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Colquitt County Extension Ag Update 7/23/22

Cotton:  The cotton crop in Colquitt County ranges from first square to fourth week of bloom.  Target spot has been noticed in a couple of fields that have a history of this disease and rank growth. These fields are in the third to fourth week of bloom. Stinkbug pressure ranges from 10 to 25 percent and the wet conditions have made bug killer applications a challenge.

 According to Dr. Bob, “Conditions now across much of southern Georgia are perfect for target spot. I encourage growers to scout their cotton starting with the first week of bloom, especially with onset of third week, and to weigh the need for use of fungicides to protect yield.  Use of fungicides does not always increase yield, but in high risk environments I believe they are an important investment.  Priaxor and Miravis Top are best, then Headline, then azoxystrobin.” 

Target Spot, Colquitt County,2022 — Kichler
Target Spot, Colquitt County, 2022- Kichler

Blackroot:  I ran across this week while helping a grower. According to Dr. Bob Kemeriat, this is black root.  Symptoms of black root includes a superficial darkening of the roots, gall formations that could be cracked and/or corky in texture, severe boll abortion, and foliage with symptoms that have been referred to as “window paning” and like chemical injury.  According to past references, no pathogen has ever been successfully linked to black root and the malady is now considered to be most likely the result of environmental conditions.  Black root is isolated to poorly-drained Flatwoods soils and has not been that prevalent in recent years. Rates of 3 to 4 tons of poultry litter per acre have been shown to alleviate this problem dramatically. However, at the 4 ton/A rate excess soil P will build rapidly. Therefore, this solution should only be considered a short-term fix and not a long-term strategy.

Black root — Colquitt County, 2022-Kichler

Mr. Kichler, I cannot kill the grass in my cotton and peanuts.. This is a very common question. This subject has been addressed numerous times by Dr. Culpepper and Prostko in past blog posts and newsletters.  If POST graminicides (i.e. Select, Poast, Fusilade, or generics) are applied applied to large plants, they will not work.  A flowering goosegrass plant is way too big!!!

Peanuts:  The peanut crop ranges from 40-60 days old.  Weather conditions are great for disease development in this crop. 

So I asked Bob about the current weather situation and “Why are conditions are perfect now for development of white mold in the peanut crop?” 

They are perfect because: 
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.

Below are a few words from Dr. Albert Culbreath on sulfur use in peanuts..

Priorities for use of micronized sulfur for management of peanut leaf spot

 In recent years we have had very encouraging results with micronized sulfur used as a mixing partner with several different fungicides for leaf spot control.  In many cases, mixing with sulfur has provided control comparable to (and sometimes better than) as mixing with 1 pint of a 720 formulation of chlorothalonil for leaf spot control and often for less cost.  I do not understand what is happening with those mixtures, because sulfur alone does not provide adequate leaf spot control under the pressure we have in our tests.  We still have a lot to learn, but sulfur has done especially well when mixed with Umbra, Excalia, or azoxystrobin (Abound and various products).  All three of these products are used for management of soilborne diseases, but are not adequate alone under heavy pressure for leaf spot control.  Mixing with chlorothalonil is certainly a viable option with any of these, but these products would be my top priorities for mixing with sulfur.   Our work with sulfur as a mixing partner was prompted largely by a shortage of chlorothalonil a few years back, and concerns about the future of chlorothalonil.  Currently, chlorothalonil is still an effective option as either a stand-alone treatment or mixing partner. Therefore, when a mixing partner is needed, growers might consider using sulfur mixtures with some applications and chlorothalonil mixtures with others.  Currently, I would also prefer chlorothalonil as a mixing partner with Topsin.   Based on our results, sulfur is not as effective as  chlorothalonil as a stand-alone treatment.  

Below are a few comments from Dr. Scott Monfort on PGR use on peanuts…

Over the last two weeks, I have received numerous phone calls regarding the use of the growth
regulator – Kudos or Apogee on irrigated peanuts. A majority of the questions have been related to
application timings and mixing with other products. Prohexadione calcium should not be applied until
the canopy is 90%+ lapped for singles and 100% for twin. Sequential applications (3.6 to 5.4 ounces per
acre followed by 3.6 to 5.4 ounces per acre) spaced two weeks apart are recommended in Georgia on
runner peanuts. Include a crop oil concentrate (COC, 1 qt/A) and nitrogen solution (UAN) or ammonium
sulfate (AMS) at 1pt or 1lb/A to help with plant uptake and consistency of performance.
Kudos/Apogee requires eight hours for absorption by the peanut foliage to be effective. Kudos/Apogee
is not recommended on plants that are under stress due to lack of moisture, disease pressure, or other
stress conditions. With this in mind, Kudos/Apogee is only recommended in irrigated fields.

Tank-Mix Considerations
Based on communication with Fine-Americas and BASF, Kudos/Apogee has been shown to be
compatible with many of the fungicides and insecticides growers utilize in peanut. However, I would
encourage growers to leave out the crop oil when mixing with fungicides and insecticides. I did notice a
Correct Timing for 1st application

problem last with chlorothalonil and tebuconazole causing some burn when mixed with Kudos/Apogee +
AMS + COC. I would not mix Kudos/Apogee with herbicides, fertilizers or biological stimulants. We do
not know what will happen when these products are mixed with the growth regulator. At the cost of the
growth regulator, I would not want to minimize the growth control and/or yield response to save a trip
across the field.

Mr. Kichler, What is the threshold for foliage feeding caterpillers in peanut?  I am glad you asked. The treatment threshold for combined foliage feeders is 4–8 per foot of row depending on the size and condition of the peanut plants. Use a lower threshold for very young plants or plants that are stressed
from other factors. Use a higher threshold for healthy plants with ample vine growth. 

Dr. Mark Abney gives a few comments about pyrethroid use in dryland peanut fields.

I am pretty sure there are non-irrigated peanut fields in Georgia that have been (or will be) treated with at least one pyrethroid insecticide application. This will put those fields at increased risk for two spotted spider mites. For those of you who have heard me talk about mite outbreaks in peanut but have never seen it, it is not pretty. We want to be sure that if/when mites start to show up in peanut we advise growers to avoid bifenthrin. Bifenthrin can be a very useful insecticide, and it has spider mite on its label. DO NOT USE IT. Whether or not we have a problem with mites will come down to the weather and making good decisions. If hot, dry conditions continue, expect mites to start showing up by late July/early August. Fields where infestations are “missed” are likely to be obvious from the road by the end of August. Let us all hope this does not happen. Portal and Comite are miticides registered for use in peanut.

Have a great weekend

Jeremy M Kichler

Colquitt County Extension Coordinator



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