Until the rain last night (May 13), it was shaping up to be a worst-case-scenario for early season thrips pressure in Virginia cotton. With the prevailing dry conditions, and vacillating between unseasonably hot and cold temperatures, seedlings were either slow to emerge, or if emerged, were standing still. Slow growing plants have reduced root growth and are slow to pick up the systemic insecticides. Couple that with what appears to be, at least so far, a very active thrips population, and it was setting up to be a ‘perfect storm’ for thrips problems.
Last week we began to see adult thrips crawling on cotton seedlings and volunteer peanut plants (peanut seedlings emerging from last year’s crop in cotton, soybean and corn fields). We also set out a series of 3×5 inch sticky cards for monitoring adult thrips. We trapped over cotton and peanut fields, brought the cards in after 3 days, and counted over 100 adult thrips per card (counting both sides). A lot of them were not pest species, but there were plenty of tobacco thrips, our primary cotton and peanut pest. This week we sampled two peanut trials and one cotton trial for thrips (10 peanut leaflets per plot, and 5 cotton seedlings per plot)using our standard soapy-water sampling technique and found an average of about 1 adult and 0.1 larvae per plant in cotton, and 0.5 adults and zero larvae per peanut leaflet. These are very low numbers compared with where it will go from here, but shows that we are definitely at the beginning of what I call ‘Thrips Season’. We are already seeing evidence of thrips feeding damage on untreated cotton and peanut seedlings.
Last night’s rain, about 1 ¼ inches, fell across most of the cotton/peanut counties. Before that rain we were facing the problem of having fields with two crop ages. Cotton planted in rows where moisture was available is up and into the first, even second leaf stage. In areas of the same field where no moisture was available to seeds, plants are not up yet. A long gap between emergence dates results in plants being in different growth stages in the same field which greatly complicates thrips management decisions, that is, when to treat for thrips and where. The rain last night should go a long way towards clearing this up.