Question
worm collage
Hello, I live in Virginia Beach, VA, and over the last couple of days I noticed leaves being stripped from my two birch trees. I found a lot of small worms/caterpillars bunched on some of the leaves and started by removing them. It didn't take long to realize I'd be there all day trying to remove all the worms and probably still not get them all - especially if the "dots" on many leaves are more waiting to hatch.
I have attached a collage of some large worms, a mass of small worms (not focused very well but I can try again if necessary), and a leaf with many dots.
First, can these worms kill the trees? AT the rate they appear to be going they may strip the entire trees (relatively small trees). If I should remove them, is it possible to do so without using something really toxic like soapy water? I try to keep my use of herbicides and pesticides since I have a small dog that roams the yard at will and tends to eat/mouth stuff she finds.
I realize this is similar to a question you recently answered, but wanted to ask separately because I have pictures and would like to not have to use a poison. Thank you for your time.
AnswerThe smaller ones are the Dusky Birch Sawfly,Croesus latitarsus. Larvae are yellow-green with black blotches on their sides and have a black head; they are about 24 mm (1") long when full grown. They have one generation per year.
For deciduous plants, late season defoliations (i.e. late August - September) usually have little effect on tree health, as the plant will not try to produce new leaves and it has stored most of the reserves it needs for the following season. Defoliations at other times of the year may present problems for health and/or aesthetic reasons.
IF the tree is small enough to reach the branches you can use a mechanical control method. Mechanical Control -Examples here include methods such as hand picking larvae from plants, physically dislodging them by using forceful water sprays, or other means of nonchemical control. Population size and distribution will determine the effectiveness or suitability of the chosen method.
Or you can spray the foliage with an insecticide called acephate (Orthene). Because sawflies often feed in groups, chemical applications should be directed only to the areas they are feeding on; entire tree sprays are unnecessary unless populations are wide-spread throughout the plant.
It will not be a problem with the animals in fact it is sometimes used to control fleas in bedding sites.
The other caterpillar looks like the horned devil caterpillar. It can eat a good amount of foliage since it is fairly large. The Orthene will work on it also or picking it off will work too.
Nether of these insects will kill the tree. IF there were complete defoliation for a couple of years in a row you could get some growth loss but usually this does not happen.
The bumps look like a gall wasp injury. The wasp will lay its eggs on the leaf and the chemical that is secreted will cause the leaf cells to grow over the eggs. This is not a real health concern and does not need to be controlled.
