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