By Nick McGhee
While in most years we are mainly worried about thrips on early planted cotton (April and early May), several of you have asked questions in the last few days about spraying thrips and there is some young cotton out there that is showing some thrips injury. However, only some of the area cotton fields have reached a threshold that would warrant an insecticide application, so growers are encouraged to scout each field for thrips pressure if you do not make automatic thrips sprays.
Here is a picture I took earlier in the week showing cotton with some thrips injury:
The 2014 Cotton Production Guide has a good description of cotton thrips management in it and I have include some of the key points below:
Thrips are consistent and predictable pests of seedling cotton that infest cotton at emergence. Thrips initially feed on the lower surface of cotyledons and then in the terminal bud of developing seedlings. Excessive feeding results in crinkled malformed true leaves, stunted plants, delayed maturity, reduced yield potential, and in severe cases reduced stands.
Supplemental foliar sprays may be needed if environmental conditions are not conducive for uptake of at-planting systemic insecticides or if heavy thrips infestations occur. Systemic foliar insecticides should be applied to cotton which had an at-plant systemic insecticide when 2-3 thrips per plant are counted and immatures are present. The presence of numerous immatures suggests that the at-plant systemic insecticide is no longer active. If no at-plant thrips insecticide is used, multiple well timed foliar applications will be needed.
The following factors related to thrips biology and ecology should be considered when planning thrips management programs:
• Thrips infestations are lower in reduced tillage systems compared with conventionally tilled systems (winter cover crops should be killed at least 3 weeks prior to planting and no green vegetation should be present at planting).
• Seedling injury and potential yield impacts from thrips feeding are compounded by slow seedling growth due to cool temperatures or other plant stresses.
• A rapidly growing seedling can better tolerate thrips feeding.
• Seedlings become more tolerant of thrips feeding as they develop; small seedlings (<2-leaf) are more sensitive to thrips injury in terms of yield loss compared with 3-4 leaf seedlings.
• Slow growing seedlings will remain in the thrips “susceptible window” for a more extended time compared with a rapidly growing seedling; it is unlikely that seedlings which have reached the 4-leaf stage and are growing rapidly will benefit from supplemental foliar sprays.
In fields planted after May 10 or where reduced tillage is used, the risk of high thrips infestations is lower and an automatic foliar spray should not be applied; scout and treat when thresholds are exceeded.