Anthony Hanson - Extension Educator Field Crops IPM
The ninth session of Strategic Farming: Field Notes for 2026 was held on July 15 covering corn reproduction and nitrogen use and availability, especially considering the hot weather and localized heavy rainfall in some areas of the state. Ryan Miller, Crops Extension Educator, discussed these topics with Jeff Coulter - Extension Corn Agronomist, and Brad Carlson - Extension Educator in Nutrient Management. To listen to the full podcast, visit https://strategicfarming.transistor.fm/episodes. Two Wednesday webinar sessions remain for 2026 on Aug. 5. and 12, and you can register at z.umn.edu/FN2026.
Corn
Coulter mentioned that crop development has progressed quickly this season with tasseling happening about a week ahead of normal. Consistent moisture across much of the state has kept stress on corn to a minimum, but it is starting to dry out with little chance of rain looking forward.
A couple questions were asked about the effects of the recent heat dome and high heat on corn. In general, corn tolerates the low 90s fine, but upper 90s and dry conditions can stress corn, especially around pollination. Under these conditions, tassels develop quicker and pollen may shed before all silks emerge. Conditions in southwest Minnesota are more prone to stress corn currently due to persistent drought conditions.
High temperatures can also affect pollen viability. In the mid-90s pollen viability begins to drop significantly, and around 100°F corn pollen dies. Generally this not a major concern in Minnesota, and temperatures generally did not approach this range outside of the Twin Cities heat island. Cooler temperatures the week of July 20 will be helpful for setting yield and avoiding kernel abortion for corn that tassels that week. Had this warmer weather trend happened the week of July 20, there may have been more yield loss.
An attendee asked a question wondering when we'd know if there were issues with pollination. One sign is that very long silks will indicate lack of pollination. Unpollinated silks can grow about an inch a day. To check for pollination few days after the bulk of the pollen has dropped from tassels, carefully unwrap a husk. If the silks fall off after shaking, this indicates pollination occurred. When a single pollen grain lands on a silk, it takes about 24 hours for the kernel to be pollinated. A tassel drops pollen over several days, but under hot windy conditions pollen will be mostly be depleted in a few days. Generally pollination and ear fill occurs first in the middle part of the ear first followed by the base and then the tip.
A grower also asked a if it appears there's a shift to silking happening before tasseling. Coulter has also noticed this trend, though he said silking happening a day before pollen shed may be helpful.
Coulter also discussed moisture demand for corn. Corn is currently using about one-third of an inch of water per day. Since the first part of the growing season was drier, this year's corn should have a deeper root system that is able to access more moisture. Areas of the state that don't get enough moisture in the coming weeks though may see some kernel abortion.
Overall, we are in a important period when the corn plant sets its overall yield. The first two weeks after silking is a critical zone for setting yield. Stress in early August also can have a major impact on yield, but as we move into late August, the effect from stress on yield like moisture or heat should be reduced.
Nitrogen
Brad Carlson mentioned that rainfall has been highly variable across the state with some areas even seeing excess rainfall, while southwest areas of the state are dealing with dry conditions. Over 10 inches of rain fell in a short period in Mower County prior to the webinar, which prompted some questions about nitrogen loss. Some areas had recent rainfalls around 3 inches in one night, while 10 miles down the road fields only received about an inch of rain. This highly variable rainfall but seems to have shut off for the time being and transitioned to dry conditions across the state.
When asked about supplemental nitrogen after tasseling, Carlson said there is likely no need for most growers as higher organic ground likely has enough nitrogen at this time of year. He addressed suggestions farmers have been hearing about late-season nitrogen after tasseling. Many of those recommendations come from southern states where organic matter is 1.5% or lower. Significant moisture earlier in the growing season can sometimes warrant a rescue treatment of nitrogen. In Minnesota, we usually have enough nitrogen coming from organic matter to satisfy the needs of the plants this time of year.
For seasonal timing, the critical point for nitrogen need for corn was in June during its rapid growth phase, but some nitrogen is still used this time of year. He hasn't seen widespread signs of nitrogen stress yet this year. Ample moisture and heat will help with the mineralization of nitrogen in the soil.
Other updates
Miller addressed some questions about weeds that came in during the webinar. Many growers are reporting problems with waterhemp surviving after the first post-emergence application. These issues are likely either due to application issues (e.g., missed rows) or herbicide resistance. Recent rainfalls and delayed emergence can also make managing this weed a challenge. Problem waterhemp fields may need another post-emergence application, but be careful to follow labels on any pre-harvest interval restrictions, and if resistance is suspected, use different modes of action rather than reapplying the same chemistries from earlier in the year.
Miller also gave some updates that Dean Malvick, Extension Plant Pathologist, forwarded along focused on fungicide applications. Tar spot in the state is at low levels with a few finds in southwest and southeast Minnesota. This disease tends to be more prevalent later in the season when temperatures are cooler and moist, so conditions have not been favorable yet. It is time to scout, but fungicide treatments generally would not be warranted at this time. Northern corn leaf blight is also an issue in cool-moist conditions, but may be a disease to scout for in fields at higher risk such as corn on corn. Southern rust caused 20% yield reductions last year in some trials, but spores need to blow in from southern states. So far there isn't a high risk in these states yet, so it may not be as much of an issue in Minnesota this year.
Comments
Post a Comment