Home > Great Big Greenhouse Blog > April 2016 > IN THE DIRT with DOUG - TIME TO CONTROL BAGWORMS


Those of you who have had problems with bagworms on evergreens, such as Arborvitae, Cypress, Junipers, and other evergreens know how they can kill these beautiful plants.    The best defense against any future devastation starts now.
                There is a system used by Virginia Tech and our Cooperative Extension offices called “GDD”.  GDD stands for Growing Degree Days.  This is a system of estimating insect development and control timing.  Bagworm control starts with understanding the worm itself.  Knowing how to get rid of bagworms is half the battle.  Treatment for bagworms can only start at certain times during their lifecycle.  Because of our warmer days in March, the GDD time is now for control of bagworms while they are in the crawling stage of life and before they start developing their “bag”.
                Two things to do right now:
  1.  Pick off all existing bagworm “bags”.  Picking off existing bags is a great control measure.  Realize that each bag can contain upwards of 1,000 eggs that will turn into hatching larvae at this time of year.  Before tossing into a trash bag inspect these bags.  Check for opening at the bottom of the bag.  This is where the larvae crawls out of the bag and begins to eat. 
  2. Spray with a control insecticide.  Larvae will begin feeding and start to build a camouflage bag with plant parts within a few weeks after hatching.  They will continue to feed and eventually build a bag.  Most of the emerging larvae will feed on same tree that contained their winter home.
The control insecticide that I strongly recommend is a biological insecticide Bacillus thuringiensis var. kurstaki (Bt).  The product is a Bonide product called THURICIDE.  Bt products are more environmentally friendly since they are selective for larvae of many moths, such as bagworms, without harming beneficial insects.  Please keep in mind that Bt products have short residual activity and will require more than one application.  So, I recommend a follow up spray in 30 days.  Also, complete vegetative coverage is important for Bt products since the worm has to actually ingest the insecticide while feeding to be effective.
                                                                Happy Spring
Posted: 4/28/2016 by Doug Hensel | with 0 comment(s)
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