Caterpillar pests persist in many cotton fields although their numbers have declined considerably in the last week. The threat of large numbers of bollworms moving out of corn and into cotton has yet to be realized although there have been some infestations in the 20,000 to 40,000 per acre range. Most fields have seen considerably less pressure, perhaps 2,000 to 12,000 per acre. Beet armyworm and looper problems are winding down with the exception of some fields in the northwestern area of the High Plains. Aphid infestations are quite variable but there has been a trend toward increased numbers recently as producers finish up their worm applications.

Boll weevil numbers are at menacing levels with dramatically increased activity predicted just over the horizon. Much of the cotton is safe from yield losses due to this pest but late fields will feed a lot of weevils and they will find cozy sites to pass the winter. The eradication programs are closing in on the diapause phase of eradication again this year, after successfully battling weevils during the early and mid season periods.

There are a lot of western flower thrips out there in the cotton patch but research has indicated that they will not impact yield. They could help control some developing spider mite problems though.

Has the Fat Lady Sung?

This year’s cotton crop is generally coming in early, like it or not. Continuing hot, dry conditions have pushed many cotton fields to the limit with only those fields with a light boll load, or late planted, or under sprinklers with lots of available water, able to hang on to most of their boll load. Otherwise, the vast majority of fields hit cutout early and hard and have shed most of their late fruit. These fields are no longer attractive to insect pests although aphids could still be a challenge.

The remaining fields with squares, blooms and small bolls will bear the brunt of the last hurrah of insects for the 2000 growing season. Some areas have seen recent increases in aphids, beet armyworms, loopers, bollworms, lygus bugs and boll weevils; although not necessarily all in the same field. And western flower thrips have been the heaviest I have ever seen.

We are in the short rows of 2000. Just hang on a little while longer. And don’t spend any more than you have to on insect control in the remaining weeks. Most late season investments in pest control do not provide high returns.

Boll Weevils Moving Into Lusher Fields

Trap catches of boll weevils went down this past week compared to the previous week and compared to the same week in 1999 (Tables 1 & 2). This will only be a temporary reprieve as higher trap catches are expected as we move through September and October. Most of these weevils are still "reproductives" although a few are achieving diapause status and will be ready to enter overwintering sites as soon as they accumulate some fat. But these weevils will most likely fail to live long enough to see squaring cotton next year. Probably most of our surviving overwintered weevils come from weevils that enter overwintering sites in October. This would put them in cold storage for about 7-8 months on average. Definitely a long time to go without a meal!

Punctured square and boll counts have continued to escalate to high levels in late fields. Remember to stop using square damage and rely on punctured boll counts alone. Check bolls that are about the size of a quarter. Once a field approaches a count of 15% punctured bolls, and there are a sufficient number of undamaged bolls remaining that have a good chance of being taken to harvest, start spraying for adult weevils. It may take 1, 2, 3, or more applications on a 4-5 day schedule to protect the remaining fruit. It will take over 6,000 undamaged, potentially harvestable bolls to pay for a single application. This would be a boll every 10 plants in 60,000 plants per acre cotton or a boll every 2-2.5 row feet on 40 inch rows. Insecticides to use for boll weevils alone would be methyl parathion, Guthion, or ULV malathion. Don’t use the EC formulation of malathion, it doesn’t work.

Table 1. Total boll weevils caught per week and percent of traps catching boll weevils since April 24, 2000 in the GRID trapping program.*

*Includes three counties in the Rolling Plains.

Table 2. Comparison of average weekly boll weevil trap catch in the Southern High Plains/Caprock Zone between 1999 and 2000.*

*These data represent the average number of weevils caught per trap catching weevils. Zeros are not counted.

The big gainers for this week were Crosby, Floyd and Lubbock counties (Table 3). The big losers as far as reductions compared to last year were Andrews, Dawson, Deaf Smith, Gaines, Howard, Lamb, Lynn, Martin, Terry and Yoakum counties. Again, this is both a reflection on the eradication program and the continuing expansion of the boll weevil problem in zones yet to be activated.

Table 3. Week 34 (week beginning August 21)— Accumulative average number of boll weevils caught per trap in the GRID trapping program starting with week 18.

This data represents the average number of weevils caught per trap catching weevils. Zeros are not counted. Refer to the Plains Cotton Growers, Inc. web page for actual total numbers caught and percent of traps catching weevils each week.

*Includes traps both inside and outside active eradication zones.

Eradication Update

The Texas Boll Weevil Eradication Foundation (TBWEF) is less than a week away from when it can launch the full diapause phase of the eradication program. If secondary pest problems are deemed enough of a concern, then the TBWEF could hold off another week. With more weevils moving around the area, trap catches are expected to go up in active zones and the big reductions recorded thus far could begin to decrease under this pressure.

After 34 weeks of trapping, the GRID indicates an overall reduction of 50% for the Northwest zone, 84% for the Western zone, and 68% for the Permian Basin zone (Table 3). A season long increase of 6% has been recorded for the Northern High Plains zone and 1% for the Southern High Plains/Caprock zone. These differences will begin to increase exponentially as the end of the season approaches. As Table 4 indicates for the Northern High Plains zone, boll weevils got off to a slow start with less than half the number of emerging weevils in 2000 compared to 1999. Thus far, weevils have increased to levels that have compensated for their slow start.

Table 4. Grid trap catches 1999, 2000. Northern High Plains Zone. Total number of weevils caught in all traps.

*8 week trapping period

**7 week trapping period

A better comparison might be made looking at Gaines, Hale and Floyd counties. Gaines County is my best case scenario where a multiple year history of serious weevil problems has been turned around in less than one year of eradication program activities (Table 5). A reduction of 86% has been recorded for Gaines County while weevil trap catches have increased by 14% in Hale and 71% in Floyd counties. Information in this table was provided at two referendum education meetings last week in the Northern High Plains zone.

Table 5. Average total number of boll weevils caught per trap during 16 week period (weeks

18-33). Texas.

Table 6 provides Foundation data on the total accumulated acres sprayed, average number of boll weevils trapped (both in 2000 and in 1999) and beet armyworm trap activity. Basically, Foundation traps are showing significant reductions in boll weevil numbers compared to 1999 (about 97% for the past week). Their beet armyworm trap catches show increases in all three zones, with the highest catches in the Northwest zone. This is also the zone with the most new beet armyworm activity in fields.

Table 6. High Plains Eradication Program weekly report for week ending August 20.

* = 1999

Beet Armyworm and Looper Problems Declining

While new beet armyworm (BAW) egg lays have continued for the area northwest of Lubbock, much of the other areas has fewer BAW problems than in previous weeks. This is largely due to the condition of most fields (cutout and under moisture stress). Looper numbers are also on the slide although looper moth activity has been of biblical proportions in some fields. BAW trap catches are up in the northern areas, indicating that egg laying pressure is not finished but the yield impact threat is rapidly diminishing. While some boll feeding is occurring, a lot of feeding of BAWs is now concentrated on leaves, flowers, squares, and bracts of bolls and squares. There is considerable outer boll wall (carpel wall) feeding in some cases. None of this is going to affect yield. An insecticide application on such infestations will affect your wallet.

Some fields have soybean loopers rather than the more common cabbage looper (see last week’s FOCUS for pictures). While the soybean looper is harder to kill, both Tracer and the newer Bt products will work just fine.

Bollworms Trickle Into Fields

The bollworm egg lay continues, primarily across the northern cotton acreage. Huge numbers have not been reported with most larval infestations remaining below the threshold I use at this time of year of 12,000 to 20,000 small larvae per acre, depending upon the fruiting pattern and vulnerability of the fruit load in a given field. Usually these late infestations fail to establish high numbers of damaging worms. Establishment is improved in fields with lots of squares and young bolls and under late sprinkler or in late row watered cotton.

Reports of control failures last week were either due to coverage problems or the presence of pyrethroid resistant tobacco budworms. Resistant budworm reports were from the Sudan and Enochs areas. We have looked at caterpillars in other fields in the Sudan area. Not all fields appear to have a budworm problem. Where pyrethroids are not working, I would suggest looking at Tracer, Curacron, Lannate or Larvin. If Steward is available, this too could be used. If you have questions about the identification of your caterpillars, you might collect a sample of the larger worms and take them to your local IPM agent or me for ID.

Aphid Infestation Levels Variable

Aphid numbers are up or down, depending upon which field you are standing in. Some infestation crashes have been due to the activities of predators and parasites, most notability the lady beetle. Other crashes have gone unexplained. In other areas, such as the northwest area, aphid numbers have continued to escalate above our suggested treatment levels. Remember that our 50 per leaf threshold is to protect yield during the boll filling stage. Once this is achieved then our concern shifts to sticky cotton avoidance.

The treatment level for sticky cotton avoidance once cotton begins to open is 15 aphids per leaf. I have seen levels as low as 5 per leaf cause problems. It all depends upon how long these aphids are out there and how hot it gets. Higher temperatures usually mean higher rates of honeydew excretion.

Will you have a sticky cotton problem? No one can predict for sure. It depends upon whether you get a honeydew-cleansing rain before harvest and whether mills are smart enough to blend your cotton with cleaner cotton to avoid a potential mill problem. Blending and the use of newer machinery has cut down on the problem dramatically. Last year we probably had a lot of sticky cotton but did not see a major problem develop at the mills. What about this year? Only time will tell. I can’t tell you if you will need to spray when the threshold is reached. This is because I can’t control these other factors.

If you opt to treat late aphid infestations, realize that some of the products you will use will have pre-harvest intervals approaching 30 days. Please read the label carefully before using. Also remember that Furadan can only be applied twice in a season under the provisions of the current Section 18.

Lygus Bug Numbers High In Some Fields

Lygus bugs have continued to attack isolated cotton fields in many areas. Often these problem fields are next to other hosts such as peanuts and alfalfa, but not always. The threshold of two or more Lygus per three foot of row, using a drop cloth for sampling, is used at this time of year. Damage is going to be most pronounced in late cotton with young, tender bolls. We don’t care about squares at this time. Our insecticide tests continue to indicate that Orthene is our best control choice.

Western Flower Thrips Infestations Heavy

The number of western flower thrips in area cotton is just incredible. I have never seen anything like it! A few years ago there was considerable concern and discussion about heavy infestations causing flower retention problems. What studies that were conducted indicated no significant impact or yield loss due to these high numbers of thrips. On the plus side, these same thrips are killer predators on spider mites. And there are some problem fields out there with spider mite concerns. Our best spider mite treatment (very expensive) was two applications of Curacron (the second application is necessary to get nymphs hatching from eggs).

Tests, Tests, and More Tests

You know what they say, strike when the iron is hot. Well this has been a "hot" year for insect pests and we have been very busy putting out tests in between scouting fields and handling an incredible phone call load. How many tests? My last count was 2 thrips tests, 3 beet armyworm/looper/bollworm tests involving ground applications, 4 chemigation tests for beet armyworm/looper/bollworms, 2 aphid tests, 1 Lygus control test, 4 Bollgard tests and 4 COTMAN tests. These tests are the combined efforts of nine IPM agents and myself. Hopefully the data we will summarize this winter will be helpful in your farming operation next year. JFL

The crop is moving along at a quickened pace due to lack of rainfall and somewhat above normal temperatures. Most dryland fields across the region have "crashed" due to lack of rainfall, and many earlier planted dryland fields are beginning to have a considerable percentage of open bolls appear. Even irrigated cotton is moving along rapidly. The effects of this are enormous for many producers who have spent considerable money up front on the dryland, especially after mother nature teased us with record (or at least high) rainfall during the month of June. Boll size in many dryland fields will be less than desirable. It looks like we are headed for a record dry August, with only 0.01 recorded thus far for the month at Lubbock. If we go back into July, the last significant rainfall was in mid-month. We have encountered essentially no rainfall across the region since then, with the exception of a perhaps few spotty rains.

Long-term average heat unit accumulation per day is being surpassed due to higher than normal temperatures. Over the past few days, Lubbock heat unit accumulation has averaged about 21.1 per day, nearly 5 above the 30-year long-term average. Halfway has averaged about 19.3, and Lamesa about 21.2. Daily PET has ranged from about 0.21 to 0.27 inches per day at Halfway, 0.20 to 0.26 inches per day at Lubbock, and 0.21 to 0.30 inches per day at Lamesa.

Where Do We Stand With Accumulated Heat Units After Cutout?

As noted in an earlier newsletter, we have worked some with the COTMAN cotton management program developed by personnel at the University of Arkansas with funding from Cotton Incorporated. Identification of cutout is one of the key components of COTMAN for determination of insecticide termination and crop termination. For a discussion of insecticide termination using COTMAN rules, see the previous newsletter.

COTMAN uses 850 heat units past bloom as a point at which a bloom can make a "normal" boll. In the High Plains, heat unit accumulations of 750 past bloom will probably make an "acceptable boll" that may not have "normal" lint production or may be lower quality (low micronaire).

We have the table that indicates where we are as of August 28 (Table 7). It is based on actual Lubbock heat units from August 1 through 27, and from that point forward, it uses the 30-year long-term average for each day. For example, the table shows that for a field that reached cutout (here defined as 4 NAWF) on August 1, we should have obtained 350 heat units by about August 19. For the 450 total, it should be around August 23. For cutout at August 10, we obtained 350 heat units by August 27, and should hit 450 heat units by September 3. This table also indicates the likelihood of obtaining maturity of late season bolls.

Table 7. Heat unit events based on date of cutout (4 NAWF) and actual Lubbock August 1-27 temperatures with subsequent long-term average values for the remainder of the season.

Since it appears that we are again in a warmer than normal late summer (at least thus far), it is possible that the targeted maturity levels (750 and 850 heat units past NAWF=4) will be obtained earlier than projected using the long-term data after August 27.

To Terminate or Not To Terminate?

When considering potential impacts of adverse weather conditions, many producers view harvest aid application as a means to reduce overall economic risk. However, with all of the money spent on producing this year’s crop, the additional expense of harvest aid application may not make financial sense to some. The yield potential of the crop must of course be factored in, but we also need to look at the calendar and see where we are at this stage of the game. First, we have many fields that are finishing up early this year. If we take the National Weather Service’s word for it (at least based on long-term averages), then Table 8 is worth checking out.

Table 8. Average first freeze date for various High Plains locations. 1/

1/ From Public Information Statement, October 14, 1998, National Weather Service, Lubbock, TX.

If we take Lubbock as an example, we would expect the first freeze around October 31. With the early crop we have this year, this implies that we would have a crop opening up early sitting in the field undergoing at least some weathering. If cotton reaches a high percentage of open bolls in early- to mid-September, then it could possibly experience 6 weeks (or more) of weathering. Last year, we did not have a killing freeze at Lubbock until just before Thanksgiving (November 23rd). The highest quality that a boll has is when it first opens, and from that point on, lint and seed quality deteriorate. Weight also decreases with time of exposure. Weathering losses are hard to determine, but the following information may be worth reading. No recent projects have been conducted investigating the effects of weathering on cotton yield and quality. However, we can look at some of the existing older data.

Dr. Levon Ray (TAES cotton breeder prior to Dr. John Gannaway) and E. B. Minton (USDA) conducted a 3-year trial in the late 60’s and early 70’s which investigated the effects of weathering on stormproof cotton at Lubbock. In this small-plot trial, hand harvests were initiated at 2-3 weeks AFTER the first killing freeze. Please note that harvest aid use was not as popular during that period of time. The losses reported here are relevant for after a freeze. However, this also implies that the losses prior to a freeze would NOT be included in these data. Therefore, I submit that actual losses due to field weathering are greater than those reported in the above paper because the weight losses prior to the killing freeze were not determined. The total precipitation during the harvesting period was 1.65 inches in 1969, 0.17 inches in 1970, and 1.32 inches in 1971. Since STORMPROOF varieties were used, no preharvest losses (cotton falling onto the ground) were reported in the study.

They concluded that rate of weight loss was greater in the early weeks of the harvesting season, based on regression analysis of the 3-year dataset. Total weight losses of cotton lint were estimated at 3 percent the first week, 8 percent after 4 weeks, and 12 percent after 11 weeks. For 600 lb/acre cotton (their example), losses were estimated at 18, 48, and 72 lb/acre for weeks 1, 8, and 11, respectively. If we apply those same loss rates to varying yield levels, then the data in Table 9 are pertinent.

Table 9. Potential yield and gross revenue losses due to field weathering. 1/

Yield potential, (lb/acre)	Week 1 Potential yield loss (lb/acre)	Week 1 Potential gross revenue loss ($/acre)	Week 4 Potential yield loss (lb/acre)	Week 4 Potential gross revenue loss ($/acre)	Week 11 Potential yield loss (lb/acre)	Week 11 Potential gross revenue loss ($/acre)
250	7.5	3.75	20	10.00	30	15.00
500	15	7.50	40	20.00	60	30.00
750	22.5	11.25	60	30.00	90	45.00
1000	30	15.00	80	40.00	120	60.00

1/ Assumes 3%, 8%, and 12% yield potential loss due to weathering in weeks 1, 4, and 11, respectively. Assumes cotton price of $0.50/lb.

The project also noted that fiber length was significantly reduced by field exposure. They concluded that 6-7 weeks of exposure would likely result in a 1/32 inch decrease in fiber length. Colorimeter readings of reflectance (or rd) were also detrimentally affected over time and were highly correlated with field weathering. This indicates that color grades have the potential for reduction over time. They concluded (using 1972 loan prices and their estimates of yield loss) that the combined weekly loss in terms of both yield and quality at the beginning of the harvest season would be about $9.50/acre for their 600 lb/acre yield. A separate economic study of the above mentioned data indicated that highest cotton prices were generally obtained earlier in the harvest season. Total gross returns are generally higher earlier in the season, and by the last week of January, severe reductions can usually be expected. This year we will be working with Dr. Alan Brashears (USDA-ARS agricultural engineer) and others on a stripper harvest timing project near Lubbock.

Estimating Lint Yields

Dr. Will McCarty, Extension Cotton Specialist at Mississippi State University, has developed an excellent publication on yield estimation. It is available at here. Basically it says that it takes about 155,700 normal bolls to produce a 480 lb. bale of cotton (High Plains average of 4.0 g seed cotton/boll = 1.4 g lint assuming a lint percent for seed cotton of 35%). This is equivalent to about 325 bolls/lb of lint. For 40-inch rows this calculates to 11.9 bolls per row-ft for a one bale/acre yield (155,700 bolls/13,068 row-ft/acre for 40-inch rows). This is very close to the "one boll per inch = one bale per acre" number that many folks use to estimate yields in 40-inch rows.

To help determine a "worst case scenario" I checked the report from our 1998 High Plains Cotton Survey we conducted for Plains Cotton Growers and which was submitted to FCIC and USDA-RMA . One of the worst locations (in terms of boll size and lint yield) was the Lamesa dryland replicated variety test site. It averaged about 480 bolls/lb of lint across several varieties. This implies that it would take about 230,500 bolls/acre of that size (about 2.7 g seed cotton/boll) to produce a 480-lb bale of cotton. This works out to about 17.6 bolls per row-ft for a one bale per acre yield. It is possible that the numbers could be worse, but I still think this may be a good number to use for a worst-case scenario. The highest number of bolls/lb of lint for dryland samples in the survey was just over 600. This translates to 288,000 bolls/bale, or 22 bolls/row-ft in 40-inch rows.

2000 High Plains Cotton Harvest Aid Guide

The High Plains Cotton Harvest Aid Guide is being updated and will include information on new materials and changes in formulation of older types. It should be available by the end of the week. RB

Table 10. Data from the South Plains PET Network, August 22—August 28, 2000:

[a] Potential Evapotranspiration, often referred to as "PET" or "ET", is an estimate of maximum crop water demand based upon weather data. Actual water use by a crop will vary with soil and crop conditions.

In the August 22, 2000 edition of Focus on Entomology, irrigation termination on cotton was discussed. Additional publications that address crop-specific irrigation management and termination are available on the Internet. Some of these materials are written for Nebraska and Kansas growing conditions; hence, the reader is cautioned that specific maturation rates, cultivars, and climatological factors may be quite different than those on the Texas South Plains. There is some useful information in these materials, however, so we wanted our readers to be aware of them. Readers who do not have Internet access may contact me for a hard copy. DP

From the Texas Agricultural Extension Service:

Texas Peanut Production Guide. B-1514. http://agpublications.tamu.edu/pubs/scs/b1514.pdf

From the University of Nebraska Cooperative Extension Service:

Predicting the Last Irrigation for Corn, Grain Sorghum and Soybeans. NebGuide G82-602-A. http://www.ianr.unl.edu/pubs/irrigation/g602.htm.

Irrigating Soybean. NebGuide G98-1367-A. http://www.ianr.unl.edu/pubs/fieldcrops/g1367.htm.

Irrigating Corn. NebGuide G98-1354-A. http://www.ianr.unl.edu/pubs/fieldcrops/g1354.htm.

From Kansas State University Cooperative Extension Service:

Predicting the Last Irrigation for Corn, Grain Sorghum and Soybeans. Irrigation Management Series MF2174. http://www.oznet.ksu.edu/library/AGENG2/mf2174.PDF

Grain Sorghum Production Handbook. C-687. http://www.oznet.ksu.edu/library/crpsl2/c687.pdf

Soybean Production Handbook. C-449. http://www.oznet.ksu.edu/library/crpsl2/c449.pdf

Alfalfa Production Handbook. C-683. http://www.oznet.ksu.edu/library/crpsl2/C683.pdf