Despite a hot start last week, temperatures dropped to below normal in most areas of Iowa for the rest of the week. Two thirds of the state's corn and soybean crops are now in good to excellent condition, according to the weekly crop conditions report issued August 11.
The weekly survey by the Iowa field office of USDA's National Ag Statistics Service shows corn tasseled in the state is at 96%, which is behind the 5-year average of 100%. Corn silked is 87%, which is 13 days behind last year and 11 days behind the 5-year average.
Corn condition in Iowa now rates 2% very poor, 7% poor, 25% fair, 49% good and 17% excellent. For Iowa soybeans, the Aug. 11 report shows 89% of the bean acreage is blooming, which is two weeks behind the 5-year average. Soybean condition rates 2% very poor, 7% poor, 26% fair, 48% good and 17% excellent statewide.
Plants shorter than normal
How are soybeans doing right now in Iowa in August? "They are doing okay," says Palle Pedersen, Iowa State University Extension soybean agronomist. "They look great from the road. When you walk into the fields they don't look as good. The plants are shorter than normal."
One thing that means is the pods will be lower to the ground than normal, making it harder to harvest without leaving some yield in the field.
"We are getting cooler temperatures now in August which is helping slow crop development down a bit, which is helping to set more flowers on the plants," says Pedersen. "So this is a big help for soybeans to have these cooler than normal temperatures now."
What about soybean aphids?
This insect pest is still invading some soybean fields, particularly in northern Iowa. Brian Lang, ISU Extension area crop specialist in northeast Iowa, says the amount of aphids has nearly doubled on his plots near Decorah, from last week to this week. So aphids are continuing to increase and you need to keep scouting your bean fields at least once a week.
"Even though you may have already sprayed for aphids, you need to go back and scout and take some aphid counts," says Pedersen. "The beans are developing behind normal this year so there is still a lot of yield potential to protect."
How do you tell when the aphid population has crossed the economic threshold and it is time to spray? "If you have an average of 250 or more aphids per plant, that's the economic threshold," says Pedersen. "The best thing to do is to walk into the field and look at plants in multiple areas and do the counts. The other option is to do the speed scouting technique."
Help for scouting soybean aphid
For directions on how to do the speed scouting technique, email [email protected] and you will find the information you need for aphid scouting and treatment decisions.
What about corn in Iowa? How is it doing as of August 11?
Analysts are" The cooler than normal temperatures Iowa is getting here in August are slowing down corn development," says Pedersen. "The big question I have both in corn and soybeans is whether we have enough days left to finish out the crop. Fall is approaching fast and the worst thing that can happen here is to get an earlier than normal freeze."
The cool temperatures right now are not too bad as long as we have sunshine and sunshine is the most important thing Iowa crops need right now, he adds.
Is SDS in your bean fields?
What else should farmers watch for on corn and beans this time of year? "Right now what is happening in soybean fields is that we have sudden death syndrome symptoms starting to show up," notes Pedersen. "We predicted that would happen. It's occurring right now and it's very important for farmers to go out and look at their fields. Make a note of which bean varieties you planted and how well they are holding up against SDS."
Keep that in mind when you choose which bean varieties to plant for next year. You can't manage SDS with a fungicide. "It's all about variety selection," emphasizes Pedersen. "So, you should start working with your seed dealer now, ask about the tolerance of soybean varieties to SDS and make sure you don't plant varieties that are susceptible to this pathogen on your farm in the future."