Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Corn Spraying

Posted by romeethredge on May 23, 2015

Some corn spraying is going on now by plane or helicopter. Much of our field corn is now tasseling and especially in fields where Northern corn leaf blight (NCLB) has been found and where growers are going for very high yields, they are choosing to apply a fungicide.  Fortunately the real bad yield stealer, southern rust, hasn’t been found yet and we’re hoping it will hold off a while.  Stink bugs aren’t at high levels at this time but a few have been sighted.

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We flew over a few corn fields this week and they are looking good. The heat this year is pushing the corn on and it is a week or more ahead of the past 2 years, which is good news. In cases where corn has been stressed due to water or nutrient needs, it is short and not looking as good.

Now is a very critical time in the corn fields, the slight cooling this week has been better for pollination and water use but may cause NCLB to increase.

I  read the following from the University of Nebraska:

“Corn was originally a tropical grass from the high elevation areas of central Mexico about 7,400 feet above sea level, 2,000 feet higher than Denver. Today, corn still prefers conditions typical of that area — warm daytime temperatures and cool nights. Areas that consistently produce high corn yields share some significant characteristics. These areas — central Chile, the west slope of Colorado, etc. — are usually very bright, clear, high light intensity areas with cool nights.

Corn maximizes its growth rate at 86°F. Days with temperatures hotter than that cause stress. In the high yield areas, cool night temperatures — at or below 50°F — reduce respiration rates. These are optimum conditions for corn.

In years when we get high day and nighttime temperatures coinciding with the peak pollination period, we can expect problems. Continual heat exposure before and during pollination worsens the response.

Corn is a “C4 Photosynthesis” plant, making it extremely efficient at capturing light and fixing CO2 into sugars. One drawback of this system is that with high daytime temperatures, the efficiency of photosynthesis decreases, so the plant makes less sugar to use or store. High nighttime temperatures increase the respiration rate of the plant, causing it to use up or waste sugars for growth and development. This results in the plant making less sugar and using up more than it would during cooler temperatures.

Heat, especially combined with lack of water, has devastating effects on silking. If plants are slow to silk, the bulk of the pollen may already be shed and gone. Often in dryland fields we see seed set problems because of “nick” problems between pollen and silking.

Even in some stressed areas within irrigated fields (extreme sandy spots, hard pans or compaction areas where water isn’t absorbed and held, and some “wet spots”) we can see stress-induced slow silking and resulting seed set issues. Once silks begin to desiccate, they lose their capacity for pollen tube growth and fertilization.

Heat also affects pollen production and viability. First, heat over 95°F depresses pollen production. Continuous heat, over several days before and during pollen-shed, results in only a fraction of normal pollen being formed, probably because of the reduced sugar available. In addition, heat reduces the period of pollen viability to a couple hours (or even less). While there is normally a surplus of pollen, heat can reduce the fertility and amount available for fertilization of silks. It’s been shown that prolonged exposure to temperatures reduced the volume of pollen shed. Even with adequate moisture and timely silking, heat alone can desiccate silks so that they become non-receptive to pollen.

For each kernel of grain to be produced, one silk needs to be fertilized by one pollen grain.”


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