Got citrus? Dan Gill explains problems that may affect your trees and what to do about them – NOLA.com

Citrus trees can be hit with many problems, but most aren’t fatal.
The harvest from 30-year-old citrus trees takes place at a commercial nursery in Belle Chasse in 2020.
Splitting is common in citrus fruit this time of year.  
Citrus black fly
Citrus leaf miners attack the flushes of new growth, occurring now and into the fall. The affected leaves are crinkled and deformed, but established trees are not greatly bothered.
Mealy busgs on citrus.
The orange dog caterpillar.
Rust mite damage.
Citrus trees can be hit with many problems, but most aren’t fatal.
Citrus trees are a popular choice for home fruit production in southeast Louisiana. Although relatively carefree as backyard fruit trees go, various problems do occur. I thought it would be helpful to cover a few issues that you may be noticing now and over the next few months.
LEAF MINERS: A very common pest called the citrus leaf miner is showing up. The adult female is a tiny moth that lays her eggs on the late-summer flush of new growth. After the larvae hatch, they enter the leaf and feed on the inside, creating a silver sheen, serpentine trails and twisted, deformed leaves.
Citrus leaf miners attack the flushes of new growth, occurring now and into the fall. The affected leaves are crinkled and deformed, but established trees are not greatly bothered.
Using insecticides is difficult in controlling the citrus leaf miner because the damage is done by the time most people notice it. Fortunately, the damage looks a lot worse than it is.
Affected trees recover very well, and the overall health of the tree is not greatly affected. The crop on a tree is not affected. So, despite the terrible appearance, most home gardeners do not bother to treat for this pest.
To reduce the amount of damaged caused by citrus leaf miners, you must begin spraying with the organic insecticide spinosad as soon as you begin to see the new growth emerging in late summer and before you see damage. Once a lot of damage has already occurred, spraying the tree will not accomplish much.
Citrus black fly
SUCKING INSECTS: There are a variety of sucking insects that attack citrus trees. One of the most common pests of citrus trees is the citrus whitefly. These gnat-sized, white insects and their disk-shaped larvae under the leaves suck the sap from the tree. Blackfly is similar, but the adult and larva are black. As they feed on the sap, the whiteflies excrete a sugary substance called honeydew.
Mealy busgs on citrus.
Another sucking insect, the mealybug, looks like cottony white patches on leaves and fruit. The wooly whitefly is another insect that appears as patches of slightly fuzzy white patches on the leaves. These insects also produce honeydew that leads to sooty mold.
The harvest from 30-year-old citrus trees takes place at a commercial nursery in Belle Chasse in 2020.
Deposits of honeydew on the leaves and fruit provide food for the growth of fungi that produce sooty mold. It does not actually attack or significantly damage the tree, and it eventually will disappear once the insects are eliminated.
Spraying trees with a light horticultural oil (such as Year-Round Oil or All Seasons Oil) is effective in controlling whitefly, black fly, wooly whitefly and mealybug infestations. Be sure to spray under the leaves, and make several applications following label directions. Light horticultural oils can be used through the heat of summer but should be applied in early morning when it is cooler.
The orange dog caterpillar.
ORANGE DOG CATERPILLARS: Finally, there is a caterpillar that feeds on the foliage of citrus trees. Called the orange dog caterpillar, it is the immature form of the giant swallowtail butterfly, one of the most beautiful of our native butterflies. The caterpillar, mottled brown and white and larger at one end, is disguised to look like bird droppings.
Unless your tree is young and has only a relatively small number of leaves, the damage done by this caterpillar is generally minor, and it’s worth some damage to have more of the butterflies that delight so many people.
If the damage is unacceptable, pick off the caterpillars and destroy them or spray your tree with BT (Dipel, Thuricide) or spinosad. Better yet, give them to friends with larger citrus trees. They would be especially welcomed by friends that butterfly garden.
Splitting is common in citrus fruit this time of year.  
If your citrus tree was planted within the past five years, don’t be dismayed if it’s not yet producing fruit or if it produces erratically. It often takes five years, and sometimes longer, for a tree to become established and begin to reliably set and ripen fruit. Time will solve this problem, along with your good care.
Late-summer fruit drop is common as a tree adjusts the crop it can carry to ripeness. Stressful weather conditions, such as drought, can make it worse. While disappointing, the loss of this fruit will allow the tree to put more resources into what is left, and this will result in higher quality fruit.
FRUIT SPLIT: As the fruits grow larger in late summer, periods of dry weather followed by rain can lead to fruit split. This occurs when the fruit swells faster than the skin can accommodate. Split fruit should be removed from the tree or gathered from the ground and discarded.
PUFFY FRUIT: These are mostly a problem on young, vigorously growing satsuma trees. Puffy fruit are unusually large, have thick rinds and relatively dry flesh. As the tree becomes older, the occurrence of puffy fruit decreases.
BIRDS: Birds will peck at the fruit of citrus. The damage looks like an ice pick was driven repeatedly into the rind of the fruit. If you have a serious problem with this, and the tree is not too large, bird netting available at local nurseries can be thrown over the tree to help prevent damage.
Rust mite damage.
RUST MITES: Fruit with a dark brown discoloration on the skin has been attacked by citrus rust mites. They generally just damage the skin, and the fruit will ripen normally with the pulp and juice still good to eat. To stop damage, spray the tree with a light horticultural oil (Year Round Oil, All Seasons Oil) once a month in June, July and August.
There are a variety of fungal diseases that affect citrus fruit, such as citrus scab, sweet orange scab and melanose. By the time you notice the symptoms, however, it is too late to do anything for these diseases. However, next year, applications of a copper-based fungicide in the spring and early summer may help minimize symptoms.
For information on how to take care of your citrus trees, see the LSU Agricultural Center’s “Louisiana Home Citrus Production” bulletin online.
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Dan Gill is a retired consumer horticulture specialist with the LSU AgCenter. He hosts the “Garden Show” on WWL-AM Saturdays at 9 a.m. Email gardening questions to [email protected].
“I love fresh citrus and always keep lemons, limes, and oranges on hand; they come in handy for spritzing up quickly grilled meats, seafoods, and vegetables.”
Chef Emeril Lagasse
Garden columnist Dan Gill answers readers’ questions each week. To send a question, email Gill at [email protected]. 
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