June 30, 2009 PONDS AND FLOODED FIELDS With the recent rains and related flooding, many are asking the question, "How long can crops be under water and survive?" Corn and soybeans can normally only survive complete submersion for 2 to 3 days (80 day air temperature) and most forages can survive for 1-2 days. I have seen survival for considerably longer periods of submersion, however. The cooler the air temperature, the longer the plants can survive. Plants NOT totally submerged will survive considerably longer. By the time the field dries out, it will be easy to see whether the crop has survived or not. A light rain shortly after the water recedes / drains might be beneficial to wash off the mud on plants. Flooding can lead to greater disease problems on all crops. HAIL Hail has danced across the area, varying from none to light to severe. To assess injury to corn and options to consider, see http://www.extension.iastate.edu/pages/eccrops/hailcorn.html. To assess Injury to soybean and options to consider, see http://www.extension.iastate.edu/pages/eccrops/hailsoy.html. As corn fields begin to recover, many are noticing whorls tied up in themselves. The vast majority of those plants will recover and become normal plants. When the plants blow out of being tied up, often the leaves are very light green to yellow in color. This is because the leaf tissue has not been carrying on photosynthesis due to lack of exposure to light. The margins (edges) of the leaves will often be wrinkled, again
a result of being tied up. The leaves should change to a green color within a day or two. Roger Elmore has two more detailed articles in the ICM News at http://www.extension.iastate.edu/cropnews/2008/0607loriabendrothro gerelmore.htm and http://www.extension.iastate.edu/cropnews/2009/061901.htm. Post-emergence Corn Herbicides on Hail Damaged Corn Many post-emergence corn herbicides have limits based on plant height and/or stage of development. If parts of plants have been removed, the limits apply to what would have been there normally. Injured corn plants will be under stress and may be more susceptible to herbicide injury, so applications should wait until the crop has had a chance to do some recovery, if possible. Injured weeds may also be less susceptible to herbicides, but in many cases, the weeds are already larger (before injury) than what is prescribed on the herbicide label. Unfortunately, there are not silver bullets for this situation. CORN Green Snap / Brittle Snap We have also had some green snap / brittle snap of corn during the high winds of some of the storms of the last several days. Fast growing corn is most likely to green snap with corn at growth stages V5-V8 and then V12 tasselling being most vulnerable. The wind speed coupled with the growth stage of the corn are the most important factors contributing to green snap. There are some genetic differences in vulnerability to
green snap. And an application of a dicamba product, such as Banvel or Clarity, can make the corn more brittle. An oldie-but-goodie article about research on green snap is at the ICM News site http://www.ipm.iastate.edu/ipm/icm/1998/7-13- 1998/greensnap.html. Potassium Deficiency Symptoms We are again seeing corn fields with areas in the fields that are stunted with the lower leaves yellowing and browning along the margins. This is a symptom of potassium (K) deficiency, but is often due to poor root function rather than a shortage of K in the soil. The end rows are often better than the rest of the field, probably due to the different soil structure where the traffic and/or tillage pattern has been different. Usually the fields look fine until the corn gets to be about calf high, then corn in areas of the field stop growing and the lower leaves turn yellow. Good corn can be right next to extremely stunted corn with no apparent reason for it. The corn in these areas remain stunted and the lower leaves remain yellow, but they usually yield better than expected. Anything that restricts root growth during the initiation of the nodal root system can lead to the problem. The nodal roots emerge within 0.75 1.0 inch of the soil surface. If there is something in the surface inch or so that the roots don't "like" they don't function properly. There can be large differences among hybrids in showing this phenomenon. Shallow planting and/or soil settling or eroding after planting aggravates the problem. This year, often there is evidence the soil was tilled and/or planted when the soil was just a little too wet. In many fields it is difficult to come up with an explanation why the problem is appearing. It is most common in no-till fields, but shows up in tilled fields as well.
In tilled fields, it can show up where the soil is fairly "fluffy", especially under dry conditions. Since the end rows usually look better, it could be that a little surface compaction actually helps to alleviate the problem. If the soil hasn't been tested recently, soil samples should be taken to make sure it is not a true K deficiency problem. Soils that are low or marginal in K are more likely to show the problem. There is nothing that can be done when the problem appears. An excellent discussion of this problem in both corn and soybean is on pages 123 124 of the June 20, 2005 Integrated Crop Management (ICM) Newsletter or at http://www.ipm.iastate.edu/ipm/icm/2005/6-20/potassium.html. SOYBEANS Cupped Soybean Leaves I have been getting a number of calls related to soybeans that have cupped up or have malformed leaves that look like dicamba or growth regulator herbicide injury. When this problem occurs, the possibility of spray drift needs to be investigated. If an herbicide has drifted from a nearby corn field or roadside, the symptoms should be greatest near the source of the drift and gradually diminish with a greater distance from the source. Also the symptoms should be less near anything that would have obstructed the drift, such as tall grass or trees. If a drift pattern is not evident, then it is unlikely to be the reason for the symptoms. If the symptoms appear after a field is sprayed and there is a sprayer pattern to the symptoms, the possibility of sprayer contamination with dicamba (Banvel, Clarity, Northstar, Distinct) or another growth regulator herbicide should be investigated. However, we do occasionally see these symptoms in the absence of a growth regulator herbicide. Occasionally additives, such as ammonium sulfate (AMS), 28% Nitrogen
solution, or surfactants can cause these symptoms. I have also seen symptoms not show up until 2 or more weeks after the field is sprayed. If dicamba was the source of the problem, symptoms should show up within a day or two. In some cases the entire field showed the problem before anything was sprayed on the field or in neighboring fields. Sometimes the symptoms are uniform across the entire field and sometimes certain parts of the field are worse than others, but there is no drift pattern. I see this most often when the soybeans go through a growth spurt when temperatures are high after some cool weather or after a heavy rainfall. Apparently under these conditions, the balance of naturally occurring hormones in the plant is disrupted, resulting in symptoms characteristic of growth regulator herbicide damage. Usually the soybeans recover from this condition with little to no effect on the final yield. See the July 19, 1999 ICM Newsletter for more information (http://www.ipm.iastate.edu/ipm/icm/1999/7-19-1999/malsoy.html). HAY Potato Leafhoppers High numbers of potato leafhoppers can be found in some hay fields. Be sure to also use a sweep net to monitor potato leafhopper numbers and treat if numbers exceed the threshold. For more information on managing potato leafhopper, see pages 107-110 of the June 21, 1999 Iowa State University Integrated Crop Management Newsletter or http://www.extension.iastate.edu/pages/eccrops/potatoleafhopper.html. Remember, waiting to see hopperburn is waiting too long as substantial losses have already occurred by that time.
Lepto Leafspot Lepto Leafspot is showing up in many alfalfa fields. In general, there is nothing that can be done except to harvest early to salvage as much leaf material as possible. For more information on Lepto Leafspot, see the following sites at The Ohio State University: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/alfalfa/lepto.htm http://agcrops.osu.edu/cropdoc/b827_128.html FOR YOUR CALENDAR Illinois Forage Expo Meier Farms, 205 N Dakota Road, Ridott, IL Stephenson County Friday, July 31, 2009 9 AM to 4 PM Directions From the West: Exit US Rt 20 at RT 75 (Freeport/Dakota) exit. Go south (right) ¾ mile on Route 75. Go east (left) 2 miles on River Road, turn right on Dakota Road 1/2 mile. Equipment Field Demonstrations times subject to change 9:00 AM 10:00 AM Mowing & Tedding 10:00 AM 11:00 AM Raking 10:30 AM Baleage 11:00 AM Noon Chopping 1:00 PM Chopping 2:00 PM 4:00 PM Baling Educational Presentations 10:00 AM Autosteer in Forage Systems Jay Solomon, U of I Extension
10:20 AM Dollars & Cents of Alfalfa Production Jim Endress, U of I Extension 10:40 AM Managing Risk with Hay Insurance Speaker TBA 11:00 AM Nutrient Management Planning & How EQIP Can Help USDA NRCS Staff 11:20 AM Forages & Today s Milk Price Dr. Mike Hutjens, U of I Extension Industry and Equipment Exhibits Advances in Precision Ag Field Day ISU SE Iowa Research & Demonstration Farm Crawfordsville September 17 See the latest in precision agriculture technology, including RTK guidance systems, auto-steer, automatic shut-off planters, and sprayers. As details emerge, they will be posted at http://www.extension.iastate.edu/pages/eccrops/meetserc.html.