Generally speaking, cotton seems to be growing slow and behind normal expectations. The good news is that this year we have not experienced significant thrips pressure. Cotton south of Lubbock has experienced negligible pressure.
Our scouting indicates that thrips numbers in cotton are really low and much below economic threshold, even where cotton was planted next to wheat. However, some areas in the northern High Plains (Hale and Swisher Counties) have experienced moderate levels of thrips and producers have treated. Although insecticidal seed treatments should protect plants from thrips for 2 to 3 weeks, plants become vulnerable to thrips if germination and growth are delayed.
Once cotton passes beyond the 4- to 5-true-leaf stage, plants can sustain thrips injury without significant economic loss.
Weeds are also growing profusely following frequent rains. It may be a good opportunity to tank mix an insecticide such as acephate with a herbicide, thus combining weed control and thrips management in a single field operation. It is important to keep the fields weed free as much as possible because some of these weeds (such as Russian thistle and silver leaf nightshade) can attract other insect pests like cotton fleahoppers and Lygus bugs into your cotton fields.
As cotton starts squaring, keep an eye on the square (fruit) retention. Cotton fleahoppers will be of primary concern during the early squaring fruit-set stage. Adult fleahoppers are pale green in color, oval shaped and about 1/8 inch long. Adult fleahoppers are quick to fly short distances once plants are disturbed. Nymphs are also pale green to greenish in color and they move fast within the plant canopy.
Both adults and nymphs can cause injury by feeding on young terminals and pin-head squares, using their needle-like piercing-sucking mouthparts. Fleahoppers can cause small squares to die off and turn brown, resulting in a “blasted” appearance. If squares have already fallen off, a resulting scar will be evident at those fruiting positions.
Start sampling for cotton fleahoppers when cotton is at the early squaring and continue until first flowering. Whole-plant visual sampling and/or drop cloth methods are appropriate for the plants at this stage. Sample every 5 to 7 days, but under heavy infestations this sampling interval should be lowered to 3 to 4 days. Besides counting the number of fleahoppers (both adults and nymphs), estimate crop growth stage and percent square set during each sampling effort. Sweep nets can also be used to sample fleahoppers, but it may be harsh on the young tender cotton plants.
The 3 following pieces of information are required to determine the threshold for cotton fleahoppers and decide when to initiate control measures:
- Number of fleahoppers per 100 terminals.
- Crop growth stage.
- Percent square set.
For west Texas cotton, use the following economic thresholds:
- On the FIRST week of squaring, 25-30 fleahoppers/100 terminals and less than 90 percent square set.
- On the SECOND week of squaring, 25-30 fleahoppers/100 terminals and less than 85 percent of square set.
- On the THIRD week of squaring to firstbloom, 25-30 fleahoppers/100 terminals and less than 75 percent square set.
As soon as our crops become more established and recover somewhat from weather or insect-related issues, accelerated plant growth and fruiting development should be possible due to good soil moisture availability following our recent rains.
Don’t hesitate to reach me at Apurba.Barman@ag.tamu.edu or 806-407-2830 (cell) regarding any cotton insect related questions.
Source: Focus On South Plains Agriculture, Texas A&M