Cotton planters
are rolling across the Texas High Plains. While lot of cotton seed will go into
the ground over the next couple of weeks, some of the early planted stuff is making
its way above ground. Thrips are one of the first insect pests that we experience
on seedling cotton. I am seeing thrips swarms all around and can find them on
almost everything that is green. It will not be too long before these tiny insects
land on the emerging cotton. We usually experience higher thrips pressure in the
areas north of Lubbock. Under good growing condition, plants do recover from
thrips injury without economic yield loss, but when additional stresses such as
cold temperatures, sandblasting and or nematodes are present, thrips infestation
can delay growth and reduce yields substantially.
Thrips species composition in the South Plains
region is mainly formed by onion thrips (Thrips tabaci) and the western
flower thrips (Frankliniella occidentalis). Preventive
insecticide seed treatments provide a good control against these species for up
to ~3 weeks after planting. However, this can vary with growing conditions and
the weather. Almost
all our in-furrow or insecticide seed treatments used are neonicotinoids (e.g.
imidacloprid, thiamethoxam). Remember, these are water-soluble insecticide
compounds that are taken up through the roots and translocated into growing
leaf tissues and hence need enough soil moisture to be effective.
When scouting for thrips, there is truly no
substitute for whole plant inspections from a representative sample from across
the whole field. We may find adult thrips (winged)
in almost every field but it is important to know that presence of adults alone
will not warrant foliar insecticide application. The presence of immature
thrips (wingless) is a good indicator of whether the seed treatments are still
effective enough or not. The action threshold for thrips is one thrips per true
leaf and our suggestions as rescue treatments include acephate, dicrotophos (e.g.
Bidrin) or spinetoram (Radiant). Timing of insecticide application is critical.
Research indicates that insecticide application beyond 1st true leaf
stage will not result in significant yield gains. Also, remember, it is not uncommon to see “look-a-like” thrips symptoms under our environment—beware
of similar symptoms from sandblasting, residual herbicides and high
temperatures before making spray decisions. We
cannot control the environment or the market but we sure can save money and
time by avoiding ill-timed or unnecessary insecticide applications.
