Agronomy Notes

August, 2003

CONTENTS:

 

CORN

Dr. Erick Larson

Borers Necessitate Early Harvest - Southwestern corn borers in the Delta and northeast Mississippi may cause substantial harvest losses if the corn crop is not harvested promptly. Third-generation southwestern corn borers literally cut stalks down by girdling the stalk internally a few inches above ground level. This "girdling" action predisposes stalks to nearly certain lodging, particularly when followed by moderate wind. Girdling activity normally commences about 20 days after egg laying. Since the third generation southwestern corn borer moth flight normally occurs in early August, producers should try to finish non-Bt corn fields by late August.

Grain moisture dockage - Corn may be harvested any time after grain reaches physiological maturity, which occurs at around 30% moisture. However, corn may not be safely stored until considerable moisture loss occurs. Thus, grain elevators discount wet corn to account for drying expenses and moisture weight loss during drying. Moisture dockage schedules between elevators may vary significantly, so thoroughly compare rates. Most schedules discount about 2.5% per each percent moisture above the standard, and may increase as moisture content rises. Water evaporated during drying (shrinkage) accounts for 1.18% of the dockage per each percent moisture. The producer loses this weight regardless of whether they sell wet grain to the elevator, dry it mechanically or let the grain field dry. Thus, a producer should subtract this value from the dockage rate to show their realized or "actual" dockage.

Harvest losses - Harvest losses are just as important as moisture dockage rate in evaluating your harvest timing decision. The longer corn stays in the field, the greater the likelihood of substantial field losses. Factors such as stormy weather and southwestern corn borer damage can cause considerable lodging in unharvested fields. Abundant July rainfall has also promoted morningglory growth in some corn fields, which can greatly inhibit harvest efficiency. Each of these factors may cause substantial field loss, which would considerably outweigh moisture savings. Producers should also consider their harvest capability -- the longer it takes to complete harvest, the earlier you should start harvest. Growers should harvest non-Bt hybrids infested with corn borers, early maturing hybrids, and those possessing below average stalk quality promptly and before other hybrids.

Producers should closely check for loss while the combine is harvesting and make adjustments accordingly. Two corn kernels per square foot or one dropped ear per 100 feet of row equals about 1 bushel per acre yield loss. Research generally indicates combine efficiency is best (harvest losses are lowest) when corn grain moisture is about 20-22%. Thus, growers seeking maximum profitability should always strive to finish harvest before grain moisture falls below 15%.

Do Not Give Away Corn - Producers selling corn at less than 15% moisture are giving away profit. A producer harvesting 150 Bu./A. corn at 14% moisture is losing $3.54 per acre or $7.08 per acre at 13% moisture (at $2.00/Bu.). This loss is solely from reduced grain weight due to lower moisture content. This moisture weight loss closely approximates the "actual" dockage most elevators charge for high moisture corn. Since corn loses approximately 0.6% per day during the harvest season, begin harvest early enough to guarantee all corn is harvested before it reaches 15%.

Aflatoxin tips - Improper grain handling, particularly with high moisture grain, can quickly promote aflatoxin development after harvest. Wet grain should be immediately dried to below 15% moisture or hauled to an elevator (which will dry the grain). Wet grain should not be stored in trucks, combines, bins or any non-aerated site more than 4-6 hours before beginning drying. These conditions are critical to grain quality, because the fungal growth which causes aflatoxin will escalate to excessive levels very quickly in wet, warm grain. Conversely, fungal growth becomes dormant when grain moisture drops below 15%. Producers should also thoroughly sanitize handling and storage facilities before and during harvest.

 

FORAGE AND PASTURE CROPS

Dr. David Lang

New Technologies in Pasture Renovation

There are exciting new technologies which will have an impact on pasture renovation. We've tried these at various experiment stations in Mississippi, found them to work, and suggest you give them a try in your operation. They involve biotechnology and are a bit expensive, but they're simple to use.

Glyphosate tolerance has been placed in corn and soybeans and you can use these crops to help kill out undesirable forages and weeds in pasture. Bermudagrass does not have deliberately introduced glyphosate tolerance, but it is tough to kill bermudagrass without repeated applications. It's possible to grow a crop of corn or soybeans in a pasture and leave a good stand of bermudagrass which is free of many undesirable weeds. No-tillage equipment is available which can plant corn and or soybean into an old pasture in need of renovation. You can harvest the corn for grain, but it is also possible to graze the standing corn and let the cattle harvest it. Grazing corn works best with growing steers. Live weight gains of 3+ lbs/day can be achieved from July through October. Soybeans can be made into hay if grain harvesting equipment is not available. Soybeans can also be inter-sown with some of the rows of corn to provide a good protein source. It's not recommended that solid stands of soybeans be grazed, or that heifers or cows graze standing corn during this time, because they will gain excess fat and have difficulty breeding.

Following glyphosate tolerant corn or soybeans, the pasture is ready to be replanted to ryegrass, tall fescue, or legumes. These plantings are also possible without tillage and without additional chemical burndown following summer grazing. If you have tall fescue in your fields, it is most likely the old type of tall fescue which has a toxic fungus living within its leaves, stems, and seed. It causes lower animal gains and poor calf crops. Tall fescue without this fungal endophyte is not toxic to livestock, but the tall fescue stand will not persist without the endophyte. Researchers in Georgia teamed up a group in New Zealand to develop a tall fescue with an endophyte which was not toxic to livestock. Spring applications of glyphosate, as part of a glyphosate tolerant corn and or soybean planting, will kill most of this toxic tall fescue. A second application of glyphosate in late spring, over the top of the emerging glyphosate tolerant corn or soybean, will kill the remaining toxic tall fescue as well as many undesirable weed species.

The new non-toxic tall fescue with the friendly endophyte will persist in Mississippi. It has good steer and heifer performance, and even pregnant mares do well on this new tall fescue. This new tall fescue will grow and do well where tall fescue has been previously grown. It will not do well on sandy or drought prone soils. Look for non-toxic endophyte friendly tall fescue when you buy tall fescue seed.

 

RICE

Dr. Joe Street

Crop Situation: In general, the rice crop looks good with the exception of the fields with glyphosate drift. Some fields have a little more grass coming through the canopy than we would like to see and although red rice was a problem last year, it is more prevalent this year. The high red rice incidence could be attributed to early planting and the cool weather early in the season, which did not let the canopy close as early as usual. With an abundance of rice on the market, it will be critical to produce high quality rice for marketing. Although the price is higher than last year, heading time is not the time to cut costs in protecting the crop.

Drift: Fields with glyphosate drift symptoms on the heads have been observed. Glyphosate drift at midseason may result in heads that look like straighthead with the typical parrot-beaked grains. The damaged heads may be scattered throughout the field and thus careful observation is necessary to detect damage. In some cases the head will be partially filled and difficult to detect even from the combine.

Stinkbug control: As this is written, the stinkbug populations are scattered and many are below threshold levels. As milo, corn and soybeans are harvested, expect stinkbugs to move into the rice. In the past, those growers who initiated stinkbug control with an insecticide with residual activity (Karate or Mustang Max) have had less peck damage than those who started with a non-residual insecticide. Apply an insecticide when the grains are filling with milk and starting to turn down and the threshold of 3 stinkbugs per 10 sweeps is reached during the first two weeks of heading or 5 per 10 sweeps two weeks after heading. Much of the older rice is already in the milk stage and perhaps will be fairly mature before the stinkbugs reach threshold levels.

Sheath Blight: Most of the early rice is beyond the stage for sheath blight treatment. In the later planted rice, if the field is fully headed and sheath blight is below the flag leaf, treatment will probably not be of significant benefit. Treat only after the threshold of greater than 35 percent positive stops is reached and the sheath blight is moving up the plant on susceptible varieties such as Cocodrie or Clearfield. With Wells and Priscilla, a fungicide will generally not return the investment. I have seen a lot of sheath blight but in most fields, it is not moving up the plant and thus, treatment has not been needed.

Smut Control: Cocodrie, Priscilla and Clearfield varieties are susceptible to kernel smut and although we have not had significant smut during the past two years, a preventative fungicide treatment should be considered. Weather conditions during flowering that favor kernel smut are high humidity, light showers, and cooler temperatures of 77 to 86 degrees. Kernel smut is more severe under high fertility conditions and rank growth. It is usually more severe on lighter soils but it can be severe on clay soils.

Blast: Leaf blast has been detected on Wells, Francis and Clearfield 161. Careful scouting should continue on these varieties. Cocodrie and Priscilla are both rated susceptible to blast but no problems have been observed in the field with either variety. Weather will play a very important role in the severity of blast. Optimum conditions for blast development are average daily temperatures of 73 to 86 degrees, prolonged leaf wetness and high humidity. Blast fungicides must be applied as a preventative treatment to protect the heads. Scout carefully for blast and if symptoms occur treat before the heads are fully emerged.

Harvesting: The best milling yield with Priscilla has been obtained when it was harvested at high moisture and dried slowly. If at all possible, harvest Priscilla before it goes below 16 percent grain moisture. Cocodrie has a wider window for harvesting without reducing milling yield.

 

COTTON

Dr. Will McCarty

Crop Situation: Mississippi's cotton crop is still in a wide range of maturity and conditions as we move into August. Early planted cotton will be ready to defoliate by the first ten days of September. Later planted cotton is catching up fast but some will have to be played out till the end. Generally the crop is in good condition. Some areas of the state are looking at a near record crop potential while other areas are just hoping for a crop. On the average, we have the potential for a better than five year average crop, if we can get it harvested. Growers are reporting fruit retention being higher than they can remember.

Late season nitrogen: There are some fields showing signs of nitrogen shortages. Before you apply nitrogen to cotton at this late date, be absolutely sure it is needed. Some fields may be showing yellow colors due to reasons other than nitrogen deficiency. Is the field one that had all the nitrogen applied pre-plant - quite early pre-plant? If so, and it is well fruited, it may indeed be running out of nitrogen. Is that all bad? Keep in mind that if the crop is carrying a good fruit load, it is doubtful that the plant has time to produce new growth that will develop into harvestable bolls. If the field is one that had a split application of nitrogen applied, it is doubtful that it is really running out. If soil-applied nitrogen is indeed low, more can be applied either as a solid material applied to the soil or as a foliar spray. A soil application will deliver more N to the crop in a single application, while a foliar program will be limited to about 5 pounds of N per application. However, it is getting too late for a soil application of 30 or so pounds and especially it is not advisable to do so in dry land cotton. Materials such as ammonium nitrate, Bulldog Soda, Calcium nitrate, urea, ammonium sulfate (or other solid source) may be used as a soil-surface-applied treatment. A nitrate source would be preferred for this treatment.

This late in the season, a foliar-feeding program using a suitable source of N is an alternative. An application of solid nitrogen to the soil could deliver more nitrogen to the crop than is needed while applications of foliar material could be tailored to meet the needs of the crop. All decisions must be made carefully. At this late date, such an application may be a little dangerous. Excessive nitrogen will delay maturity, increase rank growth, and cause the crop to be more attractive to insects and could reduce yields and grade. Prevent as much plant stress as possible. Do not apply additional nitrogen unless absolutely sure it is needed, especially this late.

Defoliation: The time to apply the chemical is often a tough decision to make. Above all else, it should be based on the maturity of the plants and field. Harvest schedules and prevailing weather conditions and forecast also are prominent considerations. The maturation processes stop when the leaves are taken off a cotton plant. Anytime the decision is made to apply a defoliate or harvest-aid chemical, there will probably be some immature bolls on the plant. However, a grower cannot wait until 100 percent of the bolls are mature; some will have to be sacrificed. As a general rule of thumb, the last boll to be consistently picked will probably be the first position boll on the fourth or fifth node down from the terminal. The maturity of this boll should be used as the key for timing an application of defoliant. The yield and quality of the bottom crop and middle crop are far more important than those last two or three little tiny bolls in the terminal. This decision is often hard to make.

Boll Maturity: It is generally safe to apply a harvest-aid chemical when the crop is 50 to 60 percent open, and the last boll expected to be picked is mature. To determine maturity of this boll, a visual field check is recommended. With a sharp knife, bolls from the last fruiting position desired to be picked (usually the first position boll on the fourth or fifth node below the terminal) should be cut in a cross-section. A mature boll is difficult to cut, but the real test is by looking at the seed. The seed cavity should be filled, no jelly present, and the seed coat should be dark in color. When the seed is mature, the boll is mature enough not to be adversely affected by a harvest-aid chemical treatment. Generally, the boll is mature enough to be defoliated at about 38 days of age, depending on the growing season.

Cut-out + DD 60's: Where a plant-monitoring program is employed, growers might want to look at heat unit accumulation after what is considered "cutout" has occurred. Depending on location, cutout is generally defined as that point when the crop has progressed to a point of development where the first position white flower is within four or five nodes of the terminal. The technique to make these counts is described in the Plant Monitoring booklets available from your local Extension office or the National Cotton Council. "Nodes above white flower" (NAWF) is a powerful tool that can help crop managers make or verify several decisions. Potential timing of defoliation is one of those. Count heat unit accumulation after NAWF 5 and when 750 to 800 DD 60's are accumulated, the field may be ready for defoliation. Before any treatments are made, the fields should be physically examined to determine maturity. If long-term weather records are available, this technique could conceivably be used to predict defoliation date several weeks in advance. This is just another tool.

Nodes Above Cracked Boll: This technique is valuable in verifying field maturity or other techniques. It has been found in research that boll maturity extends four nodes above the uppermost first position cracked boll (NACB). To use this technique, plants must be selected to represent the majority of the field, and they must have a cracked boll (one where lint is visible through a cracked suture) on a first position site. When this is done, determine how many nodes are between the cracked boll and the youngest boll to be harvested. The crop will be mature four nodes above that cracked boll. At defoliation time, the NACB should be within four of the youngest bolls you want to harvest. When you are counting heat units or cutting bolls, the NACB technique can be valuable for confirmation. If you are not sure the boll you cut is mature, count down the plant, and if you find a first position cracked boll within four nodes, the bolls are mature enough not to be adversely affected by a defoliant.

Department of Plant and Soil Sciences
Box 9555
Mississippi State, MS 39762

Will McCarty, Ph.D.
Extension Leader

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