Preliminary Soybean Yields

The 2008 soybean harvest is just getting under way. For most of the growing season, the soybean crop has been about 150 to 200 GDU's behind the 5-year average. Fortunately for WI soybean growers, the unseasonably warm weather we have been enjoying over the last 10 days has quickly advanced our crop towards maturity. However, unfortunately for our growers, preliminary yield estimates are variable. Most of the soybeans that were harvested over the weekend were early maturity group soybeans that were adversely affected by the dry conditions we experienced in August. As growers begin to harvest their later maturity group soybeans, yields will likely be higher due to the late rainfalls that aided seed-fill and the higher yield potential that full season soybeans generally exhibit. The preliminary yield reports from Jefferson (Joe Bollman), Iowa (Rhonda Gildersleeve), Dodge (Matt Hanson), and Green Lake (Carla Hargrave) counties show soybean yields ranging from the low 20's to about 50 bu per acre. Yields generally improve as we move from west to east (Iowa to Dodge County). Regardless of yield variability, if you saw a combine rolling this weekend you likely also saw a drill nearby as growers try to get their wheat crop planted in time to take full advantage of the warm weather and any crop insurance restrictions.

Check Combine Settings to Minimize Soybean Harvest Loss

Growers should take extraordinary precautions this year to check combine settings throughout the harvest day especially if they switch soybean maturity groups. Much of the rainfall that occurred in the dry areas of WI occurred too late to aid early maturity group soybeans (these soybeans were physiologically mature-R7 growth stage prior to rain); however many late maturity group varieties were still in the R6 (grain-fill) growth stage and may have benefited from the late August/early September rainfall. As growers proceed in harvest a quick in-field estimate can be preformed to assess where yield losses are occurring. The three areas of concern are pre-harvest loss (standing soybean), header loss (harvested swath in front of combine), and machine loss (harvested swath behind combine) (Images 1). In each area of interest count the number of beans per 10 ft2. Remember 40 seeds per 10 ft2 equal ~1 bushel per acre yield loss (Image 2).

For more information please see the following article.

Measuring and Reducing Soybean Harvest Losses

Image 1. Fall volunteer soybean in winter wheat caused by machine loss.

Image 2. Two bushel per acre yield loss

Charcoal Rot Showing up in Drought Stressed Beans

Phytophthora root rot is being blamed for much of the late season death we are experiencing in our soybean fields. However if you have experienced any droughty conditions charcoal rot may be the culprit. Charcoal rot is caused by the fungus Macrophomina phaseolina and is root disease of soybean. The development of charcoal rot this year has coincided with the very dry conditions we have seen since flowering. An early indicator of charcoal rot could have been seen around flowering with any premature yellowing of the upper canopy (i.e., yellowing of the top leaves) with eventual leaf drop of those leaves. This can often be mistaken for normal plant senescence. Also, at this point in the growing season, a diagnostic sign of the pathogen can be seen on the lower stem or root tissue of soybean and this is termed microsclerotia (Images 1 and 2). These are tiny, dark fungal structures that can seen with the naked eye after scraping the outer tissues. In terms of yield, the plants in the driest part of field may have unfilled upper pods and low plant vigor. The charcoal rot pathogen survives as these microsclerotia in the soil and in plant tissue and can be long-lived. At this point in the season, management for charcoal rot is not an option. Management for charcoal rot includes the following: (i) reduction of plant stress, (ii) variety selection, and (iii) rotation.

Images 1 and 2. Charcoal rot microsclerotia on lower soybean stems.

For more information on charcoal rot please click here