Diseases of lemon trees



When it comes to tree disease treatment, tree fungus treatment and keeping your trees and shrubs healthy, never underestimate the significant threats that are too small to see. Fungi, bacteria, and other microorganisms may not be as visible as exterior bugs and birds, but they present every bit as serious a danger to the life and health of your property. Fungus can affect leaf, bark, trunk, or other parts of a tree. It is important to watch out for the symptoms of the most common tree diseases in Southeast Michigan, as well as to take preventative measures that stop them from infecting your plants and curative measures to eliminate infections that have already started. Our tree care services and pest control services are designed to keep your trees and shrubs in good condition for the long haul.


In order to protect your plants from infection, it’s first necessary to recognize the sheer variety of diseases that trees ​are susceptible to in Southeast Michigan. These include:


Of all the diseases that can attack your trees, rust is one of the most varied. A family of fungus with thousands of members, rust gradually grows on the leaves of your trees, undermining it and creating an unsightly, orangish appearance. Responding to fungus quickly using a tree disease treatment and tree fungus treatment company such as Safari Tree is critical if you are to protect the health of your trees and the beauty of your yard.


In the battle to protect your yard from ​tree diseases and pests, some of the most serious threats are also among the subtlest. This is especially clear with leaf spot disease, a family of plant illnesses that are often difficult to separate from more mundane threats to your lawn and garden.


This tree disease is a grave threat to your trees. Characterized by a variety of symptoms, Anthracnose spreads quickly and causes serious damage. Anthracnose is a fungus that thrives in moist, cool climates which is why it is so prevalent in Michigan.


So named for the part of the tree that it attacks, needle cast disease is common throughout the Midwest. Needle cast infects spruce tree needles, quickly spreading from tree to tree. The sooner you treat needle cast disease, the better chance your trees have.


A tree canker is an indicator that your tree is suffering from an infection. Cankers typically form around a fungal infection or bacterial infection. Cankers tend to ooze liquid and possibly develop a foul smell. Clearing up a tree canker will help restore a tree back to health.


Oak wilt is bad news for oak trees. This tree disease is caused by invading fungus that eats away at the tree from the inside. Oak wilt commonly affects both red and white oak trees. This tree disease should not be taken lightly because of how quickly it can kill an oak tree.


Fungal infections present an enormous risk to plants in your yard, and trees are no exception. No matter how strong and healthy your trees are, they’ll always be vulnerable to fungus, which can penetrate nearly every part of these organisms, spread through them, and deprive them of the nutrients they need to survive.


Diplodia tip blight is a very harmful disease that affects several species of pine, especially in the Michigan area. Learn more about this tree disease and how Safari Tree can help your trees fight back.


  • Apple Scab – A fungal infection, apple scab infects both apple and ornamental crabapple trees. It causes yellow and dark green spots to form on the leaves, which gradually make the leaves wilt and fall off. The disease also infects the fruit, and dark spots can even spread to the lower sections of the plant.
  • Anthracnose – This fungal infection affects both shrubs and trees and tends to thrive in environments that are cool or moist. It causes wet, dark spots to form throughout the plant, particularly on the leaves, fruit, and stems. While anthracnose will not directly destroy your trees and shrubs, it does make them weaker, increasing the chance that they will be taken down by other diseases or by pests. This makes it important to address and eliminate this disease as quickly as possible.
  • Black Knot – This fungus causes a stark black gall to grow around the branches and stems of your trees, which is bumpy and rough to the touch. It attacks fruit trees, with a particular tendency to damage cherry and plum plants. It does not directly destroy the trunk of your trees, but it does open them up to infection from other fungi and bacteria that will destroy them.

Thanks to our region’s cool, wet climate and heavily forested countryside, virtually all yards in Michigan are vulnerable to these diseases. Even if you have never noticed them on your trees before, spores can blow them onto your property from miles away with little or no notice. Thus if you want to keep your trees in good condition, you must come up with a plan to prevent and manage these diseases.


Safari Tree is a tree disease treatment and tree fungus treatment company committed to eliminating every manner of tree disease quickly and comprehensively. We invest heavily in proactive care, preventing tree diseases from ever arising through:

  • Deep Root Feeding- Under our standard Tree Care Program, we fertilize your trees’ deep roots both during the spring and in the fall. This helps trees grow stronger, allowing them to resist any diseases that attack them more effectively.
  • Fungal Spray- We apply several rounds of fungal spray throughout the summer, which kills any spores that land on your tree or fungal illnesses that are at an early stage of development. As a result, fungi cannot establish themselves on trees, limiting their ability to spread and severely harm your yard.
  • Insect Control- By spraying insecticides periodically during the summer and applying dormant oil to keep them away in the spring, we not only directly protect the trees from insects. We also prevent insects from leaving openings for fungi to get into the plants.

In addition to preventing illness through our Tree Care Program, our team can eliminate established tree diseases as soon as you report them. We invest in a range of fungicides and other products that eliminate infections and will assess your trees in detail and determine which specific products they need to recover.

We then apply those products as many times as necessary to stop the disease. We will also advise you on how best to water and prune your trees, clear away debris, and otherwise address the conditions that cause tree diseases to spread. Don’t leave your trees exposed to fungus, bacteria, and other serious plant diseases in Southeast Michigan. For more information on our tree disease treatment, tree fungus treatment, and prevention services or to obtain a free estimate for your yard, contact Safari Tree today.

How To Get Rid of Black Fungus on My Tree’s Trunk or Branches

There’s nothing quite like picking fresh fruit from trees and biting into it–savoring its sweetness. What’s not so sweet? Spotting a fuzzy fungus as you reach for your tasty treat.

Not only does a fruit tree fungus spoil an appetite, but it also sparks all kinds of questions about tree health.

Cyndy W. from California asked, “It looks like my plum tree has a fungus growing on it, and I don’t know how to treat it or if it will spread and I’ll have to take the tree down. It is a white and hard growth in two different locations.”

Find out which fruit trees get infected with this fungus and learn whether treatment or tree removal is the best option.

Black Knot Fungus: What It Is and The Treatment That Gets Rid of It

Above, Cyndy’s tree appeared to have a white fungus, but don’t ignore your tree if that’s not exactly what you see. Black knot disease can look different, depending on the stage it’s in.

What is this black fungus on my tree trunk or branch?

It’s likely black knot, which is a fungal disease that most frequently attacks plum and cherry trees. In spring, a velvet-like green appears on branches. It gradually grows and becomes hard and black by fall, which is usually when you’ll spot it.

The following year, the fungus starts to expand. The chunky, black growth gets larger, wraps around branches and may invade the tree’s trunk.

In some cases, older black knots will turn white or pink, like on Cyndy’s tree. But, typically, you’ll see a solid (albeit lumpy) black growth.

What trees get black knot fungus?

Primarily, this fungus goes after plum and cherry trees, especially American plum, purple-leafed plum and chokecherry. It can affect other fruit trees, like apricot and peach, but it’s not as common.

Can you eat plums and fruit from trees with black knot?

Because the disease only affects the tree’s wood, it’s A-OK to eat fruit from trees with black knot. But as always, check that the fruit is fresh before digging in.

How to Treat or Get Rid of Black Knot on Trees

The best way to get rid of black knot disease is to have your arborist prune out the affected branches. Specifically, here’s how they’ll approach the treatment of black knot on your trees.

  1. Check the damage. See if your tree is worth saving. If your tree has a significant number of infected branches, it might be better to remove and replace it with a black knot resistant plum tree. Susceptible trees often become reinfected in future years.
  2. Wait it out. If your tree only has a bit of damage, your arborist will wait until the dormant season (when the tree loses its leaves) to begin pruning.
  3. Clean up right. When a professional treats black knot, they’ll destroy removed parts to completely get rid of the fungus and all its spores.

Photo Credit:
Joseph O’Brien, USDA Forest Service, Bugwood.org

Citrus diseases and their control

Citrus diseases and their control

18.7.2017 0

Major Citrus diseases are given below:-

1.Gummosis: Phytophthora parasitica, P. palmivora,P. citrophthora

  • First symptoms are dark staining of bark which progresses into the wood.
  • Bark at the base is destroyed resulting in girdling and finally death of the tree.
  • Bark in such parts dries, shrinks and cracks and shreds in lengthwise vertical strips.
  • Later profuse exudation of gum from the bark of the trunk.
  • Infection extends to crown roots.
  • Prolonged contact of the trunk with water as in flood irrigation; water logged areas and heavy soils.
  • Soil inhabitants.
  • Sporangia spread by splashing rain water, irrigation water and the wind.
  • Irrigation water and wind.
  • Injuries to crown roots or base of the stem during cultural operations should be avoided.
  • If the lesion has girdled less than ½ the girth, remove the diseased bark with a knife along with ½” of uninvaded bark.
  • The bark of trunk should be coated with Bordeaux paste.

2.Scab/Verucosis: Elsinoe fawcetti

  • Attacks leaves, twigs and fruits of mandarin.
  • Sour orange, lemon, mandarin, tangelos extremely susceptible Grapefruit, sweet oranges and acid lime highly resistant. Severe in rainy seasons.
  • On the leaves, the disease starts as small pale orange coloured spots.
  • The leaf tissue is distorted to firm hollow conical growths with the lesion at the apex.
  • The crest of these growth becomes covered with scabby corky tissue colour at first but later becomes dark olive with age.
  • Lesions most common on the undersurface of the leaf. They penetrate leaf and are later visible on both sides.
  • Infected areas run together and cover a large area.Leaves wrinkled, distorted and stunted.
  • On twigs, similar lesions are produced.
  • They form corky outgrowths.On fruits irregular scably spots or caked masses produced.
  • Cream colour in young fruits; dark olive grey in old fruits.
  • Fruits attacked when young become misshapen with prominent warty projections. They drop prematurely.
  • Spray Carbendazim 0.1%

3.Citrus Canker: Xanthomonas campestris pv citri

canker on fruit

canker on leaf

  • Acid lime, lemon and grapefruit are affected. Rare on sweet oranges and mandarins.
  • Affects leaf, twig and fruits. In canker, leaves are not distorted.
  • Lesions are typically circular with yellow halo; appear on both sides of leaf, severe in acid lime (difference from scab) When lesions are produced on twigs, they are girdled and die.
  • On fruits, canker lesions reduce market value.
  • Streptomycin sulphate 500-1000 ppm; or Phytomycin 2500 ppm or Copper oxychloride 0.2% at fortnight intervals.
  • Control leaf miner when young flush is produced.
  • Prune badly infected twigs before the onset of monsoon

4.Tristeza or quick decline: Citrus tristeza virus (CTV)

  • Lime is susceptible both as seedling or buddling on any root stock.
  • But mandarin and sweet orange seedlings or on rough lemon, trifoliate orange, citrange; Rangpur lime root stocks tolerant; susceptible root stocks are grape fruit and sour orange.
  • In sweet orange or mandarin on susceptible root stocks, leaves develop deficiency symptoms and absise.
  • Roots decay, twigs die back. Fruit set diminishes; only skeleton remains.
  • Fine pitting of inner face of bark of sour orange stock.
  • Grapefruit and acid lime are susceptible irrespective of root stock.
  • Acid lime leaves show large number of vein flecks (elongated translucent area).
  • Tree stunted and dies yield very much reduced. Fruits are small in size.
  • Use of infected bud wood and Toxoptera citricida (aphid) is the important vector.
  • For sweet orange and mandarin, avoid susceptible root stocks.
  • For acid lime, use seedling preimmunised with mild strain of tristeza.

5.Greening : Liberobactor asiaticum ( Phloem limited bacteria)

  • This disease affects almost all citrus varieties irrespective of root stock.
  • Stunting of leaf, sparse foliation, twig die back, poor crop of predominantly greened, worthless fruits.
  • Sometimes only a portion of tree is affected.A diversity of foliar chlorosis.
  • A type of mottling resembling zinc deficiency often predominates.
  • Young leaves appear normal but soon assume on outright position, become leathery and develop prominant veins and dull olive green colour. Green circular dots on leaves.
  • Many twigs become upright and produce smaller leaves.
  • Fruits small, lopsided with curved columella. The side exposed to direct sunlight develops full orange colour but the other side remain dull olive green.
  • Low in juice and soluble solids, high in acid. Worthless either as fresh fruit or for processing. Seeds poorly developed, dark coloured, aborted.
  • Infected budwood; psyllid vector-Diaphorina citri
  • Control psyllids with insecticides.
  • Use pathogen free bud wood for propagation.
  • 500 ppm tetracycline spray, requires fortnightly application.


  • TamilNadu Agritech Portal

Citrus Insects & Diseases

Citrus Diseases

Citrus Canker

Citrus canker is a highly contagious bacterial infection of citrus trees causing yellow halo-like lesions or scabs on the fruit, leaves and twigs of citrus trees. Severe infections can cause leaf loss, blemished fruit, fruit drop and die back. The canker bacterium spreads easily and quickly on air currents, insects, birds and on humans by means of clothing and infected implements. There are a variety of sprays designed to protect against infection including using Liquid Copper Fungicide as a preventative treatment, especially when citrus canker has been detected in the area. Unfortunately, already infected trees are generally destroyed quickly to slow down the spread of the bacteria.


Melanose is a fungal infection of young citrus fruit, primarily but not exclusively grapefruit. The scabbed fruit rind does not affect fruit quality but it is unsightly. The disease is generally more severe in older trees over 10 years of age. As the fungus propagates in dead wood, prompt pruning is an effective way of combating this disease. Liquid Copper Fungicide say can also be used as a treatment.

Greasy Spot

Greasy spot is another fungus disease of citruses. Telltale signs include yellowish-brownish blister spots on leaves, often on the underside of the leaf. As the disease develops, the spots develop into oily looking blisters. Greasy spot can cause significant leaf loss, particularly during winter and can also infest citrus, particularly grapefruit, rind. To control Greasy Spot, regularly collect and remove any fallen leaves, thus reducing the source of new spores. Spay the tree with Liquid Copper Fungicide in June or July. A second spray application may be needed to be applied in August or September to protect late-summer growth.

Sooty Mold

Sooty mold is a fungus, which causes the blackening of the leaves of citrus trees. The mold forms on the leaves as a result of honeydew secretions from insects such as whiteflies, aphids and mealybugs. Insect control is the most effective way to prevent the incidence of this disease. To control the insects and prevent the secretion of their honeydew discharge, spray the tree with Bug Buster Insecticide. When spraying the tree ensure that both the top and undersides of the leaves are adequately sprayed. A second treatment spray may be required about 10 to 14 days later depending on the severity of the insect infestation.

To control and eliminate the mold growth that has already developed, spray the tree with Liquid Copper Fungicide. Generally one application of Liquid Copper is adequate for sooty mold control, but a second application about 14 days later may be required in major outbreaks.

Root Rot

Root Rot also referred to as Brown Rot or Collar rot is a tree disease caused by the soil-inhabiting fungus from the phytophthora species. Symptoms of this disease are dark brownish patches of harden bark on the trunk of the tree. It is common for ooze to seep from the dark brown infected area. Over time, as the disease advances the bark dries, cracks and dies. The infected area is then left as a dark sunken canker. The disease can also cause browning and decaying on the fruit and yellowing and die-back on the foliage. The disease causing fungus inhabits the soil and is most prevalent in wet soil and during periods of excessive rain. The fungus then attacks the fruit as it is splashed up on the tree by rain or irrigation spraying.

To control for brown rot it is important to remove all leaves and damaged fruit when it falls to the ground; prune of all lower branches off the tree so that the tree branches are more than 2 feet from the ground; spray the tree with a fungicide, when the disease is identified and again the following spring to prevent reinfection. There are two fungicides that can be used to control for the Brown Rot fungus: Agri-Fos and Captan.

Insect Pests


Aphids, when in small numbers, do little damage to a tree, however, under favourable conditions the aphid population can grow very rapidly and cause serious damage to a citrus tree during the growing season. The aphids attack the tree by sucking the sap out of the leaves. The symptoms are very visible on the leaves in the form of multiple puckered marks, yellowing and the twisting of the leaves, which gives the appearance of deformed leaves. As the severity of the aphid infestation increases, leaf drop and twig and branch die back can be seen.

Often during an aphid infestation, the leaves appear to be dripping sap from the underside of the leaves. This is actually an excretion from the aphids and is called honeydew. It often drips onto other leaves, other plants and on to the ground. The honeydew then becomes an attractant to ants, which feed on it. In most cases the ants are only symptoms of the honeydew and are not actually attacking or hurting the tree.

Aphids can be controlled using newer and safer insecticides, rather than older more harmful chemicals. For major outbreaks spray the tree with either Bug Buster or Trounce. The spray should be directed at the undersides of the leaves and other areas of visible feeding and insect concentrations. Normally only one or two spray treatments are required to achieve control. For less severe infections or as a preventative treatment, spray the leaves with Insecticidal Soap in the early summer and as needed.

Citrus Whitefly

The citrus whitefly is a tiny white winged insect that is about 1/12 of an inch in length. It is most commonly found feeding on the underside of the tree’s leaves. When the branches are shaken, the Citrus whitefly will rapidly take flight and can be seen fluttering around the tree. In addition to feeding on the citrus tree, the whiteflies also lay their eggs on the underside of the leaves. When the eggs hatch, the juveniles are small oval, almost transparent larva, which attach themselves to the underside of the leaves and begin sucking the sap from the leaves. As a result, the tree’s leaves begin to curl and appear to be covered with a sticky, sooty mold substance.

The mold like substance is actually honeydew that is excreted by the whiteflies because they are not able to metabolize all of the sugars contained in the leaf sap. The honeydew can often be seen dripping from the tree’s leaves and becomes an attractant to other insects such as ants.

Over the growing season, several generations of whiteflies can emerge. To effectively control Citrus Whiteflies spray the tree with Bug Buster or Trounce. It is hard to achieve full control of the adult flies, but several sprayings of the tree with either Trounce or Bug Buster will significantly reduce the juvenile population and in doing so the overall population.

Orangedog Caterpillars

The Orangedog caterpillar is a large caterpillar about 1.5 to 2 inches in length. Its body is a brown color. The caterpillar attaches citrus trees by eating the tree’s leaves. A good indicator that the Orangedog Caterpillar is attacking a tree is leaves throughout the tree appear to be partially eaten or chewed from the outer edges.

The caterpillar is the juvenile stage of the black and yellow swallowtail butterfly that is common in most areas of Florida. The adult butterfly lays her eggs on new citrus leaves and as the eggs hatch and new caterpillars emerge, they can very rapidly defoliate an entire tree in on a few days.

To control the Orangedog caterpillar, physically remove and destroy the caterpillars by hand. It is important to note that the caterpillars when disturbed will push out two red hornlike antennas from just behind their head that emit a strong repugnant smell. If the infestation is intense or physically removing the caterpillars is not possible, the Orangedog caterpillar can be controlled by straying the tree with Garden Insect Spray with Spinosad or BTK Biological Insecticide Bacillus thuringiensis (Bt). Both of these products are safe to use around the home and garden and are made from a naturally occurring bacteria. Be sure to completely spray the tree. With the BTK a second spraying will likely be required in about 7 to 10 days. With the Garden Insect Spray with Spinosad a second spraying may be required in 3 to 4 weeks, depending on the severity of the infestation.

Citrus Thrips

When a tree is infected with Citrus Thrips the most visible sign of the infestation are shrivelled leaf buds and leaves that are curled, distorted and often a silvery grey color. The fruit may be scabbed, streaked or a silvery color.

Citrus thrips are tiny orange or pale yellow insects that attack citrus as well as many other types of fruit trees. They mainly attack young leaves and juvenile fruit and feed on the tree’s sap. The adult thrips lay their eggs in the fall and the juvenile thrips emerge the following spring and begin feeding on the new leaves and fruit. The damage continues throughout the growing season and is most noticeable during hot, dry weather when the tree is already under moisture stress.

To control Citrus Thrips spray the tree with Garden Insect Spray with Spinosad. A few repeat spray applications may be required every 14 to 21 days to achieve full control. Garden Insect Spray with Spinosad is safe to use around the home and garden and is approved for organic gardening. It is also important to keep the tree well irrigated and property fertilized, (see TreeHelp Annual Care kit for Citrus) to help maintain the tree’s vigour.

Brown Soft Scale

Brown soft scale is a common problem on citrus trees, as well as many other types of trees. Soft scale insects are small, non-mobile insects that attached themselves to the wood, foliage and sometimes the fruit. Scale is most common on the new tender woody growth. When adult scale is attached to the tree, it often appears as crusty or waxy bumps on the tree, often it is mistaken for part of the tree’s own growth, but it is actually an insect. The scale sucks sap from the tree and causes the leaves to turn yellow and drop. Often a sticky substance can be found near the scale or on the leaves. This is a secretion from the scale called honeydew and often acts as an attractant for ants or as a growing source for sooty mold.

In the spring or mid-summer, small, almost invisible nymphs emerge from under the female shells and move to infect new areas of the tree. This is the only time in the life cycle of scale that the insect moves.

To effectively control scale insects and limit damage, Horticultural Oil should be sprayed on the tree. The Horticultural oil serves to suffocate the scale and eggs. In the spring or early summer if the crawling nymphs are present, spray the trees with Bug Buster to prevent the new nymphs from further infecting the tree.

Citrus Bud Mite

The citrus bud mite generally attacks lemons, particularly in coastal areas. It is a small-elongated insect with four legs near the mouth and a tapered posterior. As the incidence of this insect peaks in summer, summer and fall lemon blooms are most at risk. The bud mite is difficult to detect but large infestations may be visible by closely examining fruit buttons. To control Citrus Bud Mites spray the tree with Bug Buster or Trounce.

Citrus Red Mites

Like most mites, the citrus red mite is an extremely tiny pest, only 1/50th of an inch long and red or purple in color. These mites infest leaves and fruit. Intense infestations during hot, dry weather can cause leaf drop. To control Citrus Bud Mites spray the tree with Bug Buster or Trounce.


When snails are present it is common to see holes chewed into leaves and the fruit may be pitted or scarred. You may also see silvery trails winding around the trunk and branches near the soil. Lifting lower branches and inspecting under leaf debris under the tree can also detect snails.

To control for snails, a proper sanitation program around the tree is important. Clean-up and remove all leaf debris under the tree. The leaves on the ground become a good breading and hiding place for snails. Prune and remove any low hanging branches, especially lower braces that may be touching the ground. In addition to a proper sanitation program place Slug and Snail Bait on the ground around the tree trunk. A series of circular rings around the trunk is the most effective placement. Placing a physical barrier on the tree trunk, such as a TreeHelp Bug Band, will also prevent the snails from migrating up the tree trunk and eating the leaves.



Lemon, Citrus limon, is a small evergreen tree in the family Rutaceae grown for its edible fruit which, among other things, are used in a variety of foods and drinks. The tree has a spreading, upright growth habit, few large branches and stiff thorns. The tree possesses large, oblong or oval, light green leaves and produces purple-white flowers in clusters. The lemon fruit is an ellipsoid berry surrounded by a green rind, which ripens to yellow, protecting soft yellow segmented pulp. Lemon trees can reach 3–6 m (10–20 ft) in height and can live for many years, reaching full fruit bearing capacity in approximately 40 years. Lemon may also be referred to as bush lemon or Persian apple and likely originated from the eastern Himalaya of India.
Fruit sliced open to reveal flesh
Lemon tree
Lemon fruit ripening on tree
Cluster of lemon fruits
Seeds inside fruit ‹ ×


Due to their bitter taste, lemon fruit is not usually consumed fresh. It is used widely to make juices such as lemonade, as garnishes in cooking and as a flavoring in cooking and baking.


Requirements Lemon is a subtropical plant and the trees grow best in regions with a pronounced change in season. They will grow best at temperatures between 26–28°C (79–82°F) and are very sensitive to cold. Trees and fruit will be damaged or killed by freezing conditions without protection.The trees will tolerate drought conditions but perform poorly in water-logged soil. Trees will grow best when planted in a well-draining sandy loam with a pH between 6.0 and 7.5. Soil must be deep enough to permit adequate root development. Lemon trees will grow best when positioned in full sunlight. Budding Budding should be carried out when seedling stems have reached roughly the diameter of a pencil (6–9 mm/0.25–0.36 in) and at a time when the bark of the rootstock tree is slipping (this is the term used to describe a period of active growth when the bark can be easily peeled from the plant). Twigs (budwood) should be collected from the previous growth flush or the current flush so long as the twig has begun to harden. The twigs should have well developed buds and should be as close as possible to the diameter of the rootstock onto which it will be joined. It is extremely important to only collect budwood from disease-free trees. The use of diseased budwood can cause the spread of many serious citrus diseases which can kill trees. The budwood to be used for propagation should be trimmed to create budsticks which are 20–25 cm (8–10 in) by removing any unwanted wood and leaves. These budsticks can be stored for 2–3 months under the correct conditions but it is best to use them as soon as possible after cutting. The simplest way to join the budwood the the rootstock is by T-budding. The area to be joined should be pruned to remove any thorns or twigs and the cut made approximately 15 cm (6 in) from the ground. Using a sharp knife, a 2.5–3.8 cm (1–1.5 in) vertical cut should be made in the stem of the rootstock, through the bark. A horizontal cut should be made at either the top or the bottom of the vertical cut to produce a “T-shape” The horizontal cut should be made a slightly upward-pointing angle and should reach through the bark. Remove a bud from a budstick by slicing a thin, shield-shaped piece of bark and wood from the stem, beginning about 1.25 cm (0.5 in) above the bud. This piece should measure 1.9–2.5 cm(0.75–1.0 in) in length. Immedietely insert the piece of bud into the cut on the rootstock by sliding it under the opened bark so that the cut surface lies flat against the wood of the rootstock plant. Finish the join by wrapping the bud with budding tape. After the union has formed and the tape is removed, the bud is forced to grow by cutting the rootstock stem 2.5–3.9 cm (1.0–1.5 in) above the join about 2/3 of the way through the stem on the same side as the join. The top of the seedling should then be pushed over towards the ground. This process, known as “lopping” allows all of the nutrients to be diverted to the bud Once the bud begins to grow and reaches several inches in lengthe, the lop can be removed completely from the seedling. Planting seedlings Lemon trees can be purchased as seedlings which have already been grafted and only require planting in the garden or orchard. The best time to plant citrus trees is in Spring after all danger of frost has passed in your area. Trees should be planted at or higher than the level of the nursery pot. Once the tree is positioned in the planting hole, backfill the soil by about half and water to allow the soil to settle around the lower roots before filling in the hole. The newly planted tree should be watered every few days. General care Newly planted trees require proper irrigation to ensure they become established. During the first year, water should be applied at the base of the trunk so that the root ball is kept moist to allow the roots to establish in the soil. Newly planted trees should be provided with water every 3–7 days. The soil should be moist, but not wet. Trees planted in sandy soils will require water more frequently. Young trees will also require a light application of fertilizer every month in the first year. Lemon trees will need protected from cold temperatures to prevent damage. Soil can be mounded up around the trunk during the winter and removed in the Spring. Young trees can also be protected from frosts by covering them with tarps or blankets as required.

CABI Crop Protection Compendium. (2008). Citrus limon (lemon) datasheet. Available at: http://www.cabi.org/cpc/datasheet/13450. . Paid subscription required. Lacey, K., Ramsey, H. & Hoffman, H. (2009). Growing healthy citrus. Department of Agriculture and Food. Available at: http://archive.agric.wa.gov.au/objtwr/imported_assets/content/hort/fn/cp/citrus_propagation.pdf. . Free to access. Timmer, L. W., Garnsey, S. M. & Graham, J. H. (2000). Compendium of Citrus Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/42481.aspx. Available for purchase from APS Press.

Scientific name

Anamorph – Phyllosticta citricarpa (McAlpine) van der Aa (syn. Phoma citricarpa McAlpine)

Teleomorph – Guignardia citricarpa Kiely

Other common names

Often abbreviated as CBS. This however may lead to confusion since citrus bacterial spot uses the same abbreviation. Many of the common names for black spot are based on observed symptom types but all refer to the same disease which can be confusing. The symptom based names are: hard spot (shot-hole spot), false melanose (speckled blotch), freckle spot, lacy-spot, cracked spot and virulent (spreading or galloping) spot.

Disease cycle

As in many diseases, timing is important for black spot to occur. Inoculum in the leaf litter needs to be available during the period when the host is susceptible and the environment is favorable for infection. Fruit are susceptible from fruit set until 5-6 months later, when they become age resistant.

Both the ascospores (sexual spores) and the conidia (asexual spores) of G. citricarpa are able to infect susceptible tissues.

Ascospores are found in microscopic fungal structures embedded in the leaf litter. They are the most important source of inoculum, in some regions causing nearly all infections. Ascospores have never been found in fruit lesions or lesions on attached leaves. Spores are released when the leaf litter is wetted by heavy dew, rainfall, or irrigation and can be carried by air currents over long distances.

Dark brown or black pycnidia, structures that produce conidia, are formed on fruit, fruit pedicles and leaf lesions. They are also abundant on dead leaves. Conidia are not wind-borne, but may reach susceptible fruit by rain splash. These spores are not considered a significant source of inoculum in climates with dry summers; however, in climates with frequent summer rains, conidia play a larger role in the epidemic when there are multiple fruit ages present on trees simultaneously. Often late hanging fruit with lesions remain on the tree and spores can be washed onto young susceptible fruit.

Infections are latent until the fruit becomes fully grown or mature. At this point the fungus may grow further into the rind producing black spot symptoms months after infection, often near or after harvest. Symptom development is increased in high light intensity, intensifying temperatures, drought, and low tree vigor.


Leaf – older lesions are small, round, sunken necrotic spots with gray centers. The lesions are bordered with a dark brown ring. Young lesions are small, reddish, and slightly raised. A yellow halo can be associated with the lesions. Foliar lesions are most commonly seen on lemons. They are rarely seen in well managed groves. Similar lesions can be seen on twigs and pedicles.

Hard spot (1) is the most typical and diagnostic symptom of black spot as the fruit mature, often appearing around color change. The lesions are circular depressions with a diameter of 3-10 mm (0.12 – 0.4 inch). The brick red lesions have tan to grey centers with a distinct brown to black margin. Pycnidia are usually, but not always, present in the lesions. Pycnidia appear as small black dots and are visible with a hand lens but can be confused with acervuli of Colletotrichum spp. Preharvest, hard spot lesions tend to develop on the side of the fruit exposed to sunlight.

False melanose/speckled blotch (2) symptoms appear as numerous, small (< 1 mm (0.04 in) in diameter), raised, brown to black lesions. Most frequently, false melanose occurs on green fruit. The lesions can coalesce as the season progresses and do not contain pycnidia. False melanose/speckled blotch-type symptoms can develop into hard spot-type symptoms at the end of the season.

Freckle spot (early virulent spot) (3) symptoms are a sign of heavy infection. They occur on mature fruit, most often after harvest but can be seen when fruit is on the tree. The lesions are 1-3 mm (0.04 – 0.12 in) diameter depressions, potentially with pycnidia present. Lesions can be several colors, most often reddish with a dark red to brown border, but may be gray to tan, brownish, or have no color. Late in the season or during storage, freckle spot can develop into virulent spot or hard spot.

Virulent spot (4) lesions are sunken and irregular in shape and occur on heavily infected, mature fruit toward the end of the season. In high humidity, large numbers of pycnidia may develop. The lesions can turn brown to black with a leathery texture that eventually covers the entire fruit. Virulent spot may cause premature fruit drop and serious post harvest losses since the symptoms may extend into the fleshy part of the fruit.

Lacy spot-type (5) lesions are superficial, small, and yellow with dark yellow to brown centers and no defined margins. The fruit is still green when the lesions become apparent and can cover a large portion of the fruit surface. These lesions are considered to be a variation of false melanose. This term is not commonly used, and these symptoms have only been reported from South America.

Cracked spots (6) type lesions are superficial, slightly raised, variable in size, brown to black with cracked surface and irregular margins. Pycnidia are not present in the lesions. These lesions have often been associated with rust mite damage. Hard spot lesions can eventually form in the center of the lesions.

Regulatory information

The most current regulatory information can be found at:

Host range

Citrus black spot affects all species of cultivated citrus and their hybrids. With the exception of sour orange and its hybrids, all commercially grown citrus species and cultivars have been observed to be affected by the disease. Lemon is particularly susceptible, and it has been observed that when citrus black spot moves into an unaffected area it first appears on lemons with the exception of the epidemic in Florida. Grapefruit and Valencia orange are also highly susceptible.


Citrus black spot is found in Argentina, Australia, Brazil, China, United States (Florida), Indonesia, Japan, Kenya, Mozambique, Nigeria, Philippines, South Africa Taiwan, Uruguay, Venezuela, and Zimbabwe. No reports have been made from Mediterranean countries.

Lemon Tree Problems: Treating Common Lemon Tree Diseases

If you are lucky enough to be able to grow your own lemon tree, chances are good that you have encountered one or more lemon tree problems. Unfortunately, there are a plethora of lemon tree diseases, not to mention pest damage or nutritional deficiencies that can affect how, or if, your lemon tree bears. Knowing how to identify lemon diseases and the treatment for diseases of lemons will allow you to take immediate action to mitigate potential negative impact on fruit.

Lemon Tree Diseases and Treatment

Below are some of the most common diseases of lemon with tips for treating them.

Citrus canker – A highly contagious bacterial infection, citrus canker causes yellow halo-like lesions on fruit, leaves and twigs of citrus trees. If allowed to progress unchecked, this lemon tree problem will eventually result in dieback, fruit drop, and leaf loss. This disease is spread through the air with the aid of air currents, birds, insects and even humans. Spray with liquid copper fungicide as a preventative for treating citrus canker lemon disease. If the tree is already infected, there is no treatment and the tree will have to be destroyed.

Greasy spot fungus – Greasy spot is a fungal disease of lemons whose symptoms include telltale yellow-brown blister on the underside of the leaves. As the disease progresses, the blisters begin to look oily. Treating this lemon disease also requires an application of liquid copper fungicide. Spray first in June or July and follow up with another application in August or September.

Sooty mold fungus – Sooty mold is a fungal infection resulting in black leaves. This mold is the result of honeydew excreted from aphids, whiteflies and mealybugs. To eradicate sooty mold, you must first control the insect infestation. Spray the lemon tree with Neem oil insecticide, both the top and undersides of the foliage. You may need to repeat in 10-14 days, depending upon the extent of the infestation. Follow up by treating the mold growth with liquid copper fungicide.

Phytophthora fungus – Phytophthora root rot or brown rot or collar rot is caused by the phytophthora fungus resulting in hard dark brown patches on the trunk of the tree often accompanied by oozing from the affected area. As the disease progresses, the patches dry, crack and die leaving a dark, sunken area. Fruit may also be affected with brown and decayed spots. This fungus lives in the soil, especially wet soil, where it is splashed up onto the tree during heavy rain or irrigation. To treat, remove all infected leaves and dropped fruit from the ground. Prune the lower branches from the tree, those that are more than 2 feet from the ground. Then spray with a fungicide such as Agri-Fos or Captan.

Botrytis fungus – Botrytis rot is yet another fungal infection which may afflict lemon trees. It tends to develop after prolonged rainy periods, usually along the coastline, and moves from old blooms to newly developing blossoms in the spring. For this fungal infection, spray the lemon tree with a fungicide according to the manufacturer’s instructions.

Anthracnose – Anthracnose is also a fungal infection that causes twig dieback, leaf drop and stained fruit. It is caused by Colletotrichum and is also more common after prolonged periods of rain. As with Botrytis, spray the lemon tree with a fungicide.

Other less common diseases which may plague lemon trees are:

  • Armillaria root rot
  • Dothiorella blight
  • Tristeza twig dieback
  • Stubborn disease
  • Exocortis

Consult your extension office or a reputable nursery for information on these diseases and how to combat them.

Most importantly to prevent not only disease but other lemon tree problems, be sure to be consistent with your irrigation and feeding schedules, and monitor for pests and treat accordingly at the first signs of infestation. Also, keep the area around the lemon tree free from debris and weeds that harbor fungal disease as well as insects.

Look out: Brown spots on citrus mean it’s rotting | San Luis Obispo Tribune

Brown rot on citrus. Courtesy of UC Regents

Q: What are the brown spots on my oranges?

Margot S., Arroyo Grande

A: Brown spots or lesions on citrus usually mean one thing: brown rot. Brown rot is a disease that affects all parts of the tree, but is most often observed on the fruit. It is transmitted via various forms of the pathogen, Phytophthora, which resides in the soil.

During wet weather, Phytophthora is bounced up from the ground by rain and wind. Continued moisture creates a hospitable environment for growth. Because of the nature of transmission, the lower canopy of the tree is particularly susceptible.

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In the beginning stages, the infection is not visible to the eye, but as time goes on the site will develop a whitish growth that will inevitably become a round, leathery stain.

Brown rot is not just aesthetic — infected fruit has a pungent odor and is generally inedible. It can damage branches, decrease vigor and affect the overall health and bounty of the tree.

For the commercial grower, brown rot is a significant issue. Fruit may not show signs of damage at harvest, and infected fruit may spread the disease during shipment.

In 2013 this problem was so severe that shipping of citrus to China was shut down due to infected fruit. That ban has since been lifted, but a continued system of monitoring remains.

All citrus growing regions of California have Phytophthora and no citrus is immune. Prevention is usually your best bet:

▪ Pruning the lower branches so that there is at least 24 inches between the branches and the soil decreases the possibility of infection.

▪ Keep sprinklers and hoses away from the tree and apply irrigation directly to the soil instead.

▪ Prune the canopy of the tree to allow adequate light and air circulation.

▪ Use copper spray in late August and again in October to create a layer of protection.

▪ When rains are heavy, an additional application in January may be required. Spray all parts of the tree, including the underside of the leaves, the trunk and the soil below.

With a little luck, you’ll have a ‘fruitful’ year!

Andrea Peck is a UCCE Master Gardener.

Got a gardening question?

In San Luis Obispo call 781-5939, Arroyo Grande, 473-7190 and Templeton, 434-4105. Visit us at http://ucanr.org/sites/mgslo/ or email us at [email protected] Follow us on Instagram at slo_mgs and like us on Facebook. Informative garden workshops are held the third Saturday of every month, 10 a.m. to noon at 2156 Sierra Way, San Luis Obispo. Garden docents are available after the workshop until 1 p.m. To request a tour of the garden, call 781-5939.

Solving Citrus Problems

Good organic matter

Citrus trees have a shallow root systems, this means it is vital to have good drainage system and soil that is rich in organic matter. When planting ensure you have Yates Dynamic Lifter Soil Improver & Plant Fertiliser added into the soil to ensure rich nutrients are present. Only Dynamic Lifter offers the right solution because it is processed organically and a natural product.

Fertilise regularly

Feed your trees regularly throughout the season. Yates Thrive Concentrate Citrus Food is a complete, liquid plant food that provides your citrus trees with the balanced nutrients they require for healthy growth, fruit production and development. Because Thrive feeds through the leaves and roots as you water, it starts to work quickly, so you see the results sooner. Yates Thrive Concentrate Citrus Food is suitable for all types of citrus trees. Use regularly, year round, for best results. If you have high rainfall in your area then nutrients can easily leach from the soil so you will need to fertilise extra.


When your trees have finished fruiting, it’s a good time to cut them back and prepare them for next year’s growth. To do this, cut back any dead/diseased wood, twiggy/straggly growth and any branches growing towards the centre of the tree. Also, remove any branches that are hanging low (almost touching the soil) to help lift the canopy.

Cut back any areas heavily congested with branches to help open the canopy, which will allow for better sunlight and air circulation – ideal conditions for fruit development and it will also help lessen the chance of pests/diseases. If you live in a frosty area, wait until the chance of last frost has passed before pruning.

If your trees are a little old and didn’t perform as well this year as it has in the past, it’s worth giving them a hard prune – it will rejuvenate them and give them a new lease on life! You may not have the best crop for the next couple of years (while the tree grows back), but it will be worth it. This method is called ‘skeletonising’ and involves cutting all the growth back, so that you’re left with a single trunk and strong, evening spaced branch stumps.

Ensure you use a sharp sterile pair of secateurs and/or loppers when pruning – we don’t want to introduce any new diseases or bad pruning practices!

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