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Serving: IA

Fall Spraying Of Herbicides Can Nail Winter Annual Weeds

Fall Spraying Of Herbicides Can Nail Winter Annual Weeds
Fall is also a perfect time to sample soil and have it tested for soybean cyst nematode, advises ISU agronomist.

While enjoying the great outdoors and seeding cover crops over the last couple weeks, Clarke McGrath saw that all the rain and soil moisture Iowa has received this growing season had gotten a lot of winter annual weeds off and running. While not every field is a good candidate for fall application of herbicides, you don't have to look hard across southern Iowa to find areas where fall spraying would give farmers a head start against some tough-to-manage weeds, he says.

McGrath, an Iowa State University Extension field agronomist at in western Iowa, writes the ISU "Corn & Soybean Insight" column each month in Wallaces Farmer magazine.

DON'T WAIT TOO LATE: As soon as you harvest a field this fall, if you have winter annual weeds in that field and are concerned they will be a problem next spring, consider making a fall application of herbicide.

McGrath says, "I was going to write an article on this topic, and then I remembered a great article from University of Missouri I read that hit the high points. Kevin Bradley, weed control specialist from Mizzou nailed it. He has some great points to ponder and there is even a link to a good slide set on the topic." You can read the article here.

Spray winter annual weeds as soon as you harvest the field
"Now that we've had some frosts, and some fall moisture—too much in most cases—and some time for many winter annuals to emerge, it is time to nail them as you harvest the crops, if you have concerns about these winter annual weeds being an issue by spring," says McGrath. "We had some real issues with spring burndowns not performing as expected this year again; several factors were at play, but the biggest factor was probably the wildly fluctuating temperatures. Given that we face this more often than not with our planting dates and typical weather, in some fields/areas, fall spraying may provide more weather stability for managing these weeds."


He adds, "The bottom line is that if you have challenges with winter annuals—and marestail is probably the most troublesome in our area—fall spraying can make a huge difference. A spring burndown/residual application will still need to be a component of your weed management program; the fall spraying will just help make it much more effective if escapes have been an issue on some of your farms."

Farmers need to sample soil for soybean cyst nematode
On another topic, McGrath says he's had a lot of calls again this fall pertaining to soybean yield variability and questions surrounding that topic. And harvest was just really getting going strong prior to the recent rains, he notes. "On the soybean side of things, during these conversations I've been surprised at how many fields haven't been sampled for SCN, either recently or ever. I had similar conversations with farmers last fall as well. We still have some work to do as far as SCN testing and awareness."

Fall is a perfect time to sample fields for the presence of SCN. Knowing if SCN is present and at what population densities will increase the chances of profitable soybean production in 2015 and beyond. "While we typically prioritize corn stalks for SCN sampling as those are acres more likely to see soybeans planted there the next season, fall also is a good time to determine if SCN was present in soybean fields in 2014. Sometimes the results help address yield variability questions."

Collecting samples for this purpose is done in the same manner as sampling fields of corn stalks for SCN in anticipation of the 2015 soybean crop, notes McGrath.

Following are some SCN sampling guidelines:

• Collect 8-inch-long soil cores.

• Collect 15 to 20 soil cores per sampling area.

• Limit the area sampled to 20 acres or so, if possible.

• Collect numerous multiple-core samples from different areas in large fields

• If grid sampling, collect one or two soil cores from every grid cell and combine    cores from the number of cells that represent approximately 20 acres.


• Collect cores from underneath crop row if soybeans were grown this season.

• Do not collect samples if the soil is muddy or frozen.

• Send samples to a private soil-testing laboratory that does SCN testing or to: Plant and Insect Diagnostic Clinic, Iowa State University, 327 Bessey Hall, Ames, IA 50011

"If SCN is discovered at low or moderate population densities, SCN-resistant soybean varieties should be grown in 2015 to maximize soybean yields in the presence of the nematode," says McGrath. "Farmers have a lot of SCN resistant soybean varieties to choose from when deciding which soybeans to plant. The last list I got from Dr. Greg Tylka's yield testing trials contains information on 673 varieties offered by 33 companies and two universities. So if your SCN soil tests come back positive, you have a lot of good seed selection options. Make sure at least all your planned soybean acres for 2015 have up to date tests so SCN issues can be addressed."

Quality and handling of the 2014 Iowa corn crop
On another topic of concern this fall, McGrath points out that ISU grain quality expert Dr. Charles Hurburgh has put together a nice article talking about some grain quality and handling issues. Hurburgh provides the following quick summary of the highlights, as follows:

• Overall quality is likely to be good with a few uncertainties because of weather.

• Carryover of the 2013 crop will create complexities because of its poor storage. Do not mix crops from multiple years in bins and recognize that considerable quantity of 2014 corn will be stored for at least two years.

• Corn will probably be wetter than usual as it comes out of the field this fall, but not extremely wet. Higher test weight may offer some operational flexibility to increase dryer capacity.

• Basic grain science and management principles still apply; some grain is being stored for 2016 use or beyond. For more information, click here.

TAGS: USDA Extension
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