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Crop watch

By Staff | Jul 22, 2019

With projected high temperatures above 90 degrees for the next week, after the months of March through June setting all time yearly records for amount of rainfall, we have to wonder if we are living up some biblical prophesies.

Coupled with the immediate switch to dry conditions for much of the state and Midwest, one has to wonder how the crops are going to tolerate hot and dry soils. Everyone was in a rush to get planted in the short few planting windows and growers knew they were risking sidewall and deep profile compaction by working ground that was wetter than desired.

The calendar said the optimum window was passing them by. The consequences were that if it turned hot and dry their plants may have a limited root system and some degree of soil compaction their plants could be affected. Reality was hitting down in southeast Iowa last Friday where they have missed the rains the last three weeks. There were fields where the plants were firing up two to three feet in the lighter areas of the fields. In central Iowa by Sunday the corn plants on the beach areas surrounding each water hole were rolling quite a bit.

Two weeks ago there were several nights when a midnight check of Doppler radar showed showers lined up north to south across central Nebraska headed east into Iowa. At the time we were still needing extra days to get the delayed spraying done and to finish up on bean planting. Those moisture fronts got blocked by some force and one wondered where that moisture went. The answer appeared as a large cropping region centered around and south of Kearney received 6 to 10-inches of rain, covering up quite a few fields with flood waters. The erosion was severe erosion with many fields inundated for days. The question on those acres is how well will those plants recover after the flooding. The conditions and the water were warm and the water often covered the whorl so the crazy top and bacterial rots could be severe. Downstream fields where the high Platte water table limits root function will now be affected. The area was supposed to be the garden spot for corn production this year.

The heat goes on

Most seasoned growers can quickly name the years when heat and drought took a major toll on them and their crop yields. 1977, 1983, 1988, 1995 and 2012 were the widespread events with many more on a local level. How might this year compare against them? Hybrids are much better at withstanding a drought, partly because every mid and major sized corn genetics breeding company has been screening their inbred and hybrid lines at irrigated western locations in Nebraska and Kansas where they can limit the amount of water being applied to the field in July and August.

With such screening they can evaluate each of them for their tolerance for drought and see how well the tasselling and pollen shed timing match up with the silk emergence. Every hybrid is now selected to have the two pollen shed and silking timed properly. At a corn breeding field day a few years ago long time corn breeders Forest Troyer (Pioneer and Pfizer Genetics) and Arnel Haulauer (Iowa State) were in attendance. While they were visiting they both agreed that the conditions in that summer would have affected the performance of the best hybrids of their era, while not harming the popular ones of that year very much.

The one soil property that has declined in recent seasons is that a high percentage of the fields have seen their organic matter levels decline by as much as 50 percent.

They do not have the sponge capacity of two or three decades ago while their water infiltration rates have declined. If each observant farmer were quizzed as to what two things, fertilizer or herbicide could be blamed for that decline, most would guess correctly. The focus on soil health and using regenerative methods of farming is important. The use of cover crops and using biological inoculants has to take place on a large scale while microbial destructive steps need to be dropped.

The temps are projected to be hot for the next week. We typically view early tasselling and silking a positive, but those fields showing moisture stress around the state could be penalized if the plants are under severe stress at this critical time. The degree of moisture infiltration has determined which fields have ample stored moisture deeper in the soil. Now the plants with a healthy and active rhizosphere should have a deep enough root profile to access that water and nutrients in that zone.

Crop development

The jury is still out as to how those corn fields planted in June will fare. The crop could speed up by harvesting more hours of heat in July and August, but small plants don’t tolerate stress as well. The late planting and grain filling during the shorter days of September and October will still be charged.

There are several concerns in the many late planted bean fields where the plants are so slow to develop and flower. Many remain in the V3 to V4 growth stage. Is it lack of O2 that is slowing their development? It may be worth doing a few rounds with a row crop cultivator to see if opening the crust to let in O2 and the CO2 out would help spur growth.

In a number of bean fields the plants are at the V5 to V6 stage and should be flowering, but aren’t. A foliar application of one or two simple items should change that. With the beans beginning to flower close to July 20th versus the normal June 20th date, how many days will their flowering be reduced by? Being they are nighttime dependent they should quit flowering at the same day as they normally would.

Corn and soybean insects

Most insects operate on a base 48 – 52 degree temperature schedule and have been running 7 to 10 days behind. Now is time to find the rootworm larvae feeding on corn roots. They range from .5 inch to pupated and didn’t all drown.

The second appearance of the second brood of the European Corn Borers moths is also getting closer. July 25th through August 15th is typically their egg laying peak. The best way to monitor them is to consult any black light traps catches in your area and latitude to see what they are listing in their tabulations. The 1st brood which shows up in the whorl was almost nonexistent as there were not many plants large enough in diameter to play host to the larvae. Don’t ignore the second brood as they can still be damaging to conventional hybrids. The eggs and larvae are more difficult to find on the leaf undersides or in the leaf sheathes.

In soybeans the gall midge flies and larvae have both been found in several locations in this and surrounding states. It appears they will be with us for the foreseeable future. Kansas is finding the Dectes stem borer beetles the bean fields where they will be laying their eggs in the petioles, where they will later tunnel into the stalks.

Northern Iowa agronomists are finding very light soybean aphid populations that are much below treatment thresholds. Reports from central Minnesota tell of widespread spraying for them. Intense heat stresses them. With our breezes being primarily from our southwest this week any infestation may have to come from a different source.

Cover crops

Planting of cover crops on prevent planted acres would normally have been done by now. Instead many fields still hold sizeable lakes with ducks and geese calling them home. Seed availability is an issue so anyone hoping to plant a cover crop needs to find a supplier to come up with a blend of species that best benefits the soil and the 2020 crop.

If corn is planned for the field next year a mix that included one or more legumes would fix enough nitrogen to replace part of the needed amount. Planting and working in a sweet sorghum or Sudax can benefit the soil structure in a field for about five years, but seed supply issues now restrict that chance.

This season and last makes a person wonder when we might see a normal season again. May you have the best of luck for this week.

Bob Streit is an independent crop consultant and columnist for Farm News. He can be reached at (515) 709-0143 or www.CentralIowaAg.com

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