Lemon trees produce beautiful foliage and fragrant flowers. Several varieties bear fruit year round, and many home gardeners get enough lemons for their own use and several lemonade stands. But lemon tree diseases can undo all your efforts to maintain this productive, beautiful plant.
In this article, we’ll tell you about the most common lemon tree diseases and what you can do about them. We’ll start with the most serious, new lemon tree diseases, which you may not have ever heard of.
Huanglongbing, or HLB, formerly known as citrus greening disease, is one of the most destructive lemon tree diseases worldwide. Scientists used to think HLB was caused by a virus, but they have more recently learned that the organism that causes it is a form of bacteria that can’t be grown in the laboratory. This lemon tree disease infects trees in Florida, Georgia, South Carolina, and Louisiana, and the insect that transmits it has recently arrived in Southern California.
In newly infected lemon trees, HLB first causes leaves to take on a mottled appearance. Leaves will have blotches of yellow. Once a lemon tree becomes chronically infected, the leaves will show blotchy brown and yellow spots on one side but not the other.
You can tell the difference between HLB and zinc deficiency by the asymmetry. Zinc deficiency causes blotches on both sides of a leaf, while HLB causes blotches on just one.
It just takes a glance to identify fruit from lemon trees that have HLB. They will be greener at the navel end of the fruit, and more yellow closer to the stem. HLB-infected fruit will grow lopsided. They will have aborted seeds that won’t germinate (not that you should be growing lemon trees from seed). Their juice will be unusually thin and bitter.
You can’t use lemons that have been infected by HLB. There is no cure or treatment for HLB. The only thing you can do is to uproot the tree and burn it. Don’t reuse potting soil that has held a lemon tree infected with HLB, and don’t plant another citrus tree where you have uprooted an infected lemon tree outdoors.
If you live in one of the states where HLB infects lemon trees, you may be able to prevent the disease by controlling Asian citrus psyllids, the insects that spread it. There’s no single insecticide that eradicates psyllids, because they live in different parts of the tree at different times in their life cycle.
If you are using organic insecticides, you need to apply them every 10 days after your tree flowers until it sets fruit. There are parasitic wasps called Tamarixia radiata and Diaphorencyrtus aligarhensis that eat the psyllids. You may be able to get them from an organic supply store. They don’t sting. They won’t wipe out the psyllids, but they will slow them down enough that you may be able to get a few years of production.
Growing your lemon tree indoors all year round is your best bet for stopping HLB if you live in one of the states where the disease is already a problem.
Citrus tristeza virus is the most destructive virus of lemon tree diseases. It affects all kinds of citrus. The virus is spread by transportation of infected trees from one home to another, and by aphids.
One strain of this virus causes the entire tree to die quickly, with dead leaves remaining attached to branches. Another strain causes pitting of stems and branches. You will most likely see stems infested with large numbers of black or brown aphids sucking sap on the underside of leaves before the tree shows signs of infection a few weeks later.
You are most likely to have a problem with tristeza virus if you have a Meyer lemon tree that has been grafted onto a sour orange rootstock. You can prevent the disease by killing aphids as soon as you see them, and you can clone a highly productive lemon tree by taking an uninfected branch and having it grafted onto some other kind of rootstock. Once your lemon tree has tristeza, there is nothing you can do to save it. You can only prevent its spread to other trees.
Citrus Stubborn Disease
Citrus stubborn disease is a bacterial infection that is spread by leafhoppers. It causes mild symptoms similar to HLB in lemon trees, but it can kill nearby orange trees. Lemon trees infected with citrus stubborn disease will have leaves mottled yellow and bear oddly shaped, bitter fruit.
There are a few things you can do to keep your lemon tree from catching citrus stubborn disease. Make sure you don’t plant periwinkles near container-grown lemon trees, and if your lemon tree is near your garden space, don’t plant Brassicas (cabbage, broccoli, Brussels sprouts, and similar vegetables) within 50 feet (15 meters) of your lemon or other citrus trees. Periwinkles and Brassicas harbor the infection. Make sure there are no weeds near your lemon tree, too. Weeds feed leafhoppers.
Don’t be hesitant to ask the nursery where you are buying your lemon tree whether their plants have been raised with precautions against citrus stubborn disease. Citrus stubborn disease is most likely to affect lemon trees that are less than six years old. Once a lemon tree is infected, the only thing you can do is to remove the infected tree and replace it with a healthy plant.
Exocortis or scallybutt disease is a viral infection that doesn’t usually kill lemon trees outright, but can cause stunted growth. It is spread from tree to tree by infected pruning tools. It only takes one cut with a knife or pruning shears contaminated by the virus to infect a tree. Heat doesn’t kill the virus. Pruning equipment must be sanitized with bleach between uses.
You are most likely to have a problem with exocortis if you are growing a Meyer lemon tree on a trifoliate rootstock. Once your lemon tree has this problem, the only thing you can do is to remove and burn it. You can prevent transmission by bleaching pruning tools between trees.
Citrus Leaf Blotch Virus
Citrus leaf blotch virus is a disease that interferes with strong graft unions. The scion of the lemon tree you want may fall off its rootstock, leaving you with a hardy tree that produces fruit you do not want to eat.
The virus is transmitted by seed. This is why it is so important not to start lemon trees from seed. You never know when the seeds of imported grocery store fruit contain a virus like citrus leaf blotch virus. These viruses can affect your lemon tree and spread to others. Always get your lemon trees from a reputable nursery.
CitrusTatter Leaf Virus
Citrus tatter leaf virus has been in the United States since 1908, when it was brought in with the first shipment of Meyer lemon trees. Depending on the rootstock, the virus can cause graft incompatibility and stunt the growth of your lemon tree. You can recognize the infection by the tattered appearance of the leaves, with yellowish areas on an otherwise healthy leaf.
Scientists have developed and cloned a version of the Meyer lemon free of citrus tatter leaf virus. Ask for the Improved Meyer Lemon when you buy your Meyer lemon tree. If your Meyer lemon has this condition, you don’t necessarily have to remove it, but it will never produce well and can transmit the virus to other Meyer lemon trees.
Citrus Variegated Chlorosis
Citrus variegated chlorosis is a bacterial infection that causes yellowing and curling of leaves and a brown, gray scale fruit that becomes unusually hard. It’s a condition that is spread during grafting and by sharpshooter insects found in California.
The best way to prevent citrus variegated chlorosis is to be very careful about where you buy your lemon tree. You want to be sure the nursery that grew your tree has a program to detect and prevent citrus variegated chlorosis and other lemon tree diseases. In most of the United States, citrus variegated chlorosis is not yet a major problem.
Leprosis is a viral disease of lemon trees that has been spreading north from South America and now exists as far north as Mexico. It is spread by grafting and by tiny eight-legged creatures known as flat mites. They are so small that to get a good view of them you need an electron microscope.
Newly hatched flat mites have to feed on infected plant tissue to contract the virus. Removing infected lemon trees and burning them is the way to stop the spread of this virus.
Citrus psorosis ophiovirus is a viral infection that affects citrus trees of all kinds around the world. This condition is also known as scaly bark disease, citrus ringspot disease, citrus psorosis complex, CPsV-A, and CPsV-B. It causes a number of easily recognized symptoms:
- The bark on the main trunk of the lemon tree will become scaly and begin to flake away. Damaged areas of the bar may fill with gum.
- Leaves will develop yellow spots (chlorosis) in random patterns. Leaves may seem to recover as they mature.
- Fruit may develop ring-shaped areas of discoloration that look like a green bullseye.
Psorosis may spread through the air or be transmitted by pruning tools that have not been disinfected.
You may not have to remove a lemon tree that has a mild infection with psorosis. Some strains of the virus are less of a problem than others. But if you have oranges, tangerines, or grapefruit nearby, they may be severely affected.
Want to learn about the bugs that can affect your lemon tree? Check out our post on how to identify and prevent lemon tree pests.
The Bottom Line on Lemon Tree Diseases
Most lemon tree diseases are terminal. If your lemon tree gets them, you will not get the foliage, blossoms, and fruit you want. And if you don’t destroy the infected tree, the disease can spread to other trees on your property and to your neighbors. Some lemon tree diseases aren’t limited to just citrus trees.