BY LARRY G. HEATHERLY

and alan blaine

The production year is rapidly drawing to a close. However, there are a few things that producers should keep tabs on through the middle of September.

Continue to monitor insect populations in May and June planted soybeans. Heavy populations can rapidly build to threshold levels that justify treatment, especially in irrigated soybeans where a high yield potential has been established. Most of the pests causing problems now are associated with dry weather. Salt marsh caterpillars, armyworms, and grasshoppers have been the most prevalent. In late July, some instances of podfeeding populations were detected. These were found in open-canopy soybeans (late plantings) and in fields that had reduced growth as a result of drought conditions. Only thorough scouting will detect podfeeding insect activity. Very little evidence of leaf feeding populations has been observed, but populations were heavy in the few isolated instances.

Continue to monitor soil moisture and irrigate later plantings in the absence of rain so that the soil is moist through the pod fill period, or until the seeds are touching the pods. This will ensure that the large number of seeds that were formed as a result of earlier irrigations and timely rain will fill to maximum size. A late-season drought can result in smaller seeds if irrigation is terminated too early, and this can significantly reduce yields below the level established by earlier, properly timed irrigations that resulted in a large pod load.

Harvest of the stateÕs 2.0 million acres of soybeans has started. Normal August and early September temperatures will promote rapid drying of pods and seeds, and this can result in shattering within 7 to 10 days of maturity in early-maturing varieties. Therefore, harvest delays during this time should be avoided. Producers are reminded that seed of early-maturing varieties that are being harvested during this hot, dry period should not be used for next yearÕs planting seed because germinability of seed maturing during this time is almost always low. It is believed that this results from the high temperatures during the maturation process, and no management practice will completely remedy this situation. Next yearÕs planting seed should be obtained from later plantings, and these later plantings should be irrigated for maximum yield and germination quality of seeds.

Research results have shown that subsoiling of dry soil in the fall will result in yield increases of the next yearÕs bean crop that will be grown without irrigation. The clay soils are usually the driest immediately after harvest because plant roots have extracted water from deep in the profile, and rainfall amounts are normally low during the July through September period. Thus, a first operation after harvest should be to subsoil fields that will be used for dryland production next year. It is mandatory that this operation be conducted before significant rainfall occurs, or the maximum benefit will not be realized. The objective is to use an implement that will lift and shatter the soil profile to a depth of 15 to 18 inches. It is believed that this process results in conditions that increase the amount of water that is available to plants. Again, the goal is to conduct the operation on soil that is as dry as possible. A 1.5 to 2 inch rain after harvest and before subsoiling may leave the soil too wet for effective lifting and shattering. Following subsoiling, surface smoothing for next yearÕs soybean planting should be done to minimize the number of large holes that may contribute to ponding of water during subsequent months. It is not necessary to pulverize the soil, but rather use an implement that will leave the surface uniformly rough. This will usually mean two tillage trips with a disk harrow and/or field cultivator. Rain during the following months should be sufficient to ÒmeltÓ large clods and make the surface smooth enough for planting in a stale seedbed the following spring. If corn or grain sorghum are to be planted the following year, beds should be formed in the fall to ensure that they are in place for next yearÕs early planting of these crops. Tillage operations that are performed on soft clays in the spring have the potential for delaying planting, and maximum effects from subsoiling may not be realized with the resultant later plantings.

Soil samples for fertility and cyst nematode analyses should be collected just before or immediately after harvest. The best way to accurately assess soil needs and problems is through soil testing. Soil sampling is the least expensive input with the greatest potential return. Many fields have lower-than-desirable pH levels, and fall is the ideal time to remedy this problem.

Now is an excellent time to evaluate varieties in trials that are scattered throughout the state. Variety selection continues to be the most important input in soybean production. It is difficult at times to look at varieties and determine differences; however, as leaf drop occurs varietal differences become more obvious. Variety trials conducted by companies and Mississippi State University in your area provide an excellent opportunity to visually assess and compare the many varieties that are available. This visual observation allows growers to compare varietiesÕ growth habit, height, maturity, and their ability to withstand various weather extremes, as well as differences in disease infestation.

There are many varieties on the market, and this makes choosing the proper variety a daunting task. This is why time should be spent now to start the decision-making process about next yearÕs choices. Consider cropping history, soil texture, desired maturity, row spacing, and disease history of a planting site when making these fall observations in the variety trial tests. Many varieties on the market are comparable, and this complicates making this important decision. If it appears that several varieties are similar and fit your situation, check with the company representatives about anticipated availability of seed and possible advantages such as pest resistance that may not show up in visual inspections.

To provide an opportunity for this fall variety comparison, a field day has been scheduled for September 8 at Dulaney Farms near Clarksdale. This location is the site of one of MississippiÕs state-conducted soybean variety trials. The test has several maturity groups represented, along with a test using conventional and Roundup Ready varieties. This field day offers an excellent opportunity to meet with company and university personnel who will be on-site to discuss varietal traits and answer questions. DBJ

Larry G. Heatherly is a USDA research agronomist at Stoneville, MS. Alan Blaine is an Extension Agronomist at Mississippi State University.

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