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Volume 2, Issue 7
July 19, 2019
This newsletter is an update on current topics and events in agriculture in Boone, Dallas, Jasper, Madison, Marshall, Polk, Story, Tama, and Warren counties.

Meaghan Anderson
Extension Field Agronomist

ISU Extension & Outreach
220 H Avenue
Nevada, Iowa 50201
Office:  515.382.6551
Cell:     319.331.0058
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Website
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Upcoming Events

IDALS Apr 19 - Dec 19 Pesticide Testing Schedule

July-Aug - Farmland Leasing meetings, various locations

July 25 - RUSLE2 and Iowa Phosphorus Index Workshop, Altoona

July 31 -
Bioreactor Field Day, Baxter

Aug 6-8 -
Beef Feedlot Short Course, Ames

Aug 9 -
Iowa State Fair Weed ID Contest, Des Moines

Aug 20-22 -
Iowa Drainage School, Nashua

August 28 - Ag Engineering and Agronomy Farm Field Day, Boone
 

Handy Links

Central Iowa Crop Update
Updates from an agronomist and weed nerd in central Iowa.

In this issue:

  • From the field
  • Early frost? Too soon to tell!
  • Defoliators in soybean
  • Corn rootworm beetles emerging in corn
  • Making fungicide decisions in corn and soybean

From the field


Our crops are moving right along in the heat we've been having, and the rains that came through on Wednesday were welcome relief for many areas. Most corn is in very late vegetative stages or tasseled (VT) by now, with some corn at R1 and a small amount at R2. Most soybeans are at R2 (full bloom), but there are still late-planted soybeans that have not flowered in the area as well. It seems disease pressure is relatively low for this time of year, but the insects are out in full force. I've been out mostly looking at weed management issues and insect problems in the field, but don't hesitate to contact me if you need assistance with anything crop related. Stay cool!
 

Early frost? Too soon to tell!


In early July, a group came out reporting that they expect an early frost in the Midwest this year. I know nothing about predicting frosts, but the climatologists I trust and work with closely tell me there is no way to accurately predict whether we'll have an early frost this early in the year. Perhaps we will have some more information available by the time Dennis Todey presents at the Ag Engineering and Agronomy Farm Field Day on August 28!
 

Defoliators in soybean


Defoliators continue to hang around in our soybean fields, including Japanese beetles (2018 article as it discusses both corn and soybean thresholds; 2019 article here) and a number of various caterpillar pests. Typically, levels of these pests are low, they are worse along field borders, and our soybeans are large enough this time of year that plants outgrowth defoliation with ease. Given the large numbers of defoliators, like thistle caterpillars, and the smaller size of soybean plants this season, it will be important to scout fields for feeding. Thresholds for defoliation during reproductive stages are 20% of leaf tissue lost, averaged across the entire plant and across the entire field. This article can help you train your eye to identify percent defoliation.



Two photos from two fields with thistle caterpillar infestations. I was regularly finding >1 caterpillar per plant.

I have been out in several late planted soybean fields in Boone and Dallas County this week with significant thistle caterpillar feeding, more than one thistle caterpillar per plant (on average), and a wide range of caterpillar sizes.

Corn rootworm beetles emerging in corn


Corn rootworm beetles should now be emerging in our corn fields, and it is important to scout long-term continuous corn fields to look for control issues with western corn rootworms. Please call me if you notice a significant presence of corn rootworm beetles in any of your corn fields.

Here are some corn rootworm resources that may be useful to you:

Roots with feeding injury and adventitious root production from western corn rootworm larvae.
 

Making fungicide decisions in corn and soybean


With the wide range of planting dates and significant late planted corn and soybean, fungicide decisions are not going to be easy this year. Overall, I've seen very little disease pressure so far, but the forecast will be for cooler temperatures next week that might be more desirable for disease development. ISU plant pathologists, along with several others from Midwest universities, posted an article on the Crop Protection Network website titled Foliar Fungicide Decisions for Late-Planted Crops. This is a really nice article that runs through some discussion about whether fungicide applications may be a sound investment this growing season. In the next few days, expect to see a post on "preventative" and "curative" fungicides posted to our Crops team website. If you haven't started scouting yet, I would determine which of your hybrids/varieties may be weaker against the pathogens that are out this growing season and scout those fields first. 

As you decide whether to make an application, fungicide efficacy tables for both corn and soybean are available through the Crop Protection Network as well. These are great to look at what active ingredients are known to be effective against the pathogens in your fields.

Finally, fungicide resistant pathogens have been discovered in Iowa soybean fields. Strobilurin-resistant frogeye leaf spot was identified in several Iowa fields and fungicides containing only strobilurin active ingredients (FRAC group 11) performed poorly against frogeye leaf spot in university trials in 2018. See more about those results here. Additionally, there was evidence of some questionable performance against Septoria brown spot. An integrated approach to disease management is necessary to preserve the fungicides we have left, but one important step is to avoid relying on a single fungicide class (FRAC group) to manage issues. Other important tactics include crop rotation and using disease-resistant cultivars.

 




 
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