Bagworm treatment, Halloween pumpkins and a vital nutrient         

By John Fulton

[MAY 30, 2006]  After some very severe infestations of bagworms the past few years, the calls have been coming in all year on the correct treatment times for bagworms this year. Year-in and year-out, the correct 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. With a very cool spring, a week later may be a possibility. This season's yo-yo temperatures really even out. 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 Bt products such as Dipel and Thuricide have really taken the majority of the market. Many other products will work, but the Bt products have several good points, including safety to mammals and toxicity to larger bagworms. Since the Bt treatments 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.

If you are in doubt about whether you have bagworms, check your trees and shrubs around June 15. You can actually see the small bags as the larvae build them. They become very noticeable at about one-sixteenth 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.

Most people think that bagworms affect evergreens only. 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.

Pumpkins

The primary use of pumpkins grown at home is for the Halloween symbols that we have come to know. The correct time to seed pumpkins for use at the end of October is around June 15. Earlier seeded pumpkins tend to mature earlier and are rotten by the time you want to display them. Make sure you keep plants, especially new runners, treated for vine borers. Beetles that can transmit wilt virus also must be prevented with sprays or dusts.

Iron chlorosis

It's that time of year when iron chlorosis has started to show up again as the yellowing of leaves with a darker green color immediately around the veins in a leaf. This usually shows up on the younger leaves first. This yellowing is particularly noticeable on pin oaks and sweet gums but may be seen on other species.

The cause is the lack of available iron for the plant. There can be tons of iron in the soil, but if the soil pH is not acid enough, the plant cannot take up the iron. Possible solutions include altering the soil pH with either nitrogen or sulfur (be careful, since it may take a truckload to alter the soil around a large tree), spraying leaves every two to four weeks with a foliar iron compound, or implanting iron tablets in the trunk, which would last from two to four years.

Injury from iron chlorosis is the eventual decline of the plant, and it may lead to plant death over a period of time. Also, don't expect treatments to green leaves up immediately when applied now. In fact, many times the implanted iron tablets don't lead to green leaves until the following year when the sap begins to rise. Many people have been using the iron tablets in the dormant period of the tree and have had good results.

[John Fulton, unit leader, University of Illinois Extension, Logan County Unit]