Iowa Field Reports: A “Potpourri of Insect Pests”

Japanese beetles in corn.

While parts of southern Iowa did receive some much needed rain, the western part of the state continues to be dry with parts considered to be in a D2 or severe drought.

Besides the weather concerns, other common issues ISU Extension and Outreach field agronomists saw and heard about this past week in fields across the state included a potpourri of insect pests including low levels of soybean aphids, Japanese beetles, potato leafhoppers, and corn rootworms as well as gray leaf spot becoming more prevalent in some corn fields and isolated reports of tar spot in corn.

Read on for more specifics about what’s happening in different regions across the state.

Northwest Iowa

Joel DeJong (Region 1): “We had another week with limited rainfall in the area. There are concerns about the stress from this lack of precipitation and pollination. About 1.5 counties are showing the most stress – that area is at about 50% of normal rainfall from April 1.

“The rest lag normal but not by as much. Soybeans haven’t closed 30-inch rows in much of the area, and I’m not certain they ever will. Plants that had dicamba injury are slow to recover in the drier areas.

“Some corn rootworm injury discussions on continuous corn acres were held this past week. All these discussions were from fields with multiple Bt rootworm traits, leading to concerns about trait failures.

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“Soybean aphids have been found in a few fields, but they remain at low levels at this time. Potato leafhoppers have been bad in alfalfa. Additionally, I had my first twospotted spider mite call, although I have not confirmed the damage myself at this time.”

Paul Kassel (Region 2): “Crop development continues at a rapid pace across much of the area. Corn is mostly pollinated, and the soybean crop is nearing the R4 or full pod stage. Rainfall and more importantly the lack of rainfall is a developing concern.

“Most of the weather reporting stations in the area report a rainfall deficit of about 1.5 inches for the month of July. Only two weather stations, Britt and Forest City, are reporting near normal rainfall for July. Sac City is reporting a 2.3 inch rainfall deficit for July.

“Farmers and applicators are applying fungicides to corn and soybean crops. Much of those fungicide applications will likely be completed this week.”

West Central Iowa

Mike Witt (Region 6): “Drought is the big concern in this part of the state with areas of Carroll, Greene, Audubon, and Guthrie Counties being the main areas of concern. Corn is mostly at VT. With the lack of rain and heat over the weekend, I have seen some fields shedding little pollen.

“Take time to check fields and see how pollination is going. There has been little disease pressure in corn, and on the insect side in corn I’ve seen some Japanese beetles and corn rootworm beetles. Soybeans are mainly R2 to R3 and seem to be holding their own against the heat and dry conditions.

“Japanese beetles seem to be prevalent in soybean fields. Hay fields and pastures are really struggling with the hot and dry conditions. Calls this past week have mainly been on growth regulator injury in soybeans and with concerns around the hot and dry conditions.”

Central Iowa

Meaghan Anderson (Region 7): “Central Iowa received anywhere from about 0.1 inch to small areas of over 4 inches of rain in the last week. Again, the dry area seems to be missing all the rain, with Dallas and Boone County remaining particularly dry. Parts of Polk and Story Counties caught some wind with the storms that came through last week.

“Corn ranges from R1 to nearly R3, depending on planting date and location in field; there is a lot of variability. Most corn looks really good, but the dry areas are basically tapped out, especially in light soils. Gray leaf spot is getting a good start in a lot of fields.

“Soybeans are mostly R3 and while dry areas look pretty tough in the middle of the afternoons, soybeans seem to be growing well across most of central Iowa. Weed control has been fairly good, but many 30-inch rows are still not completely closed, providing the opportunity for weeds to sneak through later this season.

“I’ve found a potpourri of insect issues – Japanese beetles, thistle caterpillars, bean leaf beetles, grasshoppers – in soybean (and some of those insects in corn), though none have been at what I would call treatable levels. Most phone calls are about fungicide or insecticide decisions, potato leafhoppers in alfalfa, and dicamba injury in soybeans (yes, still).”

East Central, Southeast, and South-Central Iowa

Rebecca Vittetoe (Region 8): “Rainfall ranged from trace amounts to 1.5 to 2 inches across my area this past week, with heavier amounts falling in my more southern counties. Corn seems to mainly range from R1 to R2, and soybeans are mainly R2 to R3.

“Gray leaf spot is more prevalent, especially in the lower corn canopy. A reminder that this disease favors warm and wet/humid conditions. While there have been reports of tar spot in corn, I personally have not seen it in a field yet.

“I’ve seen lots of fly poop that can easily be confused for tar spot, which is a good reminder to check and see if the spot wipes off the leaf. Also note that tar spot favors more moderate temperatures and wet/humid conditions.

“I’m seeing little disease pressure in soybeans currently. On the insect side, I’ve been seeing and hearing more about Japanese beetles in corn and soybean fields, corn rootworm beetles, and potato leafhoppers in hay fields. I’ve also had a couple of isolated reports of soybean aphids but at very low levels.”

Virgil Schmitt (Region 9): “Rainfall last week was generally light, with the heaviest being less than 1.5 inches. In general, temperatures last week in the counties I cover were normal to three degrees above normal. Most corn fields are at V18 to VT/R1 and generally looking good except for storm damaged fields. Gray leaf spot is increasing.

“Soybeans are mostly R2 to R3, and in general they also look good outside of the storm damaged fields. Grasshopper nymphs continue to be observed in grassy areas and some winged grasshoppers can be seen. Corn rootworm trait failure (continuous corn), Japanese beetles, and storm damage were common topics of discussion this last week.”

Josh Michel (Region 11): “Some much needed and welcomed rain fell across the area last week. Most areas received 1 to 2 inches, with a few isolated areas receiving up to 3 inches. While the rain will provide some relief, alfalfa fields and pastures continue to show signs of stress.

“I have been seeing and getting many reports of insect damage, mostly due to potato leaf hoppers in hay fields. Forage quality and quantity continues to be less than average. Corn is generally looking good with many fields around R1 to R2. Signs of heat stress continue to be seen in most fields.

“Corn related field calls have consisted of more widespread gray leaf spot, isolated corn rootworm feeding, and Japanese beetle feeding.

“Soybeans are generally R2 to R3. I’m beginning to see some weed escapes in fields with shorter beans and with 30-inch row spacing. Soybean related field calls continue to be centered around herbicide injury, herbicide drift, insect feeding, and weed management.”




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