• By Sebe Brown and Tyler Towles •
With Louisiana experiencing warm days and adequate moisture, much of the cotton has grown out of the thrips susceptibility stage (one- to four-leaf cotton) and is beginning to put on squares.
Square initiation results in an increased presence of a diverse cohort of plant bugs, and below is an adult and immature guide to aid in the identification of plant bugs in cotton. Keep in mind that corn is a suitable host for tarnished plant bugs prior to cotton squaring.
When corn silks begin to dry down, tarnished plant bugs migrate out of corn and into more suitable hosts including cotton. Cotton fields that share borders with corn fields often see large migrations of tarnished plant bugs and square retention can be significantly affected.
It is important to keep this factor in mind when scouting cotton acreage.
Tarnished plant bugs
Tarnished plant bugs (TPB) are 1/4-inch-long insects that vary in color from yellowish-brown to green with black markings and a conspicuous triangle located on the dorsal (back) side. Nymphs resemble adults in general body shape and color but do not have wings.
Tarnished plant bugs damage cotton from pinhead square to final boll set. Larger square damage affecting anthers, stigma, and styles can cause fertilization problems and fruit shed. The Louisiana threshold for bloom to harvest is two to three TPB per 5 feet of black drop cloth, 10 TPB per 100 or sweeps or 10% dirty squares.
Pre-bloom threshold levels are 10 -25 TPB per 100 sweeps.
Fleahoppers are small, 1/8 inch, insects that have an oval-shaped, elongated body. These insects are yellow to green and resemble other Hemipteran true bugs and essentially look like a very small, green TPB.
However, unlike TPB nymphs, fleahopper nymphs have dark spots on the hind legs.
Cotton should be scouted for fleahoppers during the first three weeks of squaring. Detection can be difficult due to the flighty nature of these insects. Simply casting a shadow over the pest will often make them take flight.
Louisiana pre-bloom thresholds for fleahoppers are 10 to 25 insects per 100 sweeps with pre-bloom treatment levels adjusted to maintain between 70 and 85% first position square retention.
However, scouting small cotton with a sweep net is difficult and produces questionable results. Additionally, detecting small fleahopper nymphs in a sweep net is difficult as well. A better technique is to simply examine the terminal of plants watching for adults taking flight and then examining the terminal very closely for small nymphs.
Morning is the best time to scout for fleahoppers and if the wind is blowing, they take shelter in the plant canopy.
Clouded plant bugs
Clouded plant bugs (CPB) are 3/8 inch long insects that are characterized by a thickened first antennal segment and hind legs that are noticeably larger than the first two pairs. Adult CPB are generally brown in color with mottled patches of black, yellow, or white.
Nymphs are often greenish-yellow in color possessing red and white horizontally striped antennae. Larger nymphs can also be identified by a dark spot on the dorsal side of the abdomen.
Clouded plant bugs are an occasional pest in Louisiana cotton with pre-bloom and bloom threshold levels being the same for tarnished plant bugs but each CPB should be counted as an equivalent to 1.5 TPB.
Injury by CPB is similar to TPB with square abscission, bloom injury and boll feeding (cat-facing) occurring mid to late season. As with other plant bugs, monitoring square retention and sweep net sampling prior to bloom should be used to determine levels of CPB infestations.
Sampling for plant bugs from bloom until harvest is aided by the use of a drop cloth because this technique is more suitable for detecting nymphs.
Drs. Sebe Brown and Tyler Towles are LSU AgCenter Extension entomologists.