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 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/2008/0607LoriAbendrothRogerElmore.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.
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.
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.
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 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:
FOR YOUR CALENDAR
Illinois Forage Expo
Meier Farms, 205 N Dakota Road, Ridott, IL
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
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
11:00 AM Nutrient Management Planning & How EQIP Can Help
USDA NRCS Staff
11:20 AM Forages & Todays 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
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.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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