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.

Bollworm Management on 2 Gene Cotton – 2018

Problems with damaging levels of escape bollworms were observed in 2017 on two gene cotton in numerous fields throughout the state. At harvest time, worm damaged bolls were noticed by those operating harvesters in many other fields. These escape bollworms were associated with all 2 gene varieties. This event had been noticed in a few fields statewide for several years, but the problem increased tremendously in 2017. This situation may increase in 2018 and in future years on 2 gene cotton due to bollworm resistance to both genes. Three gene varieties have been available to a limited degree for the past couple of years. More varieties will be available with 3 genes in 2018, but supplies of many will be limited. Until the 3 gene varieties are widely planted, we will need to focus on closer scouting and better management of bollworms in the 2 gene varieties. A major effort has been underway since last season to aid fieldmen on scouting, thresholds, insecticide choices, and timing of applications for bollworms. Following is a discussion on how we might manage bollworms and other cotton insects in 2018. 

Do not let plant bugs become embedded. When this happens, multiple applications will be required to prevent economic damage. An embedded situation is when a subthreshold level has been allowed to go untreated for more than a generation. This results in a plant bug population of all ages and stages from adults, to all ages of immatures and eggs. In Alabama, most adult plant bugs move from wild hosts to cotton by July 10, early bloom. This is the perfect time to control plant bugs with one timely spray and then stay out of the fields with hard chemistry until the bollworm escape window begins or until stink bugs become economic. Some of the more commonly used choices for an early bloom plant bug spray are Bidrin, Transform, Centric, or bifenthrin to control the adults. Since egg deposition has been going on for 2-3 weeks prior to that time of the season, we will have plant bug immatures hatching for the following 2-3 weeks. This is the time we want to stay out of the fields with a hard chemical. So what do we do? Add the IGR (insect growth regulator) Diamond 6-9 oz/ac to the adulticide. This will zero out most of the immatures that hatch for the following 2-3 weeks. At which time, we shift our focus to escape bollworms and stink bugs or in a worse case scenario, late migrating plant bugs.

Now back to our bollworm situation. Monitor cotton closely to detect the major peak of corn earworms coming from corn. This historically has occurred about July 10-15 in south AL; July 20 in central AL; and about Aug 1-5 in north AL. This egg lay may last from 7-10 days in any given location. When this flight is detected by increased egg numbers or five to ten 1-2 day old larvae in white blooms, have your control plan ready and implement it within 24-48 hours. Timing is everything here. You should already have your chemical choice in hand. We basically have 2 choices, a pyrethroid at the highest labelled rate, or one of the diamide selections: Prevathon 14-18 oz or Beseige (Karate + Prevathon) at 7-9 oz/ac. The pyrethroid will cost $2.00-$4.00/ac, the diamide class $14-$18/ac. If the bollworm larvae are 5 or more days old, the diamide may be no more effective than a pyrethroid. Diamides are most effective when the residue is on the plant when the egg hatches. In order to make this happen then, we must trigger the spray on or shortly after the historical date for the bollworm moth flight determined by egg or small larvae counts. Fieldmen will need to check sentinel fields every 3-4 days during these critical periods. In my research plots at Prattville, AL, I will be evaluating both types of chemistry with varying timing sprays. Until I convince myself that the pyrethroids will not work on bollworms when the application is well timed, I will be recommending a pyrethroid. This is for two reasons, one the diamide chemistry is expensive. The most we will want to spend in Alabama will be one application. The second reason I will first choose a pyrethroid is the fact that a diamide, a few days late, may be no more effective than a pyrethroid.

Are all pyrethroids equal for bollworm control? I am not sure, but they are not all equal on other species that infest cotton. Most all agree that the bifenthrin pyrethroid is better on bugs. Maybe we should never have assumed that they were all equal on bollworms. Some are better on fall armyworms that others. Originally, Pydrin was the best on worms while Pounce and Ambush were better on boll weevils. One more point on these escape bollworms. You really have one shot at the peak of this moth flight. That is the reason that first spray must be so timely. By the time you find escape worms behind this spray, it is too late for a “clean up.” Following this one well timed spray, scout only for more eggs or tiny hatching larvae. A second pyrethroid application may be needed during each moth flight. The older worms will just have to cycle out. My summary suggestion is to have an escape bollworm plan of attack for 2 gene cotton in 2018, implement it very quickly when the problem is detected, then move on. Do not call for help, panic, or waste a lot of time surveying or counting large escape worms. If you miss your target, it is too late. You only have a narrow window of time for a well timed spray. Keep in close touch with other fieldmen in your area. Listen out through the ag media, both printed and electronic, for insect conditions in other areas of the cotton belt.

Some of these sources in Alabama are:

•      My tweets: @Ron_Smith23 Click Here 
•    My blogs: Click Here
•      My Syngenta 800 line
•    Call 1-877-285-8525: when prompted, press 1, then 2, then 4
•      Weekly email newsletter from Tim Reed containing moth trap data
•    Email reedtim@auburn.edu to be placed on this list

Bollworm Damaged Boll

Bollworm in Boll