Fungus on pecan tree

Pecan Diseases

Pecan trees (Carya illinoensis) are widely grown in South Carolina mainly for both their tasty edible nuts and shade. Pecan trees are susceptible to several diseases in our area due to the hot and humid environmental conditions typical of the state. Fortunately, disease or a combination of diseases never reach a level that kills the tree. However, they generally do impact the tree in two ways. First, disease can reduce the tree’s vigor, which in-turn causes the foliage and branches to shed, resulting in a loss of shade value. Secondly, diseases can also infect the nuts and reduce both nut quality and quantity. At times the disease pressure can be so great that no viable nuts are available.

The majority of diseases are difficult to control with either natural or chemical fungicides because their application requires special, expensive equipment that most home owners do not have. In addition, the entire tree canopy must be treated by the fungicide application for effective control. Once again, this creates a challenge for most homeowners after the tree reaches a certain height. Because of these challenges it is not uncommon for many home-owners to call these trees “trashy” and then don’t reap the rewards of the wonderful nuts.

Scab

Scab is the most prevalent and challenging disease not only in South Carolina, but where ever pecans are grown. There is not a year when this disease does not impact each pecan tree to some degree. It typically infects both the leaves and nut shucks (the protective shell or husk around the nut), especially when they are young and actively growing in the early part of the growing season. Leaves are susceptible from bud break until they reach maturity. However, once leaves are full expanded, they are no longer susceptible to pecan scab. Nut shucks are susceptible from nut-set to maturity. At times, it can infect young developing twigs and catkins (male flowers) if conditions are favorable. Overall, this disease is a perennial problem without a simple solution.

Pecan scab is caused by the fungus Cladosporium caryigenum. At first, the fungus forms small, circular, olive-green to black spots on leaves, leaf petioles and outer nut shuck. With time the lesions increase in size and become blackened and sunken in appearance. Lesions crack as the leaves expand.

Scab lesions often run together, causing the terminals to die and the catkins to drop. When scab attacks young expanding leaves and nuts, it stunts and deforms them. The greatest scab damage occurs when the nuts become infected. Early-season infection can significantly reduce yield and quality. Nut shucks, infected early in the season, often drop or crack where scab lesions run together, and these lesions serve as points of entry for other pathogenic fungi.

The scab fungus survives the winter on plant parts infected the year before. Most spores are released in mid-April, just after bud break. Spores are spread locally by dew and splashing rain and over longer distances by wind. Scab spores need free moisture to germinate, usually supplied in the form of dew. Spores also require moderate temperatures to germinate, between 65 and 85 °F. This is a weather related disease, because with more rainfall and increased hot, humid conditions, the disease will become more severe. However, if the weather is dry with only minimal rainfall and less humidity, the impact of the disease will be significantly less. During favorable weather, the homeowner will typically see a healthy crop of nuts.

Improper fertilization and the excessive use of nitrogen can also produce favorable conditions for this disease. Therefore, it is highly recommended not to fertilize or lime without properly testing the soil (See HGIC 1652, Soil Testing)

Prevention & Treatment: The best way to reduce the overall impact that pecan scab will have is to plant scab-resistant pecan varieties. As of the summer of 2014, the following varieties are currently known to have the best resistance to this disease: Elliott, Excel, and Kanza. Others that offer average resistance are Cape Fear, Sumner, Creek, Candy, Moreland and Gloria Grand. However, resistance only means the trees are more tolerant of disease pressure and do not get the disease as severely. It does not guarantee that the pecan variety will not become infected at all.

Complete removal and destruction of leaves and shucks during the winter can reduce carry-over of scab. A very effective – but for homeowners not very feasible – means of controlling scab is a preventive fungicide spray program. It is critical to begin fungicide applications at bud break to prevent early scab infection. A continuation of sprays based on the label directions, weather, and rotating three different fungicides from nut start to maturity is recommended to mitigate this problem. Therefore, on average one can expect to make approximately 12 spray treatments during each growing season. In addition, thorough coverage of the entire tree canopy is very important, which makes spray treatments impractical for the homeowner.

Pecan leaf and nut are infected with the fungus Cladosporium caryigenum, which causes pecan scab.
Mark Arena, ©2014, Clemson Extension

Downy Spot

This fungal leaf spot, caused by Mycosphaerella caryigena, can cause early leaf loss on susceptible cultivars like Stuart, Pawnee and Moneymaker. Repeated defoliation from severe downy spot infection can cause losses in nut production and tree vigor. Downy spot first appears on the lower surface of young foliage in late spring as small yellow spots. These spots may turn white as spores are produced. Later in the season, the lesions turn brown and begin to appear on the upper surface of the leaf. Heavily infected leaves drop earlier than healthy ones in the fall. Downy spot survives the winter in fallen leaves. Spores are released prior to budbreak. Downy spot begins in the lower parts of the tree and spreads upward.

Prevention & Treatment: Plant resistant or tolerant varieties such as Schley, Success, Mahan and Western. Unfortunately, Schley and Western are highly susceptible to pecan scab and Success and Western are susceptible to shuck dieback. Remove and destroy fallen leaves. Apply a preventative fungicide spray program.

Brown Spot

Brown spot, caused by the fungus Cercospora fusca, only affects mature leaves and does not appear until June or July. Brown spot is found primarily in neglected orchards in areas that have abundant rainfall or high humidity. Primary lesions develop on the lower leaf surfaces as small dots, which enlarge and become reddish-brown with a gray cast. Brown spot may defoliate the tree by October if steps are not taken to control it.

Brown spot symptoms can be confused with those of Gnomonia leaf spot (see below). Brown spot lesions can develop beyond the lateral veins, while Gnomonia leaf spot lesions remain confined within the veins.

Prevention & Treatment: Brown spot is best controlled by keeping the trees healthy. Eliminate any stress by watering and fertilizing the trees when needed. Leaves on trees that are fertilized properly seldom are infected with the brown spot fungus. Fungicides that control scab also effectively control brown spot.

Gnomonia Leaf Spot

The fungus Gnomonia dispora only infects poorly nourished trees that are deficient in zinc. The first symptoms appear in June a few days after infection. The spots resemble those caused by the brown spot fungus, but as they expand, they are restricted by the lateral veins. They develop large, elongated, dead areas within the lateral veins. The fungus overwinters in fallen leaves.

Prevention & Treatment: Sanitation (the removal of dead and diseased plant material) and proper fertilization will control this fungus. Fungicides applied for scab control are also effective against Gnomonia leaf spot.

Liver Spot

Liver spot is a leaf disease caused by the fungus Gnomonia carvae. The first sign of the disease appears in May and June. Circular, dark brown spots appear along the midrib on the lower surface of the leaves. In late summer the spots turn a cinnamon brown or liver color. Liver spot can cause severe defoliation, particularly during prolonged periods of wet weather. Weak trees are more susceptible to liver spot than are healthy trees.

Prevention & Treatment: The best control for liver spot is keeping trees healthy by watering and fertilizing them when needed. This disease can also be controlled by fungicide sprays used for scab.

Zonate Leaf Spot

Zonate leaf spot, caused by the fungus Cristulariella moricola, causes severe defoliation of pecan trees during July and August of rainy summers. Leaf spots on the upper surface of pecan leaves are grayish brown, with concentric ring formations that are more distinct on the lower side of the leaf. Leaf spots on the lower surface are light brown in the center, becoming darker brown toward the edge. A film of crystalline-like fungal spores forms over the leaf spot surface. Leaves with extensive lesions dry out, curl up from the margins and eventually fall from the tree. The fungus overwinters in hard resting bodies, called sclerotia. The fungus requires moisture to develop, growing most rapidly when the leaves are wet.

Prevention & Treatment: Zonate leaf spot can be controlled through sanitation and fungicides. No pecan cultivars are known to be resistant to the fungus. Zonate leaf spot is a problem in areas with high soil moisture, high relative humidity and poor air movement. If pecan trees sustain sporadic outbreaks of zonate leaf spot, wild hosts such as hackberry, maple, poison oak, sassafras, Virginia creeper and other vines should be eradicated. Pruning out low tree branches will increase the air flow and permit better penetration of sunlight and drying of foliage. The following fungicides may be applied at first sign of the disease: copper hydroxide or thiophanate-methyl. Follow the instructions on the label. Preventative sprays are generally not required.

Anthracnose

Anthracnose is a fungal disease, caused by Colletrotrichum species. The disease starts as brown-black, sunken lesions on the leaves and shucks. There may or may not be cream to salmon-colored spores in concentric rings on shucks. The spores are spread during spring and early summer rainfall. The more frequent the rainfall, the greater the incidence of disease in the fall. The variety Wichita is very susceptible.

Prevention & Treatment: Plant resistant varieties. Remove and destroy infected plant material. There are no fungicides available for homeowners.

Powdery Mildew

This fungal disease, caused by Microsphaera alni, forms a characteristic superficial powdery-like growth on both the leaves and the nuts. Infected leaves are seldom seriously damaged by the fungus. Nuts are affected more adversely than leaflets. The amount of damage powdery mildew causes to nuts depends on their stage of development at the time of infection. Nuts infected early may abort or be undersized with poorly developed kernels. Nuts infected when they are mature sustain little or no injury from the disease.

Prevention & Treatment: Some pecan cultivars are more susceptible to powdery mildew than others. Stuart and Schley are extremely susceptible. Fungicides applied in the course of the regular scab spray program will control powdery mildew.

Crown Gall

Crown gall is caused by the bacterial pathogen Agrobacterium tumefaciens. The bacteria transform normal plant cells into tumor cells, which become wart-like growths of disorganized tissues. Initially, the tumorous growths can be confused with callus tissue, but later they become round, rough and dark. The bacteria can survive in the soil for several years. They enter pecan roots or stems near the soil line through wounds often caused by insects, grafting and cultivation. Galls reduce tree vigor by retarding the flow of water and nutrients in the vascular tissue. The external portions of the galls deteriorate from lack of water and slough off. These tissues often contain the bacteria and reintroduce them into the soil.

Prevention & Treatment: Crown gall is controlled through preventive cultural and sanitation practices. Only healthy, vigorous, disease-free trees should be planted. Take care during transplanting not to wound the roots and trunks. Biological control of crown gall with the antagonistic bacterium A. radiobacter strain K84 can only be used as a preventive measure since roots of healthy trees must be dipped in a solution of the bacterium prior to planting.

Shuck Dieback & Stem End Blight

The cause of shuck dieback and stem end blight is not fully known, but a Phomopsis species has been associated with these diseases. Both diseases kill shuck tissue and reduce nut quality. The cultivar Success is especially susceptible, but both diseases have been observed on a number of other cultivars as well. Shuck dieback is generally most severe on trees with large crops and on crowded trees. It usually begins with the shuck turning black and dying at or near the tip of the nut. The blackened area can spread over the entire shuck, and often the shuck will flare open. Almost any factor that stresses a tree can apparently increase the incidence of shuck dieback. Stem end blight begins as a brown or black spot on the shuck near the base of the nut. This black area usually enlarges to cover the entire nut. The nut can be easily dislodged from its stem. The earlier the symptoms of these two diseases appear in the season, the poorer the kernel quality.

Prevention & Treatment: No cultural practices or use of fungicides have been effective in controlling shuck dieback. Reduction of tree stress by application of sufficient irrigation to support the crop load, thinning and tree removal will greatly decrease the incidence of disease.

Note: Chemical control of diseases and insects on large trees is usually not feasible since adequate coverage of the foliage with a pesticide cannot be achieved.

By Julie Christensen

Pecan trees (Carya illinoinensis) are as beautiful as they are useful – growing 75 to 100 feet with a wide spreading canopy. Pecan trees are hardy in U.S. Department of Agriculture plant hardiness zones 5 through 10, although they are most commonly grown south of zone 7. In northern climates, they don’t bear nuts reliably.

Pecan trees can be damaged by many things, including poor, heavy soil, frost or high winds, and of course, disease. Treating diseases on full-grown trees is difficult because of their size. In most cases, prevention is a better strategy. Use disease-free seedlings and provide well-draining, light soil. Water the trees regularly during dry conditions to avoid drought stress.

Blotch

Large black or yellowish spots on the leaves are the main symptoms of blotch. This disease is rarely serious, but in some cases, it can defoliate the trees in late summer. It appears mostly on drought-stressed trees or trees with zinc deficiency.

Keep the trees healthy through proper watering and conduct a soil test to check for any nutrient deficiencies. Rake up and discard leaves in the fall to prevent the disease from overwintering.

Crown gall

This nasty disease causes brown or white nodules to form around the roots of the tree. As the disease progresses, the roots rot and the tree slowly loses vigor and dies. Unfortunately, there is no treatment for the disease. Buy disease-free trees from a reputable nursery and plant them in loose, well-draining soil. Do not plant pecan trees where crown gall has been a problem previously.

Powdery mildew

Powdery mildew affects many plants from lilacs to pumpkins to pecan trees. It appears as a white coating on the leaves and is rarely serious. It is most common in young seedlings. Use drip irrigation rather than overhead sprinklers to prevent its spread. If the condition is severe, treat it with the fungicides recommended for scab (see below).

Rosette

Rosette is caused by a zinc deficiency. In infected trees, you’ll first notice yellowing leaves in the tops of the trees. Later, leaves become small and entire branches may die back or become defoliated. To treat this condition, spray the leaves with a solution of 1 tablespoon zinc sulfate per gallon of water. You can also add zinc to the soil for a longer lasting solution. Make applications based on soil test results or at a rate of ½ pound per inch of trunk diameter. Spread the zinc evenly on the soil from the trunk to the drip line.

Scab is one of the most common diseases to infect pecan trees, depending on where you live. It first appears as damage to the leaves and nuts. Leaves develop olive brown splotches on the undersides of the leaves. As the disease progresses, the upper sides of the leaves develop markings, as well. In severe cases, the tree becomes defoliated, which can weaken the tree and reduce pecan production.

The nuts also develop olive-brown, velvety splotches on the husks. In some cases, the entire husk becomes covered or the nuts drop prematurely from the tree.

Although fungicides are available, the average home grower lacks the equipment necessary for application. Instead, your best strategy is to plant disease resistant varieties, such as Cape Fear, Desirable, Elliott and Chickasaw. Fungicides labeled for treating scab include Benlate 50WB, Enable 2F and Orbit 3.6EZ. Follow all package directions carefully and make applications every three weeks from the time leaves first emerge until the shells harden.

Wood or heart rot

These fungal diseases enter pecan trees that have been injured by storm, improper pruning or damage during home construction. Once the fungus enters the tree, it slowly rots the wood, weakening and eventually killing the tree. To prevent wood or heart rot, prune the tree regularly to remove branches damaged by ice or wind. Use proper pruning techniques and avoid ripping the bark.

For more information, visit the following links:

Evaluating Pecan Problems from Texas A and M University.

Pecan Diseases from Clemson University Extension.

Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.

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Monday – November 18, 2013

From: Gatesville, TX
Region: Southwest
Topic: Diseases and Disorders, Planting, Trees
Title: Young pecan trees with leaf and branch problems from Gatesville TX
Answered by: Barbara Medford

QUESTION:

I have a young pecan tree that had very rapidly browning Leaves. They became brittle and so did the branches with affected leaves. The branches soon fell off. We treated with fungicide during that process. We retained some healthy leaves and branches at the top of the tree.

ANSWER:

Because we probably do not have enough information to give you a complete answer, we are going to direct you to some other resources so you can do some research and compare conditions described and the conditions in your tree.

First, here is a previous Mr. Smarty Plants answer concerning twig and branch breakage; in this case, attributable to an insect called a “twig girdler.”

Another previous Mr. Smarty Plants question concerns some possible reasons for the early leaf drop, which include the fact that you may have a pecan cultivar that is not so well adapted to growth in your area as Carya illinoinensis (Pecan), which is the pecan native to Texas. While this USDA Plant Profile Map does not show Carya illinoinensis (Pecan) growing natively in Coryell County, it is shown growing in counties around it. Often when a plant does not show up in USDA plant records in a certain county, it is possible that it just has not been reported there. So, we hope you do have the native tree.

The previous plant questions we have linked you to have other possible reasons for your problem, but we would also suggest that you follow this link, Carya illinoinensis (Pecan), to our webpage on that tree in our Native Plant Database. Please note these growing conditons for that tree:

“Growing Conditions

Water Use: High
Light Requirement: Sun
Soil Moisture: Moist
CaCO3 Tolerance: Low
Cold Tolerant: yes
Soil Description: Rich, moist, well-drained soils. Sandy, Sandy Loam, Medium Loam, Clay Loam, Clay, Caliche type
Conditions Comments: The sweet, edible nut, makes pecan the best hickory for fruit production. The tree does not bear liberal quantities of fruit in the northern part of its range, but makes an interesting ornamental there. Susceptible to galls, twig girdlers, aphids, borers, weevils, pecan scab, tent caterpillars, and webworms. Slow-growing. Difficult to transplant because of a large taproot.”

This lists a need for plenty of water and a number of varmints and diseases that can affect the tree, as well as compatible soils. If you compare the conditions in which your tree is growing and find some discrepancies, that may answer your question. One more possibility we will throw in is transplant shock. You said your pecan was a young tree – how and when was it planted? We always recommend that woody plants (trees and shrubs) be planted in the coolest time of the year, November to January, especially in dry and hot Central Texas. Transplant shock caused by improper planting is one of the biggest reasons for tree death.

We will add one more suggestion; we suggest you contact the Texas A&M AgriLIFE Extension Education Office for Coryell County. They may know right off the bat what the problem is and recommended treatment due to others in your area possibly experiencing the same problems.

From the Image Gallery

Pecan
Carya illinoinensis
Pecan
Carya illinoinensis
Pecan
Carya illinoinensis

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I have black spots on my leaves and nuts. What is causing it and how can I prevent it?

The spots may be pecan scab disease, which is caused by a fungal pathogen. Severe infection of leaves can cause the tissue to die and result in leaf loss. Damage from infection of nuts can vary from complete crop loss to a minor loss of nut size depending on how severe the infection is and at what stage of nut development infection occurs. Pecan scab disease can be controlled by application of fungicides that prevent infection from occurring. Infections occur during rainfall periods, and generally four to eight fungicide applications are needed each year from spring through the summer months to prevent infection. The number of applications needed will depend on several factors, including the frequency and amount of rainfall and the susceptibility of the pecan cultivar to infection by the scab pathogen. To obtain adequate scab disease control, it is necessary to completely cover a tree with fungicide. Unfortunately, this requires an air-blast orchard sprayer for trees over 10-15 feet in height, and it is not practical to try to apply fungicide to a large tree growing in a yard.

Some level of disease control can be obtained by growing pecan cultivars with some resistance to infection. Cultivars with useful levels of resistance that are currently recommended for small plantings include Candy, Elliott, Melrose, Sumner, Jackson and Caddo. Caddo and Melrose are not recommended for the southern half of Louisiana. A description of these cultivars can be found at the USDA Pecan Breeding Program Web site.

More information can be found in the Fungicide Application Recommendations for Pecan Disease Control and in the Pecan Disease Synopsis on the Plant Pathology page of the .
Question answered by Dr. Randy Sanderlin, Pecan Research-Extension Station plant pathologist.

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday – December 24, 2008

From: Richland, IN
Region: Midwest
Topic: Trees
Title: Underdeveloped pecan kernels with brown spots
Answered by: Nan Hampton

our pecan tree was loaded this year. it is a soft shell . some of the pecan meats are not fully developed and have small dark spots on them. could this be a blyte of somekind and if so what can we do to correct this. we live in Southern Indiana Your description sounds like damage from sucking insects, the stink bugs (Family Pentatomidae) and leaffooted bugs (Family Coreidae). Here is information fromLouisiana State Universityand from University of Florida Extension Service about these insect pests that feed on the pecans and cause black (black pit) or brown (kernel spot) spots in the pecan meats. I suggest you contact your county office of the Purdue University Cooperative Extension Service for advice on current methods for controlling these insects.

Here is more information about diseases of Carya illinoinensis (pecan) from the Alabama Pecan Growers Association, Pecan Production Guidelines for Small Orchards and Home Yards from Arizona Cooperative Extension and a Field Key to Larvae in Pecans from Oklahoma Cooperative Extension Service.

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How to Identify and Control Pecan Scab

Pecans, the only native nut commercially produced in the United States, are an important crop in the Southern Great Plains. They are considered the third-most-popular nut in the U.S. and have become a profitable commodity for growers. However, there are many pests that growers must combat to produce quality pecans. Pecan scab is the most economically important disease of pecan in the southeastern U.S. and can significantly impact the amount of quality pecans produced in a season.

Pecan scab can be managed by removing orchard floor debris, thinning and pruning, and implementing a fungicide program.

What does pecan scab look like?

More than likely, the black spots you see on pecan leaves and shucks are due to pecan scab. Symptoms of the disease appear as small, dark lesions on the leaves, twigs and shucks. As the disease progresses, the lesions can expand and grow together. The easiest way to see the fungus actively producing spores is by using a hand lens.

Pecan scab appears as black spots on pecan leaves, twigs and shucks. As the disease progresses, the lesions can expand and merge to cover a larger surface area.

What causes pecan scab?

The disease is caused by spores produced by a fungus called Venturia effusa. Spores can be spread by wind or rain and cause new infections throughout an orchard. Venturia effusa is capable of several infection cycles throughout the growing season, which can contribute to greater disease severity.

The fungus needs wet conditions to initiate an infection on leaves or shucks, and young developing leaves are especially susceptible. If we have a wet spring, you can anticipate problems with scab on leaves starting early in the season.

It takes a microscope to see the individual spores that cause pecan scab. One spore is approximately 300 times smaller than a grain of rice.

How does pecan scab affect production?

Leaf scab can result in a reduction in photosynthesis as well as defoliation. Scab that occurs on the shucks during fruit development can impact the size of the harvested nut and percent kernel fill. The impact to overall yield will vary depending on the severity of nut scab.

How do I manage this disease?

Unfortunately, the pathogen is here to stay. However, with careful control measures, you can manage the disease.

The fungus likely overwinters in the orchard on the tree, in the leaf litter or on the shucks. These reservoirs of the pathogen can be the source for the coming growing season. You may be able to reduce these pathogen reservoirs by removing orchard floor debris.

Pecan scab can also be managed using cultural practices such as thinning and pruning, which help with airflow throughout an orchard.

If planting a new orchard, avoid low lying areas where humidity may be a problem. Consider planting resistant cultivars as part of your disease management strategy. Kanza and Lakota are two recommended cultivars with low scab susceptibility for Oklahoma and Texas.

If you have an established orchard of susceptible cultivars, the best way to manage scab is to implement a fungicide spray program to reduce the rate of disease. There are several other fungal diseases that can infect pecan, but they are usually controlled when using a fungicide spray program to control pecan scab. The first spray for scab control should be in early April at the prepollination stage. Spring rains likely provide the needed moisture for infection to occur. It is also important to follow a fungicide spray program throughout the season.

A look at pecan scab using a hand lens reveals the cause of the disease: spores produced by a fungus called Venturia effusa. These spores can be spread by wind or rain and cause new infections through-out the orchard.

Is there a cure for the disease?

There is unlikely to be a cure for pecan scab disease. However, Nikki D. Charlton, Ph.D., and Carolyn A. Young, Ph.D., of the Noble Research Institute’s mycology laboratory work on Venturia effusa. Their research on the life cycle of the fungus has resulted in a major breakthrough understanding the biology of this destructive pathogen. They have found that the pathogen has a sexual cycle that may initiate the disease at the beginning of the growing season. They have been able to produce a sexual cycle in the lab to produce progeny that may differ in their ability to infect pecan cultivars. This will eventually lead them to discover the features in the pathogen genome that contribute to the ability to cause disease. By better understanding the cause of the disease, they, and others, can work toward providing growers with new ways to manage the disease in their pecan orchards.

Pest & Disease Control for Pecan Trees

Every tree has the future potential for disease and insect damage. Factors such as location and weather will play a part in which issues your tree encounters. If available, disease-resistant trees are the best option for easy care; and for all trees, proper maintenance (such as watering, fertilizing, pruning, spraying, weeding, and fall cleanup) can help keep most insects and diseases at bay.

NOTE: This is part 7 in a series of 11 articles. For a complete background on how to grow pecan trees, we recommend starting from the beginning.

Trees appear stunted and slow growing; leaves may be reduced in size, little or no fruit. If tree is dead, inspect roots for hard, woody ‘tumors’. Note: many things can cause stunted trees.

Control

  • Consult County Extension Agent

Appear as small circular, olive-green spots that turn black on new leaves, leaf petioles and nut shuck tissue. Lesions expand and may coalesce, then fall out giving a shot hole appearance. Early infections may cause premature nut drop, but more commonly cause shuck to stick to nut surface (stick tights). Late infections can prevent nuts from fully expanding and decrease nut size.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Aphids

They are the size of a pinhead and vary in color depending on the species. Cluster on stems and under leaves, sucking plant juices. Leaves then curl, thicken, yellow and die. Produce large amounts of a liquid waste called “honeydew”. Aphid sticky residue becomes a growth media for sooty mold.

Natural Control

  • Bonide® Insecticidal Soap
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Pecan Nut Casebearer

Eggs are minute and change from white to pink. Larvae change from olive-gray to gray-brown and measure 1/2”, reddish brown head and sparsely covered with fine, white hairs. Adult moths are slate-gray with ridge of long, dark scales on laser end of forewings. They are 1/3” long with wingspan of almost an inch.
Larvae leave cocoon (located at junction of bud and stem) in early spring about time buds open, feed for about 2 weeks on exterior of opening buds. Then bore into tender shoots where they mature. Late May to early June, about time for pollination to occur, adults emerge and lay eggs on young nuts. 8-9 days later eggs hatch and larvae bore into nuts at stem end. Infested nuts are held together by frass and webbing and larvae feed inside nut for 3-4 weeks, pupates and 2nd generation of adults emerge in mid-July (in Missouri) and the cycle is repeated. A third generation of adults emerges in late August and September and larvae feed in nut shuck and on the leaves.
First generation is most damaging. Treat when all catkins have fallen and tips of nuts turn brown (after pollination), early June in Missouri. Timing is important and varies from year to year and from area to area.

Control

  • Consult County Extension Agent

Brown Leaf Spot

This is common in southern areas with high rainfall and neglected orchards. Reddish-brown spots often with gray rings. Can cause early leaf drop in fall, weakening tree.

Natural Control

  • Serenade® Garden Disease Control

Appears as whitish-gray powdery mold or felt-like patches on leaves and nuts. Leaves may fall off early and on nuts, shucks split and kernels shrivel.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Borers

Appears as a thick, gummy substance (SAP) leaking from round holes on the trunk or in crotch of the tree. Worms with brown heads and cream-colored bodies tunnel through trunk that will kill the tree. Once infested, use a fine wire to try to mash them or dig them out.

Natural Control

  • Dig out with thin wire or mash

Chemical Control

  • Bonide® Borer-Miner Killer

Sticky Shuck

During nut development when water begins to fill the nut. Part of the shuck turns black; nuts will not be completely filled.

Control

  • Consult County Extension Agent

Fall Webworm

Damage the leaves by both feeding and web building. Webworms over-winter within cocoons located in protected places, such as crevices in bark or under debris and fences. Adult moths emerge in summer. They have a wingspan of about 1 1/4″ and vary from pure satiny white to white thickly spotted with small dark brown dots. Females lay white masses of 400-500 eggs on the undersides of the leaves. The caterpillars hatch in 10 days and all from the same egg mass live together as a colony. They spin webs that enclose the leaves, usually at the end of a branch, to feed upon them. After they have defoliated a branch, they extend their nest to include additional foliage.
When caterpillars are mature, they leave the nest to seek a place to spin gray cocoons. The mature caterpillars are about 1 1/4″ long with a broad dark brown stripe along the back, and yellowish sides thickly peppered with small blackish dots. Each segment is crossed by a row of tubercles with long light brown hairs.

Natural Control

  • Bonide® Captain Jack’s™ Deadbug Brew
  • Bonide® Thuricide Bacillus Thuringiensis (BT)
  • Remove web with rake and burn or prune out

Pecan Weevil

Larvae are creamy-white grubs, C-shaped with reddish-brown heads and 1/2” long. Adult moths are light brown to gray and are about 1/2” long. The adult emerges as early as July 15 (Missouri), feed on nuts before they are completely formed, causing them to shrivel, the nut blacken and drop. Nuts may show a tiny, dark puncture wound extending through the shuck and unhardened shell. If larvae is found inside the nut before the shell hardens, indicates damage from other insect, usually nut curculio or hickory shuck worm.
The adult lays 2-4 eggs in separate pockets within each kernel. Grubs hatch in late August and feed for about a month then exit thru a hole about 1/8” beginning in late September. Pecan weevils remain in larval stage for 1-2 years 4-12” underground. They pupate in early autumn and become adults in about 3 weeks. The adults remain in the soil until the following summer. Complete life cycle is 2-3 years. Do not move very far from the tree under which they emerge, so certain trees may be infested while trees nearby are not bothered. Can be controlled with insecticide, but ours are not recommended.

Control

  • Consult County Extension Agent

Pecan Phylloxera

Appears as a small aphid-like insect that is seldom seen, but produces galls that are easily visible. Severe infestations cause malformed, weakened shoots that finally die and can even kill entire limbs. The insect over winters as eggs in the dead body of female adult in protected places on the branches of pecan trees. After bud break the eggs hatch and the insects feed on opening buds or leaf tissue. These are known as ‘stem mothers’. Their feeding stimulates the development of galls, which enclose the insect in a few days. The stem mother matures inside the gall and lays eggs, which emerge in mid-summer as adults and continue the cycle. Only need to treat when galls are in large numbers on shoots or nuts.

Control

  • Consult County Extension Agent

Nut Curculio

Adults are dark-gray to reddish-brown, 3/16” long, larvae are legless, creamy-white, 3/16” long and found within immature pecans. The adults attack immature pecans from mid-July to mid-August. Make punctures in the shucks where they deposit an egg. Eggs hatch in 4-5 days and the larvae feed for 10-14 days. This causes a bleeding of brown sap on the shuck and also premature nut drop. Larvae exit from a small hole and enter the soil. Adult emerges 4 weeks later, in September and October and over winters in ground trash.

Control

  • Consult County Extension Agent

Hickory Shuckworm

Adult moths are dark-gray nocturnal flyers, 3/8” long. Larvae are creamy-white with brownish heads, 3/8” long. Pupae, found within the shuck, are dark brown and up to 1/3” long. When larvae feed in the interior of the nut, mid-July until shell hardening in mid-August, premature nut drop can occur. Larvae pupate in the nuts and third generation moths emerge in early August. Damage from Hickory Shuck worms can be eliminated if insecticide sprays can control these moths.

Natural Control

  • Bonide® Captain Jack’s™ Deadbug Brew

Navel Orangeworm

Caterpillar is ¾ inch long, reddish orange to yellow. Adult moths have irregular, silver gray and black forewings and legs, snout like at front of the head. Eggs are white at first and later orange before hatching. Larvae are reddish orange then vary from milky white to pink. Pupae are light to dark brown. Larvae bore into nutmeat and later consume most of the nut. Producing large amounts of webbing and a fine powdery residue. They will over winter in mummy nuts in tree or on the ground.

Natural Control

  • Bonide® Captain Jack’s™ Deadbug Brew

Chemical Control

  • Bonide® Borer-Miner Killer

Peach Twig Borers

Adults of this insect are clearwing moths, metallic blue to black in color with bright bands of orange or yellow. They are about 13 mm long with wings folded and their forewings have a black apical band. Larvae are about 18 mm long, white with brown heads.
Symptoms:

  • Build up of reddish brown frass and gummy exudates known as gummosis. Check branch crotches on larger branches or upper trunk.
  • Heavy infestation may cause branch dieback.
  • Young tree maybe girdled and killed older trees may be weakened.

Natural Control

  • Bonide® Captain Jack’s™ Deadbug Brew

Chemical Control

  • Bonide® Borer-Miner Killer

In This Series

  • Introduction

Getting Started

  • Acclimate
  • Location
  • Planting
  • Soil Preparation

Care & Maintenance

  • Fertilizing
  • Pest & Disease Control
  • Pruning
  • Spraying
  • Watering

Other Topics

  • Harvesting

Pecan

Description

Pecan, Carya illinoinensis, is a large deciduous tree in the family Juglandaceae grown for its edible seeds (nuts). The pecan tree has a thick gray-brown trunk which can reach 2 m (6.6 ft) in diameter and a rounded canopy that spreads . The bark is ridged and has a scaly appearance. The twigs of the tree are red-brown in color and the foliage is dark green. The leaves are pinnately divided and composed of 9–17 oblong-lanceolate leaflets. Each leaflet has as serrated margin and a downward curving tip. The tree produces separate male and female catkins with the male producing pollen and the female developing into the fruit. The male catkin is slender and pendulous, measuring 22–50 cm (8.7–19.7 in) in length and the female catkins are much smaller and possess 3–6 flowers in a cluster. The fruit is an oval–oblong drupe containing a single seed surrounded by a thin shell. The outer husk (shuck) is green, turning brown-black when mature at which point it also splits open to release the nut. The edible kernel of the nut is light brown in color and ridged longitudinally. Pecan trees can reach a height of 40–50 m (131–164 ft) and can live for several hundred years in a wild state. Commercial trees usually have an economic lifespan of approximately 25 years. Pecan originates from the North America, specifically, the South.
Pecan fruits on the tree

Pecan inflorescence
Pecan inflorescence
Pecan
Pecan husks
Pecan tree ‹ ×

Uses

Pecan nuts are consumed fresh or after roasting as a snack food or may be used as an ingredient in baked goods or confection

Propagation

Basic requirements Pecan trees have a high water requirement and within their native range they are found growing in deep soils where their extensive roots can reach the water table or along river banks or streams. Pecan trees thrive in areas with long hot summers and cool winters. Trees can be grown in a range of soils but will grow optimally in a deep, well draining clay loam or sandy loam with a pH 6.0–7.5. Growing multiple pecan trees requires a great deal of space as the trees can reach a very large size. Propagation Pecan trees can be propagated from nuts or by budding or grafting. Nuts for propagation should be collected in the Fall from trees which gave good fill. The seeds require stratification prior to planting. Stratification is the name given to a cold treatment which breaks the dormancy of the seed, speeding the germination process. Nuts are stratified at 2–5°C (35.6–41°F) for a period of 3- to 90 days and then incubated at room temperature. Nuts should be soaked in water for 24 hours prior to the treatment and kept moist throughout by mixing the nuts on moist vermiculite. The nuts can be planted outdoors in late winter if they are planted in place. if growing the seedlings in containers it is best to wait to plant until all threat of frost has passed. Seedling or grafted trees should be planted in full sun to part shade although trees are sensitive to shading and care should be exercised to ensure that the trees are not too shaded. Trees should be spaced 9–10 m (30–35 ft) apart General care and maintenance Newly planted trees must be supplied with adequate moisture to meet their growing requirements in the first few years following planting. Trees must be supplied with 10 to 15 gallons of water weekly. This water can come from rainfall, irrigation, or a combination of both. Fertilization rates should ideally be based on the results of a soil test prior to planting but generally, 4 lbs of a complete fertilizer should be applied in a circular area around the base of the tree measuring 25 square feet. Fertilizer should never be placed directly in the planting hole as it can cause damage to the tree roots. A subsequent similar application in the summer should be enough to meet the growth requirements of the tree. The following year, apply 4 lbs of complete fertilizer per inch of tree diameter. Fertilizer should not be placed within 30.5 cm (12 in) of the trees trunk. Harvesting Pecans should be harvested as soon as the nuts have reached maturity, when the shuck has lost its green color and has started to split. in commercial plantations, hydraulic shakers may be used to dislodge the nuts from the tree.
Anderson, P. C. & Crocker, T. E. The Pecan tree. University of Florida IFAS Extension. Available at: https://edis.ifas.ufl.edu/pdffiles/HS/HS22900.pdf. . Free to access. CABI Crop Protection Compendium. (2008). Carya illinoinensis (pecan) datasheet. Available at: http://www.cabi.org/cpc/datasheet/17234. . Paid subscription required. Carroll, B. Starting pecan trees. Oklahoma Cooperative Extension Service. Available at: http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-1012/F-6207web.pdf. . Free to access. Polomsky, B. & Shaughnessy, D. (1999). Pecan planting and fertilization. Clemson Cooperative Extension. Available at: http://www.clemson.edu/extension/hgic/plants/vegetables/tree_fruits_nuts/hgic1356.html. . Free to access. Teviotdale, B. L., Michailides, T. J. & Pscheidt, J. W. (eds) (2002). Compendium of Nut Crop Diseases in Temperate Zones. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/42848.aspx. Available for purchase from APS Press.

New Strategies To Thwart Pecan Scab


Healthy pecan fruits. Foliar applications of nickel may protect pecans from the fungus that causes scab.
(D2911-1)

Pecans are great for eating out of the shell or in a myriad of recipes. But abundant pickings of high-quality nuts are only possible if the tree escapes the devastating disease called “pecan scab.” Caused by the fungus Fusicladium effusum, it is the most destructive disease of pecan in the southeastern United States. When scab is severe, most often when rainfall is above average, nut size is reduced, and total crop loss might occur.

Scientists at the Southeastern Fruit and Tree Nut Research Laboratory in Byron, Georgia, are working to help pecan growers mitigate the effect of pecan scab. Research leader Bruce Wood, plant pathologists Clive Bock and Michael Hotchkiss, and entomologist Ted Cottrell are using various approaches to reduce the impact of scab.

Their studies were described in a series of papers in the journals HortScience, Plant Disease, and Crop Protection.

Wood and his colleagues determined that timely foliar applications of nickel to tree canopies can improve tree resistance to the pecan scab pathogen. Nickel is toxic to the scab fungus, providing additional protection.


Pecan fruit showing symptoms of pecan scab. The black lesions are diseased areas where spores of the scab fungus are produced.
(D2910-1)

“We combined nickel as a nutritional supplement with fungicides and applied them as air-blast sprays to commercial orchards,” says Wood. “On the cultivar Desirable, the reduction in scab severity due to nickel varied from 6 to 52 percent. Fruit weight and kernel filling also increased, apparently from improved disease control.”

Bock and colleagues found that phosphite controlled pecan scab on both foliage and fruit early in the growing season. It also reduced disease on mature fruit, but not as well as an industry standard fungicide, triphenyltin hydroxide. However, scab on fruit late in the season is cosmetic and was previously shown by ARS scientists to have no effect on nut quality or yield.

“In our field tests, phosphite was directly toxic to the pecan scab fungus at concentrations similar to those in the lab,” says Bock. “Phosphite provides an alternative chemistry for growers to consider. This is particularly useful because the scab fungus has developed resistance to some fungicides currently used for control.”

Bock and his colleagues also studied whether fungicides applied from ground-based sprayers are providing adequate scab control in mature pecan trees, which can be 60 to 80 feet tall. They determined that, in pecan trees that did not receive fungicide, the disease was most severe in the lower canopy and least severe at the top of the tree. But in trees that did receive fungicide, disease was reduced only up to a height of 40 feet; above that, there appeared to be no effect of fungicide on disease severity, compared to the nontreated trees.

“There was a consistent reduction in scab severity on foliage and on immature fruit through August due to fungicide treatments below 40 feet,” says Bock. “Where tall pecan trees preclude effective ground-based spray coverage, aerial application might be an option to reduce the severity of scab in the upper canopy. The efficacy of this option is currently being investigated.”—By Sharon Durham, Agricultural Research Service Information Staff.

“New Strategies To Thwart Pecan Scab” was published in the August 2013 issue of Agricultural Research magazine.

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