Bagworms and Iron Chlorosis
By John Fulton

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[June 12, 2014]  Bagworms - 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 idea is to have all the eggs hatched before treatment.

The next problem is what to use. The traditional standby has been Sevin, and the synthetic pryrethroids such as permethrin or bifenthrin, but the B.t. products such as Dipel and Thuricide have really taken their share of the market the past several years. 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 wonít get into the discussion about Monarch butterflies lighting in the tree just after treatment. The latest research on the Monarchs shows their numbers are declining due to loss of food and habitat Ė in essence, less milkweed plants overall.

If you are in doubt about whether you have bagworms, check your trees and 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 waiting a week this time of year will also make sure all eggs have hatched into a controllable stage.

Most people think that bagworms only affect evergreens. 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, grape vines, apples, and about any other growing thing you can think of.

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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 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 2-4 weeks with a foliar iron compound, or implanting iron tablets in the trunk which would last from 2-4 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, donít expect treatments to green leaves up immediately when applied at this time of year. In fact, many times the implanted iron tablets donít show green leaves until the following year, as the rising sap carries material from the iron tablet with it. Many people have been using the iron tablets in the dormant period of the tree and have had good results.


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