Planting has been underway for awhile now in the Southern High Plains with a few fields north of Amarillo already planted or will be planted soon. Our soil temperatures are quickly rising with our hot dry conditions. The map to the right is from agweb.com and it illustrates soil temperatures at the 4” depth across the U.S for May 9.
Another source for soil temperatures is at Syngenta’s GreenCast website. These temperatures are also measured to the 4” (0 - 10cm) depth. From this site the current soil temperatures for locations in the Texas Panhandle are:
Current Soil Temperature
5 Day Avg.
Attached is a link to an Extension publication SCS-2005-17, titled Soil Temperature for Cotton Planting. In this publication by Drs. Randy Bowman and Robert Lemon, they discuss the temperature requirements for planting, seed germination and DD60 heat units for emergence. They state that “At a minimum, soil temperatures in the seed and root zone should exceed 60oF and our five day forecast for daytime maximum temperatures should exceed 80oF. Additionally, nighttime minimum temperatures should be forecast to be above 50oF for the following 5 days.”
We have excellent soil temperatures for planting and cotton emergence. And the outlook for continued warm temperatures is very good. With adequate soil moisture we should have excellent emergence and seedling growth. However, there are two insects that could potentially cause damage to the cotton seed and cotton seedlings. The first insect of concern is the cotton thrips.
There are primarily two thrips species that infest cotton across the Texas High Plains. They are the western flower thrips, Frankliniella occidentalis, and the onion thrips, Thrips tabaci. Both thrips are very small, approximately 1/15” long, and pale yellowish gray to brownish colored as adults. The immature thrips are whitish to light tan. it is difficult to distinguish between each species without the aid of a hand-lens or microscope. However, the damage caused to cotton leaves is similar. They feed on the tender leaf tissue by rasping, tearing the leaf epidermis, and sucking out the cell contents causing silvering speckling of the leaf, and leaf curling resulting in deformed leaves. This damage will stunt plants, prevent normal plant growth, and delay maturity. In our area delayed maturity from thrips damage means that we loss valuable heat units that could be needed for lint production and lint quality.
|Silvering and curled deformed leaf caused by thrips damage to cotton.|
Arrows pointing to thrips
Photo: Texas A&M AgriLife Extension Service
We can have problems with thrips during periods of extended cool temperatures and/or heavy migration of thrips from wheat during the first few weeks after cotton emerges. Our threshold is 1 thrips (adult and/or immatures) for each true leaf to the 5th to 7th true leaf stage when treatment is rarely justified.
Thrips Action Threshold
|True Leaf Stage||Treatment Threshold|
|Emergence to 1 true leaf||1 thrips per plant|
|2 true leaves||2 thrips per plant|
|3 true leaves||3 thrips per plant|
|4 true leaves||4 thrips per plant|
|5-7 leaves or square initiation||Treatment is rarely justified|
The first line of defense against thrips have become the use of insecticide seed treatments. These seed treatments generally provide protection for 18 to 21 days. Protection from the time seeds are planted, not from emergence. If immature thrips are found on cotton then the seed treatments are no longer providing protection. Under good growing conditions this will provide protection until the 2nd to 3rd true leaf stage. Therefore, under heavy thrips pressure or cold spell, a foliar insecticide application could be needed to prevent damage. The foliar insecticides, available for use against thrips, only provide no more than 5 days of protection. These insecticides must be applied only when needed and timely to provide effective control after seed treatments are no longer providing thrips control. The most important period for protection is the first two weeks after emergence because after seedlings have been excessively damaged plants may not recover quickly enough to compensate for the loss in maturity. Therefore, begin scouting and inspecting seedlings once cotton reaches 50% plant stand and scout twice weekly until cotton growth is past the susceptible stages. Carefully pull up plants to prevent adult thrips from flying off the plant. Looks through the terminal grow and all of the true leaves. Use the end of a pencil lead, toothpick or another pointed object to uncurl the deformed leaves to find any adults or immature thrips. Also, pay close attention to where leaf veins connect on both the top and underside of each leaf. Sample 25 plants from four regions of the field, keeping records of the number of thrips per plant and the number of true leaves per plant. Then calculate the average number of thrips per plant and the average number of true leaves per plant. If the number of thrips per plant equals or exceeds the number of true leaves per plant then a foliar insecticide application would be recommended.
The other insect that could be a concern to planted cotton is the wireworm. Admittedly, I am not that familiar with wireworms causing problems in cotton, but Mr. Blayne Reed, Texas A&M AgriLife Extension Agent - IPM for Hale, Swisher, and Floyd Counties, reported an alarming situation of heavy wireworm numbers causing reduced cotton stands in some fields he is scouting. He wrote an article, “Wireworms Notable in the Area and a Threat to Cotton Establishment” on Monday, May 7, 2018. What is interesting is that before Mr. Reed wrote this article, Dr. Pat Porter had told me that wireworms had completely destroyed his sweet corn seed that had been planted in April at the Agrilife research farm at Lubbock. The seed had not been treated with an insecticide and the seed had been planted in an area that was planted to cotton last year. I cannot say how widespread this may be or if there are pockets of infestations. However, one should consider checking fields for possible plant stand losses and evidence of damage from wireworms.
There are two different types of wireworms that could be causing damage to the seed and seedlings. These are the true wireworm, Click beetle larvae, and the false wireworm, larvae of the darkling beetle.
Photo: Pat Porter
|True wireworm larvae|
Photo: Pat Porter
Photo: Pat Porter
|False wireworm larvae|
Photo: David Kerns
The Click beetle larvae were the wireworms causing damage to Dr. Porter’s sweet corn seeds. Before cotton emerges larvae feed on the root, hypocotyl (stem) and cotyledon (seed leaves) of germinating plants. This feeding primarily causes plant stunting but can kill plants and reduce plant stands. Scouting for wireworms is difficult and there are no rescue treatments available after planting. Insecticide seed treatments are the most effective way to minimize damage. Additional information is available at: http://agrilife.org/lubbock/files/2017/05/Wireworms_ENTO-068.pdf.