This time of year there is a great deal to talk about regarding home and garden plants and ornamentals. Last week I observed the first bagworms of the season in the area. These bagworms are very tiny now but will become the Christmas tree ornament looking bags that most folks don't notice until late July and August when it is too late to do much about the problem. Now is the time to scout and take action. Bagworms and Japanese beetles seem to be the most common horticultural insect call during the summer. Both can completely defoliate a tree. We will talk about Japanese beetles in the future when they become a problem.
Bagworms are caterpillars that live inside spindle-shaped bags which they construct to protect themselves against birds and other enemies.
These bags composed of silken threads and bits of foliage look so much like a part of the tree that they may go unnoticed until extensive damage occurs. When the bagworm gets larger it is less susceptible to insecticide as it is in the security of the bag.
Eggs hatch from old bags of the previous year as the new insects start to spin bags and continue to grow both themselves and their bag as they feed on the tree.
If the caterpillar is disturbed it will scurry back into the bag for safety. Each female bag can produce over 1,000 bagworms. Female bagworms are wingless and never leave the bag while the male bagworm is winged and travels to fertilize the eggs of the female. Eggs stay in the female bags over winter to start the process the next year. There is only one generation of bagworms each year, unlike other insects like corn borers that have multiple generations each year.
There are several control methods. One method is to pull the bags before the eggs hatch, which you can keep in mind for next year. If pulling the old bags before eggs hatch, you should place the bags in a bucket of hot, soapy water to kill the eggs.
Once the caterpillars are hatched there are two options of spray. The best scenario is to spray now with a biorational pesticide. A biorational insecticide will kill only the caterpillars rather than killing all of the insects on the tree. There are several beneficial insects on most trees that feed on scales, spider mites and other harmful insects. These biorational insecticides though are most effective when applied to worms that are very small. Two weeks after application check trees again to see if any live bagworms are present to determine if re-treatment is needed. Purdue pub E-27 entitled "Bagworms"
has two excellent color photos. One photo is of the very small bag worm that you should look for now and the other is of the larger mature female bagworm hanging from the tree. You have to look really close to see the small caterpillars and bags right now, though it is the best time to defeat this pest.
Also there is a list in E-27 of pesticide products available that work against bagworms. If you have waited too long and the biorational insecticide either won't work or isn't available, then the second option is a rescue insecticide that will kill most of the insects associated with the tree. However, be on alert that you should be on the lookout for other pests like scales and spider mites if you use a rescue insecticide as beneficial predator insects that normally keep scales and spider mites in check are killed when using rescue insecticides.
Also there is no benefit to spraying nearly adult bagworms in late July and August. In fact doing so may kill beneficial insects and make things worse. If you have lots of time and patience, you can simply pull all of the bagworms off.
You can contact the local Purdue Extension Office by calling 829-5020 x14 in Owen County or 448-9041 in Clay County for more information or publication copies regarding this week's column topic or to RSVP for upcoming events. It is always best to call first to assure items are ready when you arrive and to RSVP for programs. While most publications are free, some do have a fee. All times listed are Eastern Time.
July 4 Purdue Extension Offices Closed for Independence Day
July 6-12 Owen County Fair
July 8 Purdue Weed Day, West Lafayette
July 11-18 Clay County 4-H Fair
August 6-17 Indiana State Fair