Column
Bagworms and Leaf Spots on Hostas
By John Fulton

[June 04, 2016]  Bagworms - Bagworms are an insect that conjures up images for many people. There are bagworms, and there are other larvae that live in a bag for at least part of their life cycle. We have bagworms, Eastern Tent Caterpillar, and Fall Webworms. For the true “bagworm,” the insect that constructs a small bag like an ice cream cone from the leaf material of the tree or shrub it is on, the year-in and year-out treatment time for bagworms is June 15. You can mark this date on your calendar for next year and be within a few days of the correct treatment time. The cool spring followed by a very warm stretch probably mean the temperatures will really even out. There are a few small bagworms already out, but the idea is to have all the eggs hatched before treatment.

The next problem is what to use. The traditional standby has been Sevin, but the B.t. products such as Dipel and Thuricide have really taken the majority of the market. Many other products will work, but the B.t. products have several good points including safety to mammals and toxicity to larger bagworms. Since they are bacteria that affect only the larvae of moths and butterflies, it does take a while for the bacteria to build up to the point where they can kill the bagworm. I won’t get into the discussion about Monarch butterflies lighting in the tree just after treatment. And an item to note: there are several different strains of B.t. now on the market. One is for control of mosquito larvae, so make sure you get the correct one by reading on the label what insects will be controlled.

If you are in doubt about whether you have bagworms, check your trees and shrubs around June 15. Many times, bagworms are concentrated in the tops of trees, so thorough coverage is important. You can actually see the small bags as the larvae build them. They become very noticeable at about 1/16 of an inch long. Treat bagworms early, since larger ones are more difficult to control, but try to ensure the eggs are all hatched out – hence the June 15 date.

Most people think that bagworms only affect evergreens. Evergreens seem to be their preferred host group, but bagworms have a huge number of potential hosts. Through the years I have seen them on oak trees, grape vines, apples, and about any other growing thing you can think of.

Leaf Spots on Hosta

The Plant Clinic is reporting seeing several hosta samples with leaf spots caused by various fungi. Anthracnose is one of the main culprits. It is related to, but different, than the anthracnose which affects sycamore and other trees. It is favored by the type of weather we have been experiencing.

Irregular dead spots form, and these can tatter out with rains and wind to look like something has been eating on the leaves, however this isn’t the case with anthracnose. There are actually several fungi which cause similar problems, including Botrytis, Fusarium, and Alternaria.

 

The best offense is a good defense. This means don’t create conditions favorable to the development of the disease. Allow for good air circulation by spacing plants adequately, water in the morning to allow for drying during the day, and try to water the soil rather than the foliage. Use of fungicides can protect good leaves, but won’t cure infections already present. Products with copper, sulfur, and many of the commercial fungicides are effective in controlling new infections when applied every 10 to 14 days.

[By JOHN FULTON, COUNTY EXTENSION DIRECTOR SERVING LOGAN, MENARD, AND SANGAMON COUNTIES]