Plant bugs are on the move. We have heard reports of adult plant bugs moving into fields across Alabama. A lot of fields in SW Alabama and some fields in Central Alabama have been treated over the past couple of days. The rain much of the state is experiencing will likely keep scouts and sprayers out of the field for a few days, but we need to get back in there as soon as we can. Until this week, we had been pretty dry in some parts of the state. The daisy fleabane has begun to play out and plant bugs are looking for better hosts. In most cases, that will be the oldest cotton around. In other areas, we have received timely rainfall and/or soils seem to be holding water better, leaving more fleabane in the environment. In these areas, plant bugs have started moving, but we will likely have another migration as the next generation matures our in a couple of weeks. We have also heard about spider mites and three-cornered alfalfa hoppers in some areas, but plant bugs are the biggest reports we have received.
I also wanted to put in plug from a post by Dr. Camp Hand at
UGA discussing hail damage in cotton. I am not sure exactly how much we have in
Alabama, but I suspect there are some fields suffering from it. You can read
his post here (link).
Managing Plant Bugs Following the Storms
I had a discussion with a consultant this afternoon in central
Alabama, and he brought up a good point to consider. He had a couple of fields
with plant bug numbers close, but just under threshold earlier this week.
Thinking the rain would cause some wash off (which it certainly would have), he
and the grower decided to wait until the storm passed to treat. Now, assuming
no more rain comes, they will likely be out of the field at least a week, potentially
longer if rains continue. Plant bugs will be in the field depositing eggs over
a 10–14-day period, meaning immature plant bugs will likely begin hatching
around June 20th and continue through the first of July. His
question was basically, is it time for Diamond as soon as we can get the
sprayer in the field. In this situation, the answer is probably “yes.” If they
can get into the field around June 22nd, that gives us good timing
for the initial hatch out (around the 20th) and we will expect to
get 2-3 weeks of residual immature plant bug suppression from the 6-9 oz rate.
Remember Diamond should be tank-mixed with a knockdown
insecticide to kill any adults in the field or immatures that have already
hatched. Diamond kills immature plant bugs when they molt from one instar (growth
stage) to the next. Plant bugs go through 5 instars with most of the damage
being done in the 3rd-5th instar stages. This is why the
timing of a Diamond application is so important. If the treatment is made too
early, then some of the residual is wasted. If the treatment is made too late,
plant bugs in the field will continue to feed and cause injury until they molt
to the next instar.
We normally do not recommend Diamond being applied until nymphs
begin to emerge, typically around first bloom (or the first of July). However,
that is considering an application went out for migrating adults in the
pre-square stage (mid-June). Others may have this unique situation where they
know plant bugs are in the field, but they cannot do anything about it for a
week or more. In these situations, I would suggest a Diamond application be
made when a treatment goes out. If the ground dries out quicker, or a plane is available,
I would suggest going ahead and treating threshold levels of plant bugs (8
bugs/100 sweeps or 80% square retention) now and waiting to make a decision on
Diamond around the first of July.
As always, if we can ever be of any help, or if you would
like to provide input on the situation in your area, please don’t hesitate to
reach out (Scott Graham: 662-809-3368; Ron Smith: 334-332-9501).
For more information on thresholds and insecticide
recommendations, visit the Alabama Cotton IPM Guide (IPM-0415). To
stay up-to-date on the Alabama cotton insect situation, subscribe to the
Alabama Cotton Shorts Newsletter,
Alabama Crops Report Newsletter,
and the Syngenta Pest Patrol Hotline.
