Bagworms and iron chlorosis    

By John Fulton

[June 05, 2007]  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. The opposite is true for a very warm spring. The idea is to have all the eggs hatched before treatment but not wait until the bagworms are almost mature. 

The next problem is what to use. The traditional standby has been Sevin, but the Bt products such as Dipel and Thuricide have really taken their share of the market the past several years. The Bt 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 (actually these products don't kill the butterflies -- only the larvae would be killed).

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. The spring we have had is probably going to zero out the timing, meaning the last two weeks of June should be ideal.

Most people think that bagworms affect evergreens only. True, that is their preferred host group, but bagworms have a huge number of potential hosts. Through the years I have seen them on oak trees, grapevines, apples and about any other growing thing you can think of. Make sure to check the tops of tall trees. An infestation may get started in a tall tree simply because you can't reach the top when applying a control. In that case, you'll have to use a taller ladder.

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. Manganese is another element that can cause these symptoms. There can be tons of iron in the soil, but if the soil pH is not acid enough, the plant cannot take the iron up. 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 show 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.

[Text from file received from John Fulton, University of Illinois Extension, Logan County Unit]