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Crop Watch

June 22, 2018
By BOB STREIT - Columnist , Farm News

Just as many farmers in central and north central Iowa watch the calendar roll past June 10 and believed they could clean up their planters and back them into the shed for the off season, scattered and intense storm lines marched across the regions and only time will tell if the beans and corn plants that have now been submerged for days will recover or if replanting will be needed.

Quite a few counties in central Iowa got hit hard by 4 to 6 inches of rain that had many smaller stream turn into roiled rivers black with eroded soil washing down to the Mississippi. As of Sunday night many of the ponds with better drainage had receded and the now mud-covered plants had a change to start growing again. Those that were underwater yet have a more questionable path to being fully productive. Will different bacteria cause problems? Will some form of root fungus claim its toll? Will there be candidates for SDS in August when the visual symptoms typically appear?

My wife woke up early Tuesday and watched it rain as hard as it has for several years. By 7 we had a creek running across the lawn towards a neighbor's, where no creek had been before. By 7:30 the fight was on to keep high water in a walkout from invading the lower story. Lots of excitement but not much fun. This was after spending part of last weekend helping family that had their basement in Charles City flooded with mud filled floodwaters after a Saturday afternoon deluge.

Then when scouting acres up north of Humboldt I saw the fields in that country and in nearby Kossuth County where there were still many fields that ranged from 'beans finally emerged and could be rowed to still have not been able to work the ground'. Even though the USDA survey will list those acres as being planted and assuming normal yields, they don't do justice to the uncertainly that any of those acres will not get flooded again or have major disease problems in a few weeks or in late August when early infections manifest into visible symptoms. It makes most growers wish they would receive two 1 inch rains in May and have it stay dry for the rest of the month.

Ponding rules

The often asked question is "how long can corn or bean plants survive when they are totally submerged"? The correct answer depends on the water temperature. When the water is less than 60 it holds much more O2 and the respiration rate of the plants is lowered. Corn seems to last 7 to 8 days with cold water. Soybeans may last 5 to 6 days. Then if the water temp is above 70 degrees, corn seems to last about 5 days and beans 3 to 4.

If there is a lot of mud on the bean plants after the water recedes there can be more leaf and growing point lesions. A light shower is helpful in washing the plants off. Corn does not seem to have as much of an issue with mud as the new leaf tissue emerges from the inner whorl. This has been a year where for some reason there has been lots of dirt inside the whorl. This can create a risk of both fungal and bacterial problems, with the best known of these being known as crazy top.

Nitrogen losses

One of the next issues that will have people guessing the best course of action will be how to judge the amount of Nitrogen that may have been lost to leaching or volitalization. It can go down or go up depending on conditions. The rule of thumb is that there can be 5 to 7 percent yield loss per day the ground temp is above 50 degrees and the soils are saturated. For many the month of May was very dry and there were few areas with problems. Now in the last two weeks the number of acres that could have lost a sizeable percentage of spring applied UAN or 82 percent that would have converted to NO3-N has increased.

This is why there are more supporters of the use of N stabilizers that keep the nitrogen in the ammonia rather than converting it to the nitrate form. Even for the operators who use Y drops or urea for sidedress or topdress the use of a stabilizer mixed in with the UAN or Urea being applied later in the season could likely justify using a half rate of a good stabilizer to prevent lost N if a big rain hits and major amounts of ponding occur. Corn plants can access ammonia as well as they do nitrate N. The latest findings have actually shown that arbuscular mycorrhizal fungal strands can actually take up nitrogen in the amino acid form.

If some of your corn was a candidate for having lost nitrogen it may be wise to spend $269 on an At Leaf Spad meter so you can take measurements on the plants in your fields to see if the levels of greenness stay above 55 or run the chance of dropping below that critical level. If the levels drop below 55 before the plants have reached the late dough stage it will be necessary to either get a high clearance sprayer with Y drops into the field or research the use of nitrogen fixing bacteria of the Azotobacter crococum or vinlandii species to fix another 50 to 60 lbs of N.

Tissue testing

This year was one of the best years in the last decade for overall corn plant color, likely because the dry conditions minimized leaching of N, S and Bo, and the roots were going deeper into the subsoil to capture nutrients that were held there. We will have to see if that changes.

I have been pulling lots of tissue samples and so far the minerals of Mn, Bo and Zn seem to commonly be low. Moly was also coming up low quite often, but with 95 percent occurrence of that issue, that was not a surprise. If you have done any sampling yet you may want to do so, as most growers could likely spend a fraction of the amount they might spend on fungicides and application and avoid major disease problems. That would be major help with efforts to manage disease thru proper nutrition and prolong the efficacy of the three fungicide families used most often.

Corn growth and development

Depending on location and planting date a field scout can walk into corn approaching V10 and then in the same county walk into one where the corn plants are in the V2 to V4 stage. Those in the V10 stage could be showing tassels in about 2.5 to 3 weeks. Days with GDU accumulations over 25 have been very common and are responsible for the fastest developing corn crops in recent years.

With corn nearing the V10 growth stage and with a surplus of hot and very humid weather, and with leaf V3 and V4 sloughing off what should they be looking for? What experience should have taught them is as those leaves slough off and water collects behind them next to the stalk, the mucigel on the developing brace roots puts sugar in the water and it becomes a perfect little bacteria incubation chamber.

I was scouting in one of those fields last Wednesday and spotted the first caramel colored lesion at ground level of the season. A colleague near Cedar Falls has also found similar lesions that we hope to test with a new batch of strips from Ag Dia for Clavibacter. Keep your eye on the lower part of the stalk and those abscising leaves in your fields. Though it is a disease it is not a fungus and cannot be controlled with a fungicide. In past years when we had a surplus of 90 plus degree days after August 15th, and we had strong south winds with low humidity, the corn crop died weeks early.

Insects

The main reason for the successful introduction of BT corn was the widespread damage that European corn borer could and did cause in their 5 year cyclical patterns. We are seeing more growers move back to conventional corn with their cheaper seed prices and overall better plant health. It does mean that with those two benefits they need to learn the insect's biology and behavior patterns. This means that if the moths have been flying the last two weeks and have been flying into your fields at night from grass water ways and grassy ditches, you may be able to find the small larvae creating shotholed patterns in your leave as those plants grow and whorl leaves continue to be pushed out. If that is the case find out what treatment costs would be, then see if economic threshold have been reached in your fields and treat if those figures say that treatment is justified.

In the southern part of the state the Japanese beetles have been flying and found to be feeding on desirable plants. Controlling them on valuable plants like fruit trees, grape vines and raspberries has been a challenge. War is always tough and takes dedication to win. Our contact with the Chitosan experts and learned growers said that they had great results with the O2 product that caused the formation of chitinase and the chitin based mouth parts of the offending insects to dissolve. They do offer the product in an organic approved form if needed.

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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