Did you have bagworms on your trees last year? Now is the time to get ahead of them for this year. Hopefully you were able to remove as many bags as possible over the winter. If half the bags had females, and each female bag contains hundreds of eggs, well… you do the math. Since it is hard to remove every single one, you will need to spray twice to kill them before they kill your tree. Organic options would be Dipel and thuricide, both are forms of bacteria that specifically kill caterpillars. There is a wide range of chemicals that will kill bagworms: pyrethrin, neem, permethrin, bifenthrin, lamda cyhalothrin, malathion, and carbaryl. Timing is the important. Spray once in mid to late April and spray again in May, following the interval listed on the label. If the weather is as crazy as last year, you may need to spray a third time, still following the interval on the label. If the tree is blooming, wait until it finishes blooming to spray to protect the bees.
Many people apply a systemic insecticide called imidacloprid to their trees at this time of year to prevent insect problems such as scale, mealybug, and some borers. Imidacloprid kills a lot of insects, but it doesn’t kill caterpillars, like the bagworms above, or spider mites. It is for ornamental trees only: do not use on fruit trees for human consumption. Imidacloprid should be applied as a drench in April for season long control. If your trees are in bloom or are about to bloom, please wait until the flowers fall off to protect the bees.