Cotton Insect Management Tips for 2019

Cotton insect management is constantly evolving or changing. It may be in the area of: genetic trait or insecticide resistance; new economic insects such as the silverleaf whitefly or the brown marmorated stink bug; the introduction of new chemistry or new traits such as the lygus-thrips trait that will likely be available about 2021 or 2022.

Our current production system in Alabama is good at present as it relates to insects. This is evidenced by the good to great yields we have produced (when not impacted by tropical storms) in recent years. We do not need to make major changes in our production system based on 2018. Let's don't let one weather related disaster change the good job growers are currently doing. Maybe tweak a few points. One of those being a major focus on earliness. Earliness would be beneficial in a wet harvest season, help in reducing whitefly damage in southeast Alabama and minimize the new cottonleaf dwarf virus disease concentrated  in southwest Alabama.

In this article I want to point out where we are with the management and control of some of our major insect pests and highlight some things we need to be aware of in 2019 and the next few years.

Beginning with thrips, where do we stand? We have documented resistance to both seed treatments - thiamethoxam (Avicta) and imidacloprid (Aeris). Resistance to thiamethoxam is higher and more widespread throughout most of the cotton belt. Imidacloprid has proven more consistent in our Alabama research trials. However, the resistance level of either chemistry did not seem to increase in 2018. This may have been due to a light and late thrips year. The peak movement of thrips from wild hosts to cotton in 2018 did not occur until about mid-late May, when early planted cotton was beyond the 5th true leaf stage.

Planting date and weather are the two most important factors influencing cotton thrips injury levels. Rainfall influences when thrips move from wild hosts to our crops. The more abundant the spring rainfall, the later the movement of thrips. The warmer the nights, the faster the cotton will grow up. Cotton is only susceptible to thrips injury from the first true leaf to about the fifth true leaf. The faster cotton is growing, the shorter the thrips susceptible window is in days.

We can use planting date, rainfall and temperature to determine when we need to help our seed treatments with a supplemental foliar spray for thrips control. In fact, a model has been developed by entomology researchers at North Carolina State that will project the level of thrips pressure to expect, based on your planting date and weather records from your nearest weather station. This model was developed for the entire southeastern cotton growing area, by utilizing thrips data generated on University research stations from throughout the southeast. This model can be accessed and utilized by growers, consultants, and fieldmen by going to http://www.climate.ncsu.edu/CottonTIP.

The second insect I wish to discuss is aphids. I am including an aphid discussion for the 2019 season because of their potential relationship to the new virus disease known as the cotton leafroll dwarf virus (CLRDV). Our usual management advice for aphids is to just wait for the naturally occurring fungus to take out the population. In the past we have recommended to control aphids with a foliar insecticide only when cotton was under extreme drought distress. In recent years we have also added a second exception for controlling aphids. It is advisable to control aphids when they are heavy and a bollworm moth flight is expected on 2 gene cotton varieties. Aphids and their resulting honeydew make it impossible for scouts and fieldmen to detect bollworm eggs or small larvae among the aphids and honeydew. Foliar sprays to control aphids would need to be done in advance of the expected moth flight.

Aphids begin to appear in June. First on select plants, maybe less than 10%, in early square cotton. The population will usually peak and die off from the natural fungus disease about mid July. The slower the population takes to build up, the longer it usually takes to crash or die off. This natural fungus usually takes about 10-14 days later than desired. The moth flight of corn earworms/cotton bollworms coming from corn depends on the maturity of corn, but usually occurs in Alabama between about July 10 in south Alabama to August 1 in the northern counties.

Aphids are vectors for the CLRDV disease that was found in several Alabama counties in 2017 and 2018. However, experts tell us that the disease can be transmitted in as little as 40 seconds. Therefore, aphid control will not eliminate this disease. In other parts of the world where the disease occurs it has been controlled primarily by developing resistant germoplasm.

Aphids may rebound in cotton in late season. This late season population is not as prone to die off from the fungal disease. Foliar sprays may be warranted if lower bolls are opening and are susceptible to being covered by honeydew which allows sooty mold to develop on the open lint. The late season aphid population could be more closely involved with the disease transmission since the disease seems to be much worse on late planted cotton.

In a follow up blog, if time permits, we will discuss management ideas for plant bugs, escape bollworms on 2 gene cotton, and stink bugs, we will mention the silverleaf whitefly (SLWF) but hopefully we will not see the pressure from this pest in the southeastern counties as we did in 2017.

Plant Bugs/Stink Bugs Overwhelm Beneficials

Cotton fruits over a long period of time compared to most other crops and attracts many species of insects, many beneficial, but a few damaging ones. When cotton reaches the fourth or fifth week of bloom, the few bad insects such as escape bollworms, plant bugs, or especially stink bugs, in the southern cotton growing areas of the US, often overwhelm the good insects. At this time many fruit, especially bolls, are at risk. Unfortunately, a decision has to be made to control the harmful bugs. Most of the bad bugs, such as stink bugs, cannot be controlled  with selective insecticides. As a general rule, if a grower can get to this point in the season without using hard insecticides, beneficial insects have carried it as far as they can and a decision has to be made to protect the fruit rather than conserve beneficials. This is a difficult decision since there may be millions of lady beetles, pirate bugs and other species present per acre. However, when we get to the gin in the fall, they will only weigh the cotton and not the beneficial insects. Beneficials are a great resource but they are just NOT any help against plant bugs and stink bugs.

We have very good thresholds for these damaging bugs, based on many years of research conducted throughout the cotton belt. When the damage threshold is exceeded, controls must be applied in order to protect the fruit and make cotton production economical. When cotton is planted during our desired planting window of late April to mid May, cotton reaches this fourth or fifth week of bloom about the last 10 days of July. This is the time we have to make the decision to either conserve beneficials or protect the fruit. In order to maximize yields and profits we should choose to protect the fruit. Beneficials are a cost free resource in cotton but they can only take us so far.

Critical Period for Bollworm Escapes on 2 Gene Cotton in AL

Ron Smith

Extension Entomologist, Auburn University

We are entering the most critical period of bollworm presence during the next 20 days (July 15-Aug 1). This increase in bollworm activity began last week (July 9-13) along the Gulf Coast and the Mobile/Santa Rosa County (Jay) FL area. By July 20^th, we should see an increased bollworm egg lay in Central AL (Montgomery, Prattville, Selma areas). By the 25^th this increase may reach Cherokee County in the northeast, and by August 1^st the Tennessee Valley area of northern AL.

Increased bollworm moth presence was noted last week as far north as Pike and Barber County (Troy) area. This increased moth activity will be influenced by the planting date and acreage of corn planted in a given region of the state. Most all bollworm were corn earworms in corn previous generation. This life cycle is about 30 days and the eggs in corn were deposited during the white or pink silk stge. About 30 days later these moths that emerged from corn are looking for their next host. Cotton is the best host they will find in AL (not soybeans or peanuts).

Many (but not all) fields in all areas of the state had more worm damaged bolls in 2017 than we had seen since 1995. If we want to prevent this from happening again, the next 2 weeks are critical.

I assume that most realize now that our 2 gene cotton has lost some level of effectiveness against the bollworm species. When resistance is a factor, the problem usually gets worse over time—it seldom gets better.

Now, what should fieldmen be looking for?

1.     Eggs in terminals or on the fruiting structures: square bracts, white or red blooms (threshold on 2 gene cotton is 20 eggs/100 plants)

2.     Damaged squares in the upper canopy – may find more damage to small squares near the terminal in Phytogen varieties (5% damage is threshold).

3.     Newly hatched larvae

May find in small squares in Phytogen varieties

May find more in open white blooms or underneath red or dried blooms in Delta Pine and other varieties

(5% of plants with small larvae is threshold)

These small larvae are white when they have just hatched and will turn pale green within a day or so.

One thing that makes them stand out in a white bloom is they will have a black or dark brown head. Often the head is the best thing to look for since being dark stands out from the white bloom petals. (See Picture)

Once a significant increase in eggs or small larvae are detected—do not waste more time in the field. Get the word to the grower and get the sprayer loaded. Every 24 hour period that passes from detection to treating means less effectiveness with your insecticide. Also note that these bollworm moths will likely seek out our oldest and most promising cotton to deposit eggs in.

Now what treatment options do we have? Basically two. We can try the older chemistry, pyrethroids, or we can go to the newer chemistry, Besiege and Prevathon.

Things to consider here: bollworms have shown levels of resistance to pyrethroids in many areas of the cotton belt. However, the pyrethroid chemistry is much less expensive. Pyrethroids have about a 4-5 day residual on bollworms, where they are still active.

The newer chemistry Beseige and Prevathon have about 10+ days of residual on bollworms, depending on the rate applied.

If using pyrethroids, I suggest the highest labeled rate. If using Beseige, I suggest 8-9 oz/ac. If using Prevathon, I suggest 16-18 oz/ac. Besiege contains a low rate of Karate pyrethroid in the mixture. If you need tarnished plant bug or stink bug control, you will need to add about 1 oz of additional Karate, or equivalent pyrethroid, to the tank mixture. Prevathon has no activity on plant bugs or stink bugs.

In summary, this is the time to be ready to react to bollworms in 2 gene cotton. I will be tweeting as I hear of increased pressure in a region, county, or area.

I will be conducting tests on thresholds, timing, and chemical choices at our research farm at Prattville in Central AL, so will be in the field a lot within the next 2 weeks or so.

Stay in touch with the Syngenta Pest Patrol reports for up to date observations on bollworms. To sign up for the Syngenta Pest Patrol Updates for Alabama, register online at syngentaus.com/pestpatrol or register via text by texting pestpat11 to 97063.

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Blog: http://alabama-insects.blogspot.com/

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Heavy Plant Bug Season May be Becoming a Reality

Last week, aphids began to build in spots in fields statewide. Ordinarily, I would recommend to let the natural fungus take out the aphids. However, each field and season presents a different picture. The fungus always works, however sometimes it is a week to 10 days later than we would like. Since we have a lot of late maturing cotton this season, I don’t feel we need to let aphids set our cotton back any further. Even if aphids do not cause yield losses, when an entire field is drooped down from aphid stress, we are likely seeing some maturity delay. For this reason, in 2018, I am suggesting that if a grower is going over a field for weed control or PGR application, then I would add an aphid control insecticide in the spray. We have some very economical choices for aphid control when they can be piggy backed with a trip over the field for another purpose.

Now on to plant bugs – I say plant bugs because we could easily have both the tarnished and the clouded species in some fields. In fact, I picked up some clouded species in sweeps in cotton last week in central AL. Historically, we have had more clouded in wet springs. Maybe because we get a better growth on button bush, a wild host for clouded in wet seasons. Button bush is a plant that likes low, swampy habitat, and excessive rainfall gives us that. No matter whether it is TPB or CPB, our scouting thresholds and controls are the same.

Now let’s talk about the TPB. The rainfall in the past month has kept their primary wild host, daisy fleabane, fresh and it appears that 2 generations have developed on fleabane. In mid May, we had mostly adults here in Central and South AL. Now, in both South and North AL (including the TN Valley), we have another generation that was just mid aged immatures the second week of June. This means that we will likely have a migration from fleabane into cotton that will last for 3-4 weeks. Therefore, feeding and egg laying in cotton by these migrating adults will last 3-4 weeks. This will result in a long emergence of immatures in cotton beginning about first bloom.

We may need multiple applications pre bloom in some fields to control migrating adults. Then we may also need multiple applications post bloom for the immatures as they hatch. I hope I am over estimating what could be a bad plant bug year. This is not what we needed on 2 gene cotton. Multiple plant bug sprays just before the CEW flight comes from corn will result in more escape bollworms in mid-late July.

One thing we can do if this scenario happens is to use a plant bug application for adults about first bloom and add the IGR Diamond to the tank mix. Diamond will add residual control on hatching immature plant bugs for 10-20 days, depending on the rate used.

I will be focusing and making observations on plant bugs for about the next 3-4 weeks, and I will keep everyone updated on what we are seeing. The first report of high numbers of adult TPBs in cotton came from west central AL on June 19.

An Extension publication overviewing plant bugs was prepared by Barry Freeman, our resident plant bug expert in 1999 and can be found online at http://www.aces.edu/pubs/docs/A/ANR-0180/ANR-0180.pdf. Life cycles, damage, scouting, and management have not changed over the years. Every season and field are different, which requires close monitoring in order to make the proper management decisions.

2018 Treatment thresholds and control recommendations can be found in ACES publication # ANR-0415, “Cotton IPM Guide” available online at http://www.aces.edu/pubs/docs/I/IPM-0415/IPM-0415.pdf

If fieldmen, growers, or consultants have plant bug observations, please call or text and share with me at 334-332-9501. You may email me at smithrh@auburn.edu.

                                         Grasshopper: Sporadic Pest of Seedling Cotton
                                                                    Ron Smith

Grasshoppers have been a sporadic pest of seedling cotton for 10 or more years. This problem emerged as a result of the conservation movement to reduced tillage. Certain seasons seem to be worse than others and 2018 has resulted in greater concern than more recent years. Growers reported observing high numbers of adult grasshoppers during harvest season in fall 2017. Overwintering populations are influenced by environmental conditions. Rainfall is likely more important than temperatures. Dry winters are favorable for grasshopper population since they overwinter as eggs in the soil. Grasshopper problems are sporadic and almost always associated with reduced tillage fields. 
The primary grasshopper that damages cotton is the differential species which also overwinters as eggs in the soil. Eggs hatch from late March throughout April, May and June as soil temperatures rise and spring rains occur. The first nymph to leave the egg pod makes a tunnel from the pod to the soil surface through which the succeeding nymphs emerge. Nymphs feed and grow for 35 to 50 days before becoming adults which can then fly. The nymphs or immatures can only jump. Their development proceeds most rapidly when the weather is warm but not too wet. Mature grasshoppers mate and continue feeding on plants About 2 weeks later, females begin to deposit clusters of eggs in the soil. Soil particles are glued together around the eggs to form a protective pod Each pod may have 25-150 eggs. Most grasshopper species only complete one generation per year.

In fields with historical grasshopper problems, growers may want to take a more preventative approach by adding a grasshopper insecticide to their burn down herbicide. Since not all grasshoppers emerge from the egg stage at the same time, a long residual IGR (insect growth regulator) insecticide could also be utilized. Dimlin has proven to be a good management tool for grasshoppers. It has extended residual that provides good control of immature grasshoppers but will not control adults.

There are no established thresholds for grasshoppers in cotton and will likely never be since their feeding habits are so unpredictable. Some fields and some years may have grasshopper damage while other fields and years have the same level of grasshoppers but no damage. Preventative insecticide applications for grasshoppers are a judgment call. When grasshoppers are observed, and cotton is in the susceptible stage, treatments can be based on the risk level that an individual grower is willing to take.

Grasshopper problems are greater in lighter soils or soils with higher sand content. Damage often occurs in the same fields or farms from year to year. Grasshopper damage as stated is unpredictable but can potentially threaten a stand. Grasshoppers may feed on foliage, but most economic damage occurs when grasshoppers feed on the main stem of emerging (in the crook or cracking stage) seedlings. In some cases, grasshoppers may completely sever the stem, but more often they will chew partially through the stem weakening the plant which will fall over at the feeding site.

Most all cotton insecticides will control immature grasshoppers when applied at a low labelled rate. Later into the spring, adult grasshoppers are very difficult to control with any insecticide, even at a high labelled rate. Acephate (Orthene) at 0.6 lb. active per acre has proven to be the most effective grower treatment for adult grasshoppers.

Old World Bollworm, Helicoverpa armigera, and Bollworms Hybridizing in Brazil

Australian scientists have confirmed hybridization of two of the world’s major pest species into what they say could be a new mega-pest. The 2 pests are: Helicoverpa armigera, referred to as the “old world bollworm;” and Helicoverpa zea, known in the U.S. as the corn earworm or cotton bollworm.

H. armigera was confirmed in Brazil in 2012 and 2013, where they settled into an area already populated by H. zea. This mating has now led to hybridization. Previously, these 2 species had been separated geographically by continents for about 1.5 million years.

H. armigera, the old world bollworm, is widespread in Africa, Asia, Australia, and Europe and causes damage to over 100 crops including corn, cotton, and soybean. This species has developed resistance to most every pesticide used against it. The U.S. corn earworm or cotton bollworm has limited resistance potential and host range.

H. armigera was detected in south Florida in 2015, but no additional finds have been reported. Alabama Extension entomologists Drs. Tim Reed, Ron Smith, and Alana Jacobson utilized pheromone baited traps at Fairhope, Brewton, and Headland AL in both 2016 and 2017 but no H. armigera were captured. These sites will be monitored again in 2018, along with those in several other southeastern states.

Researchers have confirmed hybridization between the two species in Brazil as reported in the Proceeding of the National Academy of Sciences of the USA. These hybrids could be hard to ID at borders and could go undetected once it enters another country.

In Brazil, scientists reported that among the caterpillars studied, every individual was a hybrid. The findings among the hybrids was that 51% of the H. zea (corn earworm, bollworm) larvae carried a known resistance gene from the H. armigera species.

Leading researchers believe that the hybrid study has wide-ranging implications for the agricultural community here in the U.S. Is it estimated that 65% of the U.S. agricultural output is at risk of being affected by this hybridization between H. armigera and our H. zea species.

Shown below are two H. armigera “old world bollworms” attacking a cotton boll in Australia and an H. armigera moth. Picture was taken by Ron Smith while on a cotton education tour of New South Wales and Queensland Australia in Feb. of 1999. This pest was causing major economic damage to non-genetic varieties at that time.

Dr. Alana Jacobson, research entomologist at Auburn University is using a DNA-based test to identify moths captured in both H. armigera and H. zea traps at the three trap sites in Alabama. This real-time assay is able to differentiate H. armigera and the F1 hybrids of H. armigera and H. zea from the non-hybridized moths. Funding for these efforts is provided by the Alabama Cotton Commission and Alabama Soybean Producers Committee.

Thoughts and Tips for Bollworm Scouting on 2 Gene Cotton for 2018

          If you had an economic problem with escape bollworms on 2 gene cotton in 2017 and anticipate the problem in 2018, consider a 3 gene variety. Select one with similar maturity and yield potential as those you've been planting. This reduces acres scouts/consultants must focus on escape worms.

         When planting 2 gene cotton in 2018, monitor for bug and sucking pests and only make in-season foliar sprays when economic damage is found. This will conserve beneficial insects and reduce escape bollworms.

          If monitoring 2 gene cotton in 2018, take note of the corn planting window in your area. This plays a large role in the emergence & movement of corn earworm (bollworm) moths to cotton in July & Aug. The more corn planting is spread out, the wider the emergence window of bollworms.

          Bollworm moth activity isn't constant throughout the season. Instead it occurs in cycles especially through July. By August, generations of bollworms & tobacco budworms overlap. Fieldmen should detect the start of these peaks by focusing on eggs & newly hatched larvae in terminals/white blooms.

          Based on my observations during the Bt cotton era of the past 20 plus years, escape bollworm larvae do not feed on or damage as many fruiting sites per worm as they did in the pre Bt era.

          Scouting intervals for bollworms should be reduced to 3-4 days during critical windows on 2 gene cotton in 2018. Fieldmen may monitor select sentinel fields of similar variety and planting date to detect increased activity.

When monitoring for bollworm larvae or eggs on 2 gene cotton in 2018, be more concerned about detecting population increases early, and reacting if necessary, than quantifying exact numbers-- for example: 18 vs. 28 per whatever.

Fieldmen should consider damaged fruit on 2 gene cotton in 2018, but treatment decisions will be more timely if primary focus is on eggs and/or newly hatched larvae.

In order to stay on schedule in 2018, fieldmen should consider only staying in a field long enough to make a confident treat or not treat decision.

          Pest Patrol Updates on crop insects in Alabama available again in 2018. These alerts, sponsored by Syngenta, are beginning their 10th consecutive season. University entomologists discuss current conditions and advise on insect management.

        To sign up for the Syngenta Pest Patrol Updates for Alabama, register online at http://www.syngentaus.com/pestpatrol  or register via text message by texting pestpat11 to 97063.