Hot, dry weather has become the norm for the High Plains cotton crop. Where moisture is adequate, most fields are making excellent progress with earlier planted fields well into blooming and the much later planted crop just now beginning to square. Large leaf area and good square retention due to earlier abundant rain in June has produced a crop that is vulnerable to early moisture stress. The dryland crop needs more rain in the next 7 days or so or it will "throw off" much of its fruit. The irrigated crop will probably need more water sooner than is normal for most years.

The heat got turned up on our cotton pests this past week, increasing mortality and dampening off the steady increase in problem fields. Beet armyworms can be found in most fields but infestations still remain at levels well below the record numbers observed here in 1980. The high cost of control and the earliness of this infestation should discourage producers from treating infestations near our established thresholds. Beet armyworm damage is very obvious but this foliar feeding is not what causes yield losses. Bollworms are also spread across much of the acreage as the egg lay continues into the 5th week. Pressure is generally down, but some fields are still needing treatment based on bollworms alone. For the most part, caterpillar control decisions have involved a mix of both beet armyworms and bollworms.

First summer generation boll weevils are more in evidence this week as the earlier trickle has turned into more of a flood. Expect punctured square counts to blossom over the next several days. The eradication program is still on track in spite of earlier weather and personnel problems. The Foundation has been careful to adjust trap triggers to reflect the increased secondary pest risk in some work units. So far this elevation of trap triggers has been confined to the Western Zone.

Loopers have begun to appear in cotton, confusing the issue for some folks. There should be confusion in only identification, and not management strategy. We don’t treat for loopers! Lygus bugs and fleahoppers are more of a concern this week but still are a minor problem in most fields. Cotton aphids are showing signs of getting off the fence and increasing in number. Watch out for this pest over the next few weeks.

Several caterpillar pests are infesting corn at this time. The second generation southwestern corn borer egg lay continues with infestations as high as 50% infested plants reported. Other caterpillar pests include fall armyworms, European corn borers and corn earworms, a.k.a., cotton bollworm. Most of these single pest species are at levels below threshold but may trigger a treatment when a combination treatment decision is made. There are also rootworm beetles present in many fields as well. All treatment decisions will need to take into account the presence of spider mites. If our hot, dry weather continues, some of these worm sprays may flare these mites.

Sorghum fields also have fall armyworms feeding in the whorl. These are difficult to target with an insecticide and only are a concern if they damage the head as it is exerted. Greenbugs are still not a problem but usually don’t reach levels of concern until later in the season.

Peanuts are also running the gauntlet of caterpillar pests with a few fields treated. For the most part, infestation levels have remained below the economic threshold. Spider mites are also beginning to be found. Light disease pressure has been reported thus far---mostly early leafspot and pepper spot. Diseases must be handled in a preventative treatment manner. If you are seeing these diseases, consider treatment with an appropriate fungicide.

The general lack of rain in recent weeks and with temperatures hitting the century mark, dryland cotton is beginning to stress and even some irrigated cotton planted on sand are showing signs of moisture stress. Earlier abundant rains in June resulted in plants with a large leaf surface area and excellent fruit retention. This may cause a significant fruit adjustment in dryland cotton and certainly will lead to the need to irrigate fields earlier than normal. These same conditions will tend to concentrate bollworms and even boll weevils, to a certain degree, into fields with the least moisture stress. Beet armyworms will still prefer fields in sandier areas, dryland fields, and skiprow patterns. But as you all know, irrigated cotton is not immune to the advances of this pest.

Some Producers Overreacting To Beet Armyworms

Beet armyworms (BAW) have continued to infest many areas for over 5 weeks. Recent infestations have expanded into the northwest area of the High Plains and east into Lubbock, Crosby and Floyd counties, after starting out in the southwestern area encompassing Gaines, Terry and Yoakum counties. None of these infestations have reached levels even approaching levels observed in late July and August in 1980, the "year of the beet armyworm" (pictures of damage). During that season BAW infestation levels often exceeded 100,000 to 200,000 per acre and increased to 300,000, 500,000, and yes, even 650,000 per acre. This latter infestation prompted me to refer to this field as a "snake pit". Well, I haven’t seen any "snake pits" yet this year and still hold out hope that a repeat of 1980 is not in the cards.

Most BAW infestations observed to date have been well within the range of 5,000 to 35,000 per acre. High levels have been in the 85,000 per acre range. Certainly not at the dreaded levels observed in 1980. Now I am not down playing the seriousness of our current situation, especially with it’s earliness (BAW appeared around July 25 in 1980) and particularly with early bollworm infestations in the mix. But I do believe that many producers, consultants, aerial applicators and chemical company reps have overreacted to the current situation and are throwing too much money at marginal infestations at a very early date. Is there going to be any money left for insect control if really serious infestations rear up in August? And what about bollworms, aphids and boll weevils?

Scouting for BAWs can be accomplished using two different methods: counting "hits" or counting worms. "Hits" would be defined as egg masses or recently hatched egg masses with caterpillars still feeding very close to the egg mass site. The use of "hits" is especially helpful in detecting large numbers of beet armyworms early in their infestation development. They were a particularly useful sampling unit when many of our insecticide treatments were either preventative (Dimilin) of provided less than "cleanup" type control. We now have some fairly decent beet armyworm materials (Denim, Intrepid, Steward and Tracer) at our disposal and therefore should probably stay away from using "hits" for most of our control decisions.

The biggest travesty being committed out there is the over use of the "hit" as a sampling unit. Once worms disperse down the row away from the original egg deposition site, you can no longer call this a hit. Some folks talk about "hits" covering 10 row feet. This just isn’t good scouting sense. Also, many folks are looking at the damage but not determining whether worms and fruit damage are present. In many cases, an egg mass with 80 eggs has resulted in only 5-10 worms a few days following hatch. I know that BAW feeding damage is very visible and an easy cause of concern, but let’s take emotion out of the equation and stop hunting for damage, or only counting worms in damaged areas.

I prefer using the same sampling technique used for bollworm scouting, the examination of whole plants. Check at least 40 plants per field, more in larger fields or where pest numbers are at or around threshold levels. Then use an accurate estimate of plants per acre to calculate the number of worms per acre based on this scouting technique. You have to do this for bollworms. Why not do it for both at the same time. Separate worms into at least 3 size categories: small (1/4 inch or smaller), medium (up to 1/2 inch) and large (greater than 1/2 inch). This will allow for better selection of the appropriate insecticide and for a more reliable means of evaluating the control outcome.

The current threshold for beet armyworms is 20,000 small caterpillars per acre with at least 10% of the plants scouted with the pest. Now threshold levels are based on the damage potential of the infestation, value of the crop and cost of control. Our crop is not worth as much as it should be and the cost of BAW control is higher than it used to be. This would tell me that the 20,000 threshold is pretty soft. Also realize that the threshold level is around the breakeven level, meaning that even if the infestation wasn’t controlled, the field certainly would not be devastated. This would not be true if 150,000 BAWs per acre were in the field.

The final consideration is the amount of fruit feeding taking place in the field. BAWs feed a lot on foliage and therefore their damage looks pretty bad. But oftentimes they do very little damage to the fruit. Other times only the small larvae feed on foliar with 4 day and older worms drilling squares, blooms and small bolls. Feeding on bracts doesn’t count! I’ve looked at my share of BAW infestations this year and I would have to say that their feeding pattern is similar to that observed in 1980, not 1995, when beets fed more on fruit. So, I wouldn’t get overly excited about 20,000 small larvae per acre this early this year unless some other pests were also present and of concern.

Also, unless the dryland crop planted on our sandier soils gets a rain real soon, money spent on insect control will be a total waste. Until a dryland field gets a good rain in July (early July doesn’t count), insect control is very iffy. Actually, some insect damage may help readjust the fruit load so that plants can withstand the moisture shortage without "throwing off" all it’s fruit.

Insecticide selection is important, considering the high cost of control. If BAWs persist through August, many if not all the BAW insecticide supplies will run out. Tracer, Denim, Steward and Intrepid are all good BAW materials. I think the supply of Intrepid is so limited that for all practical purposes it is unavailable for general use in the High Plains. This means that its less effective cousin, Confirm, will have to be used. This product is an insect growth regulator and has little impact on beneficial insects. Price is a consideration. The list includes:

None of these materials are pyrethroid-like in control of bollworms, often requiring two applications at the higher rate for similar control. High rates for beets alone are only needed in instances where beet armyworms are mostly medium to large in size or infestation levels are extremely high. Even so, expect control of BAWs to drop from 85-95% down to 45-65%. Except for Tracer, none of these materials can target bollworms since their section 18’s are based on beet armyworms. Tracer is a good pyrethroid alternative where bollworms are the only problem, beneficial insect preservation is high on the list of priorities and/or the risk of flaring aphids is very real.

If producers want to try to minimize the development of BAW infestations, there are a few things they can do: 1) Conserve natural enemies. 2) Restrict insecticide use. 3) Be conservative in treating for other pests. 4) Use more selective insecticides for other pests. Even with our help at prevention, certain conditions this year will be conspiring against us. Hot, dry weather following a mild winter brings out the BAWs. Weedy fields (careless weed in particular), and sandy fields can be the worst. Skiprow patterns and moisture-stressed plants are attractive. As more and more of these factors are brought together in a field, the BAW risk index increases.

Bollworm Infestations Have Moderated in the Heat

While BAWs are liking the hot, dry weather, moisture-stressed dryland fields and young fields; bollworms are not. Bollworms prefer well irrigated fields of blooming cotton and cooler, more humid conditions that favor higher survival. We went through a peak of egg laying activity in recent days after several weeks of "nickel and dime" egg lays. This resulted in quite a few fields developing economically damaging infestations in the range of 10,000 to 35,000 caterpillars per acre. These levels have generally subsided but the egg lay continues at a lower level. A combination of bollworms and beet armyworms may trigger a treatment though. Most fields in the area with the exception of fields in "corn country" are infested with bollworms. Bollworms can still be dealt with relatively cheaply but in combination with BAWs, costs start rising above $15.00 per acre for chemical alone.

Small bollworm larvae spin silken threads to rappel down plants while BAWs often use silk to "web up" on leaves or beneath bracts (pictures). Small bollworms are often difficult to detect by many individuals either under trained in the art of scouting or a little rusty since last year. The best bet is to examine plants with a mental image of a perfect plant. Move rapidly down the plant until you detect something abnormal then slow down and take a closer look. I often find the damage before locating the 1/16 inch to 1/8 inch worms we all need to locate to make good management decisions. But don’t spray for this size worm if numbers are near the threshold. There is still too much opportunity left for weather and predators to reduce these numbers to levels we can all tolerate.

Watch Out For Loopers and Fall Armyworms

Loopers are increasingly being found in cotton fields (pictures). This is a fairly common occurrence in beet armyworm years. These loopers feed only on foliage and should be ignored. I have never observed a field with sufficient defoliation from this pest to warrant concern. It looks bad but the bottom line is there is no yield impact. The main concern with loopers is confusing them with the more important pests. Like bollworms, they lay their eggs singly and usually on the upper surfaces of leaves. Unlike bollworms, loopers tend to lay their eggs much lower on the plant, often on leaves dragging on the ground. Their eggs are also a little different. Looper eggs are wider than they are tall, looking much like a pincushion. Bollworm eggs stand taller than they are wide and their ribbing is much more pronounced than that of a looper egg. Looper caterpillars "loop" because they are "missing" a pair of abdominal legs. Beets and bollworms have all 4 pairs of abdominal legs. We can have both soybean and cabbage loopers. The only importance of this would be if control was warranted since they respond differently to various insecticides.

Fall armyworms are infesting sorghum plants, often in high numbers. They are difficult to control when inhabiting the rolled up leaves in whorl sorghum. During years like this, they often spill over into cotton, especially when cotton is adjacent to forage sorghum. This insect has been less damaging in cotton than beet armyworms in past years but can cause considerable boll damage in some instances. This caterpillar tends to be more brownish in color as it obtains a larger size and has an inverted "Y" marking on it’s head (pictured in sorghum insect photo section).

With all the caterpillar activity reported across the area you might be wondering about the fate of the Bollgard cotton crop. This is a year so far that has allowed Bollgard cotton to shine. Infestations have generally not been of the "blow away" type and the Bollgard cotton has taken the latest infestations of bollworms and beet armyworms in stride. Very little insecticide has been applied to this cotton. Producers in "wormy" areas are going to be pleased with their Bollgard cotton this year. But I must caution you that if either bollworm or beet armyworm levels increase to even higher levels, especially as the Bollgard crop enters the boll maturation phase, fields may need a little help from insecticides.

Overwintered Boll Weevil Emergence Finally Dropped Off

After five weeks at a plateau of peak emergence, trap catches finally dropped off last week (Table 1). I would expect trap catches to remain low for another 5 to 6 weeks before increasing again as late season movement begins.

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

This is a similar pattern as was observed last year when boll weevil emergence extended for 4 weeks (Table 2). Average trap catches outside of active eradication zones haven’t been quite as high as last year’s but were still at bothersome levels, especially with the week longer emergence peak. Boll weevil numbers in traps were similar but lower than last year’s in zones yet to be activated (Table 3). But trap catches have continued to be significantly reduced in active zones, especially in the two southern zones. Counties with the most boll weevil activity are Briscoe, Cochran, Crosby, Floyd, Garza, Hale, and Lubbock.

Just when overwintered boll weevil emergence has started falling off, first summer generation adult weevils came surging to the forefront. What started as a trickle 10 days ago is starting to look like the beginning of a flood in some areas. While we often refer to these newly emerged boll weevils as "red" weevils, the first summer adult weevils also tend to be smaller. Why smaller? Many of these developed from grubs feeding on small squares and literally were forced into a starvation-like diet. Remember, unlike bollworms, weevil grubs cannot move from fruit to fruit as their food supply is depleted.

These smaller weevils can still puncture squares and still lay eggs that will produce the next generation. Producers and consultants alike need to get out in their fields and examine at least 100 pencil, eraser-size or larger squares for punctures. Do not choose squares that are obviously damaged (yellow or flared) and certainly don’t pick up squares off the ground. Usually, when these first weevils emerge, there will be a few days in which only feeding punctures will be found. Then egg punctures will begin to show up. I wouldn’t begin to treat a field until egg punctures appear, even if the 20% punctured square threshold is reached. But I would short cycle on my scouting to insure that I was on top of the situation.

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.

Table 3. Week 28 (week beginning July 10)— 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.

 Eradication Update

The Texas Boll Weevil Eradication Foundation Program continues to apply pressure to the boll weevil population in the three active zones in the High Plains area: Western, Permian Basin and Northwest (Table 4). I would have to say that thus far their efforts have been a success. Many producers will expect to see no weevil damage and no weevil adults in their fields. This just simply will not be the case. This is only the first full year of eradication, with another three to go. We have just finished an extended overwintered boll weevil emergence of five weeks, following a mild winter, which resulted in 20% survival in our better habitats. This year we have experienced one of our windiest springs and our frequent heavy rainfalls in June certainly contributed to the difficulty in applying ULV malathion in a timely manner. Under these conditions, eradication efforts have been excellent.

When I looked at the GRID map for last week (week 28), I didn’t like what I saw at first, especially in Gaines County. But when I reviewed the trap data and compared it to last year’s data, I felt better again. Gaines County trap catches through last week are still running less than 10% of those in 1999. What more could you ask for?

The Foundation has had a rough road to follow this year, especially with all the beet armyworms popping up across the area. Their field surveys have resulted in more changes in trap triggers in the Western Zone, in an effort to keep treated acreage near 10% of the total, especially in areas where beets are a serious threat. Work units around the Plains and Seminole area are now using a trap trigger of 4 weevils per 40 acres trapped (about 8 traps). Some work units in the Brownfield area are at 3 weevils while others remain at 2 per 40 acres. The Seagraves work units remain at three.

Their beet armyworm surveys this week in Lynn, Gaines, Terry and Yoakum counties (124 fields) indicate that less than 12% of the fields have infestations at or above the 20,000 per acre level needed to begin to have concern. Most fields (78%) are below 6,000 per acre.

There has been some idle talk about the possible connection between this year’s beet armyworm problems and the ULV malathion applications made in the eradication zones. Thus far, there is no data to support any such relationship. Let me repeat this. So far, there is absolutely no evidence that the eradication efforts this year have triggered beet armyworm problems! Conditions this year have been favorable for beet armyworm infestation development and quite frankly, there have been a lot of applications put on by individual producers outside active zones for overwintered boll weevil control. I am always surprised at the number of detractors that can come out of the woodwork to criticize a successful program. These people need to get a life! If something starts going south with the program and the Foundation becomes unresponsive, I will be the first to let you know. We’ve got a good thing going here with Dr. Charles Allen and the Foundation doing an excellent job.

Table 4. The Texas Boll Weevil Eradication Foundation status report for week ending July 16.

Other Pests

Lygus bugs continue to move out of some of the better alternate hosts such as alfalfa and peanuts, and into adjacent or nearby cotton fields. Under these circumstances, quick action is often needed. Remember that this pest can attack fruit all the way to small bolls. Cotton fleahoppers are beginning to be more of a factor in late planted fields, but certainly not like we saw last year. Once plants begin to bloom, fleahoppers are usually not a concern.

Cotton aphids are still pretty much "parked" out there although there is some indication this may soon change. Reproduction is more evident this week and with more insecticide treatments going out and more expected, the aphid situation could change in a hurry. All that you can do to delay or avoid the inevitable is to minimize insecticide applications, avoid excessive nitrogen use and use selective insecticides when spraying for other pests. JFL

Southwestern corn borers began to fly about 10 days ago with the percent emergence of adults for this generation yet to be determined. Greg Cronholm (Extension Agent-IPM for Hale/Swisher counties) will report percent emergence information in his newsletter today. Knowing percent emergence matters because it allows us to estimate how much longer the flight will continue, and when we are past peak egg lay. Last week's FOCUS featured a video on how to scout for SWCB. The published treatment threshold is when 20 to 25 percent of the plants are infested with eggs or newly hatched larvae. However, with corn prices so low, the 2000 threshold is higher. Greg reported that some fields have exceeded the threshold, and one field had egg masses on more than 50 percent of the plants examined.

Treatment thresholds are guidelines, not magic numbers. In their simplest form, they try to establish the point where the cost of the chemical application will be equal to or less than the value of the yield to be lost to the pest. This is a simple concept, but one that is almost impossible to use precisely in the real world of multiple pests and fluctuating prices. Most corn thresholds are based on $2.50 corn, not corn that sells now for 35 percent less. Also, the cost of an application varies widely and the use of more expensive products (in theory) should require a slightly higher threshold than for cheaper products. However, if the more expensive products also provide control of other pests (like mites) that may be present at sub-economic threshold levels, while cheaper products do not provide this benefit, then the more expensive product may actually provide greater economic returns. "Sub-economic level" does not mean that the pest is not causing yield loss, it just means that the value of the yield loss does not yet equal the cost of control measures for the pest. Also, insecticides that provide a long residual control window can be attractive in an extended egg lay like we see with second generation SWCB.

I realize that theory is nice, but not especially practical right now. I could be more specific if I knew whether spider mites will get out of hand in the next few weeks. Mites are a big worry, especially where fields are treated for SWCB with insecticides that kill beneficial species but do not also help reduce mite numbers. These insecticides kill the beneficial arthropods that help keep mite populations in check, and free the mites for even more explosive population increases in the future. Overall mite numbers are low to moderate in most fields, but if we continue to have hot and dry weather that could change in a matter of days.

Fall armyworm (FAW) and corn earworm (CEW) of different growth stages are present in many fields. Unfortunately, Texas does not have an economic threshold for FAW. At this point it would not matter much if we did, because this pest and CEW should be considered along with SWCB, ECB, and mites.

FAW larvae feed on ears and ear shanks and behind leaf collars. When infestations are heavy, yield losses can be substantial because larvae feed directly on the ear. Additional losses can occur when shank feeding causes ears to drop and when stalks lodge as a result of feeding damage to the nodes.

Treatment decisions for any of these worm pests should be made on all pest species combined. A field that has sub-economic levels of FAW, SWCB, ECB, and CEW may still be over threshold. Consider that the same chemical application can kill all four species, and the combined damage caused by these species can add up to more than the cost of the insecticide.

The previous discussion assumed non-transgenic (Bt) corn. If you are growing Bt corn, assume that you will get good control of SWCB and ECB, but only suppression of FAW and CEW - which should be enough at current pest levels. RPP

Scouting procedures and thresholds are presented in the Sorghum Insect Control Guide [http://entowww.tamu.edu/extension/bulletins/b-1220.html]. RPP

When dealing with foliage feeding caterpillars on runner type peanuts, several factors need to be considered before making a treatment decision:

1. Infestation level. Basically, peanuts can tolerate a considerable amount of defoliation, up to a certain stage. In runner type peanuts (irrigated) worm infestations can exceed 6 to 8 larvae per row foot before yield losses occur. Whereas, in Spanish peanuts, 6 to 8 larvae per row foot is a treatable level.
2. Number and type of beneficial arthropods present. Certain kinds of "beneficials" such as spiders and true bug predators are very good worm feeders, whereas lady beetles are not.
3. The amount of prior damage. If there has been significant prior defoliation, then economic thresholds may have to be adjusted and control measures implemented. Additionally, recent defoliation data presented by J. Scott Russell (Extension Agent-IPM in Frio/Atascosa counties), showed that on irrigated runner type peanuts in south Texas, up to 33% of the canopy can be lost before significant yield reduction is noted at 80 days after cracking.
4. Size of the worms. The last two larval instars do by far the most feeding and damage. The last two instars consume 94% of the food ingested during the larval stage. So targeting a treatment before larvae get to this size could be important.

Peanuts that are 90 days or older should not be as susceptible to damage as the younger, more tender plants in the later planted fields. Additionally, barring any major disruptions, (such as insecticide spraying) "beneficials" should keep damaging populations of worms at a tolerable level during this next increase of activity.

Spider mites are beginning to be found in Gaines County at sub-economic levels in peanut fields that are adjacent to cotton. It appears that two separate, yet similar species are infesting these fields, the two-spotted mite and carmine mite. Both have essentially the same biology.

Often a good irrigation or heavy rain can reduce mite populations, however eggs usually go unaffected and at least some mites are sheltered by upper canopy leaves. Chemical control should be considered only when lower canopy defoliation is taking place or appreciable numbers are present.

Disease Situation

Sclerotinia blight (SCB) has not been reported in any peanut fields in Gaines County as of yet. Now, although this disease has been documented in only a relatively small number of fields over the past several years, area growers need to be aware of its potential as a serious plant pathogen in peanut. I have available through my office a short publication authored by Dr. T.A. "Chip" Lee (Extension Plant Pathologist, Stephenville) regarding SCB. In this article, Chip describes the status, biology, damage, research and management strategies for SCB. Additionally, Gaines County as well as several adjacent counties received a section 18 for Botran 75W or 75WSB for suppression of SCB. Please contact my office at (915) 758-2977 or send an e-mail to c-crumley@tamu.edu for further details or for a copy of Dr. Lee's article.

Early leafspot and pepper spot are slowly increasing in a few peanut fields in the area. Control of this disease and suppression of other diseases can be achieved by using fungicides at the labeled rates and intervals. If a rainy weather pattern develops, then potential problems could develop with the area crop regarding leafspot, particularly in unrotated fields. Furthermore, leafspot in combination with the pod rotting fungi such as Rhizoctonia or Pythium (which is currently being found at low levels in some fields), could prove to be a problem this year. Therefore, I would strongly advise area growers that if you are currently seeing a combination of these disease complexes, apply an appropriate fungicide now. Remember that fungicides are preventative and not curative in their mode of action. (Edited version taken from Clyde Crumley’s, Extension Agent-IPM, newsletter - Gaines County Cotton/Peanut News, Vol. 5, No. 4.)

PEANUT FIELD DAY

The Texas Agricultural Extension Service and the Western Peanut Growers Association are sponsoring a Peanut Field Day on Tuesday, July 25th. The program will begin at 9:00 a.m. at the Gaines County Civic Center. The Field Day will include a tour of peanut fields in Gaines County and demonstration plots conducted by the Extension Service. Dr. Chip Lee, Extension Plant Pathologist; Dr. Robert Lemon, Extension Agronomist; Dr. Calvin Trostle, Extension Agronomist and Clyde R. Crumley, IPM Agent are scheduled to speak.

The last week was one of hot, dry weather. Although somewhat stressed, the cotton crop has generally progressed well. High temperatures in the upper 90s to lower 100s have been the norm, whereas the low temperatures have been in the upper 60s to lower 70s. As of this writing, no rain has fallen received across the region for the last week. Where we have good moisture conditions, the crop is moving along, but moisture stress is beginning to appear in fields which received lower rainfall amounts during the June wet spell. PET has been recently averaging about 0.30 to 0.35 inches per day. Heat unit accumulation is averaging 22-23 per day for the last week or so.

Leaf area is generally higher than normal for this time of year for many fields due to the abundant June rainfall and little weather "ragging" of the crop. This leaf area, although beneficial for photosynthesis may also increase evapotranspiration losses. In dryland fields with plants larger than normal, and lower amounts of soil profile moisture, we are going to need some rainfall soon to help preserve the yield potential. Dryland production is still risky in many places without adequate subsoil moisture. Irrigation has cranked up across the area and for good reason. The high square and boll retention in many fields coupled with larger plants will certainly place a significant demand on profile moisture.

Checking Crop Yield Potential

Nodes above white flower (NAWF) is an important plant mapping measurement. NAWF is defined as the number of mainstem nodes to the terminal above a first position white flower, and is an indicator of crop yield potential and vigor. The terminal is defined as the uppermost node with a leaf that is at least an inch in diameter. Normally, for stripper-type varieties, we expect a minimally stressed crop to have at least 8 NAWF (and preferably more) at first bloom.

Irrigation Issues

Adequate irrigation can sustain continued growth and enhance yield potential if vigor problems can be identified and the most can be made from existing irrigation capacity.

Dr. Guy Fipps, Associate Professor and Extension Agricultural Engineer, Texas A&M University, College Station, provides a good overview of irrigation requirements at the following web address: http://texaset.tamu.edu/growers.asp

To estimate the actual evapotranspiration for a particular field, the crop coefficient for cotton at a particular stage is multiplied by the PET. One can also factor in the efficiency of the irrigation system (Table 5). The equation then becomes:

Actual ET = [PET x Kc, the crop coefficient] / system efficiency

Table 5. Typical overall on-farm efficiencies for various types of irrigation systems (edited from Fipps).

1. Surge has been found to increase efficiencies 8 to 28 % over non-surge furrow systems.

2. Drip/trickle systems now are typically designed for 90% + efficiency.

3. Higher efficiencies are for low wind conditions.

Once the actual ET is estimated, then one can sum over days (irrigation interval). The balance sheet then essentially becomes the inputs (rainfall + irrigation) minus ET.

Jim Bordovsky, Experiment Station Irrigation Engineer at Halfway has provided some useful information. Research has shown that the LEPA irrigation system (circle farmed, with applications in alternate and diked furrows, dragging socks) will allow water go much further than spray-type systems. With LEPA, a more frequent irrigation interval (such as a revolution every 2 days) generally tends to increase yields when compared to intervals of lower frequency if a reduced amount of irrigation water available. Cotton responds very well to high-frequency deficit irrigation, even at amounts as low as 0.20 - 0.25 inches applied every 2-3 days. This amount of water could be applied using high-frequency LEPA center pivot irrigation with wells delivering a total of 2 gpm per acre or about 240 gpm per 120 acre pivot.

1/ Values in a row followed by the same letter are not statistically different.

1/ Dryland yield was 46 lb/acre, with 4.29 inches of rainfall.

Table 8. Limited cotton irrigation for a 1/4 mile center pivot on 120 acres.

Soil Water Holding Characteristics

A soil’s capacity for storing moisture is affected by soil structure and organic matter content, but it is determined primarily by soil texture. Approximate plant-available water storage capacities for various soil textures are summarized in Table 9.

Table 9. Available water capacity for soils.

(Source: Estimating Soil Moisture by Appearance and Feel. NebGuide G84-690-A. University of Nebraska Cooperative Extension Service. (http://www.ianr.unl.edu/pubs/irrigation/g690.htm)

Soil Moisture Monitoring

Moisture conditions at the soil surface often are not a reliable indicator of plant available water in the root zone. In order to know whether the roots are able to access water, we need to dig, probe, or otherwise sample to measure soil moisture where the roots are. A soil may appear dry on the surface and still have adequate moisture in the top 2-3 feet of the root zone. Soil water depletion over time and with depth in the root zone can be observed through periodic physical sampling (gravimetric or "feel" methods) or through regular use of soil moisture monitoring equipment.

Commercially available soil moisture monitoring devices vary in cost, accuracy, and ease of use, but even the simple, inexpensive devices offer some insight into the relative moisture of the soil with time and depth. Resistance blocks ("gypsum" blocks or WaterMarkÔ sensors), tensiometers (more applicable for drought-sensitive crops), and a variety of soil moisture probes are available through farming, forestry, and gardening supply catalogs. We are currently testing some of the newer "probe" technologies in our research activities, and we plan to report our findings in a future edition of FOCUS.

More information on soil moisture monitoring equipment is available at the crop irrigation portion of the irrigation website at Lubbock (http://lubbock.tamu.edu/irrigate/). Readers without Internet access can contact Dana Porter at (806) 746-6101 for this information. The High Plains Underground Water Conservation District No. 1 (UWCD) also has two excellent publications on soil moisture monitoring: Soil Moisture Monitoring: An Overview of Monitoring Methods and Devices and Estimating Soil Moisture by Feel and Appearance. These are available at the High Plains UWCD office at 2930 Avenue Q, in Lubbock.

Root Zone Depth

Root development is crop-specific. Approximate effective rooting depths (depths containing the majority of feeder roots) are listed in Table 10:

Table 10. Examples of depths containing the majority of feeder roots.

Roots are generally developed early in the season, and will grow in moist (not saturated or extremely dry) soil. Soil compaction, caliche layers, high water tables, and other impeding conditions limit the effective rooting depth. Most crops will extract most (70% - 85%) of their water requirement from the top one to two feet of soil, and almost all of their water from the top 3 feet of soil, if water is available. Deep soil moisture is beneficial primarily when the shallow moisture is depleted to a water stress level.

Potential Evapotranspiration (PET) Estimates

Estimated crop water demands, based upon PET weather station data, reflect recent hot, dry conditions in the High Plains. Data for the last two weeks are summarized in Tables 11 and 12. (Electrical problems have resulted in unreliable data at the USDA-ARS weather station in Gaines County, hence the Seminole station data have been omitted from this summary.)

Table 11. Data from the South Plains PET Network, July 6 — July 12, 2000:

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

 

Table 12. Data from the South Plains PET Network, July 13-July 19, 2000:

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

 

PET varies with growth stage (planting date and accumulation of heat units) and crop. You are encouraged to customize your crop water use estimate by multiplying the reference PET value by the appropriate crop coefficient. Crop coefficients for additional crops and growth stages are available from the Texas PET Website at the following:

High Plains Corn - http://texaset.tamu.edu/include/crop/corn.html

High Plains Cotton - http://texaset.tamu.edu/include/crop/cotton.html

High Plains Sorghum - http://texaset.tamu.edu/include/crop/sorghum.html

Other Crops - http://texaset.tamu.edu/include/crop/cropcoe.html

Turf – http://texaset.tamu.edu/turf.asp

PET data and weather data for Halfway, Lamesa, Lubbock, Seminole, and Ropesville are available at: [http://achilleus.tamu.edu/data/data.html].

The Northern High Plains PET Network provides detailed PET estimates by crop and by planting date for Bushland, Dalhart, Dimmitt, Earth, Etter, Farwell, Morse, Perryton, Wellington, and White Deer. Current data are available at http://amarillo2.tamu.edu/nppet/station.htm. DP