Monday, July 17, 2017

Mid-Late July Outlook for Cotton Insects

Tarnished plant bugs (TPB) have been hatching into the immature nymphal stage for about two weeks in April planted cotton. A few immatures are almost to the adult stage. In fact, the first 2017 cotton reared adults were observed in central Alabama today, July 17. Numerous more immature TPBs are still hatching from the egg stage. The point to remember is that the large immatures and adults do most of the fruit damage to cotton. In unsprayed fields, a second generation will begin to develop soon. The first generation was not at threshold or treatment levels in most fields. However, eventually you may have damaging or treatable numbers as the population continues to increase. At this point, you will have an embedded population that contains all stages from eggs to adults. When this situation develops, one insecticide application will not clean up a damaging level. There may even be a place in 2017 for a late July-early August application of the IGR Diamond added to an adulticide.

2017 is going to be different than recent years in controlling TPBs. Both 2015 and 2016 were hot and dry during July, and the plant bug population crashed on their own. Cloudy weather, abundant rainfall, and lush rapid growing cotton is a much better host for TPBs in 2017, resulting in a high level of survival this season. The numbers of TPBs will likely continue to increase until controls are applied. A sub-threshold level in July will lead to numbers and damage well above threshold by early to mid August if left untreated. A high number of TPBs of all ages is difficult to clean up. Don't blame the chemical or consultant or Extension agent when one application does not do the job. Other than Diamond on immatures, no product will give more than 3-5 days of plant bug control.

Part of the current population of plant bugs in central Alabama and as far north as Talladega is the clouded plant bug species (CPB). Both immatures and adults look different than tarnished plant bugs. Immature CPBs are not as green as TPBs. CPBs are more cylindrical in shape and have alternating dark and light bands on their antennae. Damage from both species are the same, and the same chemicals should work on both.

Attached is a picture of a clouded plant bug nymph.

Wednesday, June 21, 2017

Rambling Thoughts About the 2017 Weather and Tarnished Plant Bugs in Cotton

I will say up front that no two seasons are exactly alike when considering the weather, crop conditions, and potential insect damage. 2017 has already been uniquely different than any season I remember. Delayed planting, excessive rainfall, mild winter, and warm spring are just a few of the factors that could affect the movement, numbers, and level of damage from plant bugs to this year's cotton crop. Only by close monitoring of plant bug numbers and their damage over the next 4-6 weeks will we know how to deal with this pest.

We need to begin sampling the oldest and largest cotton immediately with sweep nets for adult tarnished plant bugs. In addition, we should keep check on our square set by making pinhead square retention counts. 80% retention is considered our treatment threshold. In other words, we do not want to lose more than 20% of our small squares to plant bug damage.

If past history is any help, abundant to excessive rainfall in June tends to keep wild host plants like fleabane fresh a little longer. This slows or prolongs the movement of plant bugs into cotton. After fleabane dries down, no other wild host is attractive to adult plant bugs, therefore cotton is the best host they have. The movement of plant bugs into cotton has already begun. This migration could continue for several weeks. This slow extended migration may not reach what we would call a threshold or treatable level, making treatment decisions difficult. In hot, dry springs, these adult plant bugs leave fleabane in high numbers over a relatively short period of time, say 7-14 days. This sort of rapid movement into cotton is easier to detect and to make treatment decisions for.

There are a number of other factors that could influence the severity of the plant bug issue in cotton this season. Overall, I would estimate that the maturity of our cotton is a little behind where it normally is this time of year. Will plant bugs move past these fields in search of the oldest most mature cotton? April cotton may serve as a trap crop for plant bugs in 2017. That would be to our advantage. Since early June, we have had a lot of cloudy days with temperatures in the 70s or 80s. Plant bug survival on cotton has likely been higher under these conditions. This could spell higher damage levels in coming weeks. Plant bug adults, and especially their immature offspring, do not fare well under drought conditions and high temperatures (over 95°F), leaving cotton plants under a stressed and wilted condition.

Water logged spoils, which many fields have had during the month of June, can result in some pinhead square abortion. This effect would be very difficult to separate from plant bug injury. How can we distinguish this square loss from plant bug injury? The easiest way would be to use a sweep net to document that some level of plant bugs are actually in the field. One additional little trick that could help us answer this question was developed by our Arkansas entomology friends several years ago. This technique takes a little time, precision, and magnification. The tool needed would be a "pinhead square slicer." Take a damaged pinhead square from the plant (square will be brown or black in color), use a sharp razor, and slice the square in half. If it aborted due to weather, the inside content will still be present but deteriorating, whereas if it has been damaged by a plant bug, the interior will be hollow. Plant bugs tend to dissolve the contents and suck the interior of the square as food.

Plant bugs will likely be the primary cotton insect focus of entomologists, consultants, scouts, farmers, and other interested parties until well into July this season. We need to recognize this and not allow plant bugs to further limit our maturity and potential yield in 2017.

Tuesday, May 9, 2017

Thrips and Grasshoppers Need Attention

Early season cotton seedling insect activity is heating up.  Both grasshoppers and thrips need attention this week (May 8-12).  Cool (cold) nights last week slowed down the growth of cotton seedling on our earliest planted cotton.  This will serve to keep cotton in the thrips susceptible stage longer.  At the same time, where we have had multiple rain events, we likely have lost some of our at-plant thrips protection chemicals to leaching.  This would be true of both seed treatments and in-furrow sprays.  Cotton planted on or after May 10th should have reduced thrips pressure and less need of a foliar spray.
Cotton that is emerging in the next several weeks will be at some level of risk from grasshopper feeding.  Immature grasshoppers are abundant in fields statewide from the Florida line in the South to Tennessee line in the North.  These immature, up to thousands per acre, will jump when disturbed but cannot yet fly.  A few grasshoppers have already spent 30-50 days as immatures and are already in the adult stage.  The most susceptible stage of cotton to grasshopper damage is the “crook” stage just as it emerges.  Damage at this stage kills the plant leading to reduction in stands.  Seed are too expensive to plant a few extra for these grasshoppers.  This is the reason I would suggest that growers treat on damage potential or risk, and not on thresholds.  In fact, it would be difficult to establish a threshold since grasshopper feeding on cotton is unpredictable.  Immature grasshoppers can be controlled with low rates of several cotton insecticides.  These include acephate, Bidrin, Lorsban, pyrethroids and others.  A couple of ounces of Dimilin added to the spray would add to the residual control of late emerging or migrating grasshoppers.  Immature grasshoppers require 30-50 days to reach the adult stage.  Development may be somewhat quicker with warmer weather which we incurred in March and April.  Adult grasshoppers are very difficult to control.  Even the highest labelled rates of insecticides often do not give 100% control.  If growers observe a need for grasshopper control to minimize stand loss risk, sooner is better than later to apply these controls.

Wednesday, March 8, 2017

Times of Greatest Importance for Cotton Insects in Alabama

THRIPS             Thrips may delay maturity if heavy damage occurs at the 1 to 5th
                           true leaf stage.
Use seed treatments or insecticide applied in-furrow at planting.
Make foliar spray when the first true leaf is just emerging if cotton is planted before
May 10 and the minimum nighttime temperature is below 65⁰ F.
PLANT BUGS   Monitor cotton for pinhead square set when squaring begins (about
                          6th true leaf).
Continue checking pinhead square set until about first bloom. During this same time period use sweep net (can be purchased for about $75 from Gempler’s ,  www.Gempler’ to sample for adults. Spray for adults if 5-8 per 100 row feet (33 sweeps) are found.
PLANT BUGS    After first bloom check for immature plant bugs (small, green with long antenna) with a drop cloth spread between two rows. Beat plants briskly to dislodge immatures from inside of the square bracts. Spray at threshold of one immature per row foot.
Continue surveys for about 3-4 weeks.
APHIDS             Only treat when over 50% of the plants have aphid clustering under leaves, honeydew is present, and cotton is under drought stress.
BOLLWORMS  For about 10-14 days, beginning July 20 in Central Alabama monitor squares and white blooms for small bollworm larvae.  Move this date 10 days earlier for South Alabama and 10 days later for North Alabama.  If the field has not been sprayed multiple times for plant bugs, fire ants will also be searching white blooms for these small larvae. Spray pyrethroid at a high labelled rate if 5 to 10 or more larvae about quarter inch in
length are found per 100 plants.  You may look at fewer than 100 plants but express the number on a 100 percent basis. Tobacco budworms do not escape genetic cotton, therefore, even large bollworms can be controlled unless they are already imbedded in a boll.
STINK BUGS     Begin looking for stinkbug damage on field borders (first 5-10 rows) about the third week of bloom. This would be about July 20 in an average plant date year. Pull 10-25 bolls that are the size of a quarter in diameter and still soft to the touch. This boll would be about 10-12 days old. If you find internal damage on the border, search further into the field and collect more bolls.  Treat border and/or the entire field when 10% of these bolls have internal damage from stinkbugs. Damage will appear as warts in the boll wall or dark areas around the seed.  Continue scouting for stinkbugs until the top bolls you hope to harvest are about 25 days old and hard. Scout for 5-6 weeks beginning the third week of bloom.


SPIDER MITES  Observe for the presence of spider mites underneath leaves. Mites will move when the leaf is pulled, inverted, and the mites are exposed to the sun. Treat when mites are detected over much of the field and the weather outlook for the next 7-10 days is hot and dry.  Mites do not reproduce or spread as fast when weather conditions are not favorable.  Rainfall does not kill mites, they just do not reproduce ad spread as rapidly.