Based on calls from consultants during the past seven days,
most insect attention on cotton in Alabama has now shifted to the stink bug
complex. This appears to be the appropriate thing to do since no other
widespread destructive insect is being reported and a high number of stink bugs
are being reported from all the major row crops. This began with wheat during
the spring months. Stink bug numbers later shifted to corn. High numbers have
been reported in recent weeks in peanuts, with increasing numbers being
reported in both cotton and soybeans.
If we back up and review the situation since the end of the
2012 season, this is as expected. Stink bugs built high numbers on soybeans
late last season resulting in a high level entering overwintering sites. This past
winter was mild and we did not have the excessive high temperatures or extended
drought this spring to limit a 2013 population build up.
This complex included both the brown and the southern green
species. In the more southern counties within Alabama, the leaf footed bug is
also in the mix. Leaf footed bug damage is identical to stink bug damage to
cotton bolls. The important thing here is that, control wise, they are more
like the brown stink bug. Phosphide insecticides do a much better job in
controlling brown stink bugs and leaf footed bugs than do pyrethroids. Growers will
need to keep this in mind as they select their chemical for treatment
decisions. In Alabama, escape bollworms on Bollgard and Widestrike cotton
varieties have not presented a big enough problem to select a pyrethroid over a
phosphate for stink bug control. Field monitoring between July 20 and August 10
will determine if that trend holds true for the 2013 season.
In a few weeks, as we begin to make more stink bug control
decisions in soybeans, we will have to work more with the pyrethroid chemistry
to suppress the brown stink bugs in the complex. Research trials across the
south point to bifenthrin as their superior pyrethroid for brown stink bugs in
soybeans. We can improve the percent control by using the higher labeled rates.
Back to cotton, here is how we suggest making treatment
decisions. First, select a minimum of 25 ten to twelve day old bolls that are
still soft to the touch and can be crushed by hand. Select more bolls from at
least two locations from larger fields. Crush these bolls and observe for
internal injury. Note, it may make this process faster by first separating the
bolls with external feeding signs from those that have none. First, crush the
bolls with external feeding only and determine the percent that have internal
injury. If a threshold is reached, then the remainder of the bolls with no
external feeding signs will not need to be crushed. Internal damage may consist
of one or more warts on the inside of the boll wall, damaged seed or stained
lint. Second, the decision maker needs to know how long that particular field
has been in the blooming stage. Most stink bug injury and loss is coming during
weeks three though five or six of bloom. This is the period when most
harvestable bolls are being set.
In Alabama, I suggest using a 10% internal damage threshold
during weeks three though six of bloom. An insecticide application will usually
suppress stink bug numbers for seven to ten days unless a field borders another
untreated crop with high numbers of stink bugs. If has been my experience that
stink bugs do not move rapidly across fields like plant bugs as they reinfest. The
first four to ten rows adjacent to corn or peanuts seem to get most of the
migration initially.
In our heaviest stink bugs years, cotton in the coastal
plains of the southeast have required up to four applications. Under most
conditions however, only two or three sprays may be warranted.
One last thing I will mention today is that, in the past,
stink bugs seem to cause more internal boll damage in wet seasons than in dry
seasons. That being the case, and unless the weather changes, we need to be
extra cautious of stink bug damage to cotton in 2013.