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.

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 10^th 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.

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’s.com) 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.

 

ESCAPE

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.

Update for the Week of August 4, 2014

The most significant insect event in the past week was the reports of plant bug tolerance to all labeled or recommended insecticides in the Tennessee Valley of North Alabama. Several of our most experienced consultants are reporting that all classes of chemistry are suppressing plant bugs but their presence and damage behind applications are still above threshold levels. This has required repeated sprays and now tank mixtures with two recommended insecticides. Under these conditions, input costs for cotton insects, particularly plant bugs, make cotton an unattractive crop option going into the 2015 season. Some areas of the mid-south have been dealing with this problem for several years. At this point, the Alabama situation appears to be confined to the Tennessee Valley area.

It has been my experience that once plant bugs get embedded in rank cotton in July, they have always been difficult to control, requiring multiple applications. So now, we have insecticide tolerance in addition to a coverage issue. Looking ahead I see a larger role for the IGR Diamond during the early bloom period in future years.

Now to a quick oversight of other insect problems on cotton and other crops; stink bugs, primarily brown, are requiring controls in some cotton fields. However, overall they are not as heavy and widespread as expected. Aphids are showing back up in some fields requiring controls. Spider mites are present in many fields. It seems like we get more calls about mite control following weeks of high temperature and dry conditions.

In soybeans we are beginning to see loopers as far north as Montgomery in older beans. So far they are only at about a third of a threshold level. Scouts are reporting an occasional corn earworm and velvetbean caterpillar in the soybean mix. The same holds true for peanuts.

Fall armyworms (grass strain) are on about every crop except cotton now. Hay, grasses, peanuts, soybeans are all experiencing the need for repeated applications for FAW. We could safely say that FAW’s have about worn out their welcome, even though they are easy to control. It seems like their preferred row crop is soybeans planted in wheat stubble. Some fields are now on their third infestation and replanting has been required due to near 100% defoliation.

In many ways, 2014 has been like “old times” to Extension entomologists with numerous phone calls about when to treat and what chemical to choose. We don’t feel like step-children to the weed resistance and disease issues this season.

Scouting crops is the first step in all insect management and control programs.

Insect Update for the Week of July 7

A combination of adult tarnished plant bugs and clumping aphids are being reported from more fields and areas around the state each day. Overall, little rainfall has fallen in about two weeks. Therefore, crops, especially corn and cotton, are under some level of stress. Therefore, most growers are choosing to target both plant bugs and aphids with this application.

I have not had any calls on mites in the past few days but that does not mean that populations are not building in select fields. So far, abamectin at 10 oz. per acre has given good control on mites in treated fields.

Immature plant bugs are present now in the oldest cotton. I have observed several fields where a threshold of three immatures per 5 feet has been recorded on a black drop cloth. When plant bugs become imbedded in cotton in July (all stages present – eggs, immatures and adults) quite often multiple applications are needed to bring the population under control. For those that want to use the IGR Diamond, now is the time to do so. An adulticide plus Diamond, at 6-9 oz. per acre, should give control of the population for 14 plus days. It is my opinion that most of the adult plant bugs have now left wild host plants and are now in cotton. We just don’t seem to get that many moving from corn here in Alabama.

Moth traps in central Alabama captured an abundant number of both bollworm and budworm moths last week. 2014 may be the year that fieldmen, consultants, and scouts really prove their worth. There is just no way to time the appropriate chemistry at the proper time without someone monitoring insects. This looks like an above average insect year for cotton and we haven’t even reached the primary stink bug window yet. In sweeping for adult plant bugs last week, I was capturing brown stink bugs in about every set of sweeps.

How to Control Spider Mite and Plant Bug Infestations

Additional reports of economic spider mite infestations continue to come in, particularly from central and south Alabama. The heaviest infestations are already causing significant leaf shed in early square cotton. Fieldmen have reported that the lower leaves that show the greatest damage do not always have high mite numbers. Mites will continue to move up the plant to fresher leaves as the older leaves get ready to drop. Fieldmen should look a couple of nodes above the most damaged leaves in order to get a good handle on the number of mites present.

Several materials are recommended for mite control. However, some of these materials only seem to work in some locations. Examples are: bifenthrin, chlorpyriphos, dimethoate and propargite. One product in our 2014 recommendations is no longer on the market – dicofol. That leaves the newer mite chemistry as our best choice for control. These are abamectin (Agri-Mek), extoxazole (Zeal), fenpyroximate (Portal), and spiromesifen (Oberon). Abamectin is the most economical and has been the most widely selected for mite control. Ag suppliers are encouraged to have some on inventory since spider mites appear to be a growing problem.

Plant bugs continue to be reported in cotton that is squaring or approaching bloom. Plant bug immatures are now present in some of our oldest cotton. This indicates that adults deposited eggs a couple of weeks ago. Plant bug eggs are deposited into the stems of the plant in the more rapid growing areas. Therefore TPB eggs are not visible to fieldmen.

Adult plant bugs feed on tiny pin head squares in pre bloom cotton. Therefore pin head square retention is a good survey technique. Adult TPB’s can best be quantified with a sweep net. Once cotton begins to bloom, plant bugs seem to prefer feeding down in the canopy on the older squares. This results in “dirty blooms”. At this point (blooming cotton) a pin head square retention count is not the most reliable survey technique. It is also at this time that we begin to focus on the immature plant bugs instead of just the adults. The best tool for measuring immatures is the drop cloth. Therefore, in normal maturity cotton, we switch from a sweep net to a drop cloth about July 1-10 each season. Early instar nymphs are very small with long antennae and pale green in color. They move about more rapidly on a drop cloth than other insect species that may appear on the drop cloth in July.

The next few weeks should be focused on adult and immature plant bug numbers by fieldmen. While doing plant bug counts, aphids and spider mites can be observed. After July, or about the 3^rd or 4^th week of bloom, our primary focus should be on stink bugs. This would be true for the lower southeastern area of the cotton belt.

Cotton Insect and Pest Contols

We were cruising along last week with cotton insects kinda quiet. Thrips control was winding down on our latest planted cotton. The most prevalent observation was the white margined borrower bug, which could be found in most all fields. They were on cotton with 3 or 4 true leaves up to cotton knee high and squaring.

This week things have changed dramatically. Not to say every field has insect problems. However, in some fields, consultants are finding some level of plant bugs, spider mites, aphids and a few stink bugs. Generally, the older the cotton, the greater the chance some combination of these pests are present.

Let’s take these pests one at a time. Some have observed adult plant bugs feeding in terminals of pre-square cotton. Others report that plant bugs have dropped square retention to below 80% in cotton that will bloom within 7-10 days. A few stink bugs can already be found in these older fields. As we know from previous experience, stink bugs will attack bolls just after the dried bloom drops off if there are no larger bolls to feed on.

Added to these bug problems are the presence of aphids and spider mites. Aphids can be found clustering in the terminals of some plants in fields of older cotton. This is typically the way an economic aphid infestation usually begins. Spider mites have been treated in some fields already. Good results were obtained with Abamectin at 10 oz. per acre. Mites are still on borders of other fields and do not appear to be spreading yet.

With the combinations of pests present, it is difficult to control multiple species without a tank mix combination. My advice to growers, agrifieldmen and consultants would be to narrow your pest spectrum to the two species that offer the most near term damage potential and select a chemical or combination that will control those. It is just too early for me to consider three way tank mix combinations. At this time I believe it would be wise to target plant bugs (and stink bugs) first and I would place aphids second. These species can be controlled with a tank mix of two materials that would be rather inexpensive. A product that will give good control of plant bugs and stink bugs would be my first choice in the tank. If this product does not control aphids, I would add one that did.

This would leave the mite issue unaddressed. I just feel that we need to protect fruit first and deal with stress from spider mites in the weeks ahead.

There are a number of ways to tackle this tank mix issue for bugs and sucking pests. One would be a mix of pyrethroid and imidacloprid. There are too many to mention all at this time. I will be happy to discuss the various options by phone at 334-332-9501 if you are having problems deciding what approach to take.

Good luck and I’ll be back as we observe or hear of other information to pass along.