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Issue No. 21, Article 2/September 10, 2010

Down to the Last Soybean Scouting Trips

The speed of soybean maturity is variable this year depending on planting date and soil moisture conditions in August. I had a lot of questions about whether the rain last week came in time to save any yield for some of our soybean fields. Generally soybeans are making yield by filling seeds in the pods while they are still green, so it certainly helped in many cases. Anecdotal evidence from crop tours this year has pod numbers elevated above normal, and the general condition of soybeans is good in most areas of the state. According to the USDA NASS crop report this week, 99% are setting pods, 49% are turning yellow, and 17% are shedding leaves. The five-year average is 99% for setting pods, 31% for turning yellow, and 10% for shedding leaves, so we are ahead of those averages. With nearly half of the soybeans in the state turning yellow, we are nearing the home stretch of the bean season, and only one or two scouting trips should remain.

Consider the following notes as you finish out your soybean scouting:

  • If you suspect sudden death syndrome (SDS) or brown stem rot, scout these fields as they turn yellow to properly identify the disease. In many cases, one or two patches of SDS are observed in a field right before the rest of the field naturally turns yellow, and then it is assumed that the whole field showed signs of SDS--which may not have been the case. Furthermore, making maps of areas affected with SDS will create a useful tool to direct fall soil sampling for soybean cyst nematodes (SCN). There has been evidence linking areas with SDS infections to elevated SCN populations. The cause-and-effect relationship between these organisms is not well understood, but sampling for SCN based on SDS symptoms is a wise idea, particularly if you do not know the current levels of SCN in your fields.
  • Continue to monitor for insect feeding, particularly by stink bugs, which can feed directly on pods, reducing yield and seed quality. If you do observe significant pod feeding, you might want to put extra emphasis on harvesting the fields as soon as possible. Soybean seed quality will deteriorate rapidly during wetting and drying cycles without the full protection of the pod intact.

Feeding damage on a mature soybean pod in a field near Urbana, September 7.

  • Scout for weeds that were not fully controlled and for fall-emerging weeds under the crop canopy. Glyphosate-resistant weeds are on the rise. Even if the escapes were not bad enough to cause economic loss in this growing season, you want to know if they are going to contribute to the weed seedbank and be a bigger problem in years ahead. In particular, look for species like horseweed, giant ragweed, common waterhemp, morningglories, and lambsquarters, to name a few. This year's scouting reports could provide important information as you plan your herbicide programs for the succeeding year. And if you are in a no-till system, scouting for fall-emerging weeds before harvest may give an indication as to whether you need to consider a fall herbicide program.
  • After the leaves have dropped, collect final stand counts prior to harvest. I have written many articles on reducing seeding rates. Understanding how you can change soybean seeding rates in your operation requires understanding how your planter system, seedbed preparations, and growing conditions affect soybean stands on your farm. Linking seeding rates, initial soybean stands, and final soybean stands will be an important consideration as you consider seed purchase and planting decisions next year.
  • Before you actually harvest, make certain your combine is properly adjusted and in good working condition. The most common loss of soybean yield due to harvest operations is at the cutter bar, so pay its adjustments and condition particular attention. As you harvest, monitor your loss and make appropriate readjustments. Monitoring loss can be done simply by counting the soybeans left on the ground behind the combine. Harvest loss can't be eliminated, but a good goal is to lose no more than 1 bushel per acre, which is 30 to 40 soybean seeds per square yard, depending on seed size. For more information, see "Combine Settings for Minimum Harvest Loss."

I suspect several fields of soybeans will reach maturity and begin to be harvested before the next issue of the Bulletin in two weeks, so I wish everyone a safe and plentiful harvest.--Vince M. Davis

Vince Davis

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