Cotton Insect Situation

Pre-Season Issue
February 12, 2001

Blake Layton
Extension Cotton Entomology Specialist

Area Specialists:
Dr. Gordon Andrews
 Dr. Mike Williams

Cotton Insect Hotline: 1-800-445-4931

Advanced Cotton Pest Management Short Course: The Advanced Cotton Pest Management Short Course is Scheduled for March 13 and 14 of 2001. The purpose of this training is to provide detailed information on the biology, management, and control of the insects, diseases, and weeds that affect cotton. The training is approved for consultant license renewal and CCA Training Credits.

Advanced Cotton Pest Management Short Course

Begins: 10:00 AM, March 13, 2001 (registration begins at 9:00 AM, $15.00)

Ends: 12:00 AM, March 14, 2001

Location: Bost Building, Theater, Mississippi State University

Program Outline:

10:00 - 12:00, AM, March 13: Plant Pathology Session

1:30 - 5:10, PM, March 13: Entomology Session

8:00 - 12:00 AM, March 14: Weed Management Session

Subscription Renewal Cards: Please complete and return the enclosed card if you would like to continue receiving the Mississippi Cotton Insect Situation Newsletter in 2001. Also, if you know someone who would like to have their name added to the newsletter mailing list, they can do so by calling 662-325-2085, or by sending their name and address to: Cotton Insect Situation Newsletter, Box 9775, Mississippi State, MS 39762-9775.

Review of 2000 Cotton Entomology Season: Each year each cotton producing state prepares a summary of the cotton insect season for inclusion in the Proceedings of the Beltwide Cotton Conference. These summaries provide a historical record of cotton insect pressure. A copy of the summary for last year in Mississippi is enclosed. One can also access summaries for the past eight years by going to the MSUCARES Cotton Insect Web Site (www.msucares/insects/cotton) and selecting "Annual Summaries of Mississippi’s Cotton Insect Season" from the menu at the bottom of the page. (http://www.msucares/insects/cotton/annualsum.html)

 

Review of the 2000 Cotton Insect Season in Mississippi
Blake Layton
Extension Cotton Entomology Specialist
Mississippi State University

Mississippi: Mississippi cotton producers planted approximately 1.3 million acres of cotton in 2000. Approximately three of every four of these acres were planted to Bt-transgenic varieties.

Mississippi entered the new millennium with active boll weevil eradication programs (BWEP) underway in all regions of the state. The East and West Hill Regions both began eradication efforts in 1997, so this was the fourth year of BWEP on the 475,000 acres located in the Hill Region of the state. The South Delta Region, approximately 223,000 acres, was in its third year of eradication, and BWEP was initiated on the approximately 590,000 acres in the North Delta Region in the fall of 1999.

Since it began, Mississippi’s BWEP has faced some very significant environmental and production changes that have made BWEP much more challenging. These include: a series of unusually mild winters, which resulted in higher overwintering survival; introduction and widespread planting of Bt-cotton, which requires fewer grower applied treatments of products that provide coincidental control of boll weevils; and the introduction of new, more target specific insecticides, which do not have activity against boll weevils. Despite these unprecedented challenges, Mississippi’s BWEP has made excellent progress toward the goal of eradicating the boll weevil from the state, and no economic yield loss was attributed to boll weevils in 2000. The average number of BWEP treatments applied to fields in the Eastern Hills, Western Hills, South Delta, and North Delta was 3.1, 5.0, 3.0, and 6.8, respectively. These treatments were applied based on pheromone trap captures and a treatment criterion that triggered treatment on any field in which the total weekly trap capture reached two or more weevils.

Although planting was delayed initially because of unusually cool weather in April, May was warmer and drier than usual, and planting was completed ahead of normal schedule. Unfortunately, this hot, dry weather persisted throughout the remainder of the season. May was also unusually windy, and this combination of weather resulted in unusually heavy thrips pressure throughout most of the state. Fields that did not receive in-furrow insecticide treatments at planting time usually required multiple foliar treatments to control thrips, and fields that did have an in-furrow thrips treatment often required a supplemental foliar spray. There were numerous reports of "hard to kill" thrips and some speculation that this was because of an unusually high abundance of western flower thrips. While it is true that thrips collected from treated fields were more likely to be western flower thrips, continuous heavy re-infestation, due to the windy conditions and high thrips populations, seemed to be the primary cause of the thrips control problems encountered in 2000.

There were also a number of unusual pest problems on seedling cotton in 2000. Sugarcane beetle was observed destroying seedling plants in several fields. This was not an especially severe or wide-spread problem, and is noted simply because it was unusual. The damage was caused by the adults, which cut the seedlings one to two inches below the soil, resulting in a distinctive ragged or shredded appearance of the cut stem. Usually all plants in a "hill" were affected, and a few fields were so heavily infested as to threaten stand loss. These infestations of sugarcane beetle occurred in both reduced-till and conventionally tilled fields.

A number of no-till fields experienced heavy infestations of false chinch bugs (Nysius spp.), which caused death of seedling plants, and in some cases, resulted in severe stand loss. The injury resulted when aggregations of nymphs and adults, up to 50 or more, fed on seedling plants, essentially sucking the small seedlings dry. As soon as a plant or hill of plants began to die, the insects would move to nearby healthy plants. A few fields were treated for false chinch bugs, and there were some reports of control difficulties.

Extremely heavy numbers of negro bugs (Family: Thyreocoridae) also were observed in many reduced tillage fields. Numbers often exceeded 10 to 20 bugs per plant, prompting concern over the potential for this insect to cause damage. Adults and nymphs could be found resting on the foliage, as well as in the seed drill, below the soil line, but these insects did not appear to cause damage to seedling cotton plants. However populations of negro bugs and false chinch bugs often occurred in the same fields, resulting in some confusion over which insect was causing the damage.

Infestations of cutworms were also more common than usual, and few fields required multiple foliar insecticide applications to control cutworms. In particular, granulate cutworms, (Feltia spp.) were more abundant in 2000.

Injury to seedling plants caused by the threecornered alfalfa hopper (Spissistilus festinus) was also reported from a number of locations in the state. The damage was similar to that caused by this insect in soybeans. Usually, the first symptom observed was a reddening and stunting of individual seedlings. Initially this injury was often mistaken for herbicide injury, but closer examination would reveal a sunken necrotic ring that completely surrounded the main stem. Usually this "girdled" area was located within one to two nodes of the first true leaf. Affected plants were often concentrated along the edges of fields, although field wide infestations were observed in some small, limited tillage fields. Once plants reached the five to six leaf stage girdling of the main stem usually ceased, but girdling of leaf petioles could often be observed. Depending on the age of plants when first attacked, girdled plants were either killed, severely stunted, or recovered. Overall, this early damage by three cornered alfalfa hopper did not appear to have any significant effects on yield.

Because early season boll weevil eradication treatments of ULV malathion often provided coincidental control of tarnished plant bugs, early season infestations of this pest were somewhat lower than normal. However, much of the Delta experienced mid-season plant bug infestations that required treatment. Plant bug infestations were much lower in the Hill region and relatively few fields in this region required treatment for plant bugs.

Compared to past years, bollworm and tobacco budworm pressure were both unusually low throughout most of the state. Statewide, approximately 0.9 foliar sprays per acre were applied to control these pests. This is less than the estimated 1.27 sprays per acre required for these pests in 1999, and is approximately one-third of the number of sprays required in the two years before 1999. Only 380,000 acres of corn were harvested in Mississippi this year and this relatively low corn acreage is thought to be one of the primary reasons for the low bollworm numbers. Heavy use of Bt cotton varieties is of course the reason for the generally low tobacco budworm numbers.

However, it must be noted that extremely heavy tobacco budworm infestations were experienced on some of the non-Bt cotton grown in the North Delta region of the state. Several consultants reported near 100% infestation levels and some fields required seven or eight applications for control of tobacco budworms. This was the first full season of the BWEP in this portion of the state, and destruction of beneficial insects due to multiple applications of ULV malathion likely contributed to the increased tobacco budworm problems experienced in these non-Bt fields. Fortunately, growers in this region anticipated the flaring of secondary pests, which often occurs during the early years of BWEP, and increased their plantings of Bt varieties in 2000.

In contrast, growers in the Hill region of the state began to experience some of the benefits that boll weevil eradication can provide in terms of secondary pest problems. Although, boll weevil eradication is not yet completed in this region, there were many fields that were boll weevil free in 2000 and did not require treatment for boll weevils. This allowed beneficial insect populations to remain in the field and help control other pests. Although non-Bt fields in the Hill region received an average of approximately 1.7 sprays per acre for control of bollworms and tobacco budworms, compared to 3.2 sprays in the Delta, there were a number of fields of non-Bt cotton grown in the Hill region, which did not receive any insecticide treatments for control of caterpillar pests. Based on results of an end of season survey, only 5.9% of the Bt fields grown in the Hill Region received insecticide applications to control bollworms. Approximately 47% of the Delta Region Bt fields received one or more bollworm treatments.

Because of concern over the potential for increased problems with beet armyworms, which often occur during the early years of BWEP, Mississippi sought and obtained approval to use Denim (emamectin benzoate), Steward (indoxacarb), and Intrepid (methoxyfenozide) against this pest under Section 18 Emergency Exemptions. The unusually hot dry conditions that persisted through out the season resulted in increased concern over the potential for beet armyworm problems. Fortunately, only a relatively small amount of acreage required treatment for beet armyworms in 2000. However, it must be observed that Bt cotton does provide some suppression of BAW, and most of the non-Bt fields in those areas of the state that were most prone to beet armworm outbreaks received multiple applications for control of tobacco budworm. In most cases the insecticides used to control tobacco budworms were products that also have activity against beet armyworms.

Fall armyworm was a more wide spread problem than beet armyworm in 2000, but still did not cause excessive amounts of yield loss. However, treatable fall armyworm infestations occurred much farther north in the state than normal and many consultants had their first experiences with this pest. Interestingly, treatable fall armyworm infestations were more common on Bt cotton than on non-Bt varieties. Presumably, this was because non-Bt fields received more treatments for bollworm and tobacco budworm and the products used to control these pests provided coincidental control of fall armyworms. Treatment decisions were often difficult to make in Bt cotton because some fields had relatively high numbers of small caterpillars that declined without requiring treatment or causing damage, while other Bt fields sustained significant levels of boll damage. It appears that there is considerable variation in the susceptibility of currently available Bt varieties to this pest.

Cotton aphid populations were low in the Hill Region of the state, with very few fields requiring treatment. However, approximately two-thirds of the fields in the Delta Region required treatment for aphids. The portion of treated fields was particularly high in the North Delta, which was involved in the first full season of BWEP. This agrees with observations from past years, in which regions involved in the first full year of BWEP received more treatments for cotton aphids. Furadan (carbofuran) and Centric (Thiamethoxam) were available for use under Section 18 Emergency Exemption. Both of these products are effective against cotton aphids and their availability helped keep aphid induced yield losses to a minimum.

Bandedwinged whiteflies required treatment in a few fields in areas that received numerous early and mid-season applications of ULV malathion as part of the BWEP, but overall populations of this pest were relatively low. Treatable populations of silverleaf whitefly (Bemesia spp.) were observed in two counties in the extreme southern portion of the state. These counties have a thriving commercial nursery industry, and cotton is often grown in close proximity to commercial nursery crops, resulting in an opportunity for whiteflies to move between these two crops.

The severely dry conditions were favorable to spider mite problems and a number of fields in the Delta Region of the state and some portions of the Hill Region required treatment for this pest. Although the incidence of spider mites seems to have increased in recent years, spider mites continue to remain a minor pest.

The unusually mild winter combined with the reduction in foliar sprays associated with the progress of BWEP and the planting of Bt cotton resulted in increased populations of stink bugs and an increased awareness of this pest by consultants and producers. A number of fields were treated for stink bugs in 2000, but very little yield loss was attributed to this pest.

In summary, the 2000 growing season was unusually hot and excessively dry. These adverse growing conditions resulted in disappointing yields, and low yields combined with low prices resulted in a generally disappointing year for most producers. Fortunately, overall insect populations were relatively low in 2000. Insect induced yield losses were estimated at 4.5%, and, excluding BWEP sprays, the estimated number of foliar insecticide treatments per field was 3.5. Still, because of fees associated with boll weevil eradication efforts and use of Bt cotton, the estimated costs of insect control were substantial at $91.07 per acre.

A black line that separates the body text from footer information