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Garden is being attacked by Leafminers and Spider Mites--never had this happen before. Help! #753448
Asked June 02, 2021, 8:30 AM EDT
Hello, I am a botanical illustrator living in church hill, va. for the first time in over ten years this Spring 2021 my garden is being overtaken by leafminers and spider mites. I have been squishing leaves between my fingers to kill leafminers chomping in between the leaves, and removing infected leaves from plants, in addition to blasting spider mites with the hose but I need specific advice on how to balance this infestation out.
Plants that are starting to show signs of stress are accumulating, such as my Passiflora lutea vine, Sambucus canadensis, Ceanothus americanus, and Malus augustafolia, Fothergilla major, and six Heliopsis helianthoides (this seems to be a leafminer favorite).
I am not wanting to use any pesticides because I have an organic garden. I've strived to create a habitat for pollinators, butterflies, Bumble bees and native bees. Bumble bees and leafcutters have already taken residence. I am wondering if biological control would be appropriate here. Through my research, I learned that applying Spinosad (naturally occurring bacillus) to the leaves with leafminer damage would stop/kill the leafminer larvae from feeding. However, it can not be used around bees and will also kill caterpillars. This is no good. Also, I wonder about birds ingesting those caterpillars--that can't be good.
I am thinking biological control could be a viable option? But I do not want to introduce anything to my garden without properly seeking advice and fully understanding the possible effects. That being said, it looks as if there are three beneficial insects that could be introduced safely.
1-2. Phytoseiulus persimilis is a mite predator as well as Neoseiulus (= Amblyseius) californicus. The latter seems to stay in the garden longer even when populations are low because it will feed on pollen. The former, Persimilis is the only species of mite that will actually go into webbing to feed on spider mites.
3. Stethorus punctillum is a spider mite destroyer that has the ability to seek out spider mites and will fly to locate them. Also seems it will survive high temperature, low humidity.
Is there a better way to combat these pests and save my plants? Or do I need to remove everything? Ugh, god forbid. Thank you for your insight and time. I've never had to intervene like this before and am seeking viable solutions.
Richmond County Virginia
Expert Response
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In terms of releasing beneficial insects outside - they typically don't work as well as expected. These insects are better released in an enclosed environment (i.e. greenhouse) where they can't escape or in a large outdoor monoculture field where everywhere they go, they come across the infected crop (i.e. fields of tomatoes.) While you could release them in your garden, they will likely quickly move out of the area.
As for spider mites, we had a hot, dry May which was the perfect environment for spider mites. Also without the rains, the mites didn't have any water to help wash them off the plants. With the return of rains this week we should see a drop in pest pressure. Non-chemical controls include frequent hosing off of plants and opening canopy to improve air flow.
For leaf miners, non-chemical control involves removing damaged leaves. https://resources.ext.vt.edu/contentdetail?contentid=2634&contentname=Agromyzid%20Leafminers
And lastly, the population of natural predators usually lags behind the population curve of the pest.
