Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service
Cotton will benefit from some of the timely rainfall
we have been receiving recently. However, it is going to make conditions better for survival
and multiplication of several pest species as well. In general, the hot and dry
weather of West Texas helps to keep bollworm numbers in check (through
desiccation of eggs). Humid and cloudy conditions over the last couple of
weeks, however, may increase egg hatch rate and worm survival in cotton. In
addition, added new growth on plant terminals will help both bollworms and aphids
thrive better.
Over the last 10 days, we have spotted many fields
with cotton aphid infestations. Aphid colonies are mainly concentrated to plant
terminals but as the numbers build-up, they may move on to the leaves. Overall,
beneficial numbers seem to be lower compared to the previous year, but they are
present. Isolated showers will also help wash out honeydew and some of the
aphids from the plants. If aphid colonies are spotty and mostly restricted to
plant terminals, I would wait and monitor the situation over the next few days.
Often aphid populations crash out in response to beneficials and rain. Click
the link below to access more detailed information on cotton aphids: http://lubbock.tamu.edu/files/2017/07/Cotton-aphid_ENTO074.pdf
I have also come across a few reports of bollworm
damage to non-Bt cotton. In our research trials, bollworm damage ranges from
5-6% boll injury in non-Bt cotton and <1% in Bt cotton. The threshold is 6%
fruit injury with the presence of live worms in both Bt and non-Bt crop. Among
various insecticide options for bollworm control, Diamide insecticides
(Prevathon and Besiege) are the most reliable choices. Remember, Besiege
contains both a diamide and a pyrethroid so it would be a better choice if
stink bugs are present too. However, if aphid colonies are present in the
field, the pyrethroid component may flare-up aphids. If a field needs to be
treated for both aphids and bollworms, Prevathon can be tank-mixed with any of
the commonly used aphidicides such as acetamiprid (Intruder).