Growers' late-season options for above-average soybeans

At the middle of July, the Mississippi soybean crop ranged from just planted to harvest in less than 30 days. The north Delta, north Mississippi and parts of south Mississippi were repeatedly plagued with above-average rainfall through early July. Although the crop as a whole is early, these areas never got a break from wet weather.

More replanting occurred this year than in previous years, but I believe some could have been avoided with the proper seed treatment. As it gets later and it warms up, the tendency is to back off seed treatments. It is the rain, however, that causes us to lose a stand more than 90 percent of the time. Everytime you decide to not use a seed treatment, you are trying to outguess the weather.

There are some late-season options you might what to consider.

The majority of fields in our SMART program have reached a stage where we are scouting for insects and mid- and late-season diseases. Some fields of early-maturing varieties are less than 40 days from being finished.

These early fields avoid some late-season insect and disease problems (primarily worms and foliar diseases). We often avoid many concerns of full-season soybeans with the early system.

Several options exist. One is the use of foliar fungicides — mainly Quadris and Topsin M. Not every field is a candidate for fungicides. Base your decision on variety, maturity group, planting date, and cropping system (rotated and irrigated vs. dryland).

Due to earliness, response to a foliar fungicide on Group 4 varieties has been inconsistent. That changes as you plant later or if you use a full-season variety.

Before making any decision regarding late-season strategies, stage soybeans to accurately time the application. Most of the products should be applied between the R1 and R3 growth stage. To stage a plant, find the uppermost node with the most fully expanded leaves. This is node one, count down four nodes and determine the stage of growth at that point.

R1 is when you observe the first bloom on the plant. R2 is when the plant is in full bloom. The R3 growth stage is when pods at this node are 3/16 inch long. R5 is when the pods are fully elongated and just beginning seed development.

Don't let the indeterminate varieties fool you. Base your decision on the fourth node down — do not consider fully elongated pods on the bottom of the plant. It is easier to determine the stage of growth of Group 5s (being determinate) than of indeterminate varieties, but the determination is easier if you always consider the same node.

A second option is Dimilin. SMART fields in the Delta are earlier than those in the hills, but we want to protect the yield potential of this crop. Why Dimilin? Dimilin is probably the most underused and misunderstood product on the market. It has been found over the years to provide three benefits: (1) insect control, (2) disease control, and (3) yield enhancement (for reasons often not understood).

When we began making late-season decisions on Group 4s, we had only 45 to 50 days until the crop was finished. We did not need long-term protection. On the basis of observations and past history, we decided to put 2 ounces of Dimilin on all SMART fields — both irrigated and dryland.

Two men working with me as early as 1983 observed there was frogeye leafspot where they applied Dimilin. It can provide a number of benefits. Which ones depend on your particular situation and cropping history.

We are applying it between the R3 and R4 growth stages. Dimilin will provide about three weeks residual.

Putting it out at that stage gets it into the plant before problems start — especially since it has a long residual. Last year we waited too long and did not stop the initial infection. According to our work, increasing the rate above 2 ounces does not increase the residual.

In the case of worms, Dimilin will provide excellent control of velvetbean caterpillars, green cloverworms, cabbage loopers and salt marsh caterpillars (it only suppresses soybean loopers). Under heavy looper pressure in the south Delta, Dimilin will suppress loopers seven to 14 days, depending on the infestation level.

If Dimilin provides just one of the benefits observed in the past, it will more than pay for itself. It is a fairly inexpensive option (2 ounces at approximately $2.60), compared to using Quadris or Topsin M. Since response to Quadris and Topsin M has been less consistent on our early-planted soybeans, we believe this is the cost-effective option for early-planted beans.

Is that application needed on every acre? No. Base your decision on the time of year, planting dates, variety and past cropping history. It is probably too late on early-planted Group 4s (we sprayed our SMART fields between June 20 and July 9).

One area of Mississippi that will benefit greatly from the use of Dimilin is the hill area. Given the spectrum of worms and average planting dates growers in this region — particularly those who have someone checking their fields — would be well-served to blanket apply Dimilin at the R3 growth stage.

Talk to your Uniroyal representative. The company has a guaranteed program on this application, but it must be applied at the proper time.

Our final objective goal was to piggyback a pyrethroid or methyl with Dimilin (if needed) to clean up any early insect problems. Of all the early-planted fields we have in our program, only three had stink bugs at a level that needed spraying prior to July 8. There are treatable numbers out there, but they are quite erratic at this time.

Fields needing spraying this early may have a history of stink bug problems, or the field may be serving as a trap crop, or the field may be near overwintering areas.

Early planting early-maturing varieties avoid a lot of late-season problems. As full-season plantings (Group 5s) approach R3 to R4, growers will be make additional decisions that will include Quadris. Achieving top yields requires late-season management.

I plan to apply Quadris plus Dimlin and a material for stink bugs (if needed) on all irrigated Group 5s. If there is no insect pressure, I will not include an insecticide at that time. Fields will be monitored for pests and treated as necessary.

Usually we have to spray for loopers every year south of Hwy. 82 (in the Delta). Since loopers usually are not as widespread north of Hwy. 82, only a well-timed Dimilin application may be needed.

Don't fail to check soybean fields for late-season insects. If loopers develop there are several excellent options: Larvin, Tracer, and others. We received a Section 18 again this year for the use of Intrepid on loopers.

The vast majority of the Mississippi soybean crop is above average. Let's do what is necessary from a pest and disease standpoint to reap the benefits.

Alan Blaine is the Mississippi Extension soybean specialist. e-mail: [email protected].

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