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Cotton and Peanut Issues

Cotton

The cotton aphid fungus is showing up in cotton fields in Bulloch County – finally. Please view comments below provided by Dr. Phillip Roberts about stink bug management in cotton:

Southern green and brown stink bugs are the two most common stink bugs infesting Georgia cotton. Both have sucking mouthparts and damage cotton by feeding on the seeds of developing cotton bolls. In addition to mechanical damage, feeding allows for the introduction of boll rot pathogens. Internal symptoms of feeding on medium sized bolls are the most reliable indicator of stink bug infestations. Internal damage is defined as warts or callous growths on the inner surface of the boll wall and/or stained lint. This wart or callous growth is easily visible less than 48 hours after the stink bug fed on the boll. As bolls mature and open, damage often appears as matted or tight locks with localized discoloration that will not fluff. Severely damaged bolls may not open at all. Research also suggests that in addition to yield loss, excessive stink bug damage can reduce fiber quality.

Scouting for stink bugs should be a priority as plants begin to set bolls. In addition to being observant for
stink bugs, scouts should assess stink bug damage by quantifying the percentage of bolls with internal
damage. Bolls approximately the diameter of a quarter should be examined. Bolls of this age are preferred
feeding sites for stink bugs can be easily squashed between your thumb and forefinger. It is important that
bolls of this size (soft) are selected. The number of bolls per plant which are susceptible to stink bugs is not
constant and varies during the year. The greatest number of susceptible bolls per plant generally occurs
during weeks 3-5 of bloom. During early bloom there are relatively few bolls present. During late bloom,
many bolls are present but only a limited number may be susceptible to stink bug damage (individual bolls
are susceptible to stink bugs in terms of yield loss until approximately 25 days of age). A dynamic threshold
which varies by the number of stink bug susceptible bolls present is recommended for determining when
insecticide applications should be applied for boll feeding bugs. The boll injury threshold for stink bugs
should be adjusted up or down based on the number of susceptible bolls present. Use a 10-15% boll injury
threshold during weeks 3-5 of bloom (numerous susceptible bolls present), 20% during weeks 2 and 6, and
30%(+) during weeks 7(+) of bloom (fewer susceptible bolls present). Environmental factors such as
drought and/or other plant stresses may cause susceptible boll distribution to vary when normal crop growth
and development is impacted; thresholds should be adjusted accordingly. Detection of 1 stink bug per 6
feet of row would also justify treatment.

When selecting insecticides for stink bug control it is important to consider other pest such as whiteflies,
corn earworm, aphids, or mites which may be present in the field. The objective is to control stink bugs but
also to minimize the risk of flaring other pest which are present. A couple of bullet points below to consider
when selecting a stink bug insecticide:
• Consider week of bloom and use the dynamic threshold.
• Determine ratio of southern green to brown stink bugs, organophosphates provide better control of
brown stink bugs compared with southern green.
• If whiteflies are present, use bifenthrin and avoid dicrotophos during weeks 2-5 of bloom.
• If corn earworm is present consider using a pyrethroid if brown stink bugs are low or using a
pyrethroid tank mixed with a low rate of an organophosphate if brown stink bugs are most
common.
• If aphids are present, include dicrotophos and avoid acephate if an organophosphate is needed. If
mites are present, avoid acephate if an organophosphate is needed.

Peanuts

Be sure to stay vigilant on your white mold fungicide program in peanuts. Please view comments below from Dr. Bob Kemerait:

Two Words: White Mold
In my 22 years as an Extension specialist at the University of Georgia, I cannot remember a season more
favorable for white mold on peanuts than this one. (White mold, also known as “stem rot” and
“southern blight”, is caused by the fungal pathogen Sclerotium rolfsii.) From pictures sent to me by
county agents and consultants, it is clear that white mold is quickly developing not only on peanuts but,
in some cases, on soybeans as well in Georgia. Conditions are perfect for the development of white
mold and growers MUST be prepared to protect their crop in order to protect yield and profitability.
Conditions are perfect now for development of white mold in the peanut crop for several important
reasons.

1. Hot daytime temperatures favor development of white mold.
2. Dry conditions can make white mold more difficult to control because of lack of rainfall to wash
the fungicide from the leaves to the crown of the plant. Also, white mold tends to go
“underground” during hot and dry conditions where is even more difficult to control.
3. High humidity favors development and spread of white mold.
4. Intermittent rain showers tends to increase severity of white mold because a) these showers
increase humidity and b) typically do not “beat” the white mold fungus down as often occurs in
more prolonged downpours.
5. Perhaps MOST importantly, white mold THRIVES during warm nights (above 75°F) with near
100% humidity. Such conditions are perfect for development and spread of white mold.
6. Growth and development of the peanut crop supports and thick canopy of foliage. Individual
“hits” of white mold begin with one plant that is infected, but with the thick canopy of leaves,
the white mold fungus can move efficiently from one plant to the next. To minimize losses to
white mold, it is critical to protect the plants from this spread with the effective use of
fungicides.
Conditions in the 2021 season were less favorable for white mold than they are now. Why is that?
1. Daytime and nighttime temperatures were generally cooler in 2021 than in 2022 and were less
favorable for development and spread of white mold.
2. Abundant rainfall in in 2021 not only cooled temperatures but also mechanically beat back the
fungal pathogen, Sclerotium rolfsii, which helped to slow the spread of the disease.
What growers should be doing now.
1. Scout fields for detection of white mold. Growers or scouts should check crown of wilted plants
for presence of active white mold.
2. Stay on a timely fungicide program. The choice of “best” product to use is a combination of
level of risk to white mold in a field and cost of material.
3. Time fungicide applications to capture irrigation or rainfall within 8 to 24 hours following
application.
4. Recognize that no fungicide program will eliminate individual “hits” of white mold but an
effective fungicide program must stop white mold from spreading. An effective white mold
program includes a) choice and rate of product, b) timing of application, and c) timing of
irrigation or rainfall following the fungicide application.
5. Best white mold products include Elatus, Excalia, Umbra, and Convoy then Fontelis and Provost
Silver and then followed by Lucento, Priaxor, azoxystrobin and tebuconazole.