July 8, 2011
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 in the next couple of weeks 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. So far corn fields are looking good, although some eyespot is starting to show up in NE Iowa. 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
I have seen and heard about several fields in EC and SE Iowa that have lost some stand due to billbugs. This is not a common pest in Iowa, but for some reason is more prevalent this year. The injury looks similar to stalk borer injury, but there is no frass and there is no stalk borer. The billbugs are small and very hard to find because they hide and blend in with the soil. At this point in the season it is not likely to pay to try to treat the problem. For a picture of billbugs and more discussion see http://ento.psu.edu/extension/factsheets/billbugs.
Western Bean Cutworm
Over the years as European corn borer problems have decreased, western bean cutworm (WBC) has moved in to fill the niche. The first few catches of WBC 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. Roundup can control small bur cucumber, but must be applied (with drops) before corn is 4 foot tall on Roundup Ready corn. Ignite can also control any emerged bur cucumber in Liberty Link corn, but must be applied (with drops) before the corn is 36 tall. 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). 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.
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. Unfortunately there is no magic bullet for this troublesome weed in corn.
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. 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 R1 stage (early flowering). 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. 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.
Judging on how the Japanese beetles are devouring everything around my house this year, it looks like this may be a bad year for the beetles. One thing to remember is that the damage on soybeans looks a lot worse than it is, and it is better to hold off spraying as long as possible, especially if soybean aphids are also becoming a problem. An early application of an insecticide can actually cause a soybean aphid problem because it will kill off the beneficial insects. I have been seeing a lot of lady beetles and lady beetle larva in soybean fields this year. I'm not sure what they are feeding on now, but at least they will be ready if the aphids move in. Also 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. Most people (including me) 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.
Before 2008, we thought one thing we had learned about soybean aphids was that they were mainly a problem every other year in odd numbered years. I don't know whether they are reverting to their old habits this year, but so far aphid counts in NE Iowa have been fairly low. Brian Lang reported that he is finding only 1.3 aphids per plant in a field he is monitoring, which so far is most similar to the 2006 season (an off year). Fortunately for us in the southern part of the state, we will get some advance warning from the north on whether we are likely to have an aphid problem this year.
FOR YOUR CALENDAR
Field Diagnostic Clinic at the Field Extension Education Lab near Ames
This program is on the fundamentals of crop plant diagnostics. Sessions focus on insect, weed and crop disease identification, herbicide injury, nutrient deficiency symptoms, and understanding crop growth and development. For more information go to: http://www.aep.iastate.edu/feel/fdc.html
Crop Management Clinic at the Field Extension Education Lab near Ames
The Crop Management Clinic is an intensive two-day training program that focuses on the latest developments in crop production and protection. Attendees select from 20 different topics to develop a course agenda that fits their specific needs. The curriculum is divided into four primary areas: crop management, pest management, nutrient management, and soil, water and tillage. A detailed listing of scheduled topics is available at: http://www.aep.iastate.edu/feel/cmc.html
MUSCATINE ISLAND (horticulture) RESEARCH and DEMONSTRATION FARM, Fruitland
SUMMER FIELD DAY
JULY 19, 2011
Details will be posted soon at http://www.extension.iastate.edu/Pages/eccrops/meetmusc.html.
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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