Perpetual hot, dry weather conditions continue to have a negative effect on the High Plains cotton crop. However, some spotty thunderstorms have resulted in small rainfall amounts for those fields which were lucky enough to be under the clouds. Cotton insect problems for the most part have taken the backseat to weather related problems. After last year's crisis, growers need a break. The exception is a developing banded-winged whitefly problem in both the High Plains and Rolling Plains areas of Texas. Not all fields have a problem with this insect, but those that do are at or approaching treatment decisions. Hopefully we will be able to apply some of the information we have on silverleaf whiteflies to our species of whitefly.

Spider mites continue to be the main worry for corn. Sorghum headworms are increasing, and insecticide decisions should be made in part on the potential to flare mites. Greenbug numbers are also on the increase.

Some area sunflowers are showing damage from the stem girdlers, Dectes texanus. Sunflower fields with high numbers of these girdlers need to be harvested as soon as possible in order to minimize lodging losses.

A Section 18 has been granted for the use of Capture to control Banks grass mite on sorghum grown for seed.

Except for the whitefly problem, there are very few fields that have cause for concern due to insects. Bollworms, plant bugs, beet armyworms and aphids have remained at levels we can all tolerate for the most part. Abundant insect and spider predators have kept most pest infestations at bay this season. I would watch out for increases in bollworm activity as we move through August, especially as corn matures and begins to dry down.

Boll weevils could become a problem for a few fields as September approaches and before diapause treatments are initiated by the Foundation in the two zones yet to be in eradication. We are already picking up adult weevils representing the 2^nd summer generation.

Cotton aphids have cooperated by staying in the plant terminal and remaining at subthreshold levels. August is usually the month when aphids can become a problem if more insecticides are used and cooler temperatures return.

Luckily, not all area cotton has a problem with this pest. In fact, most fields will probably make it through the season without a whitefly problem developing. What is the big deal with this pest? Well we don't have very much information on this species and have had to borrow heavily from management information developed for the sweetpotato whitefly and silverleaf whitefly. Why does this species pose a problem? Because treatment thresholds, sampling techniques and insecticide recommendations for one insect doesn't always apply equally to another pest. I know these are both whiteflies but assuming they are similar is like saying a basset hound should be similar to a greyhound in racing performance!

Why is the silverleaf whitefly treatment threshold set so low? There can be a number of reasons for this: 1) this species is more damaging than other species of whiteflies, 2) insecticidal control is more difficult, 3) there are resistance issues, and 4) once lots of immatures are present control is much more difficult and expensive. We don't know if any of this applies to banded-winged whiteflies.

For the moment, I'm going to assume that the threshold of 5 adults per indicator leaf for silverleaf whiteflies is inappropriate for our species. Second, I am also going to take the position that a suggested 10-15 adults per leaf threshold for our species is also too low. So where should treatments begin? Assuming that this whitefly is not vectoring any diseases, is not injecting a toxin and is feeding in a similar manner as the cotton aphid, then a threshold level that would result in the same amount of honeydew you would observe from 50 aphids per leaf might be appropriate. This may be somewhere around 75-100 per leaf (both adults and nymphs).

As presented last week, adult sampling should consist of looking at the indicator leaf of at least 40 plants spread across the field. The indicator leaf is the fifth leaf down from the terminal. Approach the plant to sample very carefully so as not to disturb and displace any adults. Turn the indicator leaf over slowly by its tip and quickly count adults.

You are not finished until you also count immatures from the same leaf. To do so you must first create a sample card from card stock or an index card. Remove a round area the size of a quarter. This is the viewing area from which counts of nymphs will be made. Detach the leaf used to count adults and count visible whitefly nymphs within this hole when it is wedged between the central and left-side main veins on the underside of the leaf. Count only large nymphs (3^rd and 4^th instar) that appear as flattened, egg-shaped disks or scales. We only count these nymphs because they do not require magnifying hand lenses to see them. Counts of both adults and nymphs can proceed very rapidly.

Multiply the nymphal count by 5 and add this to your adult count. This will give you a good estimate of total adults and 3^rd plus 4^th instar nymphs present per leaf sampled. If this averages somewhere between 75 to 100 per leaf then I would consider my control options. I would also be looking very closely at the amount of associated honeydew present.

Our insecticide recommendations today are going to have to be based on the results of tests conducted with the silverleaf whitefly since data on the banded-winged whitefly is limited. Brant Baugh (Lubbock IPM Agent) and Scott Russell (Terry/Yoakum County IPM Agent) did manage to get counts in a limited test last week near Idalou. They looked at 3.0 oz of Centric per acre, 1.66 qt. per acre of Thiodan and 2.2 oz of Karate Z+ 9.0 oz of Orthene 90S per acre. Average pretreatment counts of adults per leaf ranged from 15 to 23, while total nymph numbers ranged from 52 to 105. Total per leaf numbers ranged from a low of 75 to a high of 125. Adult control was best with the pyrethroid-Orthene combination but fell off greatly with Centric and Thiodan. We are still evaluating immature control and do not have results to report yet. The best treatment would cost about $11.00 for the materials. We plan on putting out at least another test with more insecticide entries. One of the questions we have has to do with rates. We may not be able to look at the possibility of reducing rates. The number of possible insecticides and combinations is out of sight.

So what were the best pyrethroid combination treatments for silverleaf whitefly studies in Arizona regardless of cost?

Adults only (rate per acre)

Asana 7.8 oz + Orthene or Address 90S 9.0 oz
Baythroid 2.56 oz + Orthene or Address 90S 9.0 oz
Karate Z 2.56 oz + Orthene or Address 90S 9.0 oz

Adults and nymphs (rate per acre)

Capture 5.2 oz + Orthene or Address 90S 9.0 oz
Danitol 4.2 oz + Orthene or Address 90S 9.0 oz
Capture 4.2 oz + Thiodan or Phaser 1 qt
Karate Z 2.56 oz + Thiodan or Phaser 1 qt
Karate Z 2.56 oz + Thiodan or Phaser 1 qt
Danitol 4.2 oz + Curacron 8.0 oz
Asana 7.8 oz + Curacron 8.0 oz

None of these treatments would be considered inexpensive. Cost could range from a low of $10.00 to a high of $20.00 per acre for insecticide alone. Once cotton yields are represented by full sized bolls I would no longer worry about this pest unless honeydew problems develop on open cotton. My main control concern would be whether a second application would become necessary either due to continued movement of adults into the field or less than adequate control with the first application. I am not sure how many growers could "stomach" a whitefly control program costing $27.00 to over $40.00 an acre. We could see a fairly heavy movement of whiteflies out of sunflower fields in about two weeks as growers desiccate their crop in preparation for harvest. JFL

Last week I mentioned that no one was doing the laboratory work to determine whether spider mites have developed resistance to Capture. Well, Robert Bowling, Extension IPM Agent for Moore County, will collect mites today and take them to Kansas State University over the weekend for testing. His trip is funded in part by the Texas Corn Producers Board.

Spider mite infestations are above economic threshold in some fields and light in others. European and southwestern corn borers have essentially finished laying eggs for the season.

Corn earworm numbers will continue to increase for the next two weeks. This won't matter for corn because the plants are no longer preferred for egg laying. However, it might matter for sorghum. Corn earworm and fall armyworm together are "headworms". Fall armyworm is also becoming more abundant. So, it will soon be time to begin scouting sorghum for headworms. Scout for spider mites at the same time, and if an insecticide is needed for headworms, remember that a pyrethroid might make the mite situation worse. Large numbers of mites can reduce grain filling. However, they can still reduce yields even after the hard dough stage because heavy mite infestations promote lodging. In our area, recommended miticides have given erratic control at times. Please refer to our sorghum guide for headworm and mite insecticides and thresholds.

Greenbug numbers continue to increase in sorghum. At heading, the economic threshold is when two leaves are killed on more than 20 percent of the plants. Greenbugs on drought-stressed sorghum are often more difficult to control than those on sorghum with adequate water.

Greg Cronholm, Extension IPM Agent for Hale and Swisher counties, is monitoring for resistance in greenbugs and would like reports of any control failures. His office telephone number is (806) 291-5274. Or you can call me at (806) 746-6101 for failures outside of Hale and Swisher counties. PP

Just when sunflower moth worries were fading into memory, some growers are finding lodged plants. The culprit is probably the stalk/stem girdler, Dectes texanus. Some people refer to this insect as a "sunflower borer" or "sunflower stalk borer" D. texanus is also known as the soybean stem borer, and is currently causing a lot of trouble in some Kansas soybeans.

The risk is lodging. The girdlers tunnel downward through the stalk as they mature, and then girdle the stalks before harvest. There are three significant aspects to this insect's biology and behavior that make things difficult for us. First, it emerges as an adult from overwintering over an approximate six week time span beginning at the end of June. This makes it economically impossible to control the egg laying beetles for the entire time they are a threat. So, the practical thing to do is to kill the front end of the population and hope for less severe damage from the later insects (a reasonable hope in most years). Secondly, the adult is very secretive and hard to detect, which is to say that even the best scouts may not find it. Third, eggs are laid just beneath the surface of stems and are therefore protected from natural mortality factors like beneficial insects. In sum, this insect is present for a long time, is hard to detect, and has very low mortality in the larval stages.

So what are the answers? First, never plant sunflower after soybeans or sunflower. Second, thoroughly destroy stalk residue, which is the overwintering site. Third, learn to recognize the adults. Fourth, if a field is heavily infested, harvest at the earliest possible time. Lodging losses increase rapidly once the crop dries down. And finally, I need to get to work and find a trap for the adults. None exists at present, but because they are so hard to detect, we need some help from a good trap. PP

Perpetual hot, dry weather conditions continue to have a negative effect on the High Plains cotton crop. However, some spotty thunderstorms have resulted in small rainfall amounts for those fields which were lucky enough to be under the clouds. We just finished up the month of July and according to the National Weather Service, it was the second hottest month on record going back to1914. Although we did not set that many record high temperatures, the average daily temperatures were considerably above normal (July temperature graph). Lubbock ended the month with 0.6 inches of rainfall, which fell on the 28^th in a localized manner around the official recording station at the airport. Much of the High Plains cotton acreage has had virtually no rainfall since at least June 1. Reference ET has been averaging about 0.3 to 0.35 inches per day across the area. Heat unit accumulation for the last few days has averaged 21, 23, and 25 per day at Halfway, Lubbock, and Lamesa. The accumulated seasonal totals from May 1 are now 1490, 1692, and 1810 for those locations, which is 15, 21, and 24 percent above the long-term averages.

Physiological cutout is defined as the point at which the plant reaches 5 nodes above white flower (NAWF) after an extended bloom period. We have discussed this and generally agree that 4 NAWF may better fit the High Plains region, due to our "living on the edge" with many fields lingering at 5 NAWF for several days at a time. When cotton "blooms out the top" and quits, this is an example of physiological cutout IF there is adequate time to mature the bloom on that date. Seasonal cutout is defined as the point in the season at which there is no longer enough anticipated heat units (based on long-term temperature data sets) available for a bloom to produce a high quality boll. 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 of lower quality (low micronaire). The one-third grown squares now on the plants will ultimately become the last effective blooms, if we assume that the last effective bloom dates are around mid-August. It is now apparent that we may have some cotton fields ready to terminate by early September if things stay on track.

Data accumulated from across the Cotton Belt to establish COTMAN guidelines for crop termination have generally indicated that once a boll reaches 350 heat units past bloom, it is relatively safe from boll weevil damage. To be safe from a bollworm egg lay, at least 450 heat units past bloom are required. Data collected over multiple site-years by Dr. John Benedict (formally TAES entomologist at Corpus Christi) support this concept (boll penetration graph). Of course you cannot walk away from a field once the magic number of heat units is obtained, as it is only a guideline. Since we have had many fields reach 4 NAWF over the last several days, the clock is ticking for termination of some insect management decisions.

Deadly Alternaria encountered again. Back in the August 13 and 20, 1999 issues of Focus, we reported a plant health problem of unknown origin (see previous newsletters with photographs). Isolation work conducted by Dr. Terry Wheeler, Experiment Station plant pathologist, later indicated that the disease was caused by an Alternaria species (fungus). Since the first sighting of this disease was in fields near Welch, it was jokingly dubbed the "Welch Mocus." We received some calls concerning a few fields with small areas with this symptomology in 2000. The disease has recently appeared again in a field south of Seminole. Fields infected in 1999 and 2000 were in western Dawson and eastern Gaines Counties. Crop genetics does not appear to be critical, as the varieties infected since 1999 have included Paymaster 1220 RR, Paymaster 1330 BG, Phytogen 569, Deltapine 5415 RR, Fiber Max 989, and Paymaster 2326RR.

The good news is that large affected acreage has not yet been reported or observed, but there is some concern. Rounded areas are typically about 10-30 yards in diameter. The plants are affected from the terminal down, with leaf wilting and desiccation evident. On recently infected plants, major veins on the underside of the uppermost leaves turn a brownish/maroon color. As the problem progresses, leaves eventually dry up and defoliate. The terminal in severely affected plants dies and curls downward. Symptoms then move down the mainstem. A maroon discoloration of the mainstem generally occurs, in conjunction with purplish lesions. Plants that have been affected for a longer period of time are generally several inches shorter than uninfected neighbors. Total fruit shed does not readily occur, as larger bolls are generally retained on dead plants. No vascular discoloration in the mainstem is apparent as with Fusarium and Verticillium wilts. For pictures of the infected Gaines County field and symptomology click here. If anyone observes this disease, please call the Lubbock Center so we can record the location and affected variety. RB

Concerns for dryland sorghum crop have reached a critical level due to heat and lack of moisture. Medium maturity sorghum that was planted in early June after hailed-out cotton is booted and will soon or has already attempted to head in many areas. Fields that achieved a lower plant population of about 2 plants per row foot (40" rows) are in better condition than those fields with 3 and 4 plants per row foot. These lower plant populations have a better chance of making grain, and more of it (due to more soil moisture per individual plant), if we pick up some moisture.

In numerous fields a combination of wind and heat has acted in such a way that the base of the sorghum stalk is actually sitting on top of the ground. This exposes the roots to heat and warm air, restricting growth potential. These plants are not anchored well in the soil, and will lay over with wind. For later planted sorghum farmers should consider cultivating to throw some soil around the plants, if they haven't already done so. There is always the risk of herbicide injury if a rain comes, but with larger plants this is less of a concern as long as the sorghum is rooted down. Potential herbicide injury is probably outweighed by the need to anchor plants better and cover the roots.

A few questions have come in the past few days about late-season N on irrigated sorghum. In general, if a sorghum plant has received some N and is past the stage of growing point differentiation (about 30 days for a medium maturity sorghum; essentially all South Plains sorghum is past this stage), then minimal benefit is expected from additional N. If N has been applied, and yield potential appears good, a grower may wonder if ~ 20 lbs. N through the pivot might enhance yields. Twenty lbs. N at $0.30/lb. would cost $6.00/acre, or similar to what it would cost to pump about 1" of irrigation water. This level of N would require about 180 lbs. of increased sorghum yield to pay for itself. One inch of water is equivalent to ~350-425 lbs. of grain per one inch of water. If you're looking to spend the extra money, irrigation seems the better bet at this point. CT

Harvest strategies for sunflowers with girdlers/stem borer. Please note Pat Porter's comments about the presence of girdlers (Dectes texanus) in sunflower. The late discovery of sunflower stalks with larvae burrows in the pith from two to three feet above the gound down into the root below the soil line is a concern because of lodging potential. A few fields with heavy infestations have already seen perhaps 1-2% lodging. Often many growers never know they have had girdlers until harvest, particularly if they are harvesting a week or more later than when the crop is first ready.

What about desiccants to hasten harvest? Several chemicals are labeled for desiccation in sunflower (including confectionary), such as paraquat and sodium chlorate. Desiccants are rarely if ever used in West Texas due to high temperatures and low humidities, which leads to rapid dry down. Kansas-Colorado extension literature suggests that desiccants can allow earlier harvest, but harvest temperatures are typically cooler there than for West Texas, particularly for our early planted primary sunflowers. Desiccants are more likely applied in northern sunflower producing states where maturity occurs in September and cool weather and moisture sets in.

No desiccant should be applied before sunflower is physiologically mature (R-9), which includes a lemon-yellow color on the back of the head and when leaf bracts on the back of the head have begun to brown and blacken. At that point a desiccant could be applied, but with the hot weather, I don't think a grower is really going to gain much. Could this possibly save a grower a few days in waiting to harvest? Maybe, but only a few at best, and in spite of the potential for lodging from the girdlers, I don't think it will make much difference. One possible exception to using a desiccant is if you can achieve some weed control if a field has a lot of weeds that haven't gone to seed.

At physiological maturity, much of the leaf may have been lost. As the head begins to dry down progressing down the stalk, any green color in the lower stalk should not necessarily inhibit harvest if the heads are ready. In fields where you find considerable numbers of stalks with tunneling, keep in mind that the tunnels are primarily in the pith, and only some in the vascular tissue. The harder supporting tissue around the outside of the stalk is not usualy damaged much. Though some stalks could break with wind or due to a heavy seed head, most plants can hang on for a while. Thus instead of being concerned about possible desiccation, farmers should be ready to harvest just as soon as the sunflowers are ready. Don't delay harvest! This will minimize potential losses due to lodging.

The following table demonstrates how low moisture contents in sunflower can go with various combinations of heat and humidity. South Plains temperatures are higher and humidities are lower than listed. Sunflower here can lose 1% moisture per day in many cases. Too often farmers delay harvest 1 or 2 weeks waiting for a few stragglers or late-maturing heads to mature. These heads are in fact usually 1% or less of a field, so don't worry about them. Ignore these heads and get the combine in the field. Contact your contractor or delivery point for information on harvest moisture guidelines and maximum moisture contents to avoid deductions. Sunflower test weight is about 24 lbs. per bushel. Excessive dry down can in fact increase harvest losses due to blowing lighter seed out of the combine. Long-term storage recommendations suggest 10% or less for confectionary and 8% or less for oilseed.

Combine settings for optimum sunflower threshing. Some early planted sunflowers were harvested last week. The High Plains Sunflower Handbook (available at http://lubbock.tamu.edu/sunflower) contains suggestions for proper setting of the combine to minimize harvest losses. The guide's first emphasis, as noted above, is being prepared to harvest as soon as the crop is ready. Overthreshing is the most prevalent machine problem. There is a tendency to break heads if the cylinder is improperly set for the conditions. We like to get the head to the straw walkers in one piece. This is accomplished by keeping the cylinder speed slow (250-450 rpm), concaves well open (wide open if moisture is less than 10%), low wind, and at slower ground speeds. Producers should avoid trashy samples, particularly for confectionary, as price is generally discounted 1% for each percent of foreign matter. Past growers of sunflower have commented that if they had appreciated the extent of potential deductions from trashy harvest, they would have spent more time setting their combine. CT

Continued hot and dry conditions, and the associated high evapotranspiration demand by crops are old news these days. Reference crop Evapotranspiration averaged 0.27 to 0.31 inches per day in the South Plains area during the week of July 26 to August 1, 2001. Some locations received up to an inch of precipitation on July 28, yet much of the area received no rainfall, and remains very dry.

According to Texas Water Development Board drought monitoring reports,
(http://www.txwin.net/Monitoring/Meteorological/Drought/indices.htm) crop moisture and Palmer Drought Severity indices reflect severely dry soil moisture conditions and mild to moderate drought over the area. Under these conditions we are able to see marked advantages of high efficiency irrigation systems and practices. DP

Estimated crop water demands from reference crop data (average over the South Plains area):

• Cotton at maximum bloom to 1^st open boll: 0.32 inches per day
• Cotton at 25% open bolls: 0.24 inches per day
• Sorghum at Boot to Heading stages: 0.32 inches per day
• Sorghum at Hard Dough stage: 0.26 inches per day
• Corn at Silk to Milk stages: 0.37 inches per day
• Corn at black layer stage: 0.20 inches per day
• Peanuts: 0.32 inches per day

Table 2. Crop water demand estimates (inches per week) at selected locations for the week of July 26-August 1, 2001.

* Reference crop for these ET estimates is a cool season grass. Crop-specific ET estimates are affected by growth stage; ranges of values are presented for the reader's convenience and to accommodate the ranges of crop growth stages in the field.

The U.S. Environmental Protection Agency (EPA) has approved a FIFRA Section 18 Emergency Specific Exemption for the use of bifenthrin (CAPTURE 2EC Insecticide/Miticide) to control Banks Grass Mites in sorghum grown for seed. A copy of the EPA approval notice must be in possession of the applicator at the time of application. Additional copies of the EPA approval notice may be obtained from the TDA web site at: http://www.agr.state.tx.us/pesticide/18crops.htm. PP