A question came in to Ask Gardenerd this week about Leaf Miners:
“I just watched your citrus care video and it was great! I have [citrus trees] that were all planted within the past 1.5 years… None of my trees have yellow leaves, however, they all have leaf miners and probably leaf rollers. They all also have ants crawling on them (so perhaps mites or aphids are present). I apply Tanglefoot around each trunk every 6 months, but the ants can still get onto the trees because of the angle of the slope.
I have tried spraying the trees with insecticidal soap and over the summer, I released green lacewing larvae, but still can’t seem to get the insects to go away. I live in North County, [San Diego, CA] so the bugs exist all year-round! Do you have any suggestions for me? Thank you in advance and I look forward to hearing from you soon! – Cheryl”
Pests can be an ongoing problem, and soil management is the best way to boost plant vitality so your fruit trees can outperform the pests. It sounds like you’re feeding your trees properly, but keep in mind that it can take a few years for citrus trees to take hold and become productive. Your job right now is to feed your soil (plenty of mulch to feed soil microbes, compost, and compost tea). Let’s look at other solutions:
Organic Solutions for Leaf Miners
Let’s start with leaf miners. We did a video last year on the benefits of spraying leaf surfaces and the soil with beneficial nematodes. Steinernema carpocapsae and Steinernema feltiae nematodes will penetrate the leaf surfaces and destroy leaf miners. We applied here at the Gardenerd Test Garden in fall and haven’t seen any new damage since. Those nematodes treat a host of other insect issues so you can’t go wrong with it.
Leaf rollers pupate in “loose cocoons” by rolling up leaves to nest inside them for about a month before emerging as a moth. There are many types of leaf rollers, some of which lay eggs on stems and twigs rather than leaves. Fruit tree leaf rollers only produce one generation per year, so that’s good news. The moths usually mate and lay eggs between May and June.
Tachinid flies will parasitize them, so be sure to grow plenty of beneficial insectary plants that attract Tachinid flies to the garden, such as alyssum, yarrow and other umbels. You can apply Bt spray (Bacillus thurungensis) if you really want to treat them, though most of the time the damage isn’t severe enough to merit treatment.
Another option, which will treat both leaf miners and leaf rollers is to apply an organic product with Spinosad (it penetrates leaf surfaces as well). Monterey Garden Insect Spray treats both, as well as ants if you treat the mound directly. Neem and other horticultural oils may work to some degree, but they don’t penetrate leaf surfaces, but rather smother insects instead.
Ants are only an issue if they are farming scale, aphids, or other sucking insects on your fruit trees. If they provide taxi services in exchange for the sweet honeydew these sucking insects secrete, you may want to tackle the issue. Since sticky traps aren’t quick working for you (i.e. Tangle foot), you might want to try a boric acid-based ant trap instead. Install these traps at the base of each tree and see if that reduces the population.
We hope this helps you boost your citrus trees’ vitality this season. Thanks for writing in Cheryl.
To find most solutions like these, pre-order your copy of Grow Your Own Mini Fruit Garden, due out in March, 2021.