Cotton Insect Situation

No. 4
May 30, 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

Cotton Insect Hotline: The Cotton Insect Hotline has been activated for the 2002 growing-season. This is a toll free number (1-800-445-4931) that provides a 3 to 5 minute update on current cotton insect issues. The hotline is updated 1 to 2 times per week, depending on need. Topics covered on the hotline include current and developing pest problems, new insecticides, section 18 labels, efficacy trial results, scouting and decision making tips, and much more. The hotline is sponsored by the Cotton Foundation and the National Cotton Council.

Crop Situation: The Weekly Weather and Crop Report for the week ending May 26 showed the crop as being 93% planted and 84% emerged. The 5-year average for this time period is 96% planted and 83% emerged. The crop is pretty much on schedule, as far as planting goes, but the recent cold temperatures have delayed development. The week of May 20 through 26 was cool and dry with statewide temperatures averaging 7 degrees below normal and statewide rainfall averaging 1.03 inches below normal.

Where’s the Boll Weevil Trap?: By now all cotton fields that are planted and emerged should have boll weevil traps around them. Some fields will have traps every 350 feet around the field border, and others will have traps every 600 feet; but there should be at least one trap around every field. If you know of cotton fields that are not being trapped, please let BWEP personnel know immediately!

Where Can I Get a Good Sweepnet?: The sweepnet is the most effective method of sampling pre-blooming cotton for adult plant bugs. However, most ‘insect nets’ are not sturdy enough for repeated commercial use. You need a good sturdy net with a durable bag and a 15-inch diameter, spring-steel hoop. The following three suppliers carry such nets (However, it is not our intention to endorse these over other, similar quality nets). A good scout will wear out a "bag" pretty quickly, so you may want to order extra bags when you order your net. Able Industries, (559-651-8150), - $25.00; Ben Meadows, (1-800-241-6401), - $19.50; Gemplers, (1-800-382-8473), - $39.00

2002 Cotton Insect Scouting School Schedule

County

City

Site
(phone number)
Contact

Date

Time

Lee

Verona

NE MS R&E Center
(662-841-9000)
Clint Young

Mon.
June 3

9:00 – 12:00 AM

Washington

Stoneville

B. F. Smith Auditorium
Delta Research and Extension Center
(662-332-0524)
Guy Wilson

Tues.
June 4

9:00 – 12:00 AM

Plant Bugs In Perspective: Heavy use of Bt cotton and the boll weevil eradication effort have resulted in a sharp reduction in the average number of foliar sprays applied to cotton. Overall this is very positive, but it has resulted in less coincidental control of plant bugs, and this, in turn, has resulted in an increase in the need to treat specifically for plant bugs, especially during mid and late season. Last year was the first year that boll weevil treatments were greatly reduced throughout the Delta and plant bug numbers were definitely up. This trend will likely continue, but it is important to keep the plant bug issue in perspective.

Although plant bug numbers were much higher than normal last year, especially in the Delta, it was also obvious by mid-August of last year that the plants had set a bumper cotton crop! The fact that unusually heavy rainfall in late August and early September caused huge losses to boll rot should not be blamed on the plant bugs. The final statewide yield of 708 lbs. lint per acre was not that much lower than the previous five-year average of 761lbs of lint per acre. This was despite having several hundred thousand more acres of cotton than normal, much of which was on marginal ground and under marginal care, and despite the fact that many fields sustained losses in excess of 25% to boll rot.

The point of this discussion is not to discount plant bugs as being important pests of cotton. They certainly are. They are, and will continue to be, the key pest in our current system. But we do need to recognize that their overall yield damaging potential is simply not as great as that of boll weevils, bollworms or budworms.

We can expect to see an overall increase in plant bug numbers in a post-boll weevil eradication/Bt cotton system. But it is important to realize that because the plants are losing fewer squares to boll weevils and caterpillar pests, they can actually tolerate higher plant bug numbers. This will help to at least partially offset the increased plant bug numbers. Still, when plant bug populations reach threshold numbers it will be important to treat them in a timely and effective manner.

Pin-head Square Sprays Were for Boll Weevils: Back in the days when boll weevils were a wide spread problem, "pin-head square sprays" were a routine part of cotton production. Pin-head square sprays were a great tool for boll weevil control, because they killed a very high percent of the overwintered boll weevils before they had a chance to lay eggs.

In the absence of boll weevils, some folks may have trouble giving up these pin-head square sprays. It’s just such a strong tradition to spray cotton as soon as it reaches that five to six leaf stage. After all, there’s still plant bugs, right? But, there’s a big difference between boll weevils and plant bugs. With boll weevils, most of the weevils that are going to come into the field that season have already arrived by pin-head square time. With plant bugs, most of the bugs that will enter the field that season will do so after pin-head square time.

Granted, there is a pretty good chance that most fields, at least in the Delta, will need to be treated for plant bugs one or more times between first square and first bloom. But the odds of this happening at pin-head square are slim. There is a much better way to time plant bug treatments - get your consultant to make sweepnet counts and to take percent square retention counts. Having this information makes it easy to determine whether or not a field needs to be treated for plant bugs and when those treatments need to be applied, and this results in fewer sprays and better control.

During the first two weeks of squaring the plant bug treatment threshold is 8 bugs per 100 sweeps. If a field has this number of bugs present at pin-head square time, it needs to be sprayed.

Pest of the Week: Tarnished Plant Bug: Lygus lineolaris

Tarnished Plant Bug (TPB) is an important pest of cotton throughout Mississippi. However, it is relatively more important in the Delta Region of the state than in the Hills. TPB is considered a "key" pest of cotton because it often reaches treatable levels during the early portion of the season and insecticides applied to control these early plant bug infestations often flare populations of secondary pests, such as aphids or tobacco budworms. Before boll weevil eradication the importance of TPB as a key pest of cotton was overshadowed by the boll weevil. Due to the success of the boll weevil eradication effort and the wide spread adoption of Bt-cotton, the importance of TPB has increased significantly in recent years. Not only have boll weevils and budworm/bollworm declined in importance, but the reduction in sprays applied to control these pests resulted in less coincidental control of TPB. As a result, the number of sprays required specifically to control TPB has increased in recent years, especially in the Delta.

Biology: TPB has an extremely wide host range, and develops on most row crops, as well as a large number of weed hosts. Plants bearing large numbers of floral buds are especially preferred. This insect overwinters as diapausing adults, but, in the Mid-South, reproduction may begin in late winter on winter weeds such as henbit and curly dock. Subsequent generations are produced on spring-blooming weeds, such as fleabane and coreopsis. These spring hosts can support high densities of TPB, which are forced to migrate as these plants mature. Heavy migration into cotton fields can occur at this time, but much of this population also moves into other crops or weed hosts. TPB complete several generations per year, and heavy migration into cotton can occur at any time of the season, depending on the proximity of cotton fields to other crops or alternate hosts. Intensity and duration of movement into cotton varies considerably from year to year and appears to be related to abundance of alternate hosts and availability of flower buds on these hosts. Large numbers of TPB are often noted moving into cotton fields when dry conditions or natural senescense causes a decline in blooms on alternate hosts, or when mowing or tillage operations destroy such hosts.

The eggs are inserted into plant tissue, such as stems and petioles. Eggs hatch in approximately 8 days, and it takes approximately 17 days to complete the five nymphal instars. There is also a pre-oviposition period of approximately 8 days, and it is during this time that TPB are most likely to move from one crop to another.

Damage: TPB have piercing-sucking mouthparts. Although they will feed on vegetative plant parts, they prefer to feed on developing flower buds or immature fruit. Feeding is accompanied by the injection of salivary enzymes into the plant, which liquefy and pre-digest the plant tissue.

Although pre-squaring cotton is not particularly attractive to TPB, terminals can be killed when fed upon by adults, causing a loss of apical dominance and development of numerous secondary terminals, a condition referred to as ‘crazy cotton’. Feeding on small squares (approximately 1/8 inch or less) usually results in ‘blasted squares’ that abscise within a few days, leaving an abscission scar at the point where the square was attached to the fruiting branch. Feeding on larger squares results in damage to developing anthers. Depending on severity of damage, larger squares may abort, but more commonly remain on the plant and develop into a bloom.

Although TPBs have a strong preference for squares, they will also feed on bolls, especially during late season, when squares are less available. The severity of boll damage depends on boll age. External signs of boll damage are dull, dark colored slightly sunken lesions on the outer boll wall. Close examination of such lesions often will reveal a glossy, pin-point sized spot at the site where the boll wall was punctured. Small to medium sized bolls often contain a translucent, jelly-like material at the site where salivary enzymes have been injected into the developing boll. Bolls damaged in such a way may eventually abscise, or fail to open. On larger bolls with more developed lint, feeding by TPB rarely destroys the entire boll, but may result in damaged seed, discolored lint, and reduced weight of harvestable lint.

Yield Effects: Although excessive damage by TPB can result in yield losses or delays in maturity, the overall yield damaging potential of TPB is considerably less than that of pests such as boll weevils or budworm/bollworm. This is because cotton plants can tolerate 20 to 25% early season square-loss without suffering yield loss. Still, prolonged heavy TPB infestations can result in substantial yield reductions. In research plots, yield reductions of 15% to 55% have been documented for plants infested with one to four bugs per plant. However, these numbers are much higher than established economic thresholds. During the past ten years, estimated annual yield losses attributed to plant bugs in Mississippi cotton have ranged from 0.2% to 3.6%, with losses as high as 4.7% being reported for the Mississippi Delta.

Control: During the pre-bloom stage of cotton development, adult TPB, which are migrating from senescing spring hosts, are the primary target of control. Insecticides are recommended when scouting results indicate that populations have exceeded the economic threshold, which varies from eight to fifteen bugs per 100 sweeps, depending on week of squaring. During mid and late season, insecticide applications may be required to control mixed populations of adults and nymphs. During some years, infestations can reach 50 to 100 bugs per 100 plants, which is well in excess of the threshold of 15 bugs/100 plants. Effective control of such heavy infestations requires multiple applications of effective insecticides at five to seven day intervals. Plant bugs can be difficult to control, especially in the Delta where resistance has been documented to pyrethroid insecticides, as well as to carbamates and many organophosphates. Insecticides recommended for control of TPB are listed below.

Insecticides Recommended for Control of Tarnished Plant Bugs.

Insecticide

Trade Name

Lbs ai/acre

Acephate

Orthene

0.25 to 0.5

Dicrotophos

Bidrin

0.4 to 0.5

Imidacloprid

Provado

0.047

Malathion ULV

Fyfanon

0.92 to 1.22

Methamidophos

Monitor

0.33 to 0.5

Oxamyl

Vydate

0.25 to 0.33

Profenofos

Curacron

0.25 to 0.5

Thiamethoxam

Centric

0.047

Source: Cotton Insect Control Guide, 2002, Publication 343, Mississippi State University Extension Service

Mike Williams, Northeast Mississippi:

Cotton is slowly emerging in most of NE Mississippi. The early planted crop has seemingly waited on the later planted, it's all about the same size now and just beginning to grow. A number of acres in NE Mississippi are having to be replanted. The area has gotten fairly dry in places, but rainshowers are resolving much of that problem. Warm weather is what this crop needs. Thrips have been abundant in some fields and some of the systemic insecticides have not worked to full satisfaction. It is time to begin thinking about tarnished plant bugs in the crop and to scout for them. Sweepnets are the best method for scouting young cotton for adult bugs. Monitor the plants closely for square initiation and loss and follow threshold guidelines for treatments. Below 80% square set and more than 8 bugs per 100 sweeps will warrant a spray application in young cotton.

Pheromone Traps:

Trapping has begun for the summer and we have two modified trap lines in place. The West Delta line runs circular up Highway 61 from Clarksdale to Tunica and back down Highway 1 to Greenville across to Leland and up to Clarksdale. Boll weevil traps are concentrated in two locations, one in Tunica and north Coahoma counties and the other south of Rosedale. Lepidoptera traps are located along the line approximately 2 per county. The west delta counts will begin reporting in next week's CIS report.

East Delta trapping begins in the Canton area and runs across to Yazoo City and Belzoni then up to Greenwood and on to Holcomb. The weevil traps are located in ten-mile stretches between Canton and Yazoo City on Highway 16 and north of Greenwood on Highway 7. The Lepidoptera traps are located along the trapline at approximately 2 per county.

            Trap repots for May 29, 2002

 

County

Boll weevils

Bollworms

Budworms

BAW

no. per 33 traps

no./Trap

No./Trap

no./Trap

Yazoo

2

1

1

0

Humphreys

-

14

3

26

Leflore

9

3

0

15

Carroll

-

0

1

42

Grenada

-

10

3

8

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