Stress on R6 Soybean

I have logged many miles across Southern WI the past week and have noticed several pockets of soybean that could use some rain. The U.S. Drought Monitor service verifies my wind shield scouting as it places most of southern WI in the abnormally dry category (Image 1). Across southern and central WI the average soybean field I have been in is at the R5.5 to R6 growth stage (full seed). In WI the R6 growth stage on average lasts ~18 days but will range from 9 to 30 days depending upon the weather. Soybean in this stage use about 1/4 to 1/3 inches of water per day. Lack of sufficient water during this growth stage can cause young pods and developing seed to abort reducing the number of seeds per plant (Images 2 &3).

Image 1.

Images 2 & 3. Stress induced seed and pod abortion at R6 soybean.

Soybean plants can reduce the size of their leaf pore openings to reduce the loss of water vapor. This also reduces the intake of carbon dioxide and the manufacturing of photosynthates which slows plant growth. When normal soil moisture returns, normal growth is resumed. This ability to reduce metabolic activity allows plants to tolerate dry spells without dying or harming their ability to resume growth when normal moisture returns.

If stress has severely affected pod set and seed fill, and if livestock feed is needed, soybeans can be harvested as a forage for ensiling. Highest protein and yields are obtained from soybean harvested at the R6 to R7 growth stage. Harvesting soybeans for forage between the R1 and R5 stage will result in a very high quality silage, but dry matter yields will be reduced significantly. Forage quality will be reduced from R5 soybean forward if a conditioning process is used during harvest. Conditioning will cause significant seed shattering.

Goss's Wilt of Corn

We are starting to receive an increase in the number of reports, calls and/or emails regarding Goss's wilt of corn. Goss's wilt is caused by the bacterium, Clavibacter michiganensis subsp. nebraskense. This disease has been on the increase in the past two years, including being found in numerous seed corn and sweet corn fields in Wisconsin in 2010. Significant yield losses can occur in very susceptible hybrids.

Symptoms of Goss's wilt include: distinct light tan/yellow to gray lesions, with wavy or irregular margins that follow the leaf veins. Within the lesions, dark green to black specks or flecks [freckles] are common and the lesions often have a shiny appearance due to the bacteria oozing onto the leaf surface. As symptomology progresses, lesions can coalesce causing whole leaves to be blight, and furthermore, there can be wilting and stalk degradation leading to entire plant death. To examine the stalk for Goss's wilt, split the stalk and look for an orange to brown color with water-soaked and slimy tissue.

Currently, there is no good, in-season management tactic for control of Goss's wilt. As a bacterial disease, foliar fungicides are not effective.

Reports from Wisconsin follow on several recent reports from surrounding states. The links below will take you to several of these bulletins, which also provide several excellent photos of this disease:

1) Illinois

2) Iowa

3) Minnesota

Since yield losses can be significant, it is important to properly diagnose Goss's wilt in order to develop an effective management plan. This disease can be confused with another bacterial disease, Stewart's wilt, as well as fungal diseases like Northern corn leaf blight and Diplodia leaf streak. We recommend that you submit samples for proper identification of Goss's wilt to the Plant Disease Diagnostic Clinic. Make a note of the hybrid from fields where Goss's wilt was found and talk to your seed dealer about hybrids that have better Goss's wilt ratings if this disease has been confirmed. Cultural management includes tilling fields immediately after harvest and burying residue. Planting corn into the same field in the next growing season is not recommended. Instead, rotate to a non-host crop like soybean.

The Official 2011 WI Winter Wheat Performance Test Results

Wisconsin saw a 37% increase in winter wheat acres harvested (315,000) in the 2010 -2011 growing season compared to the previous year. The forecasted yield for the 2011 crop is 68 bu/a, up 4 bu/a from last year. The increase in winter wheat acres was due to timely corn and soybean harvest coupled with increased commodity price. Wheat that was established in a timely manner last fall looked very good to excellent going into winter dormancy; however some areas had delayed emergence and poor fall growth due to dry soil conditions. Late planted wheat suffered from poor tiller development that led to thin stands and weed control problems. Spring growing conditions were mostly favorable across the state; however excessive rainfall did impact wheat in some low lying areas. Warmer-than-normal temperatures in July accelerated crop maturity, however yields were largely unaffected by the hot weather.

Winter wheat yields were variable across our testing locations due to variable rainfall, planting date, and disease pressure. Wheat yields at the Janesville, Lancaster and Arlington, and Chilton locations averaged 86, 102, 97 and 71 bu/a, respectively. Wheat yield and test weight at Chilton was reduced due to variable stands and poor tillering caused by adverse weather conditions (extremely wet and cool early spring) as well as delayed harvest caused by frequent rainfall events. Overall, winter wheat test weights were excellent in 2011. No winterkill was noted at any location in 2011.

Please visit www.coolbean.info to view the official results.