The insect management season is almost over for cotton with but a few exceptions. While bollworm and beet armyworm egg lays continue for some fields, less than 10% of all fields probably remain vulnerable. Aphid infestations are also following this trend of declining numbers. Heat, natural enemies and plants with low aphid-carrying capacity are probable reasons for this. Aphid numbers have increased in some fields where recent applications on lusher cotton have been made. Boll weevil trap numbers and punctured boll counts are going through the roof, which is typical for this time of year when much of the crop can no longer support them. The only difference this year over last year is that all these weevils are in the two zones that have yet to vote in an eradication program. Producers in the three active zones are for the most part very happy. No one is happy about the expensive insect control year where problems with aphids, bollworms, loopers, beet armyworms and boll weevils have taken all the profit and fun out of growing cotton.

Cotton is opening like popcorn in heat stressed fields. Many farmers have continued to irrigate with sprinklers, afraid to terminate and risk not filling out their top bolls. They all know that once they stop watering, its over, and their cotton will go into permanent wilt. While the drought and abnormally high temperatures have taken a toll on our crop’s yield potential, these same conditions have all but signaled the end for insect control this season. There will be a few fields left that may need yield protection, but these probably represent less than 10% of all our acreage.

With the end of the insect management season well at hand, it probably is important to emphasize how little the top crop that many are wanting to protect is worth. There have been studies (most recently one by John Robinson, Extension Economist at Weslaco) that put a value on each fruiting position. Most of our yield comes from first position bolls from the lower two-thirds of the fruiting branches. The rest of the cotton generally represents less than 5% of the final yield. At a lint value of $0.50 to $0.60 per pound. This represents about $6.50 to $8.00. Our weevil sprays have been averaging $6.00-$7.00 per acre, bollworm sprays-$10.00/acre, beet armyworm sprays-$15.00/acre and aphid sprays-$10.50/acre. It would appear to me that most insect control applications are no longer justified.

There are still fields receiving egg lays from bollworms and/or beet armyworms. The level of this activity is much reduced and far below the outbreak levels observed just a couple of weeks ago. Looper moths are still present in many fields but larvae are pretty much a thing of the past. That leaves aphids and boll weevils. Aphid numbers are "crashing" in many instances due to the activities of predators and parasites, and the condition of the plants they infest. There are still some fields with increasing aphid numbers though. Boll weevil numbers continue to explode across the area, much like last year but with one important exception. The bulk of the weevils are now in the two remaining areas without an eradication program while weevil numbers in active eradication zones continue at very low levels. The Texas Boll Weevil Eradication Foundation is set to launch their full scale diapause program next week.

Boll Weevil Numbers Explode in Traps

Trap catches of boll weevils skyrocketed last week as weevils left fields in search of their "last supper" in preparation for the long host free period between our plant killing frost and squaring cotton next year (Table 1). Trap catches more than tripled in the Southern High Plains/Caprock Zone where producers have yet to support an eradication program (Table 2).

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.*

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

The big gainers for this week were Briscoe, Crosby, Floyd, Garza, Hale, Lubbock, and Swisher counties (Table 3). The big losers as far as reductions compared to last year were Andrews, Borden, Castro, Dawson, Deaf Smith, Gaines, Martin, Midland, Parmer, and Terry 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.

Accumulative trap catches through last week for both the Northern High Plains and the Southern High Plains/Caprock Zones have passed last year’s numbers and will continue to distance themselves from 1999 totals as the season progresses. The percent reduction for active zones for the entire trapping period is 52% for the Northwest Zone, 86% for the Western Zone, and 68% for the Permian Basin Zone. The percent increases for the last 18 weeks has been 21% for the Northern High Plains Zone and 12% for the Southern High Plains/Caprock Zone. The average spread between active and inactive zones is 83%. This spread will get bigger as we move through October.

Table 3. Week 35 (week beginning August 28)— 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.

Punctured boll counts continue to increase in the lusher fields as the mass exodus of weevils from stressed dryland and limited irrigated fields continues. But do you still need to protect late bolls from weevil damage? The answer is probably no! It’s over. No need to worry about this year’s weevils (Table 4).

Table 4. The date when a late boll is safe from boll weevil puncture.*

* Assumes 350 HUs needed from white flower to be safe, a seasonal cutout date based on historical temperature records and a 750 HU boll.

All that is left this year from a producer weevil management prospective is to terminate this crop as soon as possible, avoid regrowth and add a weevil insecticide in with your harvest aid if weevils are present in your field.

Eradication Update

It is my understanding that the Texas Boll Weevil Eradication Foundation will be launching the diapause phase of the eradication program next Monday. I have already seen an increase in spray plane activity the last few days. This is probably in response to two factors: 1) weevil numbers in traps are increasing, triggering more fields and 2) the Foundation has lowered trap triggers to 1 weevil per 40 acres trapped in the Western and Permian Basin zones and in the area north of Hwy 70 in the Northwest Zone. The 2 per 40 acre trigger remains in effect for the area in this zone south of Hwy 70, probably because of concern for secondary pests such as aphids and the remaining few beet armyworm problem fields.

Last week, GRID trap catches exploded in areas outside active eradication zones but remained low in the three active zones (Table 5). The differences between 1999 and 2000 are huge, almost beyond belief. The data and GRID map clearly show the success of the program but also what happens when producers are left on their own to manage weevils. I hope this is a valuable lesson for producers and landlords in the two zones that will be voting on the eradication issue this and next month. The program works! For some, it will pay out each year over their own efforts to battle the weevil. For others, it is a cost-effective long-term investment.

Table 5. Grid trap catches for the 35^th week in 1999 and 2000. High Plains, Texas. Average number of weevils caught per trap.

There has continued to be talk about the eradication program’s effect on the significant beet armyworm/looper problems we suffered through this year. We all know that the increased insecticide pressure that can be associated with the eradication effort in the early program years can exacerbate an already existing beet armyworm problem by reducing natural enemy numbers of this caterpillar pest. We saw this in the LRGV in 1995 and in other locations in the Southeast in other years. I did not see this happen here. The 2000 season provided conditions that optimized both beet armyworm and looper infestation development, much like we saw in 1978 and 1980. The trend with "beets" is to start in the southern acreage and then move progressively northward into the better irrigated cotton late in the season. This started in the Western Zone even before cotton was squaring and before eradication sprays had commenced.

The naysayers of eradication are busy trying to convince producers in the two zones that remain outside eradication that eradication did and will bring more pestilence to their farms and that these added problems are not worth the benefits of eradication. To these folks I say shame on you! You are using unfounded scare tactics to encourage producers to vote against a program that will mean long term viability to this regions cotton crop. The Foundation this year did an extraordinary job of adjusting trap triggers to avoid treating too much acreage in an area during any given week. This protocol was not used in 1995 when beet armyworms devastated the LRGV crop. I have information that supports my position on this year’s beet armyworm problem, do you have anything that remotely resembles good data to support your position? I think not.

Beet Armyworm and Looper Problems All But Over

While new beet armyworm (BAW) egg masses can be found in some fields and new infestations of small larvae can be found, these latest infestations are failing to cause very much damage to bolls that have a chance of maturing for harvest. Let these worms have your squares, your blooms, your small bolls. These late fruit are meaningless as far as yield is concerned. I won’t even talk about spraying for beet armyworms at caterpillar levels below 150,000 per acre at this time of year. In fact, based on the feeding pattern that I have observed in recent field visits, I have turned my back on infestations as high as 400,000 per acre in some fields. I know it is hard to stop protecting this crop after so much has been invested thus far but enough is enough. It is now time to think about harvest aids and getting the stripper ready, not "nuking" worms anymore.

While lots of looper moths continue to fly in fields, looper caterpillars are getting hard to find. It is over for this pest too. Count your blessings. Between loopers and beet armyworms, we had considerable defoliation in many fields, with some fields probably severe enough to cause yield reductions.

Potential Bollworm Problems Near An End

The big movement of bollworms out of corn and into cotton failed to materialize. There were some pretty significant egg lays in some fields last month and larval infestations of 15,000 to 30,000 per acre were encountered, but these were fewer and far between than the more normal infestations of 5,000 to 12,000 per acre. My threshold for this time of year is more like 20,000 per acre. This level should be pretty scary out there by now. Once there are fewer than 5 squares per foot of row, bollworms rarely are able to establish viable infestations. There was another documented pyrethroid control failure north of Draw that was due to the presence of significant numbers of resistant tobacco budworms.

Aphid Infestation Levels Winding Down

Aphid infestation levels remain variable with increases occurring in some fields with recent insecticide applications for caterpillar control. But for the most part, aphid numbers have declined as predators and parasites have finally caught up with the reproductive capacity of aphids. I’ve also noticed that plants this year appear to have a lower carrying capacity for aphids compared to previous years. Aphid infestations often "crashed" at levels in the 200-400 aphids per leaf, whereas in previous years this might have happened at levels such as 500-1000 per leaf. My guess is that plants that have been under heavy moisture and heat stress for the last several weeks have a reduced carrying capacity. Maybe there is a positive outcome from all of this heat?

Any applications for aphids that go out from this point on would have to target sticky cotton avoidance. It is too late for aphids to have an impact on yields by reducing boll size. The sticky cotton avoidance threshold is when cotton begins to open and infestations average 15 per leaf. I doubt that very many producers will spend the money for this year because of their already excessive spray bill. There isn’t much hope even for a timely rain to wash off any honeydew. Thus far the threat of sticky cotton is low. But if you opt to control aphids, remember that many of the materials you will select from will have a pre-harvest interval approaching 30 days. JFL

The crop is continuing to move along at a quickened pace due to lack of rainfall and above normal temperatures. Dryland fields continue to "go down" with marginal irrigated fields not far behind. No significant rainfall has been observed at Lubbock since July 23rd (0.49 inches). The last date of a high amount of rainfall was July 13th (1.46 inches). We have recently set records for high temperatures, and low rainfall in August (trace on the 7th, 0.01 on the 8th, and a trace on the 9th). It could thus be argued that there was no rainfall in August, another record. This is a very tough situation, because with the record high rainfall at Lubbock in June many producers were extremely optimistic with increased inputs into the dryland crop in many places.

The long-term average heat unit accumulation per day is being surpassed due to recent record or near record temperatures, and have averaged 21, 23, and 22 per day at Halfway, Lubbock and Lamesa. Our 30-year mean daily heat unit accumulation is about 13-14 per day for early September.

Daily PET has averaged about 0.25 inches per day across much of the region. As we move into the boll opening growth stage of cotton, the crop coefficient decreases from about 1.0 at first open boll to about 0.8 at 30 percent open bolls and decreases rapidly after that. That implies that once we get to the boll opening phase, if reference PET is averaging 0.25 inches per day, the crop will use about 1.4 inches per week (0.25 x 0.8). The value of continued center pivot irrigation after 30 percent open bolls is probably questionable, especially if significant numbers of late bolls have been punctured by boll weevils. Generally, we can observe about 2-5 percent boll opening per day once bolls begin to open (based on replicated harvest aid project data from 1997). This implies that if the last irrigation is made at a few percent open bolls, then it should take about 10 days to reach 30-60 percent open bolls. With the depleted soil profiles in many fields, the rate of boll opening will be on the high side this year.

Update on 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 and/or may be of lower quality (low micronaire).

Table 6 provided data that indicates where we are as of September 5. It is based on actual Lubbock heat units from August 1 through September 5, 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 20, 350 heat units were obtained by September 5, and the field should hit 450 heat units by September 13 — probably quicker if these high temperatures remain. This table also indicates the likelihood of obtaining maturity of late season bolls.

Table 6. Heat unit events based on date of physiological cutout (4 NAWF) and actual Lubbock August 1- September 5 temperatures with subsequent long-term average values for the remainder of the season.

2000 High Plains Cotton Harvest Aid Guide

The High Plains Cotton Harvest Aid Guide has been completed and includes an updated Decision Aid Table. We have also included two other documents; the new materials for the 2000 harvest aid season and a list of harvest aid prices. RB

Table 7. Data from the South Plains PET Network, August 30—September 5, 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.