Cucumber Diseases and Pest Problems

Most cucumber diseases are caused by pest problems in your cucumber patch. Many hybrid cucumber varieties today have been engineered to be disease resistant, but not disease proof. And they certainly aren’t resistant to pests.

Cucumber plants are susceptible to three main pests:

  • Cucumber Beetles
  • Slugs
  • Aphids

Cucumber Beetles will generally wreak the most havoc in your cucumber patch. They love to suck on the young seedlings and will carry wilt disease from plant to plant. They also chew holes in leaves and flowers. Cucumber beetles are usually identified by their black and yellow stripes. They are easily controlled throughout the growing season. When seedlings first emerge, a cone made of mesh wire or cheesecloth can be placed over the plants. Additionally, pesticides can be applied to keep the bugs at bay. Make sure that the product you choose will eliminate cucumber beetles. When the blossoms appear, stop spraying for bugs temporarily so that the bees will be able to pollinate the plants. If you start early in the season and can manage to keep away the beetles, you’ll greatly lessen the chances of the development of cucumber diseases.

Slugs may appear when the fruit is just beginning to form. Slugs love to suck on young cucumbers. Most garden centers sell special slug pellets that can be spread around your cucumber plants. If you are interested in growing organic cucumbers, you can put down a layer of sand under and around the developing fruit. As slugs do not like to crawl across sand, they won’t be able to reach the young fruit and no damage will be done.

Aphids have been known to colonize on cucumber plant leaves and buds. They can be controlled the same as cucumber beetles with a small mesh cone for emerging seedlings and an occasional dose of appropriate pesticide before the blossoms appear.

To address pest problems in our own garden, we’ve implemented a preventative spray program using a homemade soap spray. We mix together 2 gallons water, 4 tablespoons liquid dish soap and 4 tablespoons hot sauce in a pressure sprayer. We spray this mixture all over our cucumber plants every 10 days or so or after every heavy rainfall. This mixture doesn’t actually kill any pests, but it does encourage them to move elsewhere.

Depending on the cucumber variety you plant, you may rarely have problems with other cucumber diseases. Most of them are fungal infections. You can avoid these problems by choosing diseases-resistant cucumber varieties. One of the more common diseases is powdery mildew. This is identified by white, mildew-like patches on the leaves. It can be controlled fairly easily. At the first sign of mildew, apply an all-purpose fungicide to the plants. These spray products are available at most garden centers. A good fungicide will also eliminate downey mildew. Downey mildew is identified by yellow, mildew-like patches on the leaves. If you are trying to grow cucumbers organically, most garden centers carry soap sprays and other organic ways to combat fungal and bacterial problems.

We’ve implemented a preventative spraying program in our own garden and we’ve had good results. We mix together 2 gallons water, 4 tablespoons baking soda and 4 tablespoons hydrogen peroxide in a pressure sprayer. We spray this mixture all over our cucumber plants every 10 days or so or after every heavy rainfall. We cover the plants, spraying to the point of runoff. We rarely get any fungal infections and when we do, we switch to a commercial fungicide product.

Most cucumber diseases are preventable and curable. To prevent the development of disease, choose disease resistant varieties and consider implementing a preventative spray program in your own garden. Keep your garden weeded and clean.
It’s also best to avoid handling the plants when they are wet. When watering your cucumber plants, avoid watering the foliage and concentrate your efforts at the base of the plant instead. If needed, apply an appropriate pesticide or fungicide at the first sign of problems.


Cucumber – Diseases, Pests and Problems

Basic Information

Problem: Flea Beetles
Affected Area: Leaf
Description: Small 1/16 ? brown jumping beetle. Makes tiny holes in leaves causing them to develop a shot-hole? appearance.
Control: Do not generally do serious damage. Dust with Rotenone, Remove debris each year. Rotate location

Problem: Aphids
Affected Area: Leaf and Stem
Description: Small Insects found on new stems and the underside of the leaf. Usually green. They suck fluids from the plant leaving a honey dew substance behind. Leaves turn pale yellow.
Control: Insecticidal soaps or a strong stream of water. Diazinon, sevin, and thiodan are also registered for aphids on cucumbers. * Pesticide use and recommendations for various areas are constantly changing. Check with your County agent for current recommendations.

Problem: Slugs and Snails
Affected Area: Entire plant
Description: Large portions of young plants missing.
Control: Slugs and snails are very susceptible to desiccation (drying) and require a moist, shady place to live. Cultural practices which promote a sunny, dry environment will discourage them. Avoid too-frequent waterings allowing soil surface to dry out between irrigations. Keep garden free of debris, boards, bricks, and stones where they hide. Hand picking these pests is very effective. Create ?traps? for hand picking by laying boards in the garden. Slugs and snails will congregate under them. Lift the boards each morning and collect the slugs and snails. Dispose of them completely as they will crawl back if tossed out of the garden and eggs inside dead pests can still hatch to produce more of these pests. Slug and snail bait containing metaldehyde can be placed near food plants as long as they do not contact edible portions of the crop. Most effective when moistened, but not water logged. Snail bait attracts slugs and snails from several feet away so bait stations are effective. Stations help protect birds, pets and other non-target animals which are also attracted to the bait. Place small piles of bit under a slightly propped up board or use container such as a cottage cheese or yogurt carton. Bury carton to the mouth of the container. Place small amount of commercial bait inside and moisten with apple juice, orange juice or water. Cut hole in lid to allow access and place lid on container. Containers may also hold beer or yeast water to attract slugs and snails in where they drown. Place bait stations wherever slugs and snails are active or around perimeter of garden.

Problem: Cucumber Beetle
Affected Area: Leaf, Stem, and Root
Description: Western Spotted Cucumber Beetle and Western Striped Cucumber Beetle are the two most common to attack vine crops in the West. Adults are about 1/4 inch long with black heads, yellow thorax and yellow wing covers. Spotted species are greenish yellow, with 12 black spots on their back. Striped are pale orange-yellow with three longitudinal black strips on their backs. Both winter over as adults and deposit eggs in the soil. ? Larvae bore into roots and stems below soil line. Adults chew leaves. May spread wilt and mosaic diseases.
Control: Pick by hand, spray with hose (both sides of leaves) but this will not kill. Dust with rotenone or apply diazinon. * Pesticide use and recommendations for various areas are constantly changing. Check with your County agent for current recommendations.

Problem: Damping-off
Affected Area: Seedling
Description: Young seedlings wilt and die.
Control: Use treated seed and let soil dry out between waterings.

Problem: Cucumber mosaic
Affected Area: Leaf, Stem, and Fruit
Description: Vines are stunted, new leaves are dwarfed, mottled, distorted and may wilt and die. Fruit distorts and yellows early.
Control: Plant resistant varieties. Control aphids and cucumber beetles. Rotate placement from year to year.

Problem: Powdery mildew
Affected Area: Leaf
Description: White powdery substance on the leaves. Spores are transmitted by wind to healthy plants.
Control: Use surface or underground watering method to avoid wetting leaves. Plant resistant varieties. Change location from year to year. Fungicidal sprays are only moderately effective.

Problem: Alternaria Leaf Spot
Affected Area: Leaf
Description: Dry flecks surrounded by yellow halos appear on the leaves and enlarge into spots, which may group together to form nearly circular lesions. The lesions bear the black brown conidia of the pathogen. Severely infected leaves become yellow and senescent and then die.
Control: Satisfactory control can be achieved by reducing relative humidity in greenhouses, removing infected plant debris prior to crop establishment, and applying protectant fungicides.

Problem: Anthracnose
Affected Area: Leaf, Petiole, Stem, and Fruit
Description: On cucumber leaves, lesions usually first appear near veins, are roughly circular, range from light brown to reddish, and can reach more than 1 cm in diameter. The leaves may be distorted, and the centers of lesions may crack or drop out, creating a shot-hole appearance. On petioles and stems, lesions are shallow, elongated, tan areas. On fruit, lesions are circular, sunken, water-soaked areas which first develop as the fruit.
Control: Chemical control and resistant cultivars are the most effective controls of the disease.

Problem: Aphids
Affected Area: Leaf
Description: Aphids damage cucurbits by direct feeding, by contamination with excrement, and as vectors of plant pathogens and can occur just after the formation of the first true leaf.
Control: Insecticides are not effective in preventing the spread of aphid borne viruses, but may be helpful in control the onset of infection. Refer to current recommendations for registered insecticides.

Problem: Aster Yellows
Affected Area: Leaf, Flower, and Fruit
Description: Infected plants are easily detected by the conspicuous yellowing of young leaves, the proliferation of secondary shoots, and the rigid, erect habit of the plants. Leaves are often misshapen and smaller than normal and have stiff, thick laminae. Flowers are usually malformed and greenish yellow and often have prominent leafy bracts. Fruits are small, malformed, and lighter than normal color.
Control: Application of insecticide can drastically reduce leafhopper populations but is often ineffective in reducing the disease.

Problem: Bacterial Brown Spot
Affected Area: Fruit
Description: In honeydew melons, symptoms appear as conspicuous yellow brown, smooth, firm lesions up to 40 mm in diameter. Symptoms on melon are very similar with firm lesions that are slightly yellow brown, and up to 10 mm in diameter, extending 1-2 mm below the epidermis. Symptoms on melon fruit are obscured by the net.
Control: No control measures have been developed.

Problem: Bacterial Soft Rot
Affected Area: Fruit
Description: Early symptoms of bacterial soft rot are a distinct water-soaked appearance and pronounced softening of the surrounding tissue. As the decay progresses, the fruit tissue becomes extremely soft and mushy and often collapses, losing its original form.
Control: Avoiding bruising and injury to the fruit is the first step in controlling bacterial soft rot.

Problem: Bacterial wilt
Affected Area: Runner and Leaf
Description: Individual runners or whole plants wilt and die rapidly. Affected runners appear dark green at first and then dry out as the wilt becomes irreversible. Plants may wilt dramatically during the heat of the day but partially recover by morning. Foliage of affected plants often appears yellow.
Control: Control of bacterial wilt depends on control of the cucumber beetle vectors. Roguing wilted plants, using trap crops, and implementing appropriate insecticide programs are the best forms of control.

Problem: Belly Rot
Affected Area: Flower
Description: On the undersides and blossom ends of cucumber fruit, the disease produces water-soaked, tan to brown lesions, which become sunken, cratered, irregular, and dried as they enlarge.
Control: Soil may be fumigated before planting. In humid areas, artificial barriers can be placed between the soil and the fruit to prevent infection. Another effective method of avoiding the pathogen is deep plowing before planting.

Problem: Black Rot
Affected Area: Fruit
Description: In cucumber, fruit rot can develop before harvest, but it usually develops during transit or storage. Before harvest, a black decay occurs, especially at the blossom end, and can extend into the pulp. On watermelon, distinct, circular, greenish tan to black spots first appear on any part of the fruit. The lesions later have black centers, and under moist conditions many pycnidia and perithecia develop near their centers. In squash, if fruit are damaged prior to or during storage, a brown to pinkish water-soaked area develops, followed by blackened areas with conspicuous fruiting bodies.
Control: Special care should be exercised to avoid rind injuries to all fruit, especially winter squash and pumpkins, as wounds provide entry for the black rot organism in storage.

Problem: Blossom-End Rot
Affected Area: Flower and Fruit
Description: Symptoms first appear as small, light brown spots at the blossom end of immature fruit. As affected watermelons grow, these spots can enlarge rapidly to form dark, sunken, leathery lesions. The lesions are generally dry and can be as large as the diameter of the fruit. A soft, secondary wet rot may develop if affected areas of the fruit are invaded by decay fungi or bacteria.
Control: NA

Problem: Blue Mold
Affected Area: Fruit
Description: In general, cucurbit fruits with blue mold have been predisposed by temperature, bruising, and injury, and they typically have other problems.
Control: Blue mold can be effectively prevented by eliminating predisposing conditions, maintaining low temperatures in storage, and moving the produce within its reasonable postharvest shelf life.

Problem: Choanephora Fruit Rot
Affected Area: Flower and Fruit
Description: The disease affects both blossoms and fruit. When flowers are invaded early, they turn soft and usually drop off the plant. Later infections cause the flowers to turn brown, and if the fruit has begun to develop, the fungal mycelium invades the fruit tissue, causing it to decay in a wet rot.
Control: No practical control measures have been developed.

Problem: Crater rot
Affected Area: Leaf and Fruit
Description: The disease is characterized by shallow to deep, sunken lesions, 2-50 mm in diameter. Large lesions often penetrate to the seed cavity in melon and honeydew. Lesions on leaves are round to irregular in shape, 2-15 mm in diameter, with a tan center, brown margins, and a yellow halo, and they often form concentric rings. Abundant greenish black sporodochia may also be arranged in concentric rings on either surface of the leaf.
Control: Foliar diseases can be controlled with fungicides.

Problem: Cucumber Mosaic
Affected Area: Leaf, Flower, Stem, and Growth
Description: In cucumber, melon, and squash, cucumber mosaic virus causes severe plant stunting, prominent foliar yellow mosaic, malformation, prominent downward leaf curling, and drastic reduction of leaf size and stem internodes. Flowers of severely affected plants may have prominent abnormalities and greenish petals.
Control: The best forms of control include using resistant cultivars, insecticides, reflective mulches, and mineral oils.

Problem: Phytophthora blight
Affected Area: Root
Description: Mature plants show symptoms of root and crown rot. Initially, feeder roots are depleted and soon after, brown lesions develop on lateral roots. Sudden wilt is another symptom when healthy-appearing plants suddenly collapse during the heat of the day.
Control: Control of root rot can be achieved by planting on raised beds to allow for maximum water drainage after each irrigation.

Problem: Downy Mildew
Affected Area: Leaf
Description: Symptoms of downy mildew are first evident as small, slightly yellow to bright yellow areas on the upper leaf surface with the color less vivid on the corresponding lower leaf surface. Lesions appear first on the older crown leaves and appear progressively on the younger, more distal leaves as these leaves expand. As the lesions expand, they may remain yellow or become dry and brown. Lesion margins are irregular on most cucurbits, but on cucumber they are angular and bound by leaf veins.
Control: The best forms of control include using resistant cultivars, applying fungicides, and using good cultural practices.

Problem: Fusarium Rot
Affected Area: Fruit
Description: The disease can penetrate in a number of ways including, the epidermis, the stem end, and lesions on the surface. It is one of the more common preharvest and postharvest diseases of cucurbit fruits.
Control: Avoid wounding the fruit during harvest and packing, proper storage and transit temperatures, and prompt handling of melons upon arrival at the market provide some protection against postharvest decay.

Problem: Gummy Stem Blight
Affected Area: Leaf and Stem
Description: Circular, tan to dark brown spots appear on the leaves, often first at the margins, and enlarge rapidly until the entire leaf is blighted. Circular, black or tan spots appear on the cotyledons and stems of young plants.
Control: Satisfactory chemical control may be obtained by regular applications of protectant fungicides.

Problem: Lasiodiplodia
Affected Area: Root and Fruit
Description: The disease causes a root rot, and a vine decline in melon at the stem end. Infected tissue is somewhat soft and has a water-soaked appearance. As the disease progresses, the affected tissue becomes brown and shriveled. In the latter stages of decay, the shriveling becomes more pronounced, and black pycnidia and dark gray mycelium develop internally.
Control: Fungicide pastes applied to cut peduncles have been successful in controlling the disease. Care should be taken to reduce injury in the harvesting, handling, and packing of the fruit.

Problem: Leafminers
Affected Area: Leaf
Description: Adult leafminers are small flies that are black and yellow. Adult females puncture the upper surfaces of leaves for feeding and egg laying. Eggs are cream-colored and oval, laid singly in separate leaf punctures.
Control: Scouting should be initiated prior to bloom in all crops, and treatments should be initiated when numerous leaf punctures or small holes are observed on the majority of leaves on the plant.

Problem: Lettuce Infectious Yellows
Affected Area: Leaf
Description: In cucurbits, the characteristic symptom is pronounced interveinal yellowing and leaf curling, and in melons and cucumbers the striking yellow color is accompanied by a green mosaic. Symptoms develop primarily on older leaves.
Control: Allowing a host-free period and stringent weed control is the best control method.

Problem: Mites
Affected Area: Leaf
Description: Spider mites damage cucurbits by puncturing cells of the leaves, mainly on the lower surface. They extract plant juices and chlorophyll, interrupting the normal production of photosynthate. An early sign of infestation is stippled areas on foliage. As feeding progresses, leaves become yellow.
Control: Use recommended insecticides for control.

Problem: Papaya Ringspot
Affected Area: Leaf and Growth
Description: Most susceptible cucurbit species respond to infection with very prominent foliar symptoms and severe plant stunting. Foliage of infected plants often exhibits green mosaic, malformation, puckering, blisters, distortion, and narrow laminae.
Control: Where available, the use of resistant cultivars is the most effective control.

Problem: Pickleworm
Affected Area: Fruit and Stem
Description: Primary damage is due to burrowing within fruits, which renders them unfit for consumption. Often, the only outward sign on an infested fruit is a small entrance hole. In heavy infestations, larvae may burrow into stems and kill plants.
Control: Chemical treatments are the best form of control, but must start when eggs or small larvae are first noticed.

Problem: Pink root
Affected Area: Root
Description: Pink root of cucurbits is characterized by pink to red lesions on secondary and tertiary roots. The disease causes no aboveground symptoms in melon and watermelon plants.
Control: There are no control measures available for the disease.

Problem: Powdery Mildew
Affected Area: Leaf, Petioles, and Stem
Description: Whitish, talcum-like, powdery fungal growth develops on both leaf surfaces and on petioles and stems. Symptoms usually develop first on older leaves, on shaded lower leaves, and on abaxial leaf surfaces. Older, fruit-bearing plants are affected first. Infected leaves usually wither and die, and plants senesce prematurely.
Control: Resistant cultivars and fungicides on the undersides of the leaves and the lower canopy are used to manage powdery mildew.

Problem: Red Rot
Affected Area: Fruit
Description: Symptoms of red rot include a bright red discoloration of the rind with no aerial mycelium or fruiting bodies. The texture of the decayed area is similar to that of healthy tissue. Decayed and healthy tissue are not easily separated.
Control: The growth of the fungus is greatly retarded at 5(C making proper storage temperatures an important role in controlling the disease.

Problem: Rhizopus Soft Rot
Affected Area: Fruit
Description: The initial symptoms of Rhizopus soft rot of cucurbits are a water-soaked appearance and softening of the tissue. As fruits become completely colonized, they often collapse from the weight of other fruit. The diseased tissue is wet, soft, and somewhat pliable, and large portions of it can be removed intact. Internally, the diseased tissue in most cucurbits is characteristically water-soaked and darker than the surrounding healthy tissue.
Control: Rhizopus soft rot can be controlled most effectively by minimizing injury and bruising of the fruit and by proper cooling and temperature maintenance during shipping and storage.

Problem: Scab
Affected Area: Leaf, Runners, and Fruit
Description: On leaves and runners, pale green, water-soaked areas are the initial symptoms. These spots gradually turn gray to white and may become “shot-holed” in appearance. A yellow halo appears around the lesion. Scab can produce the greatest damage on fruit. Spots first appear as small, sunken areas similar to insect stings. A sticky substance may ooze from the infected area, especially on fleshy fruit.
Control: Using resistant cultivars, rotating the crops, and using protectant fungicides are recommended measures for control.

Problem: Sclerotinia Rot
Affected Area: Tendrils, Petioles, and Flowers
Description: Infection tends to occur in dead tendrils and petioles or through withered flowers still attached to developing fruit. The disease is favored by low temperatures and extended wet periods.
Control: Because the disease is relatively minor in cucurbits, no control procedures have been developed.

Problem: Squash Bug
Affected Area: NA
Description: Damage results from the withdrawal of plant fluids. Moderate feeding by a single adult can result in rapid death of seedlings and death in older plants may result from heavy feeding.
Control: Prior to the advent of modern pesticides, hand picking of squash bugs and clean culture were suggested as the best methods of control. In small plantings with only moderate populations of squash bugs, these methods are efficient and cost-effective. In large plantings, often the only alternative for control is the application of insecticides.

Problem: Squash Mosaic
Affected Area: Leaf, Growth, and Fruit
Description: Generally, infected plants respond with a variety of symptoms, including green veinbanding, mosaic, spotting, blisters, ring spots, and protrusion of veins at the leaf margin. Plants are often stunted, producing malformed and mottled fruits.
Control: The best forms of control include using virus-free seed and applying insecticides to control the beetle vectors.

Problem: Squash Vine Borer
Affected Area: Vines, Stalk, and Petioles
Description: Burrowing in vines and stalks can cause wilting of the plant. A telltale sign of borer infestation is holes in vines or at the base of the petioles, from which greenish frass is extruded. Heavy infestations can considerably reduce yield.
Control: Chemical control with recommended insecticides should begin when eggs are found on foliage. The field planting should be turned under as soon as the crop is harvested.

Problem: Striped Cucumber Beetle
Affected Area: Seedlings
Description: Only cucurbit plants are attacked. The principal damage results from adults feeding on young seedlings. These beetles are also important as vectors of pathogens, which cause bacterial wilt.
Control: Newly germinated seedlings should be monitored regularly for beetles, and recommended insecticides should be applied as a foliar spray.

Problem: Thrips:
Affected Area: Leaf, Flower, Bud, and Fruit
Description: Adults and nymphs cause injury. Thrips feed by piercing the cells of bud, flower, and leaf tissues and then sucking plant juices from the feeding sites. They also feed on pollen. Feeding causes silver colored leaves, discoloration of flowers and buds and can result in fruit abortions. Small plants can be stunted and deformed.
Control: Insecticides are recommended for control and should be applied when thrips are present and damage is evident. Management of weeds within the crop is also recommended.

Problem: Tobacco Ringspot
Affected Area: Leaf and Fruit
Description: Newly infected leaves usually exhibit very bright yellow mosaic, ring spots, drying, distortion, and in some cases enations. During the first phase of infection, fruits tend to abort or remain small and become spotted and distorted.
Control: Intense cultivation and a methodical weeding program drastically reduce the presence of the vectors and the presence of the disease.

Problem: Tomato Ringspot
Affected Area: Leaf, Bud, and Fruit
Description: Infected plants react with yellow mosaic, reduction in leaf size, shortened internodes, proliferation of flower buds, and prominent ring spots on the discolored fruits. Generally, symptoms are very prominent in the initial, acute stage, which is followed by a chronic stage in which growth is mildly affected.
Control: Intense cultivation and eradication of weeds drastically reduce the presence of the virus in vectors.

Problem: Ulocladium Leaf Spot
Affected Area: Leaf
Description: Immature lesions are dark brown and 1-2 mm in diameter. As the lesions age, the central area becomes beige, surrounded by a dark brown ring and a circular brown halo, 6-7 mm in diameter. Several of these lesions may group together to form larger, irregular spots, but they retain their light beige centers.
Control: The best forms of control include using resistant cultivars, fungicidal sprays, and destroying old vines from cucumber fields.

Problem: Watermelon Mosaic
Affected Area: Leaf and Fruit
Description: Foliar symptoms include green mosaic, leaf rugosity, green veinbanding, yellow rings, and malformation. These symptoms often are very prominent in some winter and summer squashes, but affected leaves develop to nearly normal size. Fruits are not distorted, but green spots, particularly on yellow fruit, adversely affect some of their coloration.
Control: The best forms of control include using resistant cultivars, applying mineral oil sprays to interfere with virus transmission, and insecticides to control aphid populations and slow virus spread.

Problem: Whiteflies
Affected Area: NA
Description: Whiteflies damage cucurbits by direct feeding damage, by contamination with excrement on honeydew, and by inducing physiological or apparently phytotoxic disorders.
Control: Whitefly monitoring should begin at the time of seedling emergence. Yellow sticky traps can be used to trap adult whiteflies moving into a field and give an indication of when to initiate plant sampling for nymphs. Other components of a management plan include consideration of natural enemies, including predators, parasites, and pathogens.

Problem: Zucchini Yellow Mosaic
Affected Area: Leaf and Growth
Description: The virus incites yellow mosaic, severe malformation, blisters, and extreme reduction in the size of leaf lamina, drying, and severe plant stunting. Malformation is the greatest symptoms that will be observed.
Control: Resistant cultivars offer the only resistance that provides consistent control.

A Post-Halloween Trick: the Moldy Pumpkin

Each October, sights of carved pumpkins greet passersby on doorsteps and porches across the country. Ghoulish faces and spooky sayings illuminated by candles on bright orange gourd-like fruit are a sure sign that Halloween is just around the corner. In early November, however, drooping and discolored pumpkins still on stoops are a sure sign that Halloween has come and gone. So what causes a carved pumpkin to rot and how can you ensure this doesn’t happen to a jack-o’-lantern until after trick-or-treaters have filled their bags with candy?

Pumpkins, just like all produce, do have an expiration date. Once they are cut to be carved into glowing creations, this expiration date arrives even faster. Pumpkins typically soften and rot within a week after being cut, so keep that in mind when planning out a pumpkin carving session.

Emerson the Pumpkin (gone before his time…)

Emerson was taken by an unidentified rot

The ideal temperature for carved pumpkins is 50-55 degrees Fahrenheit. Warmer temperatures will speed up deterioration while freezing temperatures will slow deterioration. On the other hand, the cold will damage plant cells once the pumpkin warms up again, leading to the aforementioned softening and rot.

After they are cut, a lot of organisms like to reside on pumpkin flesh and break it down, including fungi, bacteria, mold and insects. Some of the top contenders for pumpkin destroyers are:

  1. Black rot: this is the most important disease contracted during the storage of pumpkins in the Northeast. Affected fruits might show lesions of black rot or collapse soon after harvest. Black rot typically appears as black specks in a ring pattern on pumpkins. Large Halloween pumpkins are more susceptible to this than smaller types for pies.

  1. Phytophthora blight: fruit that develop with phytophthora blight are typically undersized and distorted. White mold and fungus spores will develop on areas affected, which later become covered with a yeast-like growth.

  1. Sclerotinia white mold: pumpkins are particularly susceptible to this white mold. Decay is rapid and is characterized by rot that is watery and odorless along with an abundance of white cottony mold containing embedded black bodies of fungus. The rot can spread by contact from fruit to fruit.

While the outlook isn’t great for long-term survival of carved pumpkins, you can take some precautions to try to extend the stoop-life of your pumpkin for following Halloweens:

1) Pick a healthy pumpkin: choose a pumpkin that is fresh, healthy, and firm.

2) Get rid of all guts: make sure the inside is as clean and dry as possible before carving.

3) Use some petroleum jelly: apply a thin layer of petroleum jelly to the inside of your pumpkin to reduce mold and slow down decay.

4) Put your pumpkin in the refrigerator: if you are able to, placing your pumpkin in a refrigerator each night can go a long way in rehydrating your carved fruit as well as keeping it away from bugs and critters.

5) Soak overnight: another rehydration method is soaking the pumpkin overnight to keep it fresh. This is great to try if you notice that your pumpkin is beginning to wilt or fade. Make sure to use cold water as warm water can speed up the rotting process.

Hopefully staying informed about what can afflict pumpkins in addition to taking steps to prevent pumpkin deterioration will be more of a treat instead of a trick for the next Halloween. What was the best jack-o-lantern you saw this year? Do you have any good tips for keeping carved pumpkins rot-free longer for next year’s Halloween? Let us know in the comments section.

PathSensors’ Pumpkin Palooza

A Pumpkin Lesson

by Michael Rossman

When Halloween comes, I ask my students to save their carved pumpkins, in their back yards or gardens. A week later, I bring two rotten ones to class, so that we can feast our minds on decay. For even the youngest classes, it’s a spectacular introduction to the subject, and we take some time going over the actual meanings of these terms. By rot and decay, we don’t mean that a thing is dead, or smelly, or icky-repulsive — for something may be any of these yet not be rotten. We mean that microscopic organisms are at work eating it, breaking down its cells and tissues, changing its chemicals — which accounts for the different smells, the changes in its appearance and strength.

On one pumpkin, macro-scopic agents are also at work, for its ruined walls are covered with thick fuzzy growths of mold — here and there in white patches, but mostly black. I set up the projection microscope, take two samples of mold, put them on a slide with a drop of water on each, and project their images on the whiteboard. The white sample shows us the branching filaments (hyphae) that form the mold itself. We see that each thin hypha is almost transparent, so the white appearance of their tangled mass (called the mycelium) is not a color but a play of light, like the whiteness of clouds.

When I switch to the black sample, the reason for the difference shows vividly, for thick spheres appear at the tips of the hyphae. As we watch, we can see one spore-ball coming apart, as the tiny black spores drift off into the surrounding water — much as dandelion seeds do, revealing the smaller, light-colored center to which they were attached. The spore-balls are large enough to see with a hand-lens. On the intact mold on the pumpkin, they cluster so thickly that the mold’s as dark as soot. A light breath sends their dust-sized spores swirling into the air around us.

Since the rainy season’s here and mushrooms will soon be popping up, we review what we know about these higher fungi and why they differ from molds. I sketch the ground, with the thin threads of a fungus’s hyphae going every which way underneath, feeding on the decaying leaves mixed in the soil. Here’s where the real action is, not in the mushroom that later sticks up from the surface. But what good would it do the fungus, to grow spore-balls like the mold does on its hyphae tips, if these were underground? The spores couldn’t go anywhere. So I sketch the hyphae coming together into a mat, into a knob sticking up from the surface, growing rapidly to a mushroom profile with gills held high above the ground. A detail sketch shows spores forming in a small cavity on the gill, dropping out and down when they’re ripe, to be caught and spread by the breeze.

Enough, back to the fuzzy pumpkin. Looking more closely, we see a few patches of different color, grey and blue-grey. The children identify them as different molds, with differently-colored spores. I promise a minor prize next week, for whoever brings in the pumpkin with the most interesting molds. Then I show them a small, fresh cut on my thumb, before plunging it into the mold. “Yew, ick,” says a newcomer, not yet used to my ways. “So am I in much danger of infection?” I ask. Those who know me know I’m fishing for a no. But it takes a while to lead them to deduce why — for the mold is specialized to feed upon the pumpkin’s chemicals, mainly carbohydrates, whereas I am mostly animal proteins and fats, offering it no nourishment.

Stepping back from the moldy ruin, I tell them how I spent the afternoon before Halloween, going round to commercial pumpkin patches with my young son and a plastic bag. At each lot, some pumpkins start to rot early, can’t be sold, are discarded as garbage. I rolled up my sleeves and scooped out the seeds, we filled half a garbage-bag. Took them home, rinsed them off, spread them on cookie-tins, sprinkled lightly with salt, toasted them for half an hour at 350 degrees — and presto, munchies to last all winter. Suppose you found a pumpkin even this rotten — I ask them, of our mold-garden — would it be okay to take its seeds, roast and eat them?

They puzzle the matter, and decide that it would, provided the mold washed off and the seeds themselves weren’t rotten. So why would it turn out okay? They are quick to decide that the seeds have a protective coat, that keeps them from decay. But it takes more discussion to bring out the subtle rightness of the reason. For how are pumpkin seeds meant to be released into the world, anyway, but by the pumpkin’s rotting? They’re designed by evolution to resist the flesh’s decay, preserving the life within. In this and other ways, pumpkins are like other members of the squash family, from melons and cucumber to the big Hubbards and zucchini — all of their seeds are edible, can be roasted, though only the large are worthwhile.

Of the two pumpkins before us, one still stands high despite its covering mold. The other has hardly any mold on its surface, but lies slumped almost into slush, in a big puddle of water tinged light-brown, held within a garbage bag. We wonder why they are different, and decide that different kinds of fungi may be at work on them, or that the pumpkins themselves might be of different strains, or both. Focusing now on the second pumpkin’s lessons, we start with the smell. They pass the garbage bag around to savor it closely. It reminds them of rising dough, wine, last year’s experiments fermenting apple juice. We identify the distinctive chemical odor as alcohol. How did it get there? From last year, we know: yeast organisms turned sugar into alcohol. But if you chew a piece of fresh pumpkin, it doesn’t taste sweet. So where was the sugar in the pumpkin?

We go back to basics, review the most complicated and important chemical equation I give them:

6 H2O + 6 CO2 + —> C6H12O6 + 6 O2

Photo-synthesis means using light to put together; here sun-energy is used to put water and carbon dioxide together to form a molecule of sugar plus waste oxygen. Animals run the equation backward, burning (oxidizing) the sugar to get the energy back, to run their own chemical processes. So do plants at night, and in daytime too; but during sunny hours they synthesize much more sugar than they burn.

So why don’t plants taste sweet then, except for their small flowers/fruits, if they’re always making sugar? Because they use the sugar molecules to build two kinds of larger molecules — one for constructive purpose, the other for storage. Both kinds are polymers. Poly means many; and a polymer is a big molecule formed by putting together many copies of the same smaller molecule. Some children know poly-ethylene, the soft plastic used for food containers; almost all know poly-ester, the plastic clothing fiber made from chains of ester molecules. Just so, each green plant hooks its sugar molecules into polymers. Put them together one way and we get cellulose, the molecule that builds the strong cell-walls of plants; put them together another way and we get starch, stored in grains inside the cell-walls.

We remember the potato-starch experiment. A raw potato doesn’t taste sweet at all, because it’s mostly starch. But chew a piece, mixing it well with saliva, and in time it starts to taste sweet — because our saliva contains a special chemical, molecules of an enzyme (amylase) that takes the starch polymer apart, breaking it down to sugar molecules again. Just so with the starch of the pumpkin: one yeast has provided an enzyme to break it down to sugar; and another yeast has changed the sugar to the alcohol we smell. What we have here is a puddle of pumpkin wine. If it sits around longer, some ubiquitous bacteria will turn its alcohol to acetic acid, giving us pumpkin wine vinegar.

But we could chew the cellulose of stiff plant walls all day and still not have its taste turn sweet, since human bodies have no enzyme to break the cellulose polymer back down to its component sugar molecules. In this, we’re like every other animal larger than one cell. The grass-chewing cow, the wood-eating termite, the wood-boring beetle larva — all depend on symbiotic microorganisms (protozoans, bacteria) in their intestines, who do have enzymes that can digest (take apart) cellulose. The larger animals then digest these sugars, and the microorganisms themselves, eating their internal gardens. (An adult cow eats half a pound of protozoans daily.)

So much for sugar. Meanwhile, we’re looking at this big puddle. Where did the water come from? From inside the pumpkin, clearly — but where was it hidden? It doesn’t spill from the hollow interior, whose seeds and stringy fibers are much too small to have contained it; nor does it gush from the thick sides when we prick them. Where could it be? We consider another example, pretend we’re in a hot desert, where I get so irritated with them for not listening that I have a stroke. It’s three weeks till they can come back and get my body, which had weighed 150 lbs. What does it weigh now? Much less, they guess, maybe 75 pounds. What did it lose? Evaporated water. Yet my blood, urine, and saliva together couldn’t have been over ten pounds; so where was the other 65 pounds of water in my body? For me and the pumpkin both, it must have been in the cells — after all, that’s what our bodies are built of, right?

But why were the cells full of water in the first place? The answer is so fundamental and simple that it’s very hard to guess. We go back to basics, recall the three states of matter, and solutions, and how molecules behave in each. We recall also what a chemical reaction is — molecules interacting and changing to become other molecules — and note that all living things depend on chemical reactions, to make the molecules that build their bodies and to change molecules to get the energy to run them. Now we think about two chemicals that might react. If they’re in solid form, they can hardly begin, because hardly any of their molecules can come into contact to interact, being bound almost in place. For reactions to occur, the molecules must be able to move around freely, in liquid or gas or in solution, to encounter each other.

In the fluid leaked from the pumpkins, and even more within our own cells, hundreds or thousands of different chemicals are dissolved in water, to participate in the many kinds of reactions necessary to run such complex organisms. So water in cells is necessary simply to let life proceed. Dry the cell, and all the other chemicals remain, but can’t interact. I cite the tardigrades, cute, microscopic, bear-shaped animalcules who live in mosses, and dessicate so thoroughly when the mosses dry, as to enter a state of suspended animation; yet their life resumes when water greens the moss and reenters and reanimates their cells.

So how did the water get out of the cells to form the puddle — given that the fungus has no teeth to tear open the tough cell-walls? We consider the action of a single microscopic strand of fungus, one hypha. Fungus is to green plant as salamander is to reptile. The salamander’s skin is permeable to water both ways, it dries to death in a dry room but can drink through its skin (whereas a reptile’s skin is impervious, keeping it safe in dry climes but forcing it to drink through its mouth.) Similarly, though most green plants are protected against water-loss, by their bark or waxy cuticle, most fungus hyphae can’t survive dryness but must have humid environments, can absorb water from their surroundings.

So here’s the leaky fungus filament atop the thick-walled pumpkin cell. From it oozes a bit of water, with some molecules of an enzyme that can digest cellulose, breaking the polymer down to its sugars. The sugar molecules promptly dissolve in the exuded water, which is joined by the rich fluid now leaking from the cell; and the cells of the fungus now re-absorb this amplified soup, which furnishes the fungus with the water and sugar it needs to keep living and growing, plus all manner of other useful chemicals.

This explains why one pumpkin sits slumped like wet clay, and why even the other, that seems to hold its shape better, yields like stiff mud to the poking finger, that once would have bounced off its proud citadel. The cell walls are damaged, no longer hold, so the whole structure built of them loses its strength. I go on to discuss how the strength and tall-standing of grasses comes from cellulose walls, but the greater strength and durability of wood comes from a combination of cellulose and lignin. These last forever if dry, but in damp forest the woody body’s components are eaten first one and then the other, or vice- versa, by two different classes of fungi that feed on these different substrates — leaving the wood powdery and collapsing if lignin’s eaten first, brittle and weak if cellulose goes first, until the other kind of fungus comes to finish the recycling.

There is scarcely any end, to the lessons that unfold so naturally from decay. But since our hour together is at an end, I leave them with a homework assignment: Take your used pumpkin, stick it in the backyard, on the dirt, where no one will be bothered by the smell and mistake it for a pile of garbage instead of for what it is, a big heap of food — and not just for molds and microorganisms. If you leave it there for for several weeks, a multitude of small animals will visit it, drawn by the complex odors of decay spreading on the wind, to eat or leave their offspring, or perhaps to eat those who do. Snails, slugs, beetles, worms, moths drawn by fragrant esters, three kinds of fruitflies, five kinds of spiders to eat them — who knows what? I promise a small prize, for whoever brings in the most different kinds of visitors to their crumbling golden treasure, and bid them farewell till next week.

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From squash skulls to pumpkin owls, there’s no end to the creations you can make to celebrate Halloween. But that excitement quickly fades as you watch the pumpkin that took you forever to carve wither away on your front porch. It’s inevitable that your pumpkins will eventually rot, but we’ve rounded up some tips on how to keep them fresh longer.

First, make sure you buy your pumpkin from a local patch. Since it’s grown on-site, it will be spared from any damage it would have experienced in shipping. Second, make sure the one you pick is firm. If you feel any soft spots, the rotting process will start sooner rather than later (if it hasn’t already).

After you’ve found the perfect pumpkin, keep these tips in mind:

1. Clean the inside.

Since they’re moist, any bit of exposed pumpkin guts will start to go moldy very quickly. Pumpkin Patches and More suggests cleaning the surface of the veggie and the interior with a teaspoon of bleach per one quart of water. (Putting it in a spray bottle makes it easier to apply the solution to the whole pumpkin.) This will sterilize the gourd, killing any existing bacteria. Let it dry fully before you start carving.

2. Give it a bleach-water bath after you carve it.

The bleach comes into play again post-carving, giving it an good cleansing. Submerge your creation in a bucket filled with water and 2/3 cup of bleach. Leave the pumpkin there to soak for up to 24 hours.

After carving your pumpkin, give it a bleach-water bath to preserve it longer. Westend61Getty Images

3. Apply petroleum jelly.

As an extra layer of protection, apply Vaseline on the carved edges. This will keep them moisturized and prevent the edges from drying out too fast. If you don’t have Vaseline, vegetable oil or WD-40 works too. But since all three are flammable, don’t put a candle inside your pumpkin — use a flameless votive instead. Don’t put on the jelly before you clean the pumpkin with bleach, either. Since the jelly is trapping the moisture in the vegetable, it will trap the bacteria along with it if you don’t clean the gourd first.

4. Rehydrate the pumpkin daily.

Pumpkins shrivel up because they run out of moisture. Spraying it every day with water mixed with a few drops of bleach will keep it moist and ward off bacteria. As an even easier solution, spray it with Pumpkin Fresh daily to fight off mold.

5. Store it in the fridge overnight.

When you’re not showing off your Jack-o’-Lantern on your porch, put it in a plastic bag in your refrigerator. No room? Keep it in the basement (or any other cool, dark area of your house).

If you live in a warm climate, your pumpkins could rot quicker. Getty Images

6. Give it an ice bath.

If you see your pumpkin starting to wilt, give it an ice bath overnight for some serious rehydration. Once you take it out, dry it thoroughly to prevent mold growth.

7. Don’t use real candles to light it.

Using candles inside your carved pumpkins can have a negative effect on them as the heat is essentially cooking the pumpkin. Try using a flickering flameless candles or glow sticks instead.

8. Display it in a stable temperature.

Avoid leaving your pumpkin outside during freezing temperatures. Ideally, you want to place it somewhere with a temperature in the upper 50s to lower 60s Fahrenheit. So if you’re in an area where freezing weather is likely during October, be sure to bring your pumpkins inside each night.

9. Don’t carve it.

We know, not carving your pumpkin sounds tragic. But an untouched pumpkin will stay fresher for a longer period of time compared to a carved one. As an alternative to pumpkin carving, try our favorite pumpkin painting and no-carve ideas.

Marlisse Cepeda Web Editor Marlisse is the Web Editor of, and she hails from Bronx, NY. Madison Alcedo Assistant Editor Madison Alcedo was the Assistant Editor at and

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