JenREES 8/9/21

4-H youth receiving medals for Ag Hall exhibits at the York Co. Fair.

Thank You to all the volunteers; ag society and 4-H council members; Extension staff; and all the youth and families who made the 2021 York and Seward County Fairs successful! It was a joy for me to see ‘normal’ fairs, youth and adults excited to find their projects and show their ribbons, the number of people out attending activities, walking through buildings, and just talking with each other!

Crop Update: Thanks also to the crop consultants and ag industry agronomists who dropped off samples during fair and kept me in the loop with what you were seeing in the fields! Southern rust was also confirmed in Hamilton and York counties this week. Frogeye leaf spot is also showing up on some soybeans with the high humidity and dew on soybean leaves.

Many have asked why the crops aren’t using much water. ET is evaporation from soil and leaf surface + transpiration (process of water lost through leaf stomata) from the crop. The high humidity has kept plants wet, especially soybeans, longer during the day (which is why I think the soil moisture use has been showing up less on soybeans than corn). I know many, including myself, have been trained that crops automatically remove 0.30”+ a day upon tassel and flowering, but that’s just not true. That thinking doesn’t account for the environmental factors at play which change every day of every year. Higher ET occurs on sunshiny days with high heat, higher wind, low humidity. Cloud cover, humidity, and low wind all reduce ET (and we’ve had a lot of these lately). As I’ve worked with farmers through the years, I’ve heard many say how helpful their ET gage was, because it’s such a visual representation of what’s going on with the environment and crop water use. If you don’t have an ET gage, the UBBNRD is sharing daily crop water use from the High Plains Regional Climate Center via email, so you can contact Marie there if you would like this info. each day. Thankfully, the humidity has allowed non-irrigated crops to hang on longer, due to lower crop water demand, in spite of the humidity being harder on us and animals.

Pollination: I realize there’s pockets of really good looking corn out there. And, I also realize that a lot of corn may look good from the road, but there’s concerns and questions about pollination and tip back in fields. As I think about when pollination occurred, the smell of pollen was thick in the air some mornings, and even early evenings when pollen shed was delayed from high humidity. Many fields I walked into had ample pollen shed. There’s a range of pollination dates in the area, so heat/humidity could have played a role for your specific fields. Dr. Tom Hoegemeyer shared the following about high heat and humidity during corn pollination in a CropWatch article, “Just a day or two difference in flowering, or planting, or other factors can make a substantial difference in (kernel) set. Stress during pollination and silking could result in shorter ears, increased tip back and fewer kernels per ear. All of these contribute to less yield potential.”

  • When soil moisture is sufficient, one day of heat over 95-98F during pollination has little to no yield impact. After four consecutive days, there can be a 1% loss in yield for each day above that temperature. Greater yield loss potential occurs after the fifth or sixth day.
  • Heat over 95°F depresses pollen production. Prolonged periods of heat can reduce pollen production and viability (ability of pollen to fertilize silks).
  • High humidity helps reduce crop water demand. High humidity, without a drop in humidity during the day, can delay pollination or prevent pollen from leaving anther sacs. “The process of releasing the pollen from the anthers is called “dehiscence.” Dehiscence is triggered by the drop in humidity, as the temperature rises. However, when it is extremely humid and the humidity falls very little, dehiscence may not occur at all, or it may be delayed until late in the day. If one has breezes, while the humidity is still very high, the anthers may fall to the ground before pollen is released.”

I also think about what I’ve seen the past few weeks with all the silk balling, pollination misses, tip back, and what’s being shared with me by others in the field. The July 9 wind event that hit a portion of this area seems to have impacted plants more greatly that were within 1 week of tasseling. With the resources it took to right plants in developing additional brace roots, thickened nodes, etc., I wonder how much of the resources that would’ve been put into “normal” pollination were used for these other purposes instead and how that may have impacted pollination timing, silks pushed out of husks, etc.? A number of agronomists are reporting abnormal ear development they’re seeing in addition to pollination misses and tip back of various levels. This is what’s known from the research regarding wind impacts to yield on lodged plants (however the specific causes of the yield losses are not mentioned):

  • Research found lodged plants after a wind event had yield reductions of 2-6% (V10-12 stage), 5-15% (V13-15 stage), and 12-31% (V17 and after stages).
  • We’ve also personally observed yield losses greater than this due to abnormal ear development on lodged plants in the area after wind events.

Regarding tip back, it’s important to count kernels long as there may be more kernels than one realizes in spite of tip back occurring. Tip back on corn occurs most often from some sort of stress. One can tell the approximate timing of stress events by the appearance of the kernels. If kernel formation isn’t evident, the stress occurred before or during pollination. If kernels are very small or appeared to have died, the stress was after pollination as the kernels were filling. Japanese and rootworm beetle silk clipping can impact tip pollination. We’ve also had high heat with humidity since pollination in addition to cloudy/hazy days and I haven’t dug into the weather data yet. Hopefully this helps a little for the questions received thus far.

About jenreesources

I'm the Crops and Water Extension Educator for York and Seward counties in Nebraska with a focus in irrigated crop production and plant pathology.

Posted on August 9, 2021, in Crop Updates, JenREES Columns and tagged , . Bookmark the permalink. Leave a comment.

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