Much of the Delta received little or no rain during June. Only about 1.5 inches fell at Stoneville between May 30 and July 1. This early season drought is uncommon, considering that Stoneville typically receives an average of 8.7 inches of rain during May and June, almost 3 in. more than has been received during those months this year. The shortage of rainfall has been compounded by the higher than normal average maximum air temperatures of 87 degrees during May and 92 degrees during June. Average daily pan evaporation at Stoneville during May was 0.29 inches, while June had a daily average of 0.33 inches. Both of these values are over 0.04 per day greater than the 30-year averages. Water use by a well watered soybean crop that is at or near a full canopy is similar to pan evaporation. Thus, it is safe to say that soybeans that were planted during April and that are irrigated are using at least 0.3 inches of water per day. Simple math shows that the crop will need 3 inches of water every 10 days to maintain a 0 water balance under this water use pattern.

Weed control efforts in April and May soybean plantings (82% of Mississippi soybean crop) should be complete by now. Any expenditures for weed control made after this time to these plantings will not be economical except in extreme cases of salvage control, or for control of large weeds such as Johnsongrass and coffeeweed that will continue to grow because of an open canopy and that can still be controlled by herbicides. Regardless of the system, a good rule of thumb is to keep the crop weed-free for 4-5 weeks following emergence.

MG IV varieties that were planted in wide rows (30-40 inches) probably have not and will not make a complete canopy, and this could result in late season weed infestations. These infestations will result in reduced yield where irrigation is applied, but probably will be of little or no consequence in nonirrigated plantings with normal July and August rainfall patterns. Late weed infestations are the result of failing to match the row spacing with the variety, and continued application of herbicides will increase costs with no assurance of benefit. If this situation has occurred, use it as a lesson and an impetus to consider changing to narrow rows for early plantings in 1999. Most of the currently used varieties will not form a complete canopy in wide rows when planted early, and even the best early-season weed control efforts may not be enough to overcome yield-reducing weed infestations that will continue to occur until harvest.

Plantings of MG IV soybeans such as DP 3478 made in early to mid-April started setting pods in early to mid-June, and started seedfill in late June early July. Thus, they are in a critical period of development. Drought stress that is occurring will result in reduced pod set and underdeveloped seeds in pods. There is not much room for compensation once these later stages of development have started. Timely rainfall or properly timed irrigation is the only remedy for this extreme situation since soil moisture is greatly depleted due to the lack of rainfall. Producers who can irrigate should have started irrigating these plantings in mid-June and should be applying about 3 inches every 10 days as a rule of thumb. Rains of 0.5 inches or less probably should be disregarded as insignificant supplements to irrigation. The bottom line is that irrigation during this drought is extremely important for maintenance of high yield levels. Given the stage of this crop, irrigation of April planting will be approaching completion in late July-early August. The dryland crop has thus far relied heavily on subsoil moisture. If soil water reserves are not replenished soon, only dry land plantings that were subsoiled last fall appear to have promise for excellent dryland yields.

April plantings are rarely susceptible to late-season insect infestations. Therefore, insecticide applications should not be necessary for these plantings except in isolated, unique situations that are verified by reliable scouting. Pests that are currently on soybeans are grasshoppers, bean leaf beetles, and stink bugs. Stink bug numbers will warrant monitoring and possible treatment as corn matures. Recent research indicates that treatment for insects in early soybean plantings is not justified in the Delta region.

The bulk of this crop is rapidly approaching the time frame for considering foliar fungicide or Dimilin/Boron applications. The foliar fungicides can be applied in split applications; one at beginning podset (R3) and one at beginning seedfill (R5). To accurately determine the growth stage of soybeans, find the uppermost fully expanded trifoliolate leaf, and count down to the third node below this leaf. When 50% of the plants have a pod 3/16 inches long at this node, the stage is (R3). When 50% of the plants have a 1/8 inches long seed in a pod at this node, the stage is R5. Growers should also consider making only one application at R5 to realize a savings in material and application costs. Applications of these materials should be considered only in high-yield environments or on soybeans that are being grown for next year’s planting seed, since yield enhancement is small and/or erratic in the Delta.

The application of Dimilin and Boron to soybeans has created recent interest. Dimilin is an insect growth regulator that will control several insect species and provide suppression of loopers. It has exhibited fungicidal properties. Tests conducted on the coarse-textured soils of the southeastern Coastal Plains have shown yield increases of over 25%. Dimilin should be applied at the R3 growth stage, which many MG IV’s have already passed. The cost of the material is low, so a small yield response will pay for the material and its application. Currently, it appears that the addition of Boron will not provide any benefit to soybeans grown on the clay soils or irrigated soils of the Delta.

Harvest of early and mid-April plant-ings of 1998 soybeans should start about August 10 - 20 and continue into early September. Last year’s early-harvest price bonus is probably a pipe dream this year, so a respectable price for this crop probably will come only from early pricing in the $6.25 - 6.50 range. If harvesting early, producers should ensure that elevators will be expecting soybeans since many will be receiving corn and sorghum at this time. Also, hauling capability should be finalized early to ensure that conflicts with corn and sorghum do not occur. Remember, early-planted MG IV soybean varieties mature during the hottest, driest time of the year, and this causes them to have a tendency to shatter soon after maturity. Therefore, their timely harvest is crucial. DBJ

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Site last updated January 10, 1999.