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    Iowa Field Reports: Dry Conditions, Insect Pests, and Weed Escapes

    Western Corn Rootworm Photo: Purdue University

    The past week brought again spotty rainfall across the state. With the dry conditions and warmer temperatures forecasted there are concerns about what this may mean for the crops. Spider mites, corn rootworms, grasshoppers, aphids, and weed escapes were other observations or concerns coming from the fields this last week. Read on for more specifics about what’s happening in fields across the state.

    Northwest Iowa

    Joel DeJong (Region 1): “Rainfall in the past week was again very spotty and limited for most. On Monday (August 1) I toured some of the areas with more stress – along the western edge of my region. The closer to the border I travelled, the tougher the crops look.

    “You can find a lot of curled corn, and some have curled for a lot of days already. Many fields in that area aren’t over about 7 feet tall, indicative of long-term moisture stress. Several fields have lost most of that healthy green color and look pretty gray. Many of those have leaves that are warm to the touch – also not a good sign.

    “But, much of this region is only showing limited curling, although you can see that there isn’t a lot of room for error. I cannot imagine how much a two-inch rain would be worth for this area! The forecast is not favorable at this time, so I will be observing how much ear tip kernel abortion occurs this week.

    “Soybeans have upturned leaves in many fields, also evidence of moisture shortage. The same area with significant corn stress also has lots of spots where lower leaves are beginning to fall off, and some lower stem pod abortion occurring. But, much of the area is showing limited stress at this time, and the potential remains quite good if we get those rains we need.

    “Again, we will need to revisit this next week because I believe many fields are “on the edge.” However, soybeans appear to be hanging in there better than corn – which can be expected at their respective stages of growth. Insects of concern included several fields with significant grasshopper injury along field edges, and some pollination problems to ear tips in a couple of corn/corn fields I visited due to silk clipping from rootworm adults.

    “I expected to see more spider mite problems on my Monday tour but saw less than I had anticipated. Soybean aphid levels remain quite low so far, too.”

    North Central Iowa

    Angie Rieck-Hinz (Region 3): “Except for pop-up showers, rain has been scarce this past week in NC Iowa and stress is showing daily on eroded knobs, sandy pockets and other stressed areas in fields. Nitrogen firing is apparent in corn throughout the area. Corn is R2-R4.

    “Disease pressure remains low, but gray leaf spot is becoming more prevalent, and I have found Northern Corn Leaf Blight (as in two lesions!). Soybeans are R3-R4. Bacterial blight and frogeye leaf spot are easy to find, but still at low levels.

    “Potassium deficiency is starting to show up in areas that have been dry.  I have had a couple of phone calls from people saying they have found low levels of soybean aphids.”

    Northeast Iowa

    Josh Michel (Region 5): “Over the past week, most of NE Iowa received from 0.10 to 0.25 inches of rainfall, with local heavier amounts in Allamakee and Winneshiek Counties. Most of the corn in NE Iowa is currently at R2 to R3. I continue to see fungicide applications taking place, even though disease pressure continues to be low.

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    “Japanese beetles can be found in most fields, but I haven’t seen or heard of any severe silk clipping. Soybeans are mostly at R2 to R3, as pod development is occurring. I continue to receive calls regarding soybean herbicide injury, leaf defoliation and weed management strategies regarding late-season waterhemp emergence.

    “A good portion of oats were harvested last week, and I’d expect most of the remaining oats to be harvested this week pending favorable weather. The majority of my field calls over the past week have consisted of alfalfa pests and scouting, Japanese beetle feeding, small grains and forage management, herbicide injury in soybeans, and managing for corn and soybean diseases.”

    Southwest Iowa:

    Aaron Saeugling (Region 10): “While it was not as dry as the July of 2012 when no rainfall was measured at the Armstrong Research Farm, July 2022 was dry for SW Iowa. This week will be the turning point for some areas here in SW Iowa where little precipitation has fallen this past month.

    “Crops are rolling in the afternoon and thin soils are showing signs of stress along with hail damaged crops. Spray planes and helicopters are still spraying fungicides in some areas. Some disease can be found in fields but overall, the severity is very minimal.  Insect activity has continued to include Japanese beetles, soybean gall midge, grasshoppers, and some aphids.

    “Measurable precipitation will be needed in early August to slow the decline of the crop.  Pastures have gone dormant in the driest areas and will need moisture before coming out of dormancy.  Be on the lookout for spider mites in the weeks ahead.”

    East Central, Southeast, and South-Central Iowa:

    Rebecca Vittetoe (Region 8): “The slightly “cooler” temperatures last week helped the crops, especially considering there was minimal rainfall across EC Iowa. A few areas benefited from some pop-up showers, but we could use some more rain. Even with the slightly cooler temperatures, there were still corn fields with leaves rolling in the afternoon last week and soybean fields with the leaves flipped over.

    “The dry conditions are also taking their toll on forages. Most of the corn is R2 to R3, and soybeans mainly R3 to R4. Tipping back on corn ears and pod abortion in soybeans are a concern with the hot and dry conditions. While the hot and dry conditions are not favorable for disease development, they are more favorable for spider mites.

    “I’ve been able to find spider mites in both soybean and corn fields. Something to be scouting for this week. Other pest activity noted in fields this last week included corn rootworm beetle, Japanese beetles, and grasshoppers. I’ve also gotten more questions about late season weed control, particularly for burcucumber and concerns about weeds that didn’t die from the herbicide application.”

    Virgil Schmitt (Region 9): “Rainfall last week in the counties I cover was an inch or less, with most areas receiving 0.5 inch or less. Areas roughly south of Highway 92 are listed as DO (abnormally dry) except that western Henry County is listed as D1 (moderate drought) on the July 28 Drought Monitor.

    “In general, temperatures during the last week in the counties I cover were one to four degrees below normal. Most corn is R2-R3 and looks good to excellent, except for areas showing drought stress. There are low levels of gray leaf spot in some fields and tar spot can be found here and there, but I have seen no fields that justify a fungicide application.

    “Most soybeans are at R3 – R4 and also look good to excellent except for areas showing drought stress. Again, disease levels are very low. I have received reports of low level two-spotted spider mite activity in fields with coarser soils. Japanese beetles continue to be found in all of the counties I cover.

    “Potato leafhoppers continue to be present in alfalfa and there are winged grasshopper adults in grassy areas. Phone calls, emails, and field visits last week mostly involved fungicide and insecticide applications.”




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