Cotton Insect Situation No. 9 July 3, 2002 Blake Layton Extension Cotton Entomology Specialist Area Specialists: Dr. Gordon Andrews Dr. Scott Stewart Dr. Mike Williams Cotton Insect Hotline: 1-800-445-4931 Crop Situation: The Weekly Weather and Crop Report for the week ending June 30 listed the crop as 70% squaring and 24% setting bolls. The 5-year average for this time is 83% squaring and 26% setting bolls. Statewide average temperatures for the week of June 24 through June 30 were 2 degrees below normal and statewide average rainfall was 0.57 inches above normal. Aphid Fungus Beginning to Appear: The Neozygites aphid fungal disease has been detected in several samples submitted from Mississippi fields. Positive samples were submitted the last week of June from as far north as Grenada and Lafayette Counties. Thanks to Dr. Don Steinkraus of the University of Arkansas for providing this identification service. Region 2 Growers Vote on BWEP Containment Program: Growers in the South Delta (Region 2) will soon be voting on their Boll Weevil Eradication Containment Program. Ballots will be mailed to eligible growers and landowners on July 8. Ballots must be returned by July 19 in order to be included in the count. At least 50% of eligible voters must participate in order to have a valid referendum, and a 2/3 majority must vote in favor of the referendum for it to pass. Successful passing of the referendum will establish a 10-year Boll Weevil Eradication Containment Program for Region 2. This program is extremely important to South Delta cotton because without it boll weevils would be able to re-infest the area and all of the hard work and expense of the past five years would be lost. Similar maintenance programs or containment programs are in place in Regions 3 and 4 of Mississippi, as well as in all eastern areas of the cotton belt. The referendum specifies that the yearly assessment fee for the containment program cannot exceed $12 per acre. Mississippi legislation requires that the maximum amount of the assessment fee for containment programs be the same for all regions of the state. However, the actual amount of the assessment fee can be less than $12 per acre and can vary by region, depending on how much it costs to run the containment program in a region. Because it appears that Region 2 will complete its 5-year Boll Weevil Eradication Program under budget, it is very likely that the annual assessment fee for the Containment Program in Region 2 will be less than $12/acre. The assessment fee funds will be used to complete the job of eradication in the South Delta, to run a boll weevil trapping program that will allow early detection of any re-infestations that may occur, and to control any re-infestations that do occur before they spread. The actual amount of the assessment fee will be set by the Mississippi Boll Weevil Eradication Foundation, based on the cost of running the containment program in the South Delta. It is likely that there will still be very low numbers of boll weevils present in the South Delta in 2003. Without this containment program, there would be no mechanism for completing the eradication effort in the Region 2. Given the reduced spray environment associated with Bt-cotton and the fact that most of the new cotton insecticides (Tracer, Steward, Denim, Trimax, Centric, and Intruder) do not control boll weevils, boll weevils would quickly and thoroughly re-infest South Delta cotton given the opportunity to do so. The costs and effort required to control boll weevils under a Bt cotton system would be many-fold greater than an annual assessment fee for containment. Successful passage of this referendum is crucial for South Delta cotton growers. Aphid Efficacy Trial Results: The following tables shows preliminary results from an aphid efficacy trial conducted this year in Grenada County. This trial was conducted to compare the ‘high’ and ‘low’ rates of currently available aphid treatments. Treatments were applied using a CO2-powered backpack sprayer calibrated to deliver 10 gallons of finished spray per acre. Treatments were applied on June 21; plants were in the 6 to 7 node stage at this time. Plots were evaluated by counting the number of aphids on the third leaf below the terminal from 10 randomly chosen plants per plot. All treatments gave similar levels of control. Note that populations in the untreated plots are gradually declining, while those in treated plots are increasing. We thank Mr. Steve Winters for assistance in establishing this trial. Grenada County Aphid Trial, June, 2002. Insecticide and Formulation Lbs. Ai Per acre Avg. No. Aphids/Leaf 3 DAT 7 DAT 10 DAT Centric 40 WG 0.05 3.0 12.1 32.4 Centric 40 WG 0.031 2.5 21.9 38.1 Trimax 4SC 0.047 4.5 25.1 36.9 Trimax 4SC 0.031 10.6 22.6 28.2 Intruder 70WP 0.05 0.8 7.7 30.3 Intruder 70WP 0.031 1.2 11.8 36.0 Bidrin 8 E 0.5 2.4 15.6 33.6 Bidrin 8 E 0.33 9.2 17.8 38.3 Furadan 4F 0.25 1.3 19.8 31.6 Untreated -- 203.0 133.1 74.5 Worm Sprays: Last year Mississippi cotton growers applied an average of 0.84 ‘worm sprays’ to their Bt-cotton fields, while non-Bt fields required an average of 2.27 ‘worm sprays’. All of the treatments applied to the Bt fields were to control bollworms, but treatments to non-Bt fields targeted tobacco budworms, as well as bollworms. This information is based on results of a statewide survey involving 118 fields, 67 Bt and 51 non-Bt fields. As the following graph indicates, this pattern for Bt fields to require fewer worm sprays has been consistent since Bt cotton was first introduced in 1996. One of the key points to note here is that Bt fields do occasionally require treatment to control bollworms and that July is the month when this most often occurs. After bloom, the treatment threshold for Bt cotton is 4 larvae, that are 1/8 inches or longer, per 100 plants. Average # Worm Sprays - Bt vs. non-Bt Insect of the Week: Bollworm: Helicoverpa zea The bollworm has long been an important pest of cotton. Unlike the tobacco budworm, which is largely a ‘secondary pest’, bollworm is more appropriately considered a ‘major pest’. This is because large numbers often develop in corn fields and then move to cotton in July as corn becomes unattractive. Because of this mass movement from corn to cotton, bollworms can reach treatable levels in cotton in July, even though few or no bollworms were present in cotton fields in June. Although the damage potential of individual bollworm larvae is similar to that of tobacco budworm larvae, bollworms were considered to be relatively less important than tobacco budworm during most of the latter half of the 20th century, because they were relatively easy to control. This was because bollworms in Mississippi did not, and still have not, develop resistance to organophosphate and synthetic pyrethroid insecticides that were used to control the bollworm/budworm complex. In contrast, tobacco budworm was often very difficult and costly to control, because of the high levels of resistance that it developed to these classes of chemistry. However, since the development and introduction of transgenic Bt-cotton in 1996, the overall importance of bollworm has increased considerably, because bollworm is much more tolerant to the Bt toxin than is tobacco budworm. Bt cotton, which is currently planted on approximately 80% of Mississippi’s cotton acreage, currently provides essentially 100% control of tobacco budworm. But, although Bt cotton also provides significant control of bollworms, supplemental foliar insecticide sprays are occasionally required to keep bollworms from causing excessive damage in Bt fields. During the past six years, the average number of bollworm treatments applied to Bt fields in Mississippi has ranged from 0.27 to 1.22 treatments per field. Still, this is considerably lower than the 2.44 to 5.18 sprays per field that were applied to control bollworm/tobacco budworm on non-Bt fields over this same time period. Biology: Like all moths, bollworms have a complete life cycle. The female moths produce from 800 to 1000 eggs during an oviposition period that lasts approximately 8 to 12 days. Eggs are deposited singly and, in cotton, may be found on young leaves and other tissue in the terminal, as well as deeper in the canopy on square bracts, blooms, dried bloom tags, and other areas. The eggs hatch in three to five days; the larval stage lasts 12 to 15 days (longer when temperatures are cool), and there are five to six larval instars. Pupation occurs in the soil near the host plant on which the larva developed. Pupal chambers are usually one to two inches deep and the pupal development period requires approximately 8 to 12 days. Female moths produce a mating pheromone, which is attractive to male moths. Most mating occurs within two to three nights of adult emergence and egg-laying begins soon afterward. Bollworm has a wider host range than tobacco budworm, and this is thought to be one of the major reasons that it has been slower to develop insecticide resistance than tobacco budworm. The larger host range means that there is a larger "refuge population". During the early spring the primary hosts are similar to those of tobacco budworm: vetches, lespedezas, wild geranium, and several clovers. However bollworm also develop on a number of monocot, or grassy, plants, including corn and sorghum, and these are major hosts for bollworm during late spring and early summer. Generally, bollworms will produce two generations on these crops, one in the whorl stage and one in the ear or head stage. As these crops mature in July, cotton becomes one of the more abundant and more attractive hosts. Soybean is also an important host of bollworms, but it is uncommon to find tobacco budworms in soybeans. A portion of the July and early August generations may lay eggs on other hosts, but, where it is available, cotton is one of the most common hosts during this time. As cotton senesces in the fall, some of the maturing larvae may enter diapause and pupate in the cotton field. However, many larvae will not enter diapause at this time, and the moths that result from these larvae will complete an additional generation on alternate weedy hosts. These fall hosts are similar to those used by tobacco budworms, and include: prickly sida, hophornbeam copperleaf, velvet leaf, beggar weed, and some morning glories. Like tobacco budworms, bollworms overwinter in the pupal stage. Although bollworms generally emerge from overwintering later than tobacco budworm, bollworm moths can be caught in pheromone traps as early as March, which is before overwintering tobacco budworm emerge. These early catches are thought to represent migrating moths, which emerged in more southerly regions of the country. Bollworm moths are strong fliers and are known to be able to travel as far as 250 miles in a single night, via high altitude, wind assisted flights. Damage: Bollworm larvae feed on both squares and bolls. However, damage to bolls is considered to be the most serious type of injury. Heavy, uncontrolled infestations are capable of inflicting severe yield losses. Although Bt cotton is much less susceptible to injury than is non-Bt cotton, boll damage as high as 30% has been observed in Bt fields where damaging infestations of bollworms were not controlled. During the recent years estimated yield losses attributed to the bollworm/tobacco budworm complex have ranged from 1.9 to 4.2%. Because most of Mississippi’s cotton acreage is planted to Bt varieties, which currently provide near 100% control of tobacco budworm, the majority of this yield loss is attributed to bollworms. Control: As mentioned previously, bollworms are generally more susceptible to foliar applied insecticides than are tobacco budworms. However, because larger larvae spend most of their time feeding inside squares and bolls, where they are protected from exposure to insecticides, it is important that foliar insecticide treatments be applied while larvae are still small, less than ½ inches in length. Also, bollworm moths often tend to deposit their eggs deeper in the crop canopy, which makes insecticide coverage more difficult. During the boll-setting period, treatment is recommended on non-Bt cotton when larval numbers reach or exceed 4 per 100 plants. The threshold is similar for Bt cotton, with the important exception that, in Bt-cotton, larvae smaller than 1/8 inch should not be counted. This criterion prevents unnecessary treatment of newly hatched larvae that would be controlled by the Bt toxin. The table below lists the foliar-applied insecticides recommended for control of bollworms. Table 1: Foliar Insecticides Recommended for Control of Bollworms Insecticide Trade Name Lbs ai/acre Bifenthrin Capture 0.06 to 0.1 Cyfluthrin Baythroid 0.025 to 0.05 Cyhalothrin Karate 0.025 to 0.04 Cypermethrin Ammo 0.04 to 0.1 Deltamethrin Decis 0.02 to 0.03 Esfenvalerate Asana XL 0.03 to 0.05 Zetamethrin Fury 0.033 to 0.045 Methomyl Lannate 0.45 Indoxacarb Steward 0.09 to 0.11 Spinosad Tracer 0.067 to 0.089 Thiodicarb Larvin 0.6 to 0.9 Profenofos Curacron 1.0 Source: Cotton Insect Control Guide, 2002, Publication 343, Mississippi State University Extension Service Corn Corner - Dr. Don Parker: Many areas are reporting a decrease in southwestern corn borer trap counts. For those areas that have not treated, fields should be monitored for larvae. As corn approaches the dent stage corn borer damage will have less impact on yield. We have not reached the third generation, which typically causes lodging. To avoid yield loss due to lodging producers should harvest as soon as possible. For more information: http://www.msstate.edu/Entomology/cornforum. Delta Counties - Gordon Andrews: Much of the south delta received rain that was needed by all crops. Rains seem to have diminished the spider mite problem. Mite populations observed this week were lower and fungus was present on many remaining on leaves. Aphids seemed to be showing up in spots in some fields. Aphid numbers are not as high as the damage indicates. Hard rains may have knocked some off the plant and many parasitized aphids and adult parasitic wasps were observed. Plant bugs are persistent in cotton fields adjacent to wild hosts (including corn) which have received adequate water to keep the wild hosts attractive to plant bugs. Twelve spotted cucumber beetles and salt marsh caterpillars were observed in some fields. Talk of scattered bollworm eggs and larvae were heard this week but they were not in the fields observed. Northeast Counties - Mike Williams: We are seeing some increases in numbers of aphids in NE Mississippi and have reports that insecticide applications are being made for them. The build-up is spotted in fields and seems to be much slower than usual in those fields where they are a problem. If the fungus is on time this year it probably will come sometime in the next 10-12 days. We will get notification out via this letter and others of the progress of the fungus once we begin to get reports of it in the state. Heliothine egg lay is occurring in some areas, but it continues to be very light. High numbers of beneficial insects will probably take care this egg lay. Tarnished plant bugs continue to be a problem in much of our pre-bloom cotton and unfortunately we have a number of acres in NE Mississippi which is still a week to 10 days away from first flower. The afternoon thunder boomers are finally bringing rain to most of the area and some relief from the drought. They may also flush some of this years final weevils from hibernation. The boomers also cause us some problems with spray operations at times. A general rule of thumb on any insecticide application is that it will probably be effective if it has time to dry on the leaves (about 3 hours) before a rainfall event, but in most cases the full effect will be lost if rains come sooner than 6-12 hours. Some materials, ie - ULV malathion are completely lost after even a light shower. So if applications are important to make it may be important to reapply some if they are rained on during the same day of application. Trap reports for week ending July 3, 2002 County Boll weevils Bollworms Budworms BAW no. per 33 traps no. per trap/week no. per trap/week no. per trap/week Coahoma   4.5 12.5 0.5 Tunica 0.0 6.0 21.0 0.5 Bolivar 0.0 10.3 12.3 3.7 Washington   2.0 12.0 0.0 Madison   3.0 5.0 2.0 Yazoo 0.0 7.0 11.5 4.5 Humphreys   39.0 19.5 13.5 Leflore   20.0 7.5 13.5 Carroll 3.1 27.0 5.0 10.0 Grenada 0.0 9.0 3.0 10.0 The information in this newsletter is provided for educational purposes only. Mention of specific products or trade names does not imply their endorsement above other products that are labeled and recommended for a similar use.

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