Posted by Sunset, July 28, 2009 in Q&A
By Jim McCausland, Sunset Magazine
Photos by Emily Bartnikowski
Dear Fresh Dirt,
I have a webworm infestation. At least - I assume they're webworms. I've attached photos of some of the webs I've found in my fruit trees. The first two are in a dwarf plum and the third is in an orange. I also have them in my apple tree, my lemon tree, and my pomegranate tree. I intend to eat all of the fruit produced by these trees, but I have a feeling the worms have beaten me to it. I'd like to remove them from my food trees without the use of poison because - as mentioned - i want to eat the food on the trees.
I'm completely new to this gardening gig, so don't be afraid to tell me that the answer is simple enough a monkey could figure it out. I suspect I often overthink my problems. Oh, and I live in San Jose - if that makes any difference.
Thank you!
Emily
Hi Emily,
Thanks for your note about the webs on your fruit trees. I think your trees have spider mites, not web worms, but I'll address the other possibilities too.
Besides orb-weaving spiders, three kinds of creatures make fairly noticeable webs on fruit trees.
Spider mites are very tiny spiders. Though you may need a magnifying glass to see them and count their eight legs, their webs are plainly visible, as in your pictures. Spider mites suck the juices out of leaves, giving them a mottled look—and they do feed on both citrus and deciduous fruit trees.
Tent caterpillars show up in spring around the time deciduous trees leaf out. They usually make their web-like tents in crotches of branches inside the trees. Common hosts include fruit trees and oaks, but not orange trees. This would be very late for them to still be around.
Fall web worms usually appear around mid July and keep working through fall, and they make their web-like tents over leaves, usually at the ends of branches. I see them on fruit trees and alders in the Pacific Northwest, but they also feed on willows, poplars, and other hardwoods. They don't, however, like citrus trees.
If you have spider mites, blast their webs apart with a jet of water from a hose and follow up with a spray of insecticidal soap.
If you have either tent caterpillars or fall webworms, you should be seeing lots of caterpillars devouring your trees leaves. To treat them, blast tents apart with a strong jet of water from a hose, then spray with Bt (Bacillus thuringiensis). Your local nursery has it. Bt, by the way, is a very targeted bacillus that shuts down lepidoptera larvae's ability to digest what they eat. It doesn't harm you or your pets—just caterpillars that eat leaves.
But before you spray either kind of web-making caterpillar, watch an active tent closely and you'll probably see tachinid flies, ichneumons, and parasitic wasps trying to pick off caterpillars. They often lay eggs on the backs of the caterpillars, and when the eggs hatch, they burrow into their hosts and eat them alive.
