Agronomy Notes

August, 2001

Contents

CORN

Dr. Erick Larson

Deciding when to harvest - Corn may be harvested any time after grain reaches physiological maturity, which occurs at around 30 percent moisture. However, corn may not be safely stored until considerable moisture loss occurs. For this reason, grain elevators discount wet corn to account for drying expenses and moisture weight loss during drying. Moisture dockage schedules may vary significantly between elevators, so compare rates carefully. Most schedules discount about 2.5 percent per each percentage point of moisture above the standard, and may increase as moisture content rises. Water evaporated during drying (shrinkage) accounts for 1.18 percent of the dockage per each percentage point of moisture. The producer loses this weight regardless of whether he sells wet grain to the elevator, drys it mechanically or lets the grain field dry. A producer should subtract this value from the dockage rate to show "actual" dockage.

Don't give away corn - Producers selling corn at less than 15 percent moisture are giving away profit. At 14 percent moisture, a producer harvesting 100 bushels/acre of corn is losing $2.35 per acre; at 13 percent moisture, the loss is $4.71 per acre (at $2.00/bushel). This loss is solely from reduced grain weight due to lower moisture content, and closely approximates the "actual" dockage most elevators charge for high moisture corn. Consequently, growers seeking a maximum profit should always try to finish harvest before grain moisture falls below 15 percent, because harvest losses accumulate as grain dries below 20 percent. Since corn loses moisture at the rate of approximately 0.6 percent per day during the harvest season, begin harvest early enough to guarantee that all corn is harvested before it reaches the 15 percent moisture level.

Harvest losses - Harvest losses normally increase when grain dries in the field, due to increased shattering by the combine, stalk lodging, dropped ears, weathering and predation. Corn infested with Southwestern corn borers is particularly susceptible to harvest loss, since these insects destroy stalk integrity and cause stalk lodging and ear drop. Producers should check closely for loss while the combine is harvesting and adjust the combine to minimize loss. Two corn kernels per square foot or one dropped ear per 100 feet of row equals about one bushel per acre yield loss. Research indicates combine efficiency is best (harvest losses are lowest) when corn grain moisture is about 20 to 22 percent.

Aflatoxin tips - Little aflatoxin potential is expected in corn this year, because lower than normal temperatures predominated during late May through July. However, improper grain handling, particularly with high moisture grain, can quickly promote aflatoxin development after harvest. Wet grain should be immediately dried to below 15 percent 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. This is critical to grain quality, because the fungal growth that causes aflatoxin will escalate to excessive levels very quickly in wet, warm grain. Conversely, fungal growth becomes dormant when grain moisture drops below 15 percent. Producers should also thoroughly sanitize handling and storage facilities before and during harvest.

RICE

Dr. Joe Street

In general, the rice crop looks good. Much of the rice has headed and some will soon be ready to harvest. For rice that has just headed or is near heading, this is a critical time to protect the crop. Growers should have received a post card concerning the very high population of stinkbugs. Growers who did not receive the postcard concerning stinkbugs and blast should contact Dr. Joe Street to be added to the mailing list.

The stinkbug population is higher than any in recent memory and will cause significant damage if left uncontrolled. A stinkbug puncture of the grain in the early milk stage can cause the grain to be blank or aborted. A puncture during the soft dough stage will cause pecky rice; with current supply and demand, rice with high peck will be difficult to sell, especially in the parboil market. Quality standards are increasing for rough rice being shipped out of this country, so high quality rice is a must in this marketing situation.

There has been considerable interest in using ULV malathion for stinkbug control. While ULV malathion seems to be effective, it has little or no residual activity and repeat applications will probably be necessary. Jim Robbins, MAFES Entomologist at DREC, is continuing to evaluate insecticides for stinkbug control; so far, none of them offers better residual control than Karate.

So far blast has not been a serious problem. While the cool weekend in mid-July was favorable for blast development, the recent hot dry weather is not. Based on current weather forecasts, blast should not be a problem, but careful scouting is still recommended.

According to preliminary information, about 20 to 25 percent of Mississippi's rice acreage is in Priscilla. During the past two years, with unfavorable weather conditions during maturity and harvest, Priscilla milling yields have been erratic. Since milling yields were higher in fields harvested at about 20 percent moisture, growers should initiate harvest at higher (20-21 percent) moisture levels.

COTTON

Dr. Will McCarty

Crop Situation: According to USDA crop estimates, Mississippi farmers planted 1,700,000 acres of cotton in 2001, up 400,000 from the 1,300,000 planted in 2000. Cotton went into July with good vegetative growth and a slightly lower percent fruit retention than desired. Early season plant bugs and other problems have caused a reduction in fruit retention on the lower branches. This indicates that some fields will require a longer time than usual to reach maturity. Depending on moisture through August and into September, Mississippi farmers could still pick an average or better than average crop.

Vascular Wilts: Growers are seeing significant evidence of these diseases this year. While no variety is resistant to the diseases, some varieties are more tolerant than others. To prevent this problem next year, plant tolerant varieties, implement a sound fertility program, and try to prevent stress to the plant as much as possible. No magic cures exist. If you see the problem this season, take note of the field where it occurs and which variety is having the biggest problem. If you irrigate, do not allow the crop to swing from one extreme to the other. Attempt to protect the crop from drought stress. In irrigated fields with good fruit set and yield potential, there may be a response to foliar feeding with potassium. In dryland fields, response is less likely.

Nematodes: Remember to have your fields tested for the presence of nematodes. August is an excellent time to take soil samples for nematode analysis. Keep in mind that dry soils may give misleading information. If soil conditions are dry, consider waiting for moisture before sampling. You should take subsoil samples, also; nematodes move downward in the soil profile as the soil dries. A sound nematode analysis program is as important as a sound soil fertility testing program.

Defoliation - When to apply a defoliant is often a tough decision to make. Above all else, base your decision on the maturity of the plants and field. Harvest schedules and prevailing weather conditions and forecasts are prominent considerations, also. The maturation processes stop when the leaves are taken off a cotton plant. Anytime the decision is made to apply a defoliant 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 defoliant application. The yield and quality of the bottom crop and middle crop are far more important than those last two or three tiny bolls in the terminal.

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, make a visual check of the field. Select bolls from the last fruiting position desired to be picked (usually the first position boll on the fourth or fifth node below the terminal); with a sharp knife, cut the bolls in a cross section. A mature boll is difficult to cut, but the real test is done by looking at the seed. The seed cavity should be filled, there should be no jelly present, and the seed coat should be dark in color. When the seed is mature, the boll is mature enough to not 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.

Cutout + DD 60's - "Nodes Above White Flower" (NAWF) is a valuable tool that can help crop managers make or verify several decisions, including potential timing of defoliation. Count heat unit accumulation after NAWF 5; when 750 to 800 DD 60's are accumulated, the field may be ready for defoliation. Before making any treatments, physically examine the fields to determine maturity. Long-term weather records are another tool that you may be able to use to predict defoliation date several weeks in advance.

Nodes Above Cracked Boll - This technique is valuable in measuring field maturity or verifying other techniques you may have used to determine readiness for defoliation. Boll maturity extends four nodes above the uppermost first position cracked boll (NACB). Select plants that represent the majority of the field; these plants must have a cracked boll (one where lint is visible through a cracked suture) on a first position site. 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 to not be adversely affected by a defoliant.

For more information, ask your county agent for a copy of the latest Cotton Defoliation Information Sheet (IS 529), or obtain an online version at msucares.com.

FORAGES AND PASTURES

Dr. Malcolm Broome

Pasture Arithmetic and its Application - The "3 R's" can't help your cows, especially since they can't read, but one "R" (Arithmetic) should be of some use to the cattleman. By using some mathematical calculations, you can get an idea of pasture allocation, stocking rate and number of pastures needed to better use the forage you grow.

The "cow" doesn't always eat what the book says, nor do farmers have "normal" weather. Using top quality pasture 3 to 16 inches tall will allow 3.0 to 3.5 percent body weight intake of dry matter (DM), which is considered normal; producers want to use 50 to 70 percent of this DM on average. Well-managed summer pastures will produce 300 pounds of forage per acre per inch of rainfall. Thus, 20 inches of rain would provide about 6,000 pounds of forage per acre during the growing season.

The lower 2-3 inches of forage will not be available for use if growers look at using only 50 percent of the forage produced; an alternative is to subtract 1000 pounds per acre from your estimated forage production. An easy way to estimate production is to measure the average height of your grass, using a yardstick, and then multiply the number of inches by 250 or 300 to get pounds of forage DM. Using this information, then, a grower can compute the number and size of pastures needed for his herd.

Assume a grower has 30 cows weighing 1,000 pounds each; each cow will consume 3 percent of its body weight. The grower wants to graze a pasture for 10 days, then allow 30 days' regrowth before grazing it again. The grass is measured at 8 inches, producing 2400 pounds of forage per acre (8 X 300). The producer wants to use 60 percent of the available forage, or 1440 pounds. Based on the 3 percent of body weight estimate, each cow will eat about 30 pounds each day.

FORMULAS FOR ABOVE:

Number of pastures:

Days of rest
Divided by Days of grazing

= answer + 1 = pastures needed

Acres per pasture:

Average wgt. of cows x DM consumed x # cows x # days grazing
Divided by D.M. available x percent D.M. utilized

Total acres needed:

Number of pastures x acres/pasture

= acres needed

Stocking rate:

Number of cows
Divided by Total acres

= head per acre

Stocking density:

Number cows
Divided by Pasture size

= head per pasture

Results: You will need 28 acres, divided into four 7-acre pastures, to graze 30 cows for 10 days per pasture and allow 30 days' rest between grazings. This gives a grazing pressure of 4.2 head per pasture with a stocking rate of 1 head per acre. Remember: water availability must be included for these assumptions to work.

DEPARTMENT OF PLANT AND SOIL SCIENCES
Box 9555
Mississippi State, MS 39762

Will McCarty, Ph.D.
Extension Leader

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