Insect Pressure All Over the Board
Over the past week, we have received feedback from all cotton
producing areas of Alabama. Adult plant bugs are still infesting some fields with
nymphs showing up, while other fields do not have much, if any, plant bug
pressure. Aphids are finally beginning to build, and spider mites are showing
up in hot spots. Overall, insect management is a much of a field-to-field basis
as I have seen in my career. Recommendations have been nuanced and rarely are
the same from one call to the next.
Plant Bugs
North Alabama has experienced extreme plant bug pressure so
far this year (both TN Valley and NE AL). Many fields received 2 adult plant
bug sprays and some have received 3 applications. Overall, square retention remained
above threshold (=80%) but continued infestations required multiple
applications. Overall, the immature populations building in these fields has
not materialized to heavy pressure yet. This is possibly due to a couple of
reasons.
1. Timely applications on migrating adults reduced egg lay. This is one reason why we recommend treatment if adult counts reach 8/100 sweeps, even if square retention is above 80%.
2. I believe environmental conditions also play a role in the survival of plant bugs in the egg and early instar (hatchling) stages. The hot, dry weather we have faced over the past couple of weeks has likely killed many of the immature plant bugs that ordinarily would have hatched and developed over this time.
With all of this in mind, what does it mean for plant bug
controls this week? For most of the older cotton, we are in the window where
Transform (1.5 oz/A) has the best fit. Transform does a good job on adult and
immature plant bugs, as well as aphids, without flaring spider mites.
Traditionally, this is the window where we also recommend Diamond (6 oz/A) as a
tank-mix partner to give residual suppression of immature plant bugs. However,
this year, based on reports we are receiving, some fields may not need Diamond
right now. Fields that received an initial adult plant bug spray in the first week
or 2 of June still do not have either high numbers of immatures or many dirty
blooms (a common symptom of immature plant bug damage). In these cases, we are recommending
to “treat what’s in the field” and not make an automatic Diamond spray right
now. Immature plant bug populations are too sporadic to make blanket sprays. That
is not to say that Diamond is not or should not be going out in many fields,
but our recommendations are on a case-by-case basis.
Aphids
As mentioned above, aphids are beginning to build across the
state, and we have not received any reports of the fungus showing up. Aphids
feed on plant juices and secrete a sugary substance called honeydew. This
feeding slows down plant growth and development. This is exacerbated in
situations where cotton is already not growing well, such as the hot, dry
weather we have been experiencing. We do not consistently get yield responses
when conducting efficacy trails for aphids, but we can see increased yields
when cotton is drought stressed. In trials done across the southeast in 2019-20,
Transform and Assail provided the most consistent control, while imidacloprid, Centric
and Bidrin provided less consistent control, but enough to alleviate plant
stress from heavy plant bug pressure.
In most cases, we do not recommend aphid treatments, and typically
plant bug sprays “clean-up” any aphid populations. Populations will continue to
increase until the naturally occurring fungus, Neozygites fresenii,
takes over. Generally, populations crash about a week after these grey, fuzzy
aphids appear.
Soybeans
A quick note on soybeans. Kudzu bugs have begun infesting
fields in big numbers over the past 10 days or so. In central and south Alabama,
reproduction is beginning to occur. In north Alabama, egg lay has not been
observed. The presences of immatures is important, because this generally
signals the end of adult movement into fields. Our threshold from R1 through R6
is 10 adults per sweep (250/25 sweeps) or 1 nymph per sweep (25/25 sweeps). If
immature kudzu bugs are easily and repeatedly found on petioles and main stems
during visual inspection of the canopy, treatment is likely warranted.
If we can be of any help, please don’t hesitate to reach out
and let us know (Scott Graham: 662-809-3368; Ron Smith: 334-332-9501). To stay
up-to-date on the Alabama insect situation, subscribe to the Alabama Cotton
Shorts Newsletter,
Alabama Crops Report Newsletter,
and the Syngenta Pest Patrol Hotline.
