No. 20 Article 3/August 27, 2010

Looking for that Extra Soybean Yield

Soybean harvest will happen much earlier this year than the last two. Most soybeans are somewhere in the R6 growth stage, and a few varieties of earlier maturity groups are at R7 (one mature color pod) and starting to turn and drop leaves. In a few areas, sudden death syndrome is the culprit of the early color change and leaf drop, but some of both is occurring naturally at this point. The change in soybean doesn't in general appear to be happening as fast as in corn, so I expect most growers are getting combines ready for corn and will harvest some of that crop first.

The last USDA crop report estimated an average soybean yield of 49 bushels/acre for Illinois. In some areas this might look bullish, but in my opinion it looks on target as a whole. Fortunately, many areas of the state caught a much-needed rain at the end of last week to help fill or finish filling soybean pods. It was a rain I think many would classify as a "big-yield rain" for soybean, and I think it brought many fields to an average yield and gave many good fields the "extra" yield producers were looking for. It appears that late-August and early-September temperatures may remain very favorable for soybean plants to continue good seed fill, and we have so far been blessed with several days of clear skies and sunny conditions to keep photosynthesis operating strong.

In issue 19 (August 13), I noted that many areas were experiencing dry conditions during a spell of high temperatures. Fields and areas in fields with soybeans that were established well and grew better root systems--usually in better-drained areas--managed the heat and dry conditions better than the areas that struggled early in the year. Nonetheless, I was observing pod fill in a couple of fields throughout that stretch of hot and dry days. Through the early part of the week of August 10, plants appeared to not be filling fast, but I was not observing major pod loss. However, by the end of that week, many of the smaller pods, particularly on terminal racemes, were falling off the plants. Unfortunately, I felt I watched a lot of "extra" yield drop during that time.


Soybean pods aborting on nodes in the lower part of the canopy (Urbana, August 25).


Soybean pods aborting on the terminal raceme (Urbana, August 25).

The storm front that came through much of Illinois on August 15 and 16 didn't bring as much rain to many areas as was needed, but it did bring cooler temperatures through last week that seemed to allow beans to cope better, even in the drier areas. And the higher rainfall amounts that swept much of the state last weekend seemed to be timed well for many fields to finish the pod-filling growth stages (R6).

As I pointed out in issue 19, scouting and observing the relationships among disease, insect, and agronomic practices are still important through the R6 growth stages. When scouting for diseases, be sure to correctly differentiate between sudden death syndrome and brown stem rot by splitting stems. Regarding insects, aphids remained a nonconcern this year, and I'm sure nearly all areas (with the exception of double-crop soybeans) are beyond the growth stages that would warrant an insecticide. However, continue to be on the lookout for stink bugs, which could still cause loss by feeding on pods. Lastly, as you ready yourself and equipment for harvest over the next two weeks, keep safety in mind.--Vince M. Davis

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