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CROP WATCH

By Staff | Jul 6, 2012

July is here and July 4 was celebrated in many communities within the state. It is typically a good time to review what has happened over the first half of the growing season and evaluate the cropping decisions we have made. From a winter season that really never happened to a spring time that seemed to never quite be in sync with the calendar and nature, the planting season happened in spurts as it finally decided to rain. Things seemed back to normal and we expected El Nino, our old buddy, to deliver lots of rain over the months of May and June. Unfortunately, he has not delivered the expected moisture to huge areas of the country, most noticeably the eastern, central and extreme western cornbelt. Parts of northwest Iowa and eastern Nebraska have received more favorable weather and things look very good. But the dark cloud on the horizon is the near empty moisture gas tank gauge that most of us know is critically important to how the last three months end up. The next two to three weeks should tell the story. All growers who were operating during the 1977, 1983 and 1988 seasons know that just a few days of oppressive heat coupled with strong winds and low humidity while the crop is facing a depleted water supply can push a weakened crop over the edge. So if any weather gurus are listening and can do something about it, please send rain soon.

This past week was one where fellow high school classmates had to head to the town where we all graduated from eons ago. Surprisingly at what should have been an old person’s gathering everyone looked to be in pretty good shape yet. We spent some time talking about old times, but more about current happenings and the general state of the country and ways to get it going again. Doesn’t that sound familiar? So on Saturday with a few hours to spare we hit a local hamburger and malt drive-in and grabbed one of each. Afterwards we visited Spring Park, which is just west of Osage a few miles. At the park is a big concrete cased artesian well that puts out a big flow of 39 degree water. Sitting there in 94 degree heat we had to soak our feet in the near freezing water. The question that was generated was “If the earth’s temperature gets warmer as you get deeper under the crust, what process serves to cool the water to near freezing?” and “Where is the water emerging from the well coming from?” Are there any geologists listening?

Moisture Use

It has been another two weeks without rain in many parts of the Midwest. The tank is getting closer to ’empty’ and the crops are getting increasingly thirsty as they have to tassel, silk, and begin to fill the kernels. The soybeans also have to put on more growth, flower more, pod more, and fill those pods. We have to hope that those moisture demands are met.

Now that many thoughts these days among crop growers it may be good to review the terms of Pan ET, Pet ET and ET. Pan ET is the evapo-transpiration that takes place out of a metal pan set out in the wind and sun. It takes into account temp, humidity, percent of sunshine and wind speed. Pet ET calculates the amount of moisture that would evaporate out of a plant if the plant had an unlimited supply of moisture. Then finally the ET stands for Evapo transpiration which reflects the Pet calculations given different plant growth stages. This last figure is important for irrigated growers who manage pivot irrigation and typically try to keep the crops out of serious moisture stress during this part of the season. They have to manage the water and crop moisture use just like Wayne Gretsky did. Wayne became one of the best hockey players ever by using the philosophy of not skating to where the puck was, but by skating to where the puck was. In the last vegetative stages, V15 to V19, the ET can approach 0.3 inches per day. In other words the crop can use an inch of water every three days. This hungry crop continues the rapid use of water through the tasseling and pollination phase. It will try to use an inch of moisture about every three days.

In comparison the soybeans have a shorter canopy that uses less moisture than corn through the brown silk period. Then as the bean plants enter the time when they have to fill the pods they will consume almost as much moisture as corn and eventually more than the corn plants on a daily basis. If that amount of moisture is not available from stored moisture reserves the plants will show signs of stress such as curling their leaves, letting the leaves turn gray, and trying to go thru pollination before all the soil moisture is depleted. A quick and easy way to detect this stress is to feel the leaf surface temperature. If the leaves ever feel hot the moisture supply is not longer adequate to do the cooling.

Heat and Moisture influence on Pollination

In a Des Moines Register article this past Sunday the Ag page author wrote about what physiologically happens when the plant runs into too much heat and too little rain near the tasseling and silking stage. He commented that the silks typically emerge within one to two days of when the tassels are fully pushed out. Because the silks contain 98% water being dry can mean more days between tassel emergence and silking, having the silk growth being inadequate to push clear out of the husk, or possibly unreceptive to the pollen. At the same time the tassel and pollen, which are the male parts of the corn plant, can also have their dry weather problems. If conditions are too hot and too dry the tassels could be slow in appearing, or the pollen amount could be reduced in amount, reduced in virulence, or reduced in the hours of viable pollen release.

If every factor works in favor of the plants, all of the 600 to 800 kernels on the ear will get pollinated, and then begin to receive starch from the plants’ starch factory. In 2011 we saw many areas within the state that showed serious tip back. The causes seemed to be a mix of things that combined to lessen the plants ability to form that starch needed to fill the kernels. There were questions about having the corn pollinate now versus waiting a week. Good question. The answer is a mix bag and the right answer depends on whether waiting a week will put the plants in a better moisture situation. If it doesn’t rain at all then completing the process earlier on the calendar would be an advantage.

Insects already Appearing

The Japanese beetles are a growing problem among many row cropping growers. This week they could be found in many corn and bean fields as they chewed on the leaves. Be sure to watch for the defoliation they can cause. When they mass and feed they can consumer lots of leaves. Leaves do regrow. Reproductive parts do not and yields can be hurt if silks are eaten.

The small grass hoppers are starting to appear. Their populations can increase in dry weather as their egg survival improves during dry weather.

Leaf hoppers have begun to appear in soybean fields in the last two weeks. These little sucking insects tend to blow in from southern states. We don’t know for sure if they transmit diseases, but are suspected of doing so. Watch for aphids soon after they appear.

Then the last insect to mention would be the spider mites. They have been detectable on the lower leaves of corn plants for about three to four weeks now. They are another sap sucking insect that can remove the vital juices of the plant, rendering them more likely to be hurt by dry weather. Keep an eye on them in dry areas. You will likely want to carry a hand lens to see the small insects and ID their eggs.

Best of luck in getting rain in your areas.

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