Cotton Insect Situation No. 10 July 11, 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 July 7 listed the crop as 82 percent squaring and 40 percent setting bolls. The 5-year average for this time period is 91 percent squaring and 46 percent setting bolls. Statewide average temperatures for the week of July 1 through July 7 were 1 degree above normal, but rainfall was 0.25 inches below normal. Insect Situation: This is the period of the season when Bt cotton is most likely to require supplemental treatments for bollworm control, so all fields, both Bt and non-Bt, need to be carefully scouted for this pest. While checking for bollworms we also need to be alert for plant bugs and stink bugs. "Dirty blooms" are a good, early indicator of mid-season plant bug pressure. As long as you are seeing no, or few, "dirty blooms" plant bug numbers are probably low. But, if the number of "dirty blooms" exceeds 5% or so, it’s time to make some counts and find out how many plant bugs are there. Because of the mild winter, combined with the reduced spray environment associated with Bt-cotton and BWEP, we are anticipating higher numbers of stink bugs than we have experienced in past years. Stink bugs are not likely to be a "spray every field" type of problem, but we are likely to see serious damage in some fields this year, unless the problem is detected and treated at the right time. Bollworms in Bt Cotton: Approximately 80% of Mississippi’s cotton acreage is planted to Bt varieties this year. While Bt cotton is virtually immune to damage from tobacco budworm, it does occasionally require treatment to control bollworms. Bt cotton usually provides adequate control of low to moderate bollworm infestations, but heavy infestations will usually require treatment to prevent excessive boll damage. These heavy infestations of bollworms usually occur during July, as a result of large numbers of moths moving from maturing fields of corn and sorghum. Although fields of cotton that are located near large acreages of corn are generally at higher risk, bollworm moths are strong fliers, and all Bt fields need to be scouted carefully during this time. Treatment of Bt cotton is recommended when infestation levels reach or exceed 4 larvae that are greater than 1/8 inches in length per 100 plants. When scouting Bt cotton it is important to check for larvae in white or pink blooms and in any bolls present two to three nodes below the first position bloom zone. Also check for eggs deposited on bracts of squares, blooms, and bolls and on stuck bloom tags, as well as in the terminal area. Treatment based solely on egg counts is not usually recommended, but may be warranted in situations where bollworm egg counts are extremely high (greater than 50%) in the lower part of the plant. Because bollworms are still highly susceptible to pyrethroid insecticides in Mississippi, these are the materials of choice when treating bollworms in Bt-cotton. I’ve Gotta Spray My Bt-Cotton for Bollworms. What About the Bugs?: A pyrethroid spray should also provide good control of any green or southern green stink bugs that are present, but pyrethroids are less effective on brown stink bugs. If brown stink bugs are present, but below threshold, the pyrethroid alone will be sufficient. However, if brown stink bug numbers are over threshold, an organophosphate, like Bidrin or methyl parathion, should be added. As for plant bugs, a pyrethroid alone should provide good control of any plant bugs that are present, in a Hill environment. However, in many areas of the Mississippi Delta tarnished plant bugs exhibit moderate to high levels of resistance to pyrethroids. Pyrethroids may provide adequate control of plant bugs, if no other pyrethroid applications have previously been made. However, in situations where plant bug numbers are also high enough to require treatment, it is recommended to tank mix an effective plant bug material, like Orthene or Bidrin, with the pyrethroid. Such tank mixes should also give good control of any stink bugs that are present. Is My Bt Working?: Last year we received a number of calls expressing concern over the large numbers of bollworm larvae being found in some Bt fields. Most of the fields in question were planted to either Stoneville 4892BR or Stoneville 4691B, and significant numbers of surviving larvae were found when visiting many of these fields. However, we also observed high numbers of surviving bollworms in several other varieties of Bt-cotton. In conducting our annual end of season damaged boll survey we were able to collect information from 15 fields of Stoneville 4892 and 52 fields that were planted to other Bt varieties. Results of this survey (Table 1) showed that, although the 4892 fields did sustain slightly more boll damage than the other Bt fields, this difference was not significant, and there was also no difference in the number of bollworm treatments applied to 4892 fields. There are differences in the efficacy of various Bt varieties and we will have more information on this in future newsletters. It is important to be aware of any differences in efficacy when managing different Bt varieties. However, when choosing a Bt variety to plant, traits such as yield and quality are more important considerations than subtle differences in efficacy. Table 1: Comparison of Stoneville 4892 to all other Bts, 2001.   No. Bollworm Sprays * (n) % Caterpillar Boll Damage * (n) Region Stv. 4892 Other Bts Stv. 4892 Other Bts Hills 0.43 (7) 0.18 (22) 1.42 (7) 0.89 (22) Delta 1.00 (8) 1.36 (30) 3.53 (8) 2.72 (30) Statewide 0.73 (15) 0.87 (52) 2.55 (15) 1.94 (52) * Differences between pairs were not significant (P = 0.1). Bomb-sniffing Bug: Microplitis croceipes is a common parasitic wasp that attacks bollworm and tobacco budworm. A brief note in the May 2002 issue of Outdoor Life magazine indicates that the US Defense Department is experimenting with using this wasp to detect land mines and other types of explosives. Apparently the wasp exhibits an easily recognizable behavioral response when it detects the odor of the explosive. Insect of the Week Stink Bugs Southern Green Stink bug: Nezara viridula   Green Stink bug: Acrosternum hilare   Brown Stink bugs: Euschistus spp. Historically, stink bugs were not considered a significant pest of Mississippi cotton because they were controlled coincidentally by the large number of treatments applied to control boll weevils, bollworm/budworms and other pests. However, the reduction in spraying that has occurred as a result of the success of the boll weevil eradication effort and the widespread adoption of Bt-cotton has resulted in increased opportunities for stink bugs to colonize and survive in Mississippi cotton fields. Thus, the importance of stink bugs as a pest of cotton has increased in recent years, and consultants are finding it necessary to scout and, occasionally treat for these pests.Several species of stink bugs may occur in cotton. These include the southern green stink bug, Nezara viridula, the green stinkbug, Acrosternum hilare, and several species of brown stink bugs belonging to the genus Euschistus. Of the brown stink bugs, Euschistus servus, is the most common species found in cotton. Several other species of stink bugs may be found occasionally in Mississippi cotton fields, but these rarely occur in large numbers. Biology: Stink bugs are found on a large number of agricultural crops, including soybeans, corn, and grain sorghum. Crops or weeds bearing immature seeds are especially favored. All species overwinter as adults, which emerge in early spring and begin feeding on seed bearing plants, such as wheat, clovers, and various weeds. Small nymphs often feed on vegetative portions of the plants, but larger nymphs and adults prefer to feed on developing seeds. The barrel-shaped eggs are laid in clusters which hatch in seven to twelve days. There are five nymphal instars. Newly emerged nymphs usually remain clustered together, but disperse as they grow larger. Development rate is temperature dependent, but at normal summer temperatures the time to complete one generation is approximately 45 to 50 days. There are approximately three generations per season. Adult stink bugs are strong fliers. As early spring hosts mature and senesce, stink bugs move from these hosts to other hosts that are in a more attractive stage of development. This results in a sequential movement from early spring hosts, such as clovers or wheat, to early summer hosts, such as soybeans, corn, and grain sorghum, and ultimately to late summer hosts, such as cotton. As a result, stink bug populations in cotton are usually greatest in late summer due to immigration from nearby early summer hosts. Cotton fields that are located near large plantings of corn, soybeans, or grain sorghum are especially susceptible to invasion by stink bugs. If such cotton fields are receiving relatively few foliar insecticide treatments, the potential for stink bug invasion is even greater. Damage: Although stink bugs feed on vegetative parts of the plant, and will occasionally feed on squares, feeding injury to bolls is the most common type of stink bug damage to cotton. Both adults and larger nymphs are capable of damaging bolls. Stink bugs have piercing-sucking mouth parts, which they use to pierce the boll wall to feed preferentially on the developing seed. Recent research has shown that bolls less than 350 DD60s or approximately 18 days of age are especially susceptible to injury. But stink bugs will feed on older bolls, and the effect of stink bug feeding on the ultimate fate of a boll is highly variable. Depending on the extent of the feeding and the age of the boll, bolls that have been fed upon by stink bugs may be completely destroyed or they may open normally and produce a normal amount of lint. External signs of stink bug feeding are small, somewhat sunken dark spots on the boll wall, often exhibiting a small pierced area in the center of the spot. This external injury is very similar to that caused by plant bugs. Internal symptoms of the damage include small pierced areas on the inner boll wall, wart-like growths on the inner boll wall, stained lint, and damaged seed. Bolls that have sustained heavy damage usually fail to open, but if heavy damage is confined to one or two locks, the affected boll may partially open. Often, bolls may exhibit external signs of feeding, without suffering severe internal damage. However, bolls may also exhibit severe internal damage in the absence of external symptoms. Yield Effects: Yield effects of stink bug injury are dependent on the percent of bolls damaged. Heavy uncontrolled infestations of stink bugs can cause severe yield loss. Because stink bugs often do not appear in cotton fields until the later part of the growing season, damage is often concentrated in the upper portion of the plant. Historically, the percent yield loss attributed to stink bugs in Mississippi has been near zero. However, in more eastern states where boll weevil has been eradicated for a number of years, estimates of the amount of yield lost to stink bugs have ranged as high as 3.8%. And, it is anticipated that the importance of stink bugs will increase considerably in Mississippi in the coming years. Control: Effective control of stink bugs depends on the application of foliar insecticide sprays that are applied whenever infestation levels exceed the economic threshold. Currently, stink bug is an occasional pest of cotton, with fewer than 0.1 % of fields requiring treatment each year. Although there are some differences between the brown stink bugs and other stink bugs in susceptibility to certain insecticides, stink bugs are relatively easy to control with foliar sprays. However, fields located near plantings of alternate hosts harboring high numbers of stink bugs may require multiple insecticide treatments for adequate yield protection. Insecticides recommended for the control of stink bugs are listed in Table 7. Table 7: Insecticides Recommended for Control of Stink Bugs. Insecticide Trade Name Lbs ai/acre Acephate Orthene, etc 0.75 to 1.0 Cyfluthrin * Baythroid 0.025 to 0.033 Cyahlothrin * Karate 0.025 to 0.03 Dicrotophos Bidrin 0.4 to 0.5 Tralomethrin * Scout X-tra 0.018 to 0.024 Deltamethrin * Decis 0.019 to 0.03 Pyrethroid insecticides are less effective against brown stink bug species. Source: Cotton Insect Control Guide, 2002, Publication 343, Mississippi State University Extension Service Delta Counties - Gordon Andrews: Beneficial arthropods are increasing and pest populations remain low in fields observed in the delta this week. With rains, spider mite populations have declined and cotton plants have grown. Dead mites were observed on some leaves that appear to have died from a fungus. However, some live mites were still observed on the leaves the damage less damage was noticed to the new leaves on the plant. With the heat, it will be interesting to see if these mites and recover. Aphid infested plants were observed occasionally. Ladybird beetles are present in high numbers feeding on the aphids and on some leaves observed, only parasitized aphids were seen on the leaf. Plant bug numbers remain low in most fields. A few bollworm eggs were observed in a field at Tribbett, MS and one corn earworm moth was observed on Monday July 8th. No larvae were observed in terminals. On Thursday July 11th numerous bollworm moths (corn earworm) were observed in the same field, which happens to be next to corn. No eggs were observed in a sample of 280 terminals. These observations lead one to conclude that earworm moths are just starting to emerge from some corn fields. Our parasites and predators could provide us free insect control for a short time. Knowing what is in your fields will allow for good decisions from now until maturity. Corn Corner - Dr. Don Parker: Southwestern corn borer (SWCB) moth trap counts continue to decline across the state. The third generation of SWCB will begin around the first week in August (depending on the temperatures). It is important that producers realize that the third generation SWCB is normally responsible for the girdling of corn plants that results in lodging. If the stalks are still green during their emergence, the plants may serve as an overwintering site. I encourage producers to plan a timely harvest to avoid losses due to lodging. Check with your elevators and find out what moisture level they will require before receiving grain. It may be best to harvest at moisture levels near 20% to increase the ability to harvest all acreage on a timely manner. For more information: http://www.msstate.edu/Entomology/cornforum. 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 10, 2002   County Boll weevils Bollworms Budworms BAW no. per 33 traps no. per trap/week no. per trap/week no. per trap/week Coahoma   4.0 1.5 1.0 Tunica 1.0 6.0 26.5 2.0 Bolivar 0.0 9.7 0.7 2.0 Washington   23.0 0.0 5.0 Madison   0.0 4.0 5.0 Yazoo 1.0 1.5 6.5 13.0 Humphreys   17.5 13.0 30.0 Leflore   15.5 2.5 17.0 Carroll 0.0 12.0 0.0 15.0 Grenada 0.0 3.0 0.0 7.0 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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