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The lowest level of insect injury where damage can be measured is called the damage boundary. The damage boundary is a biological relationship between the insect, crop, and environment; and is independent of input costs (e.g., seed, insecticide, etc.). Managing a pest below the damage boundary will not provide a return on investment because damage can not be measured. For soybean aphid, the damage boundary is several thousand cumulative aphid days.

This spring consisted of wet field conditions for many regions across Iowa during planting season. When soil moisture is at or exceeds field capacity, there is an increased potential for soil compaction, particularly at topsoil depths. Soil compaction at planting time can impact root growth and development for the rest of the growing season, and can be a serious problem for Iowa farmers. However, with proper field management, compaction can be minimized.

Soybean aphid feeds fluids within the phloem fluids (sometimes referred to as "sap") by inserting piercing-sucking mouthparts directly into the phloem vessels. Prior to feeding, aphids "taste" the sap to determine if the plant is a suitable host species and if the quality is acceptable. Once they settle and begin feeding, the injury from soybean aphid infestations can reduce plant growth, pod number, seed number, seed weight, and seed oil concentration.

I’ve seen more people walking beans and had more comments about it than I can remember in a long time.  Perhaps it's time for Greg Brown to re-release his classic ‘Walking the Beans’, first released on ‘The Iowa Waltz’ album in 1981.

My favorite verse of the song, and the chorus:

The current epidemic of wild parsnip has garnered much attention due to the toxins present in the plant.  Since wild parsnip is a biennial, mowing is often recommended as a control option.  The theory is that by preventing seed production, mowing can eliminate future infestations.  In practice, its a little more complicated than simply mowing when convenient; mowing needs to be timed properly in order to be effective.

Iowa State University Extension and Outreach field agronomists report crop conditions in your area of the state.

About twice a year I get asked these questions. "Angie, what are you doing to promote cover crops in north central Iowa? We just don't have many acres of cover crops up there." Or, "Angie, what can we do to get more cover crops in north central Iowa?" I usually chuckle at these questions, and for those of you who know me well, you know I have a response for everything. 

Since the last clinic update (6/17/2016), we are starting to transition from seedling diseases to foliar diseases. There is quite a bit of concern from clients about getting an early jump on foliar diseases, in order to plan for foliar fungicide applications. Similarly to the last blog, a majority of our sample are coming in with some sort of herbicide damage or other abiotic disorder. Here is what we have diagnosed, disease wise, in the last couple of weeks:

Storms hit eastern Iowa yesterday, bringing variable amounts of rainfall and enough wind to blow some corn down. The damage seems to extend across multiple counties, but I witnessed many fields with varying amounts of damage in Linn and Jones counties.

Last week, my lab crew found a few different caterpillars feeding in our soybean plots at the ISU Northwest Research Farm. They were hesitant to identify it in the field, so they brought one to me for a confirmation. First, I noticed it had a green body and green head and four pairs of prolegs on the abdomen. It is common to see green caterpillars in soybean (e.g., green cloverworm, soybean looper), but most don’t have four pairs of prolegs like this specimen.

This week, I got a note from Tristan Mueller (Iowa Soybean Association) seeing some corn leaf injury from redheaded flea beetle. The defoliation was noticeable and the farmer was considering a foliar insecticide. The fields did not have tasseled yet and he estimated 5-6 beetles per plant. 

Iowa Crop Progress Summary

Earlier this month, I wrote an ICM News article showing peak corn rootworm egg hatch in Iowa. That means at least 50% of viable eggs have likely hatched and larvae will start feeding on corn roots. To assess larval activity, some try using the float test (that’s just what I call it). Tom Hillyer in southeastern Iowa found rootworm larvae using the float test last week.

Thursday, June 23, brought great weather and a good crowd to the Northern Iowa Research Farm Field Day near Kanawha, Iowa, and the Southeast Research and Demonstration Farm Spring Field Day near Crawfordsville, Iowa; both hosted by Iowa State University (ISU) Extension and Outreach.

Iowa Crop Progress Summary
The USDA Weekly Crop Progress Report stated Iowa's corn crop has a good/excellent rating of 79%, above the current national average of 75%. The agency reported all of Iowa's soybeans as planted and 97% emerged, ahead of the 5-year-average by 9%. Iowa soybeans were given a good/excellent rating of 80%, and 17% are considered in fair condition. The U.S. Drought Monitor classifies southeast Iowa as abnormally dry on its intensity scale.

So far, this growing season has been relatively quiet on the crop disease front, likely due to the mild weather this spring has brought us. In its place we have seen quite a bit of concern with herbicide injury. Where diseases are concerned, here is what we have encountered so far in the Plant and Insect Diagnostic Clinic:

Corn
Pythium sp./spp. (Story and Wapello counties)

Rhizoctonia sp./spp. (Clinton and Polk counties)

I've been getting a lot of calls about uneven corn. Uneven corn can be caused by many factors, and there are usually multiple variables in play. Since a lot of folks have asked, here are some reasons I am seeing uneven spots in fields around west central and southwest Iowa:

1. Cold, wet soils early in the season that limited early root formation, followed by dry (and hard) soils that aren’t as conducive to root growth.

A Twitter campaign has been started to track corn and soybean diseases throughout the country. While scouting this summer, farmers and agribusiness professionals are encouraged to tweet a photo with the name of the disease, county, and state to either @corndisease or @soydisease.

The Using Manure Nutrients for Crop Production publication (PMR 1003) has recently been updated with revised beef cattle and dairy manure nitrogen (N) and phosphorus (P) crop availability ranges (Table 1, page 4). As shown below (bold values indicate revisions), beef cattle and dairy N availability ranges are now 30-50 percent of total nutrient applied and P ranges are 80-100 percent of total nutrient applied.
 

Cover crops have become quite popular in recent years, not only from a soil conservation and water quality perspective, but also due to their potential to be an additional forage source for livestock producers.

To better understand how cover crops can be used as a potential forage source, Iowa State University Extension and Outreach started a grazing cover crop project in the fall of 2015 at the McNay Research Farm near Chariton and the Allee Research Farm near Newell.