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Weather Issues for Corn

University of Minnesota Extension, Stearns County News
June 7, 2017         
Source:  Dan Martens, Extension Educator
University of Minnesota Extension
Stearns, Benton & Morrison Counties


Weather Issues for Corn
By Dan Martens, University of Minnesota Extension

FOLEY, Minn. (5/31/2017) — There is an old saying, “Rain makes grain.” In the meantime, cool wet weather can be challenging for crops. As always, we’ll see how the cards get dealt through the growing season. We can appreciate the farmer’s skill, patience and persistence in playing them the best they can. 

POPULATION. Corn germination and emergence can be challenged by cold, wet weather, crusting and related issues. Regional Extension Educator Dave Nicolai wrote recently that planting rates of 34,000 to 36,000 seeds per acre generally produce maximum economic returns in most of Minnesota’s corn growing area, allowing for a final stand about 5% less. That can vary with soils and other conditions; and the farmer’s experience counts.

Where crusting is an issue, dragging or rotary hoeing might help. Warmer weather might also help the corn (or soybeans) push through more aggressively. A little gentle rain might soften a crust. Corn that has leafed-out underground probably won’t emerge.

There might be questions about re-planting. We might compare the yield potential of a reduced stand to yield potential for late planted corn. For example, some trials show that corn planted June 4-9 might yield 77-71% of corn planted around May 1. Trials also show that a 16,000 population might yield 74% of a normal yield. So that’s about a wash without considering replant costs. These are not easy decisions. Plants likely are not lost uniformly across the field. Herbicides might be an issue with replanting. Farmers should check with crop insurance reps when making unusual decisions. 

NUTRIENT DEFICIENCIES. Extension agronomy staff posted an article recently about nitrogen, phosphorus, sulfur, and zinc deficiency symptoms. Internet users can find this easily by doing a search for “Minnesota Extension Crop News.” The first key point is that cool wet weather can cause symptoms of nutrient deficiencies because roots and plants are growing slowly. Photosynthesis is limited. Nutrient uptake is limited – even though there may be ample nutrients in the soil. Crops often grow out of these limitations with better weather and soil conditions.

Minnesota Extension has a good worksheet for evaluating whether nitrogen has been lost. Regional Extension Soils Educator Brad Carlson posted a You-tube discussion on this topic. I found it easily by searching for “Minnesota Extension You-tube Brad Carlson nitrogen.” You’re welcome to give me a call for a copy of the worksheet: 968-5077 if a local call to Foley, or 1-800-964-4929. 

HERBICIDE ISSUES. Rain may have prevented application of some pre-emerge products as early as needed. In some areas of Minnesota, dry soil limited the early effectiveness of pre-emerge products. Some weeds may have been able to grow through pre-emerge products; or are growing because of missed pre-emerge applications.

Regional Extension Educator Lisa Behnken and Ryan Miller posted a useful discussion about variations in herbicide field trials at Waseca. Internet users can do a search for “Minnesota Extension Crop News” and find the May 27 listing with links to this video – nicely done.

Key Messages include: Many pre-emerge products are pre-packaged mixtures with components that work at different times, so patience can be a virtue. Some herbicides act specifically on weed seed as they germinate. Weeds that escape control and emerge will need to be considered in post emerge control. Weed size is a key for making post emerge application decisions.

Where pre-emerge products did not get applied, it can be important to have a pre-emerge product applied with a post-emerge applications for better control of weeds like waterhemp that emerge well into the summer. Be sure to ask about potential carryover effects for crops you might plant next year.


Morrison County Dairy Breakfast on the Farm, Saturday June 10, 7:30 to 11:30 a.m. at Roerview Dairy, near Upsala. For more information call Kenneth Fellbaum (320) 630-860. Admission is $5 for breakfast and kids 12 and under free. Roerview is using robotic milking equipment.

Check other news releases for information about Summer Beef Home Study Courses. Contact Nicole Kenney Rambo at or 320-235-0726 extension 2009 with questions or visit for details.


Daniel Martens
Extension Educator, Ag Production Systems
(320) 968-5077
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