Cotton Insect Situation

No. 5
June 6, 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 2 showed the crop as being 96% planted, 89% emerged, and 5% squaring. The 5-year average for this time period is 98% planted, 94% emerged, and 7% squaring. Temperatures were average for the week of May 27 through June 2, but statewide average rainfall was 0.8 inches above normal.

Insect Situation: There are still a few fields in the state that are young enough to be susceptible to thrips. However, under the warm conditions prevalent in June, these fields are developing quickly. Many fields will begin squaring soon. While the onset of squaring no longer signals the need for an insecticide treatment, it does signal the need to begin sampling for plant bugs. Low populations of aphids are present in some fields. Given the increased number of foliar thrips treatments that were applied to many fields this year, aphids may be more of a problem this year than they were last year. High numbers of spider mites have occurred in some fields and a few fields have required treatment for mites. These mite problems are the result of mites being present on weeds in no-till fields and then moving to cotton seedlings. In the Hill Region of the state it is not uncommon to see individual seedlings that are stunted and have reddish or bronzing cotyledons, stems, and leaves. Examination of these seedlings will usually reveal that the main stem has been "girdled" by the three-cornered alfalfa hopper (Any seedling disease or other injury that girdles the main stem can cause similar symptoms). Fortunately, these "hopper damaged" plants seldom constitute a very high percentage of the plant population and this damage is usually inconsequential. High numbers of snails (snails have shells, slugs do not) are being observed on cotton plants growing in no-till fields in the northern portion of the state. High populations (up to 30 to 50 per plant) have been observed on no-till cotton for many years, but we have yet to see snails cause any damage to cotton. Slugs are a different matter, they will feed on cotton and on very rare occasions, we have had stands lost to slug injury.

Boll Weevil Eradication Maintenance Referendum Scheduled for Region 2: This is the 5th , and final, year of the BWEP in Region 2 (South Delta Region). Growers in the South Delta need to pass an eradication maintenance program in order to be able to keep boll weevils from returning to their fields in future years. Ballots for this referendum will be mailed to cotton growers on July 8 and must be returned by July 19. Two meetings will be held to provide details of the referendum and an update on the progress of the Boll Weevil Eradication Program. Dates and locations for these meetings are shown below:

Belzoni Community Center 7:00 P.M. June 18

Rolling Fork Community Center 6:30 P.M. June 20

Boll Weevil Eradication Summary, 2001 Season: Mississippi made great progress toward its goal of eradicating the boll weevil last year. Across the state as a whole, 50% of all fields remained weevil free for the entire season, and only 25.9% of the fields captured enough boll weevils to trigger a spray of ULV malathion. Statewide, season-long boll weevil captures averaged 0.18 weevils per acre, and the average number of malathion sprays applied per acre was 1.2. These were on that 31.9% of the acreage (25.9% of fields) that received 1 or more treatments. The following table summarizes the data for the 2001 season by region.

Mississippi Boll Weevil Eradication Program Program: 2001 Summary

 
 
Region
#

 
 
Region
Name

 
 
2001
Acreage

 
2001
Assessment
Fee

% Fields with 0 Boll Weevils
Season-long

 

Fields
Sprayed

 

Avg. No.
Sprays/acre

 
 
Avg. no.
Weevils/acre

1

N. Delta

850,000

$22.00

46.8

29.6

1.3

0.18

2

S. Delta

258,000

$22.00

52.6

28.5

0.9

0.12

3

Hills

426,000

$24.00

44.9

28/0

1.4

0.25

4

E. Hills

78,000

$20.00

81.1

17.6

0.5

0.03

 

State

1,612,000

--

50.0

25.9

1.2

0.18

Information provided by Mississippi Boll Weevil Eradication Program

 

2002 Boll Weevil Eradication Program: For the week ending June 3, a total of only 2702 boll weevils were trapped on 1,175,965 acres of cotton, and 95.6% of all cotton fields were boll weevil free. The percent of fields with zero boll weevils ranged from 90.8% in the Rolling Fork Work Unit to 98.2% in the Aberdeen Work Unit.

Furadan Section 18?: Mississippi has again submitted a request for a Section 18 Emergency Exemption to allow use of Furadan 4F to control cotton aphids on cotton. As of June 6 EPA had not acted on this request. However, Texas has received a Section 18 Exemption to allow use of Furadan on cotton. Because of their earlier growing season, it is not unusual for Texas to receive notification on Section 18 request before Mississippi.

Two new insecticides, Centric (thiamethoxam) and Intruder (acetamiprid), are available for use against cotton aphids this year. Both of these products are highly effective against cotton aphids. Additional information on these new insecticides will be included in future newsletters.

Pest Profile: BOLL WEEVIL, Anthonomus grandis grandis

Historically, the boll weevil was the most important insect pest of Mississippi cotton. Boll weevil was considered a key pest of cotton, because the early season treatments that were necessary to control boll weevils destroyed beneficial insects and thus "flared" secondary pests, such as tobacco budworms and aphids.

As of the end of the 2001 growing season, statewide eradication efforts have reduced boll weevil numbers to extremely low levels, and it appears that complete eradication will be achieved within the next two years. Mississippi cotton growers no longer spray for boll weevils themselves, and only 32% of Mississippi’s cotton acreage was treated by the Boll Weevil Eradication Program (BWEP) in 2001. Fifty percent of Mississippi fields remained weevil free for the entire season, and no yield loss was attributed to boll weevils in 2001. Therefore, the primary concern for Mississippi cotton with respect to the boll weevil is to successfully maintain eradication, once it is achieved. The Hill Region of Mississippi passed a 10-year eradication maintenance referendum in 2001 and the remaining two regions of the state will vote on maintenance programs during the next two years.

A successful maintenance program will require the continuation of a vigorous pheromone trapping program on all cotton in the state. This is necessary so that any re-infestations of boll weevils can be promptly detected and eliminated before they have a chance to spread. Successful eradication maintenance will also require continued education of growers and scouts, so that they will be able to recognize and promptly report the presence of boll weevils and/or boll weevil damage in their fields. Successful eradication maintenance also requires continued, ready access to insecticides that are effective against boll weevils and can be used to eliminate any re-infestations that do occur. Because of logistical, environmental, and cost considerations, Malathion ULV has been the primary insecticide used in the BWEP, but a number of other insecticides are also effective against boll weevils (See Table).

Biology: Boll weevils overwinter as adults in ground trash and leaf litter around the borders of cotton fields. Overwintered adults emerge in the spring and enter cotton fields. These adults may feed on seedling cotton plants, but cannot begin reproduction until 1/3 grown squares (squares having a floral bud diameter of at least ¼ inches) are available. Both male and female boll weevils feed on cotton squares by chewing into the square with the small mandibles that are located on the end of their long snout. After feeding, female boll weevils will usually lay a single egg into the puncture and seal the puncture with a glue-like substance. Usually only one egg is laid per square, but boll weevils will also feed upon and oviposit in bolls, which can support the development of more than one larva. Female boll weevils lay approximately 150 eggs over about a 12-day period.

Under normal summer temperatures the eggs will hatch within three to five days. The legless, grub-like larvae complete three larval instars over a seven to eleven day period. During this larval development period, infested squares are usually aborted by the plant and the latter portion of the larval stage is completed within the fallen square. However, infested bolls are not usually aborted. Pupation occurs within the square or boll in which the larva developed. The pupal period lasts approximately four to seven days. Upon completion of the pupal stage the callow adults chew their way out of the square or boll in which they developed.

Newly emerged adults often congregate in open blooms, where they feed on pollen. Female boll weevils are able to begin laying eggs within three to five days after they emerge as adults. The average time for completion of one generation is approximately 21 days, and there are four to five generations per season. Because boll weevils have few natural enemies in Mississippi, the population increases dramatically with each generation. The shortening day lengths of late summer and early fall trigger boll weevils to enter diapause. Diapause-induced adults feed heavily on cotton during late season and then enter overwintering sites. Although most boll weevils enter overwintering sites relatively near the field in which they developed, boll weevils are capable of long-range wind assisted flight, and some boll weevils travel many dozens of miles before entering overwintering sites.

Damage: Adult boll weevils have chewing mouthparts located at the end of their long snout. Both sexes feed on squares (cotton floral buds) and bolls by chewing small holes into the fruit. Female boll weevils often deposit a single egg into the hole made by their feeding. Eggs hatch into legless larvae, which feed on the contents of the square or boll. Adult boll weevils also feed on pollen in open blooms, but this feeding does no damage. Squares are not attacked until they have attained a bud diameter of approximately ¼ inches. Feeding injury by adult boll weevils does not necessarily result in death of affected squares, but squares in which eggs are deposited are aborted by the plant once these eggs hatch and the larvae begin feeding inside the square. When they are present, squares are preferred over bolls, but bolls may sustain heavy damage during late season after square counts decline.

Yield Effects: In the absence of effective control efforts boll weevils have the ability to completely destroy a cotton crop. Historically, growers applied multiple, close interval insecticide treatments to keep boll weevil populations in check. Despite this heavy insecticide use, yield losses were still significant. Before the Boll Weevil Eradication Program was initiated in 1997 the estimated annual yield loss attributed to boll weevils ranged from 0.2% to 6.5%. Yield losses were historically higher following milder winters, which allowed higher survival of overwintering weevils. Yield losses also were historically higher in the Hill region of the state than in the Delta region and often exceeded 5% in the Hills. Beginning in 2000, and continuing in 2001, the eradication effort had reduced boll weevil populations to such low levels that no yield loss was attributed to this pest.

Pheremone Trap Counts:

            Trap reports for week ending June 04, 2002

 

County

Boll weevils

Bollworms

Budworms

BAW

no. per 33 traps

no. per trap/week

no. per trap/week

no. per trap/week

Coahoma

-

1

2

1

Tunica

0

1

9

3

Bolivar

0

1

16

14

Washington

-

0

11

4

Yazoo

0

19

24

8

Humphreys

-

34

3

20

Leflore

0

21

3

26

Carroll

-

31

28

7

Grenada

-

33

0

29

Madison

-

31

2

78

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