Problems
with damaging levels of escape bollworms were observed in 2017 on two gene
cotton in numerous fields throughout the state. At harvest time, worm damaged
bolls were noticed by those operating harvesters in many other fields. These
escape bollworms were associated with all 2 gene varieties. This event had been
noticed in a few fields statewide for several years, but the problem increased
tremendously in 2017. This situation may increase in 2018 and in future years
on 2 gene cotton due to bollworm resistance to both genes. Three gene varieties
have been available to a limited degree for the past couple of years. More
varieties will be available with 3 genes in 2018, but supplies of many will be
limited. Until the 3 gene varieties are widely planted, we will need to focus
on closer scouting and better management of bollworms in the 2 gene varieties.
A major effort has been underway since last season to aid fieldmen on scouting,
thresholds, insecticide choices, and timing of applications for bollworms. Following
is a discussion on how we might manage bollworms and other cotton insects in
2018.
Do
not let plant bugs become embedded. When this happens, multiple applications
will be required to prevent economic damage. An embedded situation is when a
subthreshold level has been allowed to go untreated for more than a generation.
This results in a plant bug population of all ages and stages from adults, to
all ages of immatures and eggs. In Alabama, most adult plant bugs move from
wild hosts to cotton by July 10, early bloom. This is the perfect time to
control plant bugs with one timely spray and then stay out of the fields with
hard chemistry until the bollworm escape window begins or until stink bugs become
economic. Some of the more commonly used choices for an early bloom plant bug
spray are Bidrin, Transform, Centric, or bifenthrin to control the adults.
Since egg deposition has been going on for 2-3 weeks prior to that time of the
season, we will have plant bug immatures hatching for the following 2-3 weeks.
This is the time we want to stay out of the fields with a hard chemical. So
what do we do? Add the IGR (insect growth regulator) Diamond 6-9 oz/ac to the
adulticide. This will zero out most of the immatures that hatch for the
following 2-3 weeks. At which time, we shift our focus to escape bollworms and
stink bugs or in a worse case scenario, late migrating plant bugs.
Now
back to our bollworm situation. Monitor cotton closely to detect the major peak
of corn earworms coming from corn. This historically has occurred about July
10-15 in south AL; July 20 in central AL; and about Aug 1-5 in north AL. This
egg lay may last from 7-10 days in any given location. When this flight is
detected by increased egg numbers or five to ten 1-2 day old larvae in white
blooms, have your control plan ready and implement it within 24-48 hours. Timing
is everything here. You should already have your chemical choice in hand. We
basically have 2 choices, a pyrethroid at the highest labelled rate, or one of
the diamide selections: Prevathon 14-18 oz or Beseige (Karate + Prevathon) at
7-9 oz/ac. The pyrethroid will cost $2.00-$4.00/ac, the diamide class
$14-$18/ac. If the bollworm larvae are 5 or more days old, the diamide may be
no more effective than a pyrethroid. Diamides are most effective when the
residue is on the plant when the egg hatches. In order to make this happen
then, we must trigger the spray on or shortly after the historical date for the
bollworm moth flight determined by egg or small larvae counts. Fieldmen will
need to check sentinel fields every 3-4 days during these critical periods. In
my research plots at Prattville, AL, I will be evaluating both types of chemistry
with varying timing sprays. Until I convince myself that the pyrethroids will
not work on bollworms when the application is well timed, I will be
recommending a pyrethroid. This is for two reasons, one the diamide chemistry
is expensive. The most we will want to spend in Alabama will be one
application. The second reason I will first choose a pyrethroid is the fact
that a diamide, a few days late, may be no more effective than a pyrethroid.
Are
all pyrethroids equal for bollworm control? I am not sure, but they are not all
equal on other species that infest cotton. Most all agree that the bifenthrin
pyrethroid is better on bugs. Maybe we should never have assumed that they were
all equal on bollworms. Some are better on fall armyworms that others. Originally,
Pydrin was the best on worms while Pounce and Ambush were better on boll
weevils. One more point on these escape bollworms. You really have one shot at
the peak of this moth flight. That is the reason that first spray must be so
timely. By the time you find escape worms behind this spray, it is too late for
a “clean up.” Following this one well timed spray, scout only for more eggs or
tiny hatching larvae. A second pyrethroid application may be needed during each
moth flight. The older worms will just have to cycle out. My summary suggestion
is to have an escape bollworm plan of attack for 2 gene cotton in 2018,
implement it very quickly when the problem is detected, then move on. Do not
call for help, panic, or waste a lot of time surveying or counting large escape
worms. If you miss your target, it is too late. You only have a narrow window
of time for a well timed spray. Keep in close touch with other fieldmen in your
area. Listen out through the ag media, both printed and electronic, for insect
conditions in other areas of the cotton belt.
Some
of these sources in Alabama are:
- My tweets: @Ron_Smith23 Click Here
- My blogs: Click Here
- My Syngenta 800 line
- Call 1-877-285-8525: when prompted, press 1, then 2, then 4
- Weekly email newsletter from Tim Reed containing moth trap data
- Email reedtim@auburn.edu to be placed on this list
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