Roberts: Plant Bug Management in Georgia Cotton throughout 2024

Tarnished plant bug has been a more frequent insect pest of Georgia cotton in recent years.  More specifically we estimated 34 percent of the acres were treated for plant bugs in 2021, 17 percent in 2022, and 39 percent in 2024.  Prior to 2021, we typically treated about 10-12 percent of Georgia cotton for plant bugs.  The bottom line is that all squaring cotton should be scouted for plant bugs and associated injury (square retention).  We conducted two trials in 2021 and two in 2023 where plant bugs exceeded threshold.  On average we protected about ½ bale of cotton with treatment, so plant bugs can be an economic pest in Georgia cotton.  If thresholds are exceeded timely application of an appropriate insecticide is justified.

Left: blasted or plant bug damaged pinhead square, Middle: scar where first position square was shed, Right: plant entering bloom with excellent square retention.

Plant bugs and square retention should be monitored from the time plants begin squaring through mid-bloom.  15-inch diameter sweep nets are a good tool to monitor for adult plant bugs in squaring cotton.  During the first 2 weeks of squaring the threshold is 8 plant bugs per 100 sweeps.  Beginning the 3rd week of squaring the threshold is raised to 15 plant bugs per 100 sweeps.  It is also a good practice to monitor square retention in addition to using a sweet net.  If small square retention drops below 80 percent and plant bugs are present treatment is recommended.  Our goal is to retain 80 percent of all first position fruit as we enter bloom.  Plants with 80 percent retention at first bloom still have maximum yield potential.  It is a good idea to pull whole plants and monitor overall square retention, especially first positions to make sure we are holding at least 80 percent of fruit.

Adults migrating from other host plants typically infest squaring cotton.  When this migration occurs and the longevity of the migration period varies by year.  It is not uncommon for us to observe reinfestation of fields treated for plant bugs when the migration is heavy.  In these situations, a second treatment may be necessary.  Some may question the efficacy of their treatment, but if we achieved good control of plant bugs which were in the field on the first spray, our square retention counts should still be good.  In recent years we have observed that early planted cotton is at greater risk of plant bugs than later planted cotton.  It is especially important you scout April and early May planted cotton.  Perhaps plant bugs congregate on early squaring cotton and then diffuse across more acres as more fields begin squaring.

Only treat for plant bugs if thresholds are exceeded.  Some insecticides for plant bugs will decimate beneficial insects in the field (many of predator insects such as bigeyed bugs begin colonizing fields as they begin to square).  When treating plant bugs also consider aphid populations.  If aphids are present it makes sense to use a plant bug insecticide which also has activity on aphids.  Plant bug insecticides which also have activity on aphids include Transform, Centric, and imidacloprid.  Transform is the most consistent performer on both plant bugs and aphids and is relatively “soft” on beneficial insects.  Centric also provides good control of both plant bugs and aphids but is less consistent, especially on aphids.  Imidacloprid provides only fair control on plant bugs and aphids.  Bidrin and acephate provide good control of plant bugs but are “hard” on beneficial insects and we generally try to delay use of these products until later in the year.  Additionally, Bidrin is not labeled on squaring cotton.  I have had several questions related to the use of Diamond which is an insect growth regulator that has good activity on plant bug immatures (does not control adults).  In areas of the Cotton Belt where immature plant bugs are a consistent and predictable pest, Diamond is often used.  Ideally Diamond would be applied as immatures are hatching (immature plant bugs are not consistent nor predictable in Georgia).  If you observe immature plant bugs consideration should be given to adding Diamond to your plant bug management program.  When we have observed immature plant bugs it often occurs near first bloom.  Black drop cloths are the best tool to detect immature plant bugs.  During bloom our drop cloth threshold is 3 plant bugs per 6 row feet.

Dr. Phillip Roberts
Extension Entomology
University of Georgia

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