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Central Iowa Crop Update
Updates from an agronomist and weed nerd in central Iowa.
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In this issue:
- July 6 Corn Rootworm Mgmt. Field Day at FEEL
- July 14 ISU Weed Science Field Day
- Insect Roundup - corn rootworm, Japanese beetles
- All a Twitter about Tar Spot
- Pesticide application, drift, and crop injury
- Join the Iowa Pest Alert Network!
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July 6 Corn Rootworm Mgmt. Field Day at FEEL
RSVPs by Friday, July 1 are MUCH appreciated so we have accurate lunch numbers! Thanks to Iowa Corn Growers Association for sponsoring the lunch for this event!
Join us on Wednesday, July 6 for a Corn Rootworm Management Field Day at the ISU Field Extension Education Lab near Boone. Registration begins at 9 a.m. and the field day will begin at 9:30 a.m. with a complimentary lunch to follow.
We'll discuss management strategies for corn rootworm, look at plots comparing different Bt traits with and without insecticide to evaluate root feeding and management of rootworms, and discuss scouting strategies for rootworms including root digs, floating larvae, and using sticky cards to catch adults.
We've got 6 other corn rootworm management field days happening across the state and you can read about the other field days here.
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July 14 ISU Weed Science Field Day
Join us for the July 14 ISU Weed Science Field Day at the ISU Curtiss Farm. This field day will include many research updates from the Weed Science team at ISU and conclude with a complimentary lunch. Please RSVP to me by early next week at the latest! Learn more here.
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Insect Roundup
Corn rootworm - Egg hatch is behind normal this year, but we should be able to readily find rootworm larvae feeding on roots in corn fields now if they're present. When scouting, you can dig roots with surrounding soil and dunk them in a bucket of soapy water to do a float test for larvae (see HOW here!). Additionally, you can check roots for feeding and later use sticky traps to catch adults. We'll talk all these details at our corn rootworm demonstrations this summer!
Soybean gall midge - Adult midges are emerging in western Iowa as of nearly two weeks ago. In Central Iowa, we've found midges in Madison, Dallas, Boone, and Polk counties in past years. The Polk County infestation was in a non-crop area on another legume rather than in a soybean field. Keep an eye out on soybean field edges, especially in the western parts of Dallas, Madison, and Boone counties! You'll be looking for wilting or dead plants from the edges of fields in. If you're looking up close at plants, look for black lesions near the base of the stem as a sign to peel back the outer stem epidermis and look for larvae. See more here!
Japanese beetle - They're emerging yet again in this part of the state and possibly coming to a soybean field near you soon. We've seen a lot of chafer beetles this summer already, so be sure to check for the metallic emerald wings and the alternating black/white tufts of hair that distinguish this pest from some other common beetles. See more about ID and biology here. Thresholds in soybean are 30% defoliation in vegetative stages and 20% after R1. See more about thresholds and management here.
Soybean aphid - Soybean aphid has been found in a soybean field in Central Iowa as of almost two weeks ago. The warm temperatures are hopefully slowing their development and spread as they prefer mid-70s and <78% relative humidity. Thresholds for treatment are well-researched and treatment is warranted when densities average 250 aphids/plant, populations are increasing, and >80% of plants are infested. Speed scouting is a great way to quick evaluate populations and makes scouting for this pest over time much easier. This Encyclopedia article from our Crops webpage has more information on ID, biology, risk factors, and management.
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All a Twitter About Tar Spot
Alison Robertson wrote a nice blog earlier this week about some considerations for tar spot management this summer. Some diligent scouts have noticed that the Tarspotter App has much (all?) of the state under a "high risk" warning for tar spot based on weather conditions we've experienced recently. Before considering a fungicide application, take a look at Alison's blog and a look at the fields in question. I am hopeful that we are still far behind our eastern cornbelt friends and will not see tar spot as severely as they have in recent years.
While scouting corn, keep an eye out for raised, often shiny, black spots on the leaves. Insect frass or other black specks are often mistaken for tar spot, but tar spot will not wash off or scrape off leaves like other black specks. See my images below of a tar spot lesion on a green corn leaf. It should start on lower plant leaves if it has splashed from inoculum in the soil or may be nearer to the top of the plant if it has blown in from another nearby field.
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Pesticide application, drift, and crop injury
Triazine injury from soil applications (or carryover) on a soybean plant appears as interveinal chlorosis and necrosis.
Herbicide applications are wrapping up (I hope) and I've received a number of phone calls about crop injury and drift issues. Triazines and PPO inhibitors from PRE applications or carryover have caused injury in some fields, as well as numerous phytotoxicity issues with POST applications. Problems are not surprising due to the high winds and hot weather we had in the past few weeks. I've got a few resources below for those of you applying pesticides, looking for resources regarding drift, or trying to identify injury in your fields. As always, please give me a call if I can assist you with these issues.
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Join the Iowa Pest Alert Network!
The Iowa Pest Alert Network is a text message alert system to keep you informed of scouting and management alerts for pests we're seeing in Iowa (and beyond if you like)! Read more about the network and how to join it in this blog!
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