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East-Central and Southeast Iowa Crop Information


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July 17, 2013



Japanese Beetles Are Back



Japanese beetle problems started much later than last year, although their emergence this year is probably close to the normal time. They are easy to find in many soybean fields, and are very numerous in spots. One thing to keep in mind is that the damage in soybeans usually looks worse than it actually is. The threshold for spraying Japanese beetles and other defoliating insects is 20% defoliation during flowering and 30% defoliation prior to flowering. This is a picture showing about 20-25% defoliation that Marlin Rice took a few years ago:




Most people have a hard time waiting until they see this much damage before pulling the trigger, and many would likely call this 50%, rather than 20-25%. The longer you can hold off spraying, the more likely you can get by with one application and perhaps also control other insects later in the season. Most insecticides have good knockdown of the beetles but poor residual, so populations re-bound a week or 10 days after the insecticide is sprayed. Spraying when it is not needed can actually cause outbreaks of soybean aphids and spider mites by killing off the beneficial insects that keep other pest populations in check. It’s hard to believe we could have a spider mite problem with the way this season started, but if the dry weather of the past couple weeks continues, we could be talking about spider mites in another two weeks.


Corn fields should be scouted for the Japanese beetles when they start to silk. The beetles are not very good flyers, so the damage in corn is often the greatest in the outside dozen rows or so. They aren’t going to fly to the middle of the corn field if they don’t have to. If silks are being clipped to within half an inch of the ear before pollination is complete, it may pay to spray the beetles in the corn, at least along the field margins.


Soybean Aphids


Brian Lang reports that in the fields he is monitoring in NE Iowa that soybean aphid numbers are still fairly low, but numbers have been rebounding from the wet June weather. He is finding lower levels in fields where an insecticide seed treatment was used. The mid-season winged migration is just starting in NE Iowa. If there is a large flight, it could mean problems in early August. What happens in NE Iowa usually happens a little later in SE Iowa. Now is the time to start scouting.




Will It Pay to Spray a Fungicide?


With the early season wet weather it was looking like this might be a season where a foliar fungicide would be more likely to pay off. Now the weather is reminding me more of 2012, where the hot, dry weather resulted in fewer foliar diseases in corn and soybeans. The bottom line is that it’s best to do a little scouting and see if diseases are starting to show up before spraying. If you aren’t seeing the presence of disease lesions on leaves 3 leaves below the ear leaf and higher on the plant at this time, it is less likely the fungicide will result in enough of a yield increase to pay for the treatment. I’ve seen very low levels of gray leaf spot and other diseases so far in the corn fields I’ve been in, but conditions can vary greatly from field to field and some areas have been receiving more rain.

Usually the best time to apply a foliar fungicide on corn is from VT to R2 (tasseling to blister stage). There have been some problems in the past with arrested ear syndrome when fungicides are applied before tasseling if a surfactant or other additive is included with the fungicide. This may be more of a problem this year with the uneven corn growth where much of the corn may be tasseled but with areas of the field that have not yet tasseled. For more information on spraying fungicides on corn, see Alison Robertson’s recent article at




State Land Open to Emergency Haying and Grazing


DES MOINES - The Iowa Department of Natural Resources (DNR) will open up state land to haying and grazing to help farmers impacted by severe weather conditions. “This has been one of the most challenging weather patterns Iowa farmers have ever had to face and we want to be able to provide some additional options to our livestock producers,” said DNR Deputy Director Bruce Trautman. Most state lands in Iowa do not have proper fencing for cattle so farmers wanting to use the land for grazing would be responsible for setting up temporary electric fencing and watering tanks, making haying more likely to be the most viable option.


Haying and grazing can start after July 15th when the primary nesting season for upland birds has been completed. Land available is primarily the upland grassland areas however there are some additional opportunities for “flash grazing” in northeast Iowa and other limited opportunities on land not currently being leased to farmers. “The DNR is working very closely with the Iowa Governor’s Office and all of our stakeholders to make emergency livestock forage available and to make sure that we are helping those who need assistance the most,” said Trautman. Farmers interested in this opportunity should contact the Iowa Department of Natural Resources at 515-281-5918.



If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: July 17, 2013
Contact: Jim Fawcett

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