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September 2011 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at, and we’ll respond on this blog to provide an interactive dialogue.

How Late Can I Leave Corn in the Field to Dry Down?

Sep 27, 2011

Question:  How late can I leave corn in the field to dry before I harvest it?

Farmers should think twice before expecting Mother Nature to pay the cost of drying corn by leaving it in the field longer this harvest, says Ohio State University Extension corn expert Peter Thomison.
"We don't encourage growers to leave corn in the field much past early November, because after that there is really very little moisture loss in corn," he said. "Sometimes people think the corn will continue to dry, but typically moisture stays pretty much stable after mid-November."
Thomison said that in typical years, when corn is planted at normal dates between mid-April and late May, the crop follows the general pattern of drydown in the fall. That pattern includes drydown of up to a percentage point of moisture each day from physiological maturity, often called black layer, through early to mid-September when conditions are usually warm and dry.
In October, he said, that rate of drydown may drop down to half a percentage point, and then by November, a quarter of a percentage point, if it dries further at all.
"This, of course, isn't a normal year," Thomison said. "When we have these late planting seasons in Ohio, the historical effects on yields are pretty consistent, but effects on moisture are fairly mixed."
He noted that this year, because of recent rains, growers would likely harvest the corn crop in mid-October. With that in mind, those farmers should assume the corn will be of a higher moisture content coming out of the field than corn from fields planted during a more normal date range.
Thomison said there is no data to suggest that frost plays any role in helping dry corn, and that by that point in the season, corn is likely as dry in the field as it will get.
"The longer you leave the corn in the field, you start to see significant potential for stalk lodging issues," he said. "It can affect how effective your combine is at picking up corn. Farmers should start inspecting their fields pretty regularly as corn starts drying down for stalk quality, and earmarking problem fields for harvest as soon as conditions allow."
He recommended employing the pinch test to determine stalk health when scouting fields for potential stand issues. To determine if stalks are likely to lodge, he said, pinch the first internode about the brace roots, and if the stalk pinches, it is more likely to lodge.
He noted, however, that many modern hybrids are designed to withstand some of the issues that might cause lodging, and many have tougher rinds that allow them to stand up longer.
"But, later-planted corn typically is generally more susceptible to lodging issues," Thomison said. "Also, because we had corn in some areas that could have been subjected to three separate wind events that knocked plants down, that's going to be another complication this harvest."
Check out real-time harvest results with AgWeb’s Corn Harvest Map

What Do You Consider When Selecting Wheat Varieties?

Sep 22, 2011

Question: To pick good wheat varieties, what factors do you tell farmers to consider?

 Answer: There is no substitute for evaluating varieties on your own farm. Review local and state wheat variety performance data and compare the results with your own experience to select three high-yielding varieties with the characteristics which suit your soils, climate and management style. In addition, I strongly encourage all producers to plant at least three recently released high-yield potential varieties alongside those used on the farm. Normally, a grower can obtain a couple of bags of each of these new varieties before they become commercial the following year. When selecting varieties, there are a number of important considerations I tell farmers to consider, including:
  • High yield potential
  • Good test weight
  • Height and standability characteristics
  • Maturity—ideally, select a range of maturities
  • Standards of disease resistance, including leaf rust, tan spot, mildew, fusarium head scab
  • Tolerance to drought
  • Good tillering ability

What Can I Do to Control Marestail?

Sep 19, 2011

Question: Could you please tell me what will kill marestail? The neighbor has it in his soybeans, and it is spreading over into our farm. 

Answer: The majority of marestail emerges in the fall; however, some can also emerge in the spring or early summer. It is best to control marestail in the late fall or early spring. An application of 2,4-D ester in the fall will greatly reduce marestail populations the following spring. If you cannot apply in the fall, make a spring application when the marestail is less than 2" tall. The combination of 2,4-D ester and glyphosate is a very effective and economical treatment. Keep in mind that many populations of marestail are ALS-resistant and some are glyphosate-resistant. The Ohio State University has a great Extension bulletin with more specifics. See the following link:

We've Had a Frost -- Now What?

Sep 16, 2011

Question: We got frost early.  Do you have any advice on what to do now with our corn?

Answer: When temperatures reach around 30 F, the corn growing season halts, reports Joe Lauer, University of Wisconsin Extension corn agronomist, in his recent article "Handling Immature Corn After an Early Frost."
"Corn is killed when temperatures are near 32 F for a few hours, and when temperatures are near 28 F for a few minutes. A damaging frost can occur when temperatures are slightly above 32 F and conditions are optimum for rapid heat loss from the leaves to the atmosphere, such as clear skies, low humidity, no wind."
Lauer says symptoms of frost damage will start to show up about one to two days after a frost, and frost symptoms are water-soaked leaves that eventually turn brown. He says that because it is difficult to distinguish living from dead tissue immediately after a frost, the assessment should be delayed 5 to 7 days.
The severity of the damage depends on the length of time and the extent of the below-freezing temperatures, according to Iowa State University's National Corn Handbook. Substantial damage would occur if the temperature remained below freezing for four to five hours. Leaves are most susceptible to frost because of their whorl arrangement and thin composition, making it difficult to retain heat. 
The best and only thing a farmer can really do for corn that has been hit with a frost is to simply hold off and let it dry down, says Jeff Coulter, University of Minnesota extension corn specialist.
 Farmers should check the field the morning after a frost once the sun has risen and started thawing the plant, according to the National Corn Handbook.
Coulter's advice for future years is to avoid pushing the maturity because it only takes one bad year to cause problems. Farmers should choose plant corn varieties that are reasonable for their areas. Corn hybrids should be chosen based on when they reach physiological maturity, according to the National Corn Handbook. The plants should reach maturity before the average date there is a freeze risk greater than 50%. 

Purpling in Corn Caused by Pigment

Sep 12, 2011

Two weeks ago, Farm Journal received a question from a southern Minnesota farmer who asked about the potential impact of purple leaves in corn, and whether he should be concerned about it for the 2012 season. We responded to his question in the August 30 edition of Ask An Agronomist. That same day, we received a brief response on this topic from Dr. John Pesek, Iowa State University emeritus professor of agronomy, which we want to share with you. Here is Dr. Pesek’s feedback for your consideration:

“The absence of an ear in late summer (for whatever reason), or having only a poorly pollinated nubbin will cause an accumulation of sugars produced by photosynthesis in the plant if the growing conditions are good, and sunny days prevail.  The sugars will accumulate and lead to a production of anthocyanin (a pigment) in many corn hybrids with the capacity to show purple for whatever reason—thus the purple plant.”
-John Pesek

Why Do I Need More Sulfur?

Sep 06, 2011

Question: I thought I had a nitrogen deficiency in my corn this season, but tissue tests actually showed I didn’t have enough sulfur present to make the nitrogen available to the corn. What’s the deal with that?

 Answer: That is a problem we’re seeing increasingly and that many farmers don’t realize. You need sulfur to metabolize nitrogen and make it available to the corn plants. A bushel of corn contains 0.08 lb. of sulfur in the grain and 0.09 lb. in the stalk, for a total of 0.17 lb. That means a 200-bu. per acre corn yield removes 34 lb. of sulfur, or 102 lb. of sulfate—the form of sulfur taken up by plants per acre. Those higher yields we’re seeing today require more sulfur, and there’s not as much available. Reasons: the old single superphosphate your grandpa used contained 12% sulfur, plus today’s pesticides contain less sulfur. We also don’t burn crop residue anymore, which released sulfur into the atmosphere. Your challenge is to maintain the proper ratio between nitrogen and sulfur. Corn needs about 1 lb. of available sulfur per 14 lb. of available nitrogen. You need to pay special attention to sulfur levels in soils that have less than 3% organic matter. Organic matter is your main supplier of sulfur. In soils with more than 3 % organic matter, sulfur probably can take care of itself.
Sulfur’s role in plants includes producing lignin and pectin, producing chlorophyll and metabolizing nitrogen. Here are ideas on how to make sulfur work harder in your fields.
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