Miscellaneous

Lemon Tree Problems: Treating Common Lemon Tree Diseases

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 (.6 m.) 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.


Meyer Lemon Tree Diseases

Related Articles

A cross between a mandarin orange and a lemon, Meyer lemons (Citrus meyerii) suit several outdoor spaces, including terrace and roof gardens. Being small in stature, Meyer lemon a great choice for limited spaces. It grows best in a spot that receives full sunlight, is warm and has well-drained soil. Unfortunately, Meyer lemons are susceptible to a variety of citrus diseases. Early recognition of the worst of these diseases and prompt treatment can potentially stop the disease from spreading or killing your plant.


Citrus Pests & Diseases

Citrus trees are relatively easy to grow and with the proper care, you can have Citrus trees with beautiful blossoms and luscious fruit that will last for decades. Caring for your citrus tree starts as soon as you remove them from your box.
Please remember that if your tree came planted in a pot, you should leave it in the pot for at least 2 weeks to minimize shock. Remove the tree from the plastic bag wrapped around the pot, water it and place it in a "partially" sunny location for at least a week, before you attempt to place the tree in the full sun.
After one week you can then place the tree in full sun (IF it is not in shock.)

Tree care is based on a 4 point system

1. SUNSHINE
It is essential that your tree gets 6-8 hours of sunshine daily. In the northern regions of the US, this can be a little more problematic, (in the winter months) in this case you can supplement with a plant grow bulb in addition to sunshine. It is critical that your tree is given the 6-8 hours of daily sunshine, this is a requirement for a healthy productive tree.

2. WATER
It is crucial that you use the deep watering method when watering citrus. The majority of plant demise is due to over watering, it is detrimental and should be avoided. A simple inexpensive moisture meter can prevent an overzealous gardener.
Moisture meters are around $10.00 and can give peace of mind to the questioning gardener on whether or not to water. Watering your trees for a few minutes every few days is NOT acceptable.
Deep Watering Method
https://lemoncitrustree.com/store/citrus-blog/2018/10/19/deep-watering-method-for-potted-citrus-trees/

3. FERTILIZER
It is crucial that you remember to fertilize your tree. Nitrogen deficiency is one of the leading causes of yellow leaves. Citrus trees are heavy nitrogen feeders. Without nitrogen, your tree CANNOT produce fruit. Fruiting trees remove nitrogen from the soil and convert it into fruit.
We recommend a 2/1/1/ OR 3/1/1 ratio fertilizer. The first number of any fertilizer is nitrogen and it should be double the other two numbers.
Citrus should be fertilized in Mid- February, through mid-September. If you live in the south and your tree is planted outside do not fertilize after mid-September because that encourages the tree to start new tender growth during the winter when there is a danger of frost.
Feeding Recipe For A Happy Tree
https://lemoncitrustree.com/store/citrus-blog/2015/08/11/feeding-recipe-for-a-happy-tree/

4. PREVENTION
The old saying "an ounce of prevention is worth a pound of cure" is so true when it comes to preventing your tree from insect infestation.
It is imperative that you protect your investment, a little prevention goes a long way.
It is vital that you educated yourself on hazards that could cause undue stress or extreme danger to your citrus tree.
Pest Prevention
https://lemoncitrustree.com/store/citrus-blog/2015/08/21/bath-time-for-your-citrus-tree/

WINTER CARE AND LEAF DROP IN WINTER

After you take your tree inside in the fall before winter make sure to only water the tree with WARM WATER ONLY. Water can be frigid in the winter coming out of the tap, so be mindful of the water temperature before watering
The root area of the pot is just as important as the foliage of the tree, and if the root area gets too cold, the tree will begin to drop its leaves.
During the day it helps if the pot is elevated to the window, so the pot also receives warmth from the sunshine.
Also in the summer if you use a garden hose to water your tree DO NOT make the mistake of leaving water in the hose, the water left in a garden hose can get very hot in the summer, cooking in the sun. Make sure you always empty your hose and get fresh water in the hose, before you water the trees. Green leaf drop is a problem when trees are inside for the winter. Lighting is usually the issue when green leaves drop off an otherwise healthy tree.
Winter Recommendations For Indoor Citrus
https://lemoncitrustree.com/store/citrus-blog/2015/10/05/winter-recommendations-for-inside-citrus/

TIPS ON CARING FOR YOUR INVESTMENT

It is vital for tree care to do a few preventative steps to ensure that your tree stays healthy.
You should be familiar with the graft area of your tree, and not allow growth below the graft area, as this will eventually take over and kill your tree.


GRAFT AREA

BRACKET SHOWS GRAFT AREA
The Red arrow is a sucker and needs to be pruned off. The lighter part of the branch V-shaped is the grafted area. Any growth below the graft needs to be removed. The whiter branch near the graft is fine, it is only the branch that sprouted BELOW the graft that is a concern.

ROOT CROWN AREA

ROOT CROWN
It is critical when transplanting the tree that the root crown is not buried under the soil, as this could cause the trunk to rot away from the rootball.

CREATE A PEST BARRIER
Creating a barrier between the soil and foliage is essential.
First, take a wide piece of masking tape or tangle guard, long enough to wrap around the tree.

Tape barrier
Tape the tree with wide masking tape. It is essential to make sure that the tree is completely wrapped. Then you'll need to wrap the support stick separately or remove the stick.
Once the tree trunk and support stick are wrapped, you can add tanglefoot to the tape.
DO NOT WRAP THE WHOLE TREE TRUNK!
Only the width of wide masking tape is needed, to prevent access.
When changing the tape, wash the area that had the tape to remove the sticky glue that was on the tape and then place the tape in a different area of the truck.

This barrier will catch ants and prevent them from gaining access to the foliage of the trees. Since your tree is a good food source of honeydew.
REMEMBER- Check tape when you water your tree, to make sure ants haven't built a bridge across your barrier and do not push the tree against a wall or railing or other plants, as insects would just climb them to gain access to the foliage of the trees.

Taping the tree will also help prevent spider-mites and snails from gaining access to the tree. But it is essential to know spider-mites can get blown through the air on a windy day. Other preventives that you could consider using are essential oils, such as tea tree, eucalyptus, peppermint or wintergreen one dropper mixed with water in a spray bottle. Do not spray theses directly on your tree, use these to spray the outside of the pot and surrounding area to deter pests. Neem oil can be sprayed on your tree and is an excellent deterrent against pests.

If your tree is infested with anything you must wash your tree with Dawn dish soap and warm water, scrubbing with a dishcloth. Make sure the top side and underside of leaves are entirely washed and scrubbed of sooty mold and cleansed of any sticky substance. You can use a toothbrush in hard to reach areas, such as a crevice at the Y part of a branch. Treat the tree once it is clean with a horticultural oil or neem oil.
It is IMPORTANT that all insects are removed, so take care to educate yourself on the insect infesting your tree. These will be listed further in this article.

Ants
Ants form symbiotic relationships with a variety of arthropods including scale insects, mealybugs, cottony cushion scales, whiteflies, and aphids. Ants are a lot like humans, they domesticate other insects like humans domesticate cattle. Ants will carry these insects up the tree and drop them onto foliage and branches. These insects use sharp mouthparts to pierce into plants extracting the sugary goodies. Then the ants will walk up and tap scale or an aphid with a foreleg or antennae and on cue, the scale or aphid will give up a droplet of honeydew. Ants drive off a host of potential predators of the scale and aphids and so for payment for this ants protect their flocks and for this protection, ants are rewarded with honeydew. Ants move their herds of bugs from "pasture to pasture" as each food source is used up. Ants are like a cattle rancher moving his herd from pasture to pasture. Protecting your tree from ants is essential.

If at any point you notice that your potted tree has become infested with a colony of ants, making themselves at home in the soil of the pot, then it is an emergency. You must kill the colony!

Use a small jar lid and pour in Mountain Dew, mix in 3 pinches of Borax Laundry Detergent. Set the lid with this mixture close to your pot, about 2-3 feet away from your potted tree. If you mix too much of the borax, it will kill the ants immediately, and they will not have a chance to take it back to the colony, killing all the ants in the colony. So be sure you don't mix it too strong. If you notice a lot of dead ants near your mixture, then the mixture is too strong.

Ant getting drop of honeydew from scale


SCALE
Looks like blisters all over the branch. Included in the photo,a very faint web (spider-mite) that is attached from thorn to branch
When the scale is attached to the tree, it often appears as crusty or oatmeal-like or waxy bumps on the tree, often it is mistaken for parts of the tree’s own growth. The picture clearly shows bumpy beige like waxy growth. These are insects that suck sap from plants and produce a sticky substance called honeydew. Honeydew if left on the tree will then turn to black sooty mold.



Branch with scale, and honeydew dripping off leaves and branches


MEALYBUGS


COTTONY CUSHION SCALE


HONEYDEW
Leaves saturated with honeydew, dripping from a leaf, this will cause fruit flies to be attracted to your tree and can be a warning sign that the tree is in distress.
Also, spider mites and a web to the right of the main leaf.


SOOTY MOLD


SOOTY MOLD
As scale suck fluid, they create an environment ripe for the fungal disease called black sooty mold. Honeydew, if not removed will turn to black sooty mold and will become prevalent on leaves, twigs, and branches.
As the branches, twigs, and leaves turn black, the mold will reduce the trees' ability to conduct photosynthesis.
All that applies to the scale also applies to many other insects and how they affect your Citrus tree such as Aphids, Spider mites, Mealybugs, Citrus Thrips.


Aphids crawling on a branch




Aphids on the under-side of a leaf, with larvae and eggs


APHID


SPIDER MITE


SPIDER MITES
Infestation of mites will usually infest the tree or plant in large numbers, and they damage leaves and plants. They suck the nutrients of the plants and leave them to die.
Webs on your citrus will indicate a spider-mite infestation.


FUNGUS GNAT
Majority of Citrus Tree death is over-watering. It is imperative that you DO NOT OVER-WATER your tree. Over-watering can create a perfect environment for Fungus Gnats that eat at the root system of the tree and will eventually kill your Citrus tree. A moisture meter will prevent this from happening.


LEAF MINER
Although leaf miner is unsightly, it's typically not too damaging to Citrus Trees. Leaf miner is identified by squiggly lines in the leaves.
Treatment: spinosad to treat the adult insects


CITRUS THRIPS


Damage caused by Citrus Thrips.
Small orange-yellow insects whose feeding activities scar and damage the surface of the fruit.
The insects feed on the fruit buds and puncture the epidermal cells, leaving scabby, grayish or silvery scars on the rind.


SNAILS
Snails will eat citrus fruit so it is essential to keep a proper sanitation program around the citrus tree. Do not allow dead foliage to build up inside the pot as this could fill up pretty quickly with snails and slugs. It is essential to have a barrier between the soil and the foliage to prevent slugs from climbing up the tree and eating the foliage and fruit.


WHITEFLY
It is crucial that you inspect your tree at least once a month to ensure that you have no infestation. Egg clusters or whitefly larvae will be present on the undersides of infested leaves. Remove larvae or nymph-infested leaves from your citrus tree by hand and treat the tree with neem oil.


SWALLOWTAIL BUTTERFLY


SWALLOWTAIL BUTTERFLY LARVAE (Orange-Dog)
The swallowtail butterfly will lay her eggs on leaves of citrus trees the larvae are the Orange dog caterpillars, which eat the leaves of citrus.
They usually are not harmful to the tree unless the tree is young.


FUNGUS AND MOLD


MELANOSE FUNGUS


MOLDY FRUIT
A fungicide can prevent many fungal infections.


GREASY-SPOT

CITRUS-SCAB
It is vital that you check your tree regularly to prevent fungus and treat the tree with Liquid Copper Fungicide.
One of the first signs that a citrus tree may be suffering from root rot is that the fruit has blemishes or decaying or yellowish-brown spots.
A fungus or root rot can cause citrus leaves to become moldy or have blackened veins or black lesions. Root rot causes a slow decline of the tree so it is imperative you have adequate soil drainage and avoid overwatering. As root rot advances, the bark cracks and dies leaving dark sunken cankers on the tree trunk. Prevent any problems before they start, use Copper fungicide which is effective if used regularly to prevent many of the common fungus problems known to citrus.


CITRUS DEFICIENCY



NITROGEN DEFICIENCY
Nitrogen deficiency will limit tree growth and fruit production and is expressed by light green to yellow foliage.
Overwatering your tree will cause yellow leaves if your Citrus has yellow leaves but you know you are not overwatering then your tree has a Nitrogen deficiency.


PHOSPHORUS DEFICIENCY
Phosphorus is essential for raising healthy citrus trees, but no matter the variety, they need only modest amounts of it. Growth is reduced when the supply of Phosphorus is too low and the symptoms appear first on older leaves. Symptoms: Small leaves that may take on a reddish-purple tint. Leaf tips can look burnt and older leaves become almost black. A research project has found phosphorus deficiency to be a contributor to citrus greening disease symptoms. By applying phosphorus, growers could potentially eliminate greening symptoms and improve fruit yield.


MANGANESE DEFICIENCY
Manganese deficiency symptoms are a light yellowing or whitening of green plant tissue because of a decreased amount of chlorophyll.
As the stress increases, the leaves take on a gray metallic sheen.



SULFUR DEFICIENCY
Veins and petioles show a very distinct reddish color. Similar to nitrogen deficiency with yellowing leaves but sulfur deficiency is much more uniform over the entire plant. Brown lesions often develop along the edges, and the leaves tend to become more erect and often twisted and brittle.


POTASSIUM DEFICIENCY
Potassium deficiency causes fruit to become smoother, with thinner rinds and causes smaller fruit to develop. Leaves become yellowish with edges bent downward.


IRON DEFICIENCY
Leaves appear as dark green veins, with yellowing between.


ZINC DEFICIENCY
Extensive yellowing develops between veins when zinc is deficient.

Please contact us at [email protected] or call if you need assistance

Lemon Citrus Tree
866-216-TREE (8733)


Root Rot

Also called brown rot and collar rot, this fungus occurs when a phytophthora fungus is in your soil. Watch for dark brown patches that can ooze on the tree’s bark. The bark will later dry out, crack and die, leaving a sunken canker. Fruit can also become brown and decayed and leaves will turn yellow and die back. If you suspect root rot, take all affected leaves and fruit from your tree. Keep the area around your tree clean of all fallen leaves and fruit. Prune branches that are less than 2 feet above ground level. It's important for lemon trees to have good soil drainage, so never overwater and consider transplanting it to a planter box or raised bed if it sits in a puddle for more than one or two days. You can use a fungicide product to control root rot: Tree Help recommends Agri-Fos and Captan.


Pests & Diseases

Citrus Tree Pests & Diseases

Like all plants and trees, citrus trees can be affected by disease and insect damage. There are some disease-resistant citrus tree varieties, and they are the best option for preventing many issues. Proper citrus tree maintenance such as watering, pruning, spraying, weeding, and removing fallen fruit can help control most insects and diseases.

Citrus Scab

Citrus scab is caused by a fungus and it produces slightly raised, pink or brown scabs on fruit and leaves. As the infected areas progress, the scabs will change color to a dark grey, and often crack. The clear oval shaped type of spores are spread by splashing rain and die when they become dry. The spindle-shaped form remain viable for a short time, and in addition to moving with splashed rain, can also travel short distances by wind.

  • Raised yellow or pink outgrowths on fruit or leaves
  • Small growths on new shoots

Suggested Treament:

Citrus Variegated Chlorosis (CVC)

CVC is a bacterial disease caused by a subspecies of the Xylella fastidiosa bacterium. CVC is transmitted between citrus trees by several species of large leafhopper insects called sharpshooters. The disease can also be transmitted by grafting. Symptoms of CVC are very similar to nutrient deficiency since both result in yellowing of leaves. Early leaf symptoms of CVC closely resemble a deficiency of zinc, with yellowing areas between the veins of young leaves. As infected leaves mature, lesions become visible on the underside of the leaves opposite the yellowing areas on the leaf surface.

  • Yellow of young leaf surfaces
  • Brown lesions on undersides of mature leaves

Suggested Treament:

Citrus Black Spot

Citrus Black Spot is a disease caused by the fungal infection Guignardia citricarpa. Black Spot can reduce the quantity of fruit produced by a tree, as well as the quality of the fruit. Symptoms include black lesions on both the leaves and the fruit. All varieties of citrus are susceptible to citrus black spot fungus.

  • Black spots on mature fruit
  • Cracked or oozing black spots in advanced stages

Suggested Treament:

Huanglongbing (HLB) or Greening

HLB, or Greening, is thought to be caused by bacteria carried by psyllid insects. Greening causes leaf discoloration that appears as mottling in various shades of light green to yellow. The leaf discoloration of Greening can be distinguished from nutrition deficiencies because it crosses leaf veins and creates asymmetrical patterns upon the leaf surface. Fruit may also be affected, discolored, and may drop. Greening causes leaves to fall, small new growth to die, the decay of feeder roots, decline of tree health, and eventually tree death.

  • Asymmetrical leaf blotches
  • Falling leaves
  • Fruit drop
  • Misshaped or discolored fruit
  • Premature and random death of branches

Suggested Treament:

  • Removal of infected plants
  • Foliar Micronutrient
  • NPK

Citrus Greasy Spot

Greasy Spot is a fungus spread by wind. The fungus thrives when periods of continual wetness saturate decomposing fallen leaves. The fungus will then migrate into trees through splashing rain or wind, and infect living leaves. The symptoms include leaves with yellow spots, raised brownish blisters, and eventually, black lesions that have a greasy appearance.

  • Yellow leaf spots
  • Brown blisters on leaves
  • Black lesions that look greasy

Suggested Treament:

  • Copper
  • Valet
  • Foliar Micronutrient

Citrus Anthracnose

Citrus Anthracnose is a fungal infection that creates round, flat tan spots that have a purple outline. The fungus grows on dead wood in the citrus tree canopy, and can travel short distances by rain splashing or overhead watering, where it can then infect new growth and young fruit.

  • Premature stem dieback
  • Leaf drop
  • Post-harvest fruit decay

Suggested Treament:

  • Azoxystrobin
  • Zinc sulfate, copper sulfate, and hydrated lime

Citrus Canker

Citrus canker is a bacterial disease caused by the bacterium Xanthomonas axonopodis. Canker creates lesions on leaves, fruit and stems, and can damage overall tree health and fruit production. Citrus canker is spread by wind-driven rain, and can be spread mechanically by transportation of trees, infected limbs, and fruit.

  • Yellow lesions on fruit, leaves, and stems
  • Brown lesions on undersides of mature leaves.

Suggested Treament:

  • Removal and destruction of infected trees

Citrus Leprosis

Citrus Leprosis, also called Nailhead Rust, Scaly Bark, or Nailhead Spot, is a virus transmitted by mites that causes lesions that are visible on both sides of the leaf. The lesions are round (ten to thirty millimeters across) and have a dark brown center where mites feed. The Citrus Leprosis virus is carried by the false spider mite (Brevipalpus) and since the virus can multiply within the mites, the mites can spread the virus to trees for the insect’s entire lifespan.

  • Small, round dark brown lesions on both leaf sides
  • Yellow halo around lesions

Suggested Treament:

Citrus Bacterial Spot

Citrus Bacterial Spot is only known to occur within the nursery environment. There are three classifications of the disease: aggressive, moderately aggressive, and weakly aggressive. Only aggressive isolates are spread by wind-blown rain and overhead irrigation. All other strains can be transported among trees in a nursery by the process of moving vehicles and workers through the nursery grounds. Citrus Bacterial Spot mainly affects leaves, and infections of fruit are rare. It is easily confused with canker.

  • Yellow lesions on leaves

Suggested Treament:

Citrus Melanose

Citrus Melanose is an infectiousfungus that lives on dead or decaying plant material. Infections of Melanose are caused when a substantial amount of the fungus is present on dead twigs or branches that are wet for an extended period of time, such as twenty-four hours or more, caused by either rain, or overhead watering. The fungus creates small brown spots on leaves. TheMelanose spots evolve to exude a red-brown gum, and become raised bumps that stand above the surface of the leaf. As the fungus progresses, leaves take on a rough feel due to the numerous bumps. Severe Citrus Melanose infections result in the dieback of young shoots.

  • Small brown spots on leaves
  • Brownish-red gum on leaves and stems
  • Raised bumps on leaves

Suggested Treament:

  • Fungicide
  • Copper

Citrus Alternaria Brown Spot

Citrus Alternaria Brown Spot is a fungus spread mainly by wind-driven spores. Spores grow on mature, wilted twigs and mature leaves and produce brown lesions on leaves and fruit. Citrus Alternaria Brown Spot can also be transported by the activities of pruning, picking, and transporting trees. Citrus Alternaria Brown Spot can affect the fruit quality as it creates pits, holes, and leaking depressions as the fungus lesions mature on the fruit. Tangerine varieties are particularly susceptible to Citrus Alternaria Brown Spot.

  • Brown spots on fruit
  • Depressed and leaking spots in advanced stages

Suggested Treament:

  • Copper
  • Strobilurin Fungicides

Citrus Phytophthora

Citrus Phytophthora, also called Root Rot, is a type of mold that thrives in locations of constant moisture and high temperatures. Citrus Phytophthora enters the tree through the roots, and causes small roots and growing root tips to rot and die. Citrus Phytophthora can cause leaves to turn yellow and drop due to the resulting lack of nutrition caused by the damaged roots. Infected trees may also display bark peeling at the trunk base, and a brown to red resin oozing from the tree base. The mold also makes the roots susceptible to damage from root-feeding weevils.

  • Peeling lower bark
  • Brownish-red resin on trunk
  • Leaf yellowing

Suggested Treament:

  • Fungicide
  • Use of resistant rootstock
  • Irrigation management

Citrus Pseudocercospora

Citrus Pseudocercospora, also known as Phaeoramularia Fruit and Leaf Spot (PFLS) or Angular Leaf Spot, is caused by the fungus Pseudocercospora angolensis. The spores require moisture to propagate and are spread by both wind and mechanical means such as transportation of infected trees or the movement of leaves when pruning and removing branches. The fungus produces flat, light brown to red lesions that have grey centers and mainly affect leaves but can also appear on fruit. The lesionsoften appear amid a field of leaf yellowing.

  • Light brown to red lesions with grey centers
  • Leaf yellowing

Suggested Treament:

Citrus Psorosis

Citrus Psorosis is a citrus disease caused by multiple viruses of the family Ophioviridae. Citrus Psorosis produces an escalating array of symptoms that include yellow spots on leaves, low fruit yields, small circles surrounded by sunken grooves on fruit rinds, and eventually, scale and sticky deposits forming on bark along with deep grooves or pits in trunks and large limbs. The Citrus Psorosis virus may reside in a tree for up to ten years without any noticeable symptoms. The disease is largely transferred through bud grafts, and as such, has been greatly controlled through the application of industry bud material inspection and certification programs.

  • Yellow spots or irregular blotches on leaves
  • Circles with sunken grooves on rind
  • Deeply grooved trunks or pitted branches

Suggested Treament:

  • Prevented by proper budwood certification
  • Severely infected, older trees removed and destroyed

Sweet Orange Scab

Sweet Orange Scab is a fungal infection of citrus fruits caused by the fungus Elsinoe australis. The fungus affects the appearance of mostly fruit rinds, and less often, young twigs and leaves. The disease does not affect the quality or taste of the fruit, but may cause some fruit to drop prematurely, particularly on younger trees. The spores require moisture to reproduce and are often spread during rain.

  • Unattractive scab-like outgrowths on fruit rind exterior
  • Sometimes similar scabs appear on twigs and leaves

Suggested Treatment:

Citrus Tristeza

Citrus Tristeza, also known as Quick Decline or QD, is a virus carried and delivered to citrus trees by aphids. Aphids such as the brown citrus aphid contract the virus when feeding on a QD infected citrus tree. The Citrus Tristeza virus can also be spread or, in effect, multiplied through the process of grafting stock for new trees. Many strains of the Citrus Tristeza virus exist, and their effects range from slight, ineffectual damage to rapid decline of tree health and a resulting death.

  • Cupping of leaves
  • Leaf vein corking
  • Leaf flecking
  • Pitting of stems
  • Deep pitting of trunk

Suggested Treament:

  • Treatment and control of Aphids
  • Careful inspection for QD symptoms when grafting


Lemon Trees: 7 Common Problems

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Gardeners with lemon trees in their yards are often faced with the question: what is wrong with my lemon tree? Here are causes and cures for seven of the most common problems with lemon trees in the home garden.

Overwatering: Citrus may become stressed and more susceptible to pests and diseases as a result of poor drainage or standing water. Citrus and other trees have difficulty with proper nutrient uptake in wet soils.

Shallow Watering, Watering with Sprinklers, and Wetting Trunks or Major Roots: GardenZeus discourages planting lemon trees in lawns or using sprinklers for watering trees. Sprinklers and other shallow surface irrigation are generally inappropriate for citrus and other trees, and may encourage root rot, shallow rooting, other diseases and pests, and other problems. Avoid wetting trunks and major roots with sprinklers, and keep the upper soil dry within tree driplines.

Chlorosis: Chlorosis is iron deficiency that appears as lightening or yellowing between veins on older leaves and/or pale green or yellow new leaves. Affected leaves will never return to normal because iron is not a mobile nutrient, meaning that it cannot be relocated within a plant. Alkaline city water and alkaline soils are common causes of chlorosis iron becomes decreasingly available to trees when soil pH is above 6.0, and is mostly unavailable at pH of 7.0 and above. Chlorosis in citrus is often chronic due to naturally alkaline soils combined with watering over years with alkaline city water. Trees may also become chlorotic as a result of wet or waterlogged soils, anaerobic soils, root rot diseases, or damaged roots. Applying chelated iron will help temporarily but is not a long-term solution or cure, and chelated iron may rapidly become unavailable in alkaline soils. The best solutions are to encourage a thriving, healthy soil ecosystem that will naturally improve pH, or to provide acidity to soil by mulching with face-down cut halves of waste citrus, watering with diluted vinegar at proportions of about 1/4 to 1/2 cup of white vinegar in 2 gallons of water, or using an acidifying product such as pH Reducer.

Nitrogen Deficiency. In contrast to chlorosis, nitrogen deficiency appears as pale or yellowing older leaves while new growth is green and healthy. Nitrogen is mobile in plants and is moved from older leaves to produce new growth. Apply a nitrogen soil drench in the form of diluted urea or chicken manure at the rate of one cup of chicken manure per four 4 gallons of water (half cup if fresh manure), mixed thoroughly, and applied near the driplines of trees a few times per year. Fresh or composted manures may be applied as a surface-dressing under mulch. Adding too much nitrogen to soils may result in lush, high-carbohydrate leaves that attract insect infestation, and may delay or reduce fruit formation if added early in the fruiting cycle.

Sunburn: Citrus bark and cambium are sensitive to sunburn, and sun protection for trunks and branches may be necessary during hot Mediterranean-climate summers. Lemons are more sensitive to sunburn than other types of citrus. Avoid thinning or removing significant portions of canopy, especially those that shade internal branches from southern and western direct sun. Sunburned stems begin to show cracked, peeling, or rough sections of bark that progress to dead sections of cambium with exposed bare wood. When these symptoms occur on south-and-west-facing citrus trunk or stem sections, they are usually caused by sunburn. Wrap trunks of young trees in sleeves (consider making homemade ones from paper or cardboard). Larger trunks and stems may require painting with indoor white latex paint diluted about 1:1 to 2:1 water to paint. If you find white-painted tree stems and trunks to be particularly unattractive in the garden and landscape, try a light-colored beige, tan, or similar color that blends in better with your garden however, these paint colors will not protect trunnks as well as white.

Blossom and Fruit Drop: Sometimes a problem but often not. Citrus trees naturally drop many of their flowers and small, immature fruits when they are about the size of a pea, most commonly in late spring to early summer. On otherwise healthy and unstressed trees, loss of the majority of flowers and up to 80% or more of the tiny immature fruits may be normal. If numerous fruits are dropped at about the size of a ping pong ball or larger, this usually indicates that soil, water, sunlight and/or other environmental conditions are insufficient for the tree to produce a full crop.

Split Fruit. Fruit splitting occurs with many citrus species, ans some lemon varieties are likely more genetically susceptible than others. Fruit split tends to occur when watering is inconsistent or when trees become drought-stressed between waterings, especially when combined with other environmental stresses such as cold, heat, wind, nutrient deficiency(s), pests, disease, or physical injury. Splitting is more common on young, establishing, and shallow-rooted trees. Generally only a small proportion if fruit on a given tree is affected. Splitting usually occurs before fruits are ripe, so fruit are rarely edible when split and should be removed from the tree and composted or discarded. If left on the tree, split fruit may encourage pests and diseases. There is no short-term treatment known to be effective for citrus fruit-splitting. GardenZeus expert Darren Butler believes that the best solution is to encourage strong, healthy trees by meeting their environmental needs over a period of years, particularly with consistent and deep watering, and by feeding and nurturing soil to encourage a thriving soil ecosystem.

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Felco pruners are an essential garden tool. They can be used for removing dead branches on your citrus trees and for general garden pruning and maintenance.