If you’re like me, in early summer you are looking with satisfaction and excitement at the new leaves and beautifully fragrant flowers on your lemon tree. And then, just as you start to have visions of the juicy lemons to come, problems start to appear. Two common problems, leaf miners and fruit drop, may show up in the next few weeks.
Leaf Miners
Whenever your citrus tree puts out lush new growth, it may attract an insect called a citrus leaf miner, which is a very small moth. The life cycle of a moth is the same as a butterfly which is adult > egg > larva > pupa > adult. At any time of citrus leaf flush, the adult female lays its egg on tender new leaves and the egg hatches into a larva. As the larva feeds and develops, it enters between the leaf layers and leaves a frass (feces) trail, observed as a thin dark line inside the meandering serpentine mine just under the surface of the leaf. This visual characteristic is used to help identify the pest.
When the larva emerges from the mine and moves to the edge of the leaf it rolls the leaf around itself and pupates in preparation for adulthood, creating a rolled and deformed leaf. Sometimes people find these distorted leaves troubling, but they are a cosmetic issue and will not harm the tree. Avoid removing leaves damaged by citrus leaf miner since undamaged areas of leaves continue to produce food for the tree. You should also avoid pruning live branches more than once a year, so the cycles of leaf flushing are uniform and short. Once the leaves harden, the pest will not be able to mine the leaves.
There are a variety of natural predators that will help to keep the citrus leaf miner under control. Keep in mind that spraying with an insecticide won’t eliminate the leaf miner because the larvae are protected inside the leaf, but spraying citrus with broad-spectrum insecticides risks killing the natural enemies of the pest.
The link below provides more information on the life cycle and management of citrus leaf miners.
https://ipm.ucanr.edu/PMG/PESTNOTES/pn74137.html
Fruit Drop
Blossom and leaf drop are normal occurrences in spring and early summer when the fruit is between pea and marble size. Citrus is self-thinning, and the trees will shed excess fruit they can’t support. Hot, dry and windy weather can increase the rate of fruit drop, and excessive fruit drop can have multiple causes, including nutrient deficiencies.
To manage fruit drop, increase the amount and frequency of irrigation during periods of high heat, low humidity and strong winds. Look for additional signs of nutrient deficiencies in the leaves and fertilize if needed.
Help Desk of the UC Master Gardeners of Contra Costa County (RDH)