Cotton Insect Situation No. 14 July 26, 2001 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 Weather and Crop Report for the week ending July 23 showed that 88% of the crop was setting bolls. This is a bit behind last year, but matches the 5-year average exactly. Temperatures averaged 1 degree above normal across the state during the week of July 17-23, but statewide rainfall averaged 0.59 inches below normal. Boll Weevil Eradication Update: As of July 18, 87% of all Mississippi cotton fields have remained weevil free so far this year, and only 4.8% of the stateís cotton acreage has been treated for boll weevils. An average of 1.6 applications of ULV malathion have been applied to those acres that required treatment. (Information provided by Mississippi Boll Weevil Eradication Program) Spraying Cotton Less: Boll Weevil eradication and Bt cotton have worked together to greatly reduce the number of foliar insecticide treatments applied by Mississippi cotton growers. The following graph illustrates this reduction. (These data, which are from the annual Cotton Insect Losses Estimates compiled by National Cotton Council, do not include ULV malathion treatments applied as part of a boll weevil eradication program).   MS Insecticide Sprays   Stink Bugs: One consequence of the overall reduction in number of sprays is that stink bugs now have more opportunity to become established in cotton fields and to cause damage. Several species of stink bugs occur in cotton, but the three most common are the southern green stink bug, the green stink bug, and the brown stink bug. Historically, organophosphate and/or pyrethroid sprays targeted against other pests coincidentally controlled stink bugs and prevented them from becoming a problem. However, in low spray environments stink bugs can become a serious, but easily controlled, problem during mid and late season. It is especially important to be aware of the potential for stink bug problems in cotton once alternative crops, like corn, sorghum, and early soybeans begin to mature. When this occurs, high numbers of stink bugs can migrate into cotton fields quickly and cause significant damage to young maturing bolls. Stink bugs damage bolls by piercing the boll wall with their long stylets and feeding on the developing seed. External damage often appears as a small, dark sunken spot on the boll wall. Cracking damaged bolls will reveal stained areas of lint and/or small wart-like growths on the inside of the boll wall. Stink bugs can feed on bolls that are quite mature, but they prefer immature bolls that are approximately the diameter of a quarter. Damage results in bolls that appear "hard locked" or fail to open properly. Boll damage can occur any time of the season when bolls are present, but because stink bug populations are usually highest during late season, the top crop usually suffers the greatest damage. Stink bugs, especially the green species, can be difficult to spot during routine scouting. One good rule of thumb is to "get serious" about scouting for stink bugs anytime you see more than one in a cotton field. Keep in mind however, that stink bugs have a strong aggregation habit. So finding several within one small area of the field does not necessarily mean that they are that common throughout the field. Also keep in mind that stink bug numbers can often be heavy along one side of the field (usually the side nearest an alternative crop that is becoming unattractive), without being present throughout the field. The ground cloth is one of the best methods of scouting for stink bugs. Adult stink bugs will sometimes fly off while the cloth is being positioned and it is important to be observant and count any adults that you see fly off before the sample is taken. However, adult stink bugs are not as flighty as adult plant bugs, and if you donít disturb the plants too much when positioning the cloth, you will catch most of the adults that are present. Take a number of samples from several different locations in the field, and count adults and nymphs that are longer than º inch. Record counts as total number of bugs per 6 feet of row. Treat if counts average or exceed 1 bug per 6 row feet. One can also scout for stink bugs by careful visual examination of whole plants. The threshold using visual examination is 5 bugs per 100 plants. Another method of sampling for stink bugs is to scout for damage. To check for damaged bolls, randomly pull soft, immature bolls that are approximately the size of a quarter, crack the bolls open, and examine for internal damage. Signs of internal damage include stained lint, damaged seed, or small wart-like growths on the inside of the boll wall. Georgia entomologists have conducted several years of research on a damaged boll threshold and have recently adopted a threshold of 20% damaged bolls plus stink bugs present. At first this may sound too high, but many of these "damaged bolls" will still produce harvestable lint. Also, this threshold is based on sampling one age class of bolls, which represents only a fraction of the total boll population (ie., 20% damage to all the quarter-sized bolls in the field may represent a much smaller percent damage for the total boll population.                     Insecticides Recommended for Control of Stink Bugs Insecticide Lbs Ai/Acre # Acres Treated Per Gallon acephate (Orthene 97) 0.75 ñ 1.0 --- cyfluthrin (Baythroid 2E) 0.025 ñ 0.033 80 to 60 cyhalothrin (Karate Z 2.08E) 0.025 ñ 0.033 83 to 63 dicrotophos (Bidrin 8E) 0.4 ñ 0.5 20 to 16 methyl parathion 4E 0.5 8 deltamethrin (Decis 1.5E) 0.02 ñ 0.03 75 to 50 tralomethrin (Scout X-tra 0.9E) 0.018 ñ 0.024 50 to 37.5                   *pyrethroids are less effective against brown stink bug species.   Insecticide of the Week: Trade Name and Formulation: Intrepid 2F Common Name: Methoxyfenozide Producer: Dow AgroSciences (Rohm & Haas) Chemical Class: IGR, Diacylhydrazine Target Pest(s): Beet Armyworm, Loopers, Fall Armyworms, Use rate range: 0.06 to 0.16 lbs ai/acre (1 gal. to 33 acres to 1 gal. to 12.5 acres) Toxicity (rat/oral LD50 of technical product): > 5000 mg/kg This is the first year that Intrepid has been labeled for use in cotton, although it has had a Section 18 Emergency Exemption in past years. This product was originally developed by Rohm & Haas, but is now part of the Dow AgroSciences line. Intrepid is chemically similar to Confirm, which was also developed by Rohm & Haas, but has better overall activity than Confirm. Both of these compounds are IGRs (insect growth regulators) that function by triggering a premature molt in caterpillars that feed on treated foliage. Intrepid is active only on caterpillars. It provides no control of non-caterpillar pests, nor does it adversely affect beneficial insects. For an IGR, Intrepid is surprisingly quick acting, and has a "speed of kill" that rivals that of products like Tracer and Steward. Affected caterpillars stop feeding within a few hours after they ingest treated foliage. Intrepid is labeled for control of bollworms and tobacco budworms, but the rate required to control these pests, 0.25 to 0.38 lbs ai/acre, is very costly. However, the 0.06 to 0.1 lb ai/acre rate works well against beet armyworms and loopers, and at a cost of around $6 to $9/acre Intrepid is quite cost effective against these pests. As was seen earlier this year, Intrepid is also useful against other caterpillar pests, like saltmarsh caterpillars. One key advantage of Intrepid is that it can provide up to two weeks of residual control against beet armyworms and loopers. Intrepid also has potential as a tank mix partner with pyrethroids. Such a tank mixture would offer control of all caterpillar pests, except tobacco budworm, and some non-caterpillar pests, at a cost that would be competetive with the newer caterpillar products. The data shown below were collected by Larry Walton of Rohm & Haas Co. in 1998. This trial was conducted against a very heavy infestation of beet armyworms near Lula, MS. All rates are given as lbs ai/acre.   Beet Armyworm Control, Tunica, 1998   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.   Delta Counties - Gordon Andrews: Plant bugs seem to be the only game in town. Hopefully we can reach cutout before we see another buildup of plant bugs. Research shows that tarnished plant bugs do not do economic damage after 250 DD60ís (heat units) past Node Above White Flower 5 (NAWF5 or cutout). At the present cotton price 250 heat units (12 days at 21 heat units a day) past cutout is a conservative plant bug control termination time. In cotton field observed this week bollworm eggs have decreased. Where beneficial insects have been killed with insecticide applications for bollworms and plant bugs, aphids and whiteflies have increased. Some applications also killed the aphid and whiteflies. It will be interesting to observe how or if parasite and predator populations will rebuild behind these insecticide applications. Some insects have been observed at very low populations this week. Salt marsh caterpillars, beet armyworms, and fall armyworms are occasionally seen. We are reaching the time of the year when several foliage feeders can show up quickly. Keep looking at cotton that has cut out for foliage feeders. Southern Counties - Don Parker: Tobacco budworm/bollworm densities range from 6 to 20% in refuge cotton. Plant bug densities are below threshold in most fields but adults and nymphs are present. Several fields are approaching or have reached 5 NAWF. Producers should remember to calculate 350 to 400 degree-days beyond 5 NAWF before terminating insecticide applications. Northeast Counties - Mike Williams: It has been extremely quiet on the insect front in NE Mississippi cotton fields for the last few days. Thatís really good news, though Iíve had more than one farmer tell me that he doesnít always rest as well, wondering. The big thing to do now is remain vigilant, continue to look, but then trust what we are seeing and if itís nothing then be calm and wait. The intermittent rain showers, which come bring relief and help to assure the success of this crop. Letís hope they continue to come in a timely manner. We are seeing aphids in many of the fields, which were treated multiple times and have observed some honeydew in some of those fields. The disease is also present and is reducing the populations before they can spread. In fields, which have not been treated we are seeing almost no evidence of aphids. Tarnished plant bugs and stink bugs are probably one of the biggest concerns in NE Mississippi cotton at this time. (Dr. Layton has a good discussion on `bugsí in this newsletter.) Spider mites are cropping up in a few places, as well. Watch mite populations around edges of fields, or in areas of outbreak and spot treat them if they begin to expand. We also need to be aware of whiteflies and their danger to the crop. Look for them to begin appearing in the next few days in fields. Since the aphids havenít been bad this year, we donít really expect the whiteflies to be a problem either, but it pays to be aware. A number of scouts are reporting finding white eggs in fields, but upon return to the fields ñ no worms or eggs. This is a good sign that beneficial arthropods are taking the populations of Lepidoptera out for us. A 20 to 30% egg lay can be easily handled by the numbers of beneficial arthropods Iím seeing in fields. Check and check again in a day or so to make sure the critters are doing their jobs, but we need to rely on them as much as we can. Itís just another way to save money. Most of the moths we are catching and most we are seeing in the fields are bollworms, so a pyrethroid application might resolve your problem when it does get too big for the beneficials. You can really help your boll weevil cause by asking friends not to grow ornamental cotton for the next year or so. The presence of small numbers of boll weevils in isolated areas seems to point to the possibility that we have small plantings of cotton not being trapped or treated. These are almost impossible to find. Cotton in a yard or garden can be a source of weevils which might cause the treatment of 100ís of acres of cotton at no small expense.   Avg. No. Moths/Trap/Week County Budworms Bollworms Beet Armyworms Boll Weevils Attala 7 55 0 0 Bolivar 5 20 2 0 Calhoun 3 24 1 0 Chickasaw 25 0 2 0 Choctaw 0 53 0 0 Clay 33 56 0 0 Coahoma 15 17 1 0 Hinds 0 8 0 0 Holmes 15 7 0 0 Humphreys 8 59 0 0 Issaquena 7 34 10 0 Lafayette 4 1 1 0 Lee 11 51 2 0 Leflore 21 44 4 0 Lowndes 6 9 0 0 Madison 0 27 0 0 Monroe 9 24 0 0 Noxubee 1 0 0 0 Quitman 0 27 4 0 Sharkey 19 38 9 0 Sunflower 21 158 4 0 Tallahatchie 8 64 0 0 Tunica 5 26 6 0 Union 2 30 3 0 Warren 6 26 1 0 Washington 2 33 1 0 Webster 5 12 1 0 Yazoo 20 68 15 0 Southern Counties - Don Parker: Tobacco budworm/bollworm densities range from 6 to 20% in refuge cotton. Plant bug densities are below threshold in most fields but adults and nymphs are present. Several fields are approaching or have reached 5 NAWF. Producers should remember to calculate 350 to 400 degree-days beyond 5 NAWF before terminating insecticide applications.

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