Anticipating a Great Wheat Harvest
By Sam Custer
OSU Extension, Darke County 

I have looked at a lot of fields of corn, soybean and wheat in the last two weeks as I have checked our Western Bean Cutworm traps and checked on our Manure Side Dress research plots.  The corn and beans for the most part look great.  I am concerned with weed pressure in some fields as it appears that our population of resistant marestail and giant ragweed continues to expand. 

Pierce Paul, OSU Extension Crops Disease Specialist, reports that we are quickly approaching the end of what will likely end up being a very good season for wheat production. So far only very low levels of diseases, pests and other problems have been reported, and post-pollination conditions have been excellent for grain development. Powdery mildew, and Septoria and Stagonospora leaf blotch all remained low and restricted to the leaves below the flag leaf in most fields. Recent reports coming in from across the state indicate that the levels of head scab are also low this season, with only a few fields reporting about 5 to 10% incidence (5-10 heads out of every 100 heads showing symptoms of scab). This is very consistent with the predictions made by the scab forecasting system and is likely due to the fact that in spite of relatively frequent rainfall this season, conditions remained cool throughout the critical flowering and early grain development growth stages in most areas. 

Wheat harvest is just getting started in southern Ohio, will likely start in Darke County next week and continue across the state over the next three weeks. Contrary to the hot and dry conditions observed in 2012, which shorted the grain-fill period considerable, the 2013 wheat season has been relatively cool with good moisture during the weeks following anthesis. Typically grain-fill in Ohio lasts about 15 to 21 days, and poor growing conditions usually limit productivity to about three bushels per acre per day. However, when disease levels are low and conditions are cool during the month of June, the grain-fill period may be as long as 30 to 45 days and productivity could exceed three bushels per acre per day. Moreover, low scab incidence usually means low vomitoxin contamination of the grain. So, together, low disease levels, low grain contamination with vomitoxin, extended grain-fill, and high productivity may result in high yields and test weights and excellent grain quality in 2013.   

If you are thinking about double crop soybeans, Laura Lindsey, OSU Extension Soybean Specialist, encourages you to think about the following factors:

1.)    Soil moisture and rainfall-  Soil moisture and subsequent rainfall are essential to double crop soybean after wheat.  When seeds are planted into dry soil, it may take weeks for soybeans to germinate/emerge and only occurs after rainfall (which we saw during the drought of 2012).  If possible, adjust planter to place seed in moist soil, but do not plant deeper than 1.5 inches as soil crusting may become problematic. 

2.) Relative maturity-  As planting is delayed, there is concern about whether late maturing varieties will mature before frost.  When planting late, we recommend planting the latest-maturing variety that will reach physiological maturity before the first killing frost.  Soybean flowering is triggered by day length.  As days get shorter (and nights get longer) after June 21, soybeans are triggered to flower which generally occurs around the first week of July.  Later maturing soybeans will put on more vegetative growth before flowering.  The table (adapted from the Ohio Agronomy guide) gives relative maturity guidelines for late planted soybeans.

3.)  Row spacing and seeding rate-  Plant double crop soybean in 7.5-inch row spacing.  Canopy closure is necessary to maximize yield of late planted soybeans.  If planting during the second half of June, 225,000 to 250,000 seeds per acre is recommended.  In early July, 250,000 to 275,000 seeds per acre is recommended. 

Mark Loux, OSU Extension Weed specialist says a weed free start is the most critical aspect of a weed management program for double-crop soybeans.  This can be challenging to achieve where glyphosate-resistant marestail are present after wheat harvest.  Problems with marestail include the following:  1) most populations are now glyphosate-resistant and many of these are also ALS-resistant; 2) it’s usually not possible to use 2,4-D ester and wait 7 days until double-crop soybean planting; and 3) marestail that were tall enough to be cut off by harvesting equipment will be even more difficult to control.  Our research indicates that there are no herbicide treatments that consistently control glyphosate-resistant marestail populations that have regrown following mechanical disturbance or prior herbicide treatment.  Certainly one of the best options is to plant LibertyLink soybeans, which allows for a POST application of Liberty to help control plants that survive a preplant burndown.  The following are the most effective burndown options for control of marestail prior to double-crop soybean emergence: 

Liberty (32 to 36 oz) + Sharpen (1 oz) + MSO + AMS (can also add metribuzin)

Liberty (32 to 36 oz) + metribuzin (4 to 8 oz of 75DF) + AMS

Glyphosate (1.5 lb ae/A) + Sharpen (1 oz) + MSO + AMS 

We suggest using a spray volume of 20 gpa for any of these treatments, and avoiding nozzles that produce large droplets.  Results with a combination of glyphosate and 2,4-D may be more variable then the treatments listed. 

With regard to the control of weeds that can emerge after double-crop soybean planting, and the entire weed control system, the following approaches can be considered.

1.  Plant any type of soybean, and include a residual herbicide with the burndown treatment so that POST herbicides are not needed.  A good strategy in Roundup Ready or nonGMO soybeans even where POST treatment is needed, since POST marestail control might be impossible in these systems.  Residual herbicides used at this time of the year should be restricted to those that have little or no carryover risk – such as metribuzin, Valor, or low rates of chlorimuron or cloransulam products.

2.  Plant a LibertyLink soybean, and apply Liberty POST as needed.  Probably the best option for control of later-emerging marestail or plants that regrow after the burndown, assuming that there is any Liberty available.

3.  Plant a Roundup Ready soybean and apply glyphosate POST.  Should work for most weeds, but not a good choice if the POST application needs to control marestail.

4.  Plant a nonGMO soybean and apply conventional POST herbicides (Flexstar, Fusion, Select, etc) as needed.  This system has the most potential for soybean injury, but seed may be cheaper than the other systems.  Not a good choice if the POST application needs to control marestail. 

For more detailed information, visit the Darke County OSU Extension web site at www.darke.osu.edu, the OSU Extension Darke County Facebook page or contact Sam Custer, at 937.548.5215.