July 13, 2011
Many areas along and north of Highway 30 were affected by Monday morning's storms. From a crops perspective, corn that was flattened is probably the biggest concern. Fortunately, it appears that most of the downed corn is root lodged and not green snapped. With green snap, most research has shown a 1:1 relationship between percent green snap and percent yield loss (50% green snap results in 50% yield loss). More information on green snap is in Roger Elmore's article at http://www.agronext.iastate.edu/corn/production/management/mid/greensnap.html. With root lodging the yield prospects are much better, with perhaps less than 20% yield loss even with 100% root lodging. The stalks will straighten back out (or at least the upper stalk will straighten), so hopefully there will not be a large affect on pollination.. A study done in Wisconsin showed yield losses of about 10-20% when corn was totally flattened at V14-V18, where most of the affected corn is now. More details are in an ICM article from Roger Elmore at http://www.extension.iastate.edu/CropNews/2011/0712elmore.htm and Jim Fawcett's article at http://www.extension.iastate.edu/Pages/eccrops/jfcu110712.html.
1. be in contact with their crop insurance representatives; some policies will cover this type of damage and some will not, and
2. be starting to plan for a difficult harvest (acquiring a reel for the corn head?).
With the high corn prices, some are tempted to go ahead and spray every acre just in case. Many studies have shown that if foliar disease incidence is low, it is much less likely for fungicide applications to pay for themselves. A much better approach is to take some time and check corn fields to see if foliar diseases are showing up and also to target applications to fields where diseases are more likely to cause yield reductions, such as corn on corn and corn hybrids that are less tolerant to foliar diseases. The best time to make the decision on which fields to spray, if any, is right before and during tasseling. In most years fungicides applied from tasseling to soon after silking have been the most likely to be economical. If foliar disease lesions are showing up 3 leaves below the ear leaf or higher at tasseling and the variety is more susceptible to foliar diseases, a fungicide application is more likely to be profitable. For more discussion on factors to consider in making fungicide decisions, see Alison Robertson and Daren Mueller's article at http://www.extension.iastate.edu/CropNews/2009/0706robertsonmueller.htm.
Nematodes that Feed On Corn
Time to Sample for Corn Nematodes
Most corn nematode populations peak in early July. This is considered the best time to sample for the pest, except on sandy soils when sampling should be done in the spring or fall. The method is NOT the same as for soybean cyst nematode (SCN) because with corn nematodes you are collecting the live worm-like nematodes, not cysts or eggs as with SCN. The laboratory process is also a bit more difficult for corn nematodes, so the fee for a corn nematode sample ($30) is more than for a SCN sample ($15). The procedure for collect a corn nematode sample is:
1. Use the Sample Submission form from ISU. http://www.extension.iastate.edu/Publications/PD32.pdf On the back of this form under Tests Available and Fees, you select Complete nematode count $30.00.
2. Collect 15 to 20 soil cores taken at 12 inches deep and cored at an angle under corn plants to include root fragments in the sample.
3. Also collect and submit 3 to 4 root balls with the soil core sample.
4. Handle samples carefully (don't toss or drop samples) and mail immediately after the sample is collected.
The results from ISU will list the different nematodes found, their numbers, and what types and numbers of nematodes might be of concern.
For more information, see the article at: http://www.extension.iastate.edu/CropNews/2009/0713tylka.htm
Western Bean Cutworm
The first few catches of Western Bean Cutworm moths are now being found in pheromone traps setup across the Midwest. Scouting for this pest should be done sometime between 25 and 50% adult (moth) emergence, which is currently predicted to occur between July 13 and 17 is SE Iowa, and between July 16 and 20 in EC Iowa. If you want to check the trapping yourself, go to: http://apps.csi.iastate.edu/pipe/ For more information on WBC, see our article on ICM News at: http://www.extension.iastate.edu/CropNews/2011/0701sisson.htm
Few Options Now for Bur Cucumber Control in Corn
Bur cucumber is becoming an increasing problem in many corn and soybean fields. One problem with the weed is that it continues to emerge throughout the season. There are several herbicides that are labeled for bur cucumber control, but most corn fields are now too tall for most of the labeled products.
1. Roundup can control small bur cucumber, but must be applied (with drops) before corn is 4 foot tall on Roundup Ready corn.
2. Ignite can also control any emerged bur cucumber in Liberty Link corn, but must be applied (with drops) before the corn is 36 tall.
3. Callisto and Northstar have good activity on the weed, but Callisto should not be applied to corn taller than 30 and Northstar is only labeled on corn up to 36 tall (with drops).
4. A new herbicide with good bur cucumber activity is Peak, but this will be mainly useful on continuous corn because of the carry over potential, and it is only labeled on corn up to 30 tall.
5. Impact is labeled for bur cucumber and can be applied up to 45 days before harvest. Buctril also provides some control of the weed and can be applied until tasseling.
Late applications of Roundup can work fairly well in soybeans, although this is one weed that glyphosate is a little weak on. Additions of Classic can improve the control in soybeans.
Brown Spot, also called Septoria Leaf Spot, has been particularly widespread this year, especially in the SE where there has been excess rain. It is often present in the lower canopy this time of season. Warm dry weather may stop the movement of the disease up the canopy. However, if the disease advances up the plant canopy during the early reproductive stages (early July), it may warrant a foliar fungicide treatment typically at the R3 stage (beginning pod). Right now most soybeans in SE & EC Iowa are R2 stage (full flower). For photos and additional information, go to: http://www.ipm.iastate.edu/ipm/icm/1996/7-8-1996/soyfoldis.html.
Bacterial blight is also fairly common in many soybean fields. This disease tends to show up more in the upper canopy and flourishes in hot, wet weather. Since the disease is caused by a bacteria, fungicides have not affect on it. For photos and additional information, go to: http://www.ipm.iastate.edu/ipm/icm/1996/7-8-1996/soyfoldis.html.
Japanese beetle damage on soybeans looks a lot worse than it is, and it is better to hold off spraying as long as possible because if fields are sprayed too early, the Japanese beetles tend to repopulate the field a week or so after it is sprayed. During flowering and pod set, an insecticide is not likely to pay unless the beetles have eaten 20% of the leaf area over the entire plant. Japanese beetle injury tends to be at the top of the plant, so look at the entire plant. Most people tend to overestimate defoliation. If you think it is 20% defoliation, it is most likely only 5-10%. For help in estimating defoliation see http://www.ipm.iastate.edu/ipm/icm/2002/7-29-2002/soydefoliation.html. For more information on Japanese Beetles see http://www.extension.iastate.edu/CropNews/2009/0727hodgson.htm.
So far, soybean aphid numbers have approached zero in this part of the state and have been low in northeast Iowa, and we're seeing quite a few predators in the fields. Hopefully predators will keep any inbound flights under control. As people are making their final pass with an herbicide, it is tempting to throw an insecticide in the tank; this may kill the predators and leave the field more vulnerable to a population explosion from a small inbound flight of soybean aphids.
FOR YOUR CALENDAR
Crop Storm Damage Meeting
Thursday, July 14
John Olson Farm Site
Location: 2.5 Miles South of Vinton
Northwest Corner of Highway 218 and 63rd Street
(watch for signs)
Topics: Learn about what to expect from recent storm damage to crops, management decisions, livestock feed options, and Farm Service Agency Programs.
1. Jim Fawcett, ISU Extension Field Agronomist
2. Jim Jensen, ISU Farm Management Specialist
3. Denise Schwab, ISU Beef Program Specialist
4. Patrick Derdzinski, Benton County Farm Service Agency Director
Corn Nematode Field Day
Cedar County Coop West Branch
Evening of August 2
Greg Tylka will discuss research evaluating seed treatments for nematodes that feed on corn.
Details to follow soon.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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