Cotton: Louisiana insect management decisions

Cotton: Louisiana insect management decisions

With much of the Louisiana cotton crop well beyond cutout, insect management decisions should be based on protecting existing harvestable bolls and on insects present in the field.

Once cutout (average of 5 nodes above white flower) is reached, growers and consultants can calculate the daily heat units (DD60s) from cutout and terminate insecticide applications accordingly.

Fields that have accumulated 325 DD60s are safe from plant bugs; fields that have accumulated 350 DD60s are safe from first and second instar cotton bollworms; and fields accumulating 475 DD60s are protected from stink bugs.

Plant bugs have been persistent in many Louisiana cotton fields throughout the growing season with insect numbers often reaching 10X to 15X threshold.

Larger, more mature bolls are typically less susceptible to plant bug injury while smaller, less mature bolls may still be susceptible to adults and large nymphs.

Overall, most of the harvestable bolls we now have should be safe from most plant bug injury, although adults and large immature plant bugs may still be a problem in later planted cotton. Therefore, plant bug treatment thresholds can be increased 2.5X and small first and second instar nymphs can be omitted when determining insecticide applications.

Brown, green and southern green stink bug numbers will often increase as corn is harvested and the cotton crop matures. The Louisiana threshold for stink bugs in cotton is when one adult/nymph is found per 6 row feet, 5 percent adults/nymphs are in sweep nets, or 15 to 20 percent of 12- to 16-day old bolls have internal injury.

Late-season applications of acephate plus pyrethroid or ULV malathion give excellent control of stink bugs and plant bugs.

TAGS: Management
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