Field Crop News and Notes

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Winter Dandelion Survival 

        Dandelions pose one of our biggest weed control problems in Wisconsin.  Several years ago, Jerry Doll, UW Extension Weed Specialist, monitored the survival rate of various sized dandelions over the course of two winters and reported these results.  Seventy-three percent of the plants with only two leaves going into winter survived; 87 percent with three leaves survived, and; 94 percent with four or more leaves survived. 

        With these high survival rates (even for the little guys), it’s not surprising we encounter problems with dandelions even when fall herbicide applications are sometimes made.  This is especially true for no-till systems.  If alfalfa, quackgrass, or corn stalks are protecting the young dandelion plants from spray contact in the fall, there’s a good chance for dandelion problems the next spring.  

Chisel Plow Sweeps 

        Chisel plows are popular, but they don’t necessarily guarantee 30 percent crop residue on the soil surface the next spring.  This is especially true where twisted shovels are used as the soil engaging tool.  Sweeps offer an alternative to twisted shovels and look much like the more familiar sweeps used on row crop cultivators except they are much larger.  They offer several advantages:

·         They leave a much smoother soil surface, which may help to eliminate one extra secondary tillage operation.

·         They leave significantly more crop residue.

·         They penetrate easier than shovels or chisel points. 

        Chisel plow sweeps require no more horsepower than twisted shovels.  When choosing sweeps, select a size that is 1 or 2 inches wider than the shank spacing of your chisel plow.  This will insure good soil loosening and weed kill.  Finally, use stops to control depth.  Producers who have used sweeps report no more problems where rocks are present than with standard shovels. 

Brown Root Rot of Alfalfa 

        Brown root rot of alfalfa was first detected in Wisconsin this year, although it possibly has been present in the state for many years.  The disease is unique because the responsible pathogen can grow at temperatures below freezing.  This means that plants can become infected during the dead of winter when there is virtually no competition from other disease organisms.  The Brown root rot organism was isolated from a number of plants that had been winterkilled or injured this past spring in northern and central Wisconsin.  Currently there is an effort to determine where the disease organism is present.  Recently, the disease was identified in New York.

It Doesn’t Pay to Delay Corn Harvest 

        We’ve reached that point in time when there is simply no good reason to delay corn harvest.  From a grain moisture standpoint, dry down becomes minimal after November 1^st.  Wisconsin studies show only about a 2 percentage unit drop in kernel moisture during the month of November.  In a 2002 research trial from Ohio, stalk lodging increased from 6 percent to over 25 percent during November and grain yield decreased 30 percent.  The loss of one normal sized ear per 100 feet of row translates into a loss of more than one bushel per acre.  Bottom line:  After November 1, get corn out of the field as soon as possible. 

Nitrogen Credits from Low-Yielding Soybeans 

        Reduced soybean yields have prompted a few questions regarding the appropriate nitrogen (N) credit that might be given a subsequent corn crop in 2004.  Larry Bundy, UW Extension Soil Scientist, cites some research with corn following soybean at several Wisconsin locations to evaluate the current soybean N credit recommendations.  Soybean yields in these experiments ranged from 25 to 68 bu/acre.  There was NO relationship between soybean yield and the optimum N rate for corn following soybean.  Their conclusion was that soybean yields did not influence the soybean N credit. Therefore, it’s recommended to use the 40 lb N/acre soybean N credit at all soybean yield levels.  The 40 lb N/acre credit is an average of observed soybean N credits that vary across locations and years.  The influence of soybean on the N needs of subsequent crops is most likely due to the presence of soybean in the rotation rather than an effect of N contributions from the soybean residues.  The soybean N effect appears to be an enhancement of net soil N mineralization in the year after soybean is grown. 

“Thar’s mold in them thar kernels” 

        Moldy corn harvested off the field may or may not pose a significant problem depending on the type of mold and its intended use.  Mucor molds, which are usually black or gray in color, typically do not pose a significant health risk to livestock and often separate from the kernels if harvested for dry grain and moved through marketing channels.  White or pink molds usually fall into the family of molds called Fusariums.  They are the most common field molds we find in the upper Midwest.  If present in large amounts, cattle may be prone to reduced dry matter intakes or lower milk production.  Fusariums MAY also produce anti-quality compounds known as mycotoxins.  Penicilliums are blue-green molds.  They too can produce mycotoxins.  The presence of mycotoxins can only be confirmed with a laboratory analysis.