What's Bugging Your Crops This Summer?

What's Bugging Your Crops This Summer?

ISU Extension specialist offers insect and disease scouting tips for corn and soybeans.

It's early July and corn and soybeans are starting to finally gather some heat units and hit a faster growth period in Iowa. Keep an eye on your fields, as insects and diseases are developing, too. Iowa State University Extension field agronomist Brian Lang, located at Decorah in northeast Iowa, offers the following guidelines on what you need to be looking for in your fields.

START SCOUTING FOR SOYBEAN APHID:. "It's time to start scouting soybean fields for aphids, particularly those fields without insecticide treated seed," says ISU Extension field agronomist Brian Lang. "Soybean fields I've scouted that were planted with seed that was treated with an insecticide have very low aphid populations at this time—as of July 1" But keep an eye out, he warns. Aphid populations can explode, building up quickly if weather conditions are favorable.

* European Corn Borer: All corn is protected up to about 17 to 21-inch extended leaf height by a naturally occurring compound in corn called DIMBOA. Beyond that height you would scout non-Bt corn borer corn for 1st generation corn borer. With current market prices, it probably only takes about 1 borer per plant to justify treatment.  A 2009 ICM News article includes a "dynamic threshold spreadsheet" so that you can calculate profit or loss from a treatment based on your own economic factors.

* Japanese Beetles: First sightings of Japanese beetles were reported in southern and central Illinois. In recent years they began showing up in Iowa too. In Iowa, this insect is still mostly a problem south of Highway 3, but it has been slowly adapting northward. 

Thresholds for soybeans are based upon defoliation levels (20% between bloom and pod fill). For corn, pay attention to silk clipping. At this point in the season growing season (early July), it's still too early to tell how numerous this insect will be in 2013. This insect has a few look-a-likes. This article reviews proper identification.

For "lawn and garden" concerns, looking to protect certain trees and shrubs from this insect, go to this article for management tips.

* Potato Leafhopper: Scout and manage this alfalfa pest through August. IPM tips on thresholds and management are available here.

Don't forget to scout new seedlings of alfalfa under the oat nurse crop canopy. Potato leaf hopper can do a lot of damage to new seedings of alfalfa.

* Soybean Aphid: Soybean aphid populations at the ISU Extension trial near Decorah as of July 1 dropped considerably, possibly due to the extended wet weather in the area. Aphid activity in your region of the state might not be affected in this manner. It's probably best to assume that aphid activity in many regions, are progressing similar to trends in 2005 and 2009 on my attachment.~~~PAGE_BREAK_HERE~~~

A recent report from the University of Wisconsin near Arlington had V5 soybeans at 98% infested averaging 144 aphids per plant. "It's time to start scouting fields, particularly those without insecticide treated seed," says Lang. "Soybean fields I have scouted that were planted with insecticide treated seed have very low aphid populations at this time—as of July 1."

Watch soybean fields closely for development of these soybean diseases

* Brown Spot in Soybeans: Brown Spot, also called Septoria Leaf Spot, is easy to find in soybean fields now—as of early July. 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 of the soybean plant, it may warrant a foliar fungicide treatment typically around the R2 to R3 stage. Right now most soybeans in northeast Iowa are still vegetative or just reaching R1 growth stage. For photos and additional information, visit this link.

* White Mold In Soybeans: Does it pay to make preventative foliar fungicide applications for White Mold in soybeans? Some fields are now entering the window for preventative fungicide applications against White Mold. Cool and wet weather favors risk of white mold development, says Lang. However, reviewing an article by ISU plant pathologist Dr. X.B. Yang from 2008--a wet season with some late planted soybeans--he reminds us that canopy closure is also critical for white mold development. Late planted fields have difficultly closing their canopy during flowering, and are at low risk of white mold infection. 

Read the article here. Even for soybean fields that have a good canopy closure, the greatest concern is with those fields that have a history of problems from White Mold. Fungicides labeled for White Mold vary in their recommended applications from R1 to R3 growth stage of the soybean plant, depending on the product. Follow label directions for spraying the fungicide. Application timing and coverage is very important.

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