The cotton insect control season is basically over. I say
that realizing that there are a few late maturing fields within the state that
may still need a stink bug spray. There are even fewer fields that have high
numbers of tarnished and clouded plant bugs present. Where growers are
attempting to make a top crop, in fields that have exceptional yield potential,
plant bug controls may still be applied. Our greatest concern now in cotton is
boll rot and disease. The past few days of overcast skies and rain showers have
increased boll rot. The next weeks forecast is much the same. Other than a few
southwestern counties, the state was spared from the excessive rainfall from
Isaac.
At present, the insect action is primarily happening in
soybeans and to a limited degree in peanuts. The lep feeders are occurring on
soybeans state wide. We have more soybean loopers on beans in the Tennessee
Valley area of North Alabama than I can ever remember. This complex also
includes the green cloverworm statewide and the velvetbean caterpillar as far
north as Selma and Montgomery in central Alabama.
Loopers, (all are the soybean looper, more difficult to
control) are occurring at 1 to 8 or more per sweep. Most of our beans are drill
so we cannot use a drop cloth. Our threshold experience with loopers using drop
cloths is well established at 5-8 per row foot. We are wrestling with a sweep
net threshold. Two loopers per sweep are not causing more than 5% foliage loss
while 8 per sweep is causing 30-35% foliage loss. Our threshold is 20% foliage
loss with beans at the stage they are now. So somewhere between 2 and 8 loopers
per sweep is a treatable level. Based on my field observations I would treat in
the neighborhood of four loopers per sweep.
Stink bugs are increasing in beans and will likely continue
to do so in the days ahead. Therefore, in many fields a stink bug material
(pyrethroid) or acephate (Orthene) may need to be added as we treat for loopers
with the recommended insecticides of Tracer (Blackhawk), Intrepid, Steward or
Belt.
One or more soybean fields in Southwest Alabama are infested
with the garden fleahopper at damaging levels. This is a first for this insect
on soybeans. They occurred on peanuts in that area a couple of weeks ago.
Some peanut fields are also infested with this mix of
caterpillar pests. In this mix we are also finding fall armyworms, southern
armyworms, corn earworms, cutworms, yellow striped armyworms and immature
burrowing bugs.
Both soybeans and peanuts need to be scouted weekly for the
remainder of this season and future seasons. The old method of spraying an
insecticide on soybeans or peanuts when fungicides are applied is really just a
stab in the dark. The odds of this being good timing for insect control is
somewhere between slim and none. With the price of beans we have to do a better
job with insect control than automatic sprays based on the stage of the beans.
Most of our comments in the next week or so will be directed
towards soybeans and peanuts.
Soybean loopers became an economic threat to soybean growers
in Baldwin County (on the Gulf Coast)
this year during the first week of August. Soybean loopers were treated in many
Blackbelt (west central Alabama) soybean fields this week as looper numbers
increased and defoliation levels rose. Now farmers on both sides of the
Tennessee River are preparing to spray numerous soybean fields for this pest
for the first time since 1988. Densities of soybean loopers at the Fairhope
Research station across the bay from Mobile were an average of 8 per sweep (all
sizes) in test plots that were averaging an estimated 10 to 15% defoliation when
an insecticide was applied on August 7. Eight days later defoliation in
untreated plots ranged from 25 to 40%. Farmers in the Tennessee Valley have found
as many as 3 loopers per sweep this week and defoliation levels are steadily
heading toward the 20% threshold level in many fields. Farmers in north Alabama west of I-65 are
watching the weather hoping that they can find
an opportune time to spray the loopers during a projected 5 day period of scattered
showers. Most of the soybeans in the Tennessee Valley were planted behind wheat
and yield potential is good presently. These later planted soybeans are mostly
in the R4 to R5 stage of development and need another good rain to produce a
strong yield. One such field that is
being monitored in Franklin county was running one looper per sweep on August
25 and had 5% defoliation. This field had 2 loopers per sweep (all sizes) on August
30 and 10% defoliation. A few loopers
had pupated in the field and had attached themselves with silk to the
undersides of leaves. No diseased worms were observed while sampling. Stink
bugs are also present in these fields but numbers are mostly below the
threshold of 2 per 15 sweeps from bloom to mid-pod fill and 3 per 15 sweeps
after mid-pod. Three-cornered alfalfa hopper (3-CAH) numbers are usually
running from less than one to two per sweep .
Pod worm numbers are very low in most fields. Chemicals currently listed
in the Extension Soybean IPM guide for soybean looper control are Belt 4SC,
Intrepid 2F, Steward 1.25 SC and Tracer 4 SC. None of these products will
control stink bugs or 3CAH’s. Belt, Steward and Tracer are labeled for control of
pod worms in soybean. Hopefully, one application will be sufficient this year
to manage soybean loopers but growers should continue to monitor fields
following looper sprays to insure that populations do not rebound.
By: Tim Reed- Extension
Entomologist and Ron Smith- Entomologist and Professor Emeritus
