Cotton: The cotton crop is progressing fast. Growers could be defoliating earlier planted cotton in not-so-distant future. There is a peanut maturity and cotton defoliation meeting being held this week.
Whitefly populations have increased dramatically over the last couple of weeks due to the dry weather. Below are last week’s trap numbers from stopwhite.org and the table below shows the stick card numbers from Tanner’s locations.
According to Dr. Roberts, UGA Cotton Entomologist, there has been fields in southwest Georgia there has been high levels of “IBD” or internal boll damage. In the last “Talking Cotton Podcast” he mentioned being on the lookout for late season plant bugs in fields. He is concerned that bifenthrin might not be providing the control of tarnish plant bugs and there is evidence of this from field observations and bio essays. Scouts need to look for dirty blooms which is an indication of immature plant bugs and use drop cloths to asse the populations. The threshold for plant bugs while using the drop cloth is 3 plant bugs per drop.
What do we do? Scouting with drop cloths is a must to get a handle on populations. If you must manage plant bugs, then control options include 6 oz of Bidrin. In Colquitt County, Bidrin might not be a good idea because of the whitefly pressure. When whitefly is in the mix, Phillip mentions ½ lb. of acephate plus bifenthrin. Still, we need to watch for the potential of flaring spider mites. Other options include Diamond or Transform. Transform is a good option for plant bugs when whitefly is in the mix but does not control stinkbugs. More information about this situation can be found on the Talking Cotton Podcast and is available here.
This week we had the first absolute confirmation of areolate mildew of cotton, and it was from Colquitt County. It was found while we were in a cotton fungicide trial this past week. Less than a month before defoliation? Don’t worry about the disease. Already lost 25% of leaves to defoliation from disease, too late to do anything. More than a month to go before defoliation and disease just starting in your field or the county- I would strongly consider spraying a fungicide.
Irrigation termination in cotton: As water use declines in the earlier planted cotton crop, it is necessary to closely monitor your fields for cotton bolls that are beginning to open. UGA’s official irrigation termination recommendation for cotton is at an average of 10% open boll across a field. When you consider the math, 10% open is not a high number of bolls on a plant that are open to start considering irrigation termination. A plant with 12 to 15 harvestable bolls means you need to be looking at the available soil moisture if 1.2 to 1.5 bolls are open. In times when an application of irrigation is needed, soak the soil sufficiently so that you can limit your irrigation events to as few as possible. Frequent small irrigation events will only exacerbate or flare boll rot, areolate mildew and other diseases. Paying attention to the long term and short-term forecast is critical in your irrigation scheduling decisions as always. Keep in mind, good moisture in the soil and 10% open bolls means the end of another irrigation cotton season!
Dr. Porter discussed an interesting paper in this weeks Talking Cotton Podcast” called Effect of irrigation termination times on cotton cultivars with contrasting maturities The abstract of this paper: The hypotheses of this study were that differential irrigation termination times will affect lint yield, fiber quality, and incidence of hard lock and boll rot, and responses will be dependent on cultivar differences in maturity. In 2021 and 2022, a study was conducted in Camilla, GA, using two cotton cultivars with contrasting maturities under four irrigation termination treatments. Irrigation was terminated at cutout, first open boll, 2 weeks after first open boll, and 4 weeks after first open boll. Measurements included plant growth, cutout date, lint yield, irrigation water use efficiency (IWUE), fiber quality, and incidence of boll diseases. Gas exchange measurements and percent open boll estimates at each irrigation termination time were also conducted. Terminating irrigation at cutout did not significantly affect yield in either year; however, IWUE increased 12.6% relative to current recommendations and 13.2% relative to the latest termination time in the 2022 season. Cultivars differed significantly in cutout date, agronomic maturity, gas exchange rates, yield, hard lock/boll rot incidence, and fiber quality. However, there was no interaction between cultivar and irrigation termination time for any parameter. We conclude that irrigation can be terminated at cutout to maximize IWUE, for early and late-maturing cultivars, without limiting yield or fiber quality, assuming a water-replete soil profile at termination.
Peanuts: Peanut maturity checks will start in the near future. I finalized schedule will be announced mid to late week. If you need samples done this week call and we can set up a time. Taking a good sample is CRUCIAL in determining the proper time to dig, so here is a reminder of how to pull a sample for profiling peanut maturity. A peanut hull scrape maturity check will be as accurate as the sample that you take. Pull or dig up at least 5 to 6 adjacent plants from at least three representative parts of a field which can be dug in on day. Keep these samples from each area of the field separate. Pick ALL the peanuts off the plants until you get around 200 peanuts (a sample should contain between 180 and 220 peanut pods). Pick the vine clean. If it will be a while before you can bring the sample then pick off the sample and keep the peanuts in a bucket of water to keep them fresh.
I have started to pick up some early leaf spot in area fields. Early leaf spot as a few tufts of spores is visible on the upper surface of this peanut leaflet. The pictures below show early leaf spots which are lighter brown in color and has a yellow halo. Note sparse tufts of spores on the UPPER surface of the leaflet.
Note on yellow halos- early leaf spot more often has a yellow halo than does late leaf spot; burns often are brown with yellow halos. Spores and position of spores on top or bottom of leaf to make a 100% diagnosis.
Peanut growers can also use Aim for late season morning glory desiccation about 7 days prior to digging. Check out page 224 of the 2024 UGA Pest Control Handbook. Remember, Aim is not very effective on small flower morning glory and will cause some cosmetic (i.e. non-yield robbing) peanut leaf injury. Apply 7 days before digging for the late-season desiccation/defoliation of annual morning glories (Ipomoea spp.). Use in combination with either a NIS (0.25% v/v) or COC (1% v/v). Aim may cause peanut leaf spotting or burning. Use at least 15 GPA for optimum results. Do not graze or feed peanut hay to livestock. Only 1 application per season is permitted. Rain-free period is 6–8 hours.
I get about 5 questions a day about eclipta. Eclipta (Eclipta prostrata formerly Eclipta alba ) is a broadleaf weed that can occasionally be found in fields throughout the peanut belt. In Georgia, eclipta is not considered to be one of the most common weeds in peanut, but it can be very troublesome in years when environmental conditions (cool, wet) favor its development. Eclipta is considered to be one of the world’s worst weeds and has been reported to be a problem in 17 crops in 35 countries. Other names for eclipta include yerba-de-tago and false daisy. Postemergence herbicides that provide adequate control of eclipta include Cobra (lactofen), Basagran (bentazon), Storm (bentazon + acifluorfen), and Ultra Blazer (acifluorfen). These herbicides are most effective if applied to eclipta plants less than 2 inches in height. Postemergence herbicide applications made to eclipta greater than 2 inches often result in reduced control. Research done by Grichar in 1997 shows that control is great when the eclipta is 2 inches or less and then drops fast when the eclipta reaches 3-5 inches in height. So, attempting to control this weed when it is above the peanut canopy is not a good idea.
More information about this pest can be found in the publication Eclipta Identification and Control in Peanuts.
Several questions about using Topsin late in season to improve “peg strength” in peanuts. Bottom line from me:
To manage peg strength in peanuts:
1. Effectively manage leaf spot; use of Topsin is one way to do that.
2. Dig peanuts “on time” as delayed harvest will increase risk to pod loss at digging.
3. Effectively manage white mold which may also affect peg strength.
4. Topsin can be used effectively late season for leaf spot control (5 fl is + 1 pt chlorothalonil OR 10 fl oz Topsin one time only) but there is nothing magic about Topsin and peg strength.
Have a great week,
Jeremy M. Kichler
Colquitt County Extension Coordinator
The University of Georgia Cooperative Extension does not endorse or guarantee the performance any products mentioned in this update.