Volume 1, Issue 3
June 29, 2018
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
3109 Old Highway 218 S.
Iowa City, Iowa 52246

Office:  319.337.2145
Cell:     319.331.0058


Upcoming Events

IDALS Apr-Dec 18 Pesticide Testing Schedule

May 31, others - Greenhorn Grazing Workshop Series, Chariton

July 10 - Focus on Nitrogen Workshop, Crawfordsville

July 11 -
2018 Field Diagnostic Clinic, Boone (FEEL)

July 12 -
2018 Crop Management Clinic, Boone (FEEL)

Save the Date!

Aug. 10 - Iowa State Fair Weed ID Contest

Aug. 28-30 - Visit us at the Farm Progress Show!

Sept. 6 - SERF Fall Field Day


Handy Links

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

In this issue:

  • Nitrogen Management Workshops - first one on July 10
  • Growing season update
  • Should I apply a fungicide?
  • Insects out in field crops now
  • Herbicide drift in soybeans

Focus on Nitrogen Workshop July 10

ISU Extension and Outreach field agronomists and ag engineers will be hosting a series of workshops across the state with a focus on managing nitrogen for maximum profit and minimum water quality impact. Later this summer, we'll have an event focused on cover crops in central Iowa, but the first event is a "Focus on Nitrogen" workshop on July 10 from 5:30 - 7:30 p.m. at the Southeast Research and Demonstration Farm near Crawfordsville, IA (south of Iowa City). Learn more about this event here.

This program will highlight several important topics including:

  • Share research-based information on maximizing profitability with nitrogen management
  • Explain tools available for farmers to use in decision-making, responding to weather events during the growing season, and ISU research into nitrogen management practices
  • Discuss effectiveness of current nitrogen management practices in reducing nitrogen loss
  • Provide information on the Nitrogen Rate Calculator and how to apply it to determine profitable nitrogen rates
This workshop is free and open to anyone wishing to attend. A free BBQ dinner will be served from 5:30 - 6:00 p.m. and the workshop will be held from 6:00 - 7:30 p.m. Advance registration by July 6 is requested; please contact the Johnson County Extension Office at 319-337-2145 to register.

Growing season update

Crops are still accumulating GDDs quickly, even with our cooler and wetter weather last week. With that wet weather, some fields had significant ponding that may have affected the corn crop; this resource from Bob Nielsen with Purdue University explains more. Looking at the forecast, we'll be hitting another warm (hot, today!) period as the majority of corn shoots tassels and begins pollination. The National Weather Service predicts that July will be warmer than average, but that there is an equal chance of above, below, or normal precipitation for the month. Now that crops are reaching reproductive stages, we'd like to see temperatures cool down some and give our crops plenty of time to accumulate dry mass in the grain.

Most corn is nearing tassel stage and some corn hybrids will produce silks as soon as tassels are noticeable in the field. Whenever 50% of the plants in the fields are silked, then the crop is at that stage (R1). I've included some information below about some of the upcoming reproductive stages in corn. 

Stage Description of stage Comments Time to next stage
R1 Silk Maximum plant height About 10 days to R2
R2 Blister (clear liquid in developing kernels) Maximum vegetative dry matter.
Minimal grain dry matter.
About 8 days to R3
R3 Milk (white liquid in developing kernels) Outside of kernel is yellow.
Starch accumulation is increasing.
About 6 days to R4
R4 Dough Starch accumulation increasing.
Kernel moisture starts decreasing.
About 7 days to R5 (beginning dent stage)

Soybeans have been moving along much faster than normal as well this summer, especially given our later planting dates. Most soybeans I've seen recently are either in the early flower (R1) or full flower (R2). Most herbicide applications are only labeled through stage R1 or R2, so check both your crop and your herbicide labels before applying any products in the coming days and weeks. Jeff Gunsolus, weed scientist with the University of Minnesota, wrote a nice article for their crop blog about the uncertainty regarding the risk vs. reward of late or rescue herbicide treatments at this time of year. 

Unlike corn, our soybeans have indeterminate growth and will continue to produce new leaves, usually about one trifoliate every three days, through about R5.

Stage Description of stage Comments Time to next stage
R1 Open flower at any node Recommended time for foliar applications to manage white mold Just a few days to R2 stage
R2 Open flower at one of the two uppermost nodes of the main stem Glyphosate is labeled for use on Roundup Ready soybeans through the R2 stage About 10 days to R3 stage
R3 A pod at least 3/16-inch long at one of the four uppermost nodes of the main stem with a fully-developed leaf Most popular stage for foliar fungicide applications other than for white mold control. In some cases, R1+R3 stage applications for white mold control About 9 days to R4 stage
R4 A pod at least ¾-inch long at one of the four uppermost nodes of the main stem with a fully-developed leaf Beginning of the most crucial period of plant development in terms of stress influencing seed yield.
Rapid and steady dry weight accumulation by pods.
About 9 days to R5 stage

Should I apply a fungicide?

Conditions are good this year for the development of several common corn diseases, including Physoderma brown spot and gray leaf spot. Scouting your corn fields is the only way to be certain whether these diseases are an issue. Alison Robertson, one of our extension plant pathologists, wrote a nice article in the ICM News with more information about these disease issues.

From a management perspective, Physoderma brown spot is more prevalent in excessively wet conditions or those where water is pooling in the whorl for extended periods of time. This disease may present as either leaf lesions or a node rot, and there are some good photos of the symptoms here. There are no in-season management options for this disease.

Gray leaf spot, however, is a common disease that corn hybrids are rated for susceptibility on and can be managed with an in-season fungicide if the prevalence warrants it.  Hybrids are rated on their susceptibility to gray leaf spot, so knowing which hybrids are most susceptible is helpful when scouting and making management decisions.

While fungicides can be an important management tactic for problem pathogens, we need to take care to avoid prophylactic use of these whenever possible to reduce risk of resistance development in fields. You hear us talking about herbicide resistance with weeds, but fungal pathogens are not immune to developing resistance to fungicides. We had our first confirmed case of fungicide resistance in frogeye leaf spot in soybean last year in the state of Iowa.

How do you decide if it's worth it to spray? 
  • Doing on-farm trials with fungicide applications is one way to determine if fungicides are providing a yield benefit that pays for the application. Iowa State University research farm agricultural specialists are available to help set up and analyze results from on-farm strip trials.

    The Iowa Soybean Association also has a 
    large database of on-farm research trials and further information on setting up your own on-farm strip trials
    • For example, in their 505 on-farm trials for fungicide in soybean in the state of Iowa since 2005, the average yield response across all trials was 1.9 bu/ac.
    • In their 537 on-farm trials for fungicide in corn in the state of Iowa since 2006, the average yield response across all trials was 3.3 bu/acre. 
  • Unlike insect pests were we have more clear cut economic thresholds on when it pays to spray an insecticide or not, we don't quite have that for diseases. Instead, we need to consider if the pathogen is present, the crop suspectability, and if we have favorable environmental conditions for disease development. The University of Illinois recently published this blog post titled "Tips to help you make fungicide decisions" that does a nice job discussing factors to consider when deciding whether to spray a fungicide or not. 
  • Take time to scout and see what diseases, if any are present; where they are located at in the crop canopy; consider the hybrid and/or variety susceptibility; and look at the weather outlook to help determine if a fungicide application is warranted. 
Note that if a fungicide is necessary, using fungicides with single FRAC group numbers (modes of action) comes with a higher risk of reduced sensitivity or resistance development in a shorter period of time.

Insects out in field crops


Insects are out in field crops again this year and the only way to know if treatment is necessary is to scout!

Japanese Beetles: Keep your eyes open for Japanese beetles as they are starting to appear in corn and soybean fields. With these insect pests, leaf feeding on soybean and corn silk clipping (before pollination) are of concern.

Adult Japanese Beetles are metallic bronze and green with white tufts around the side of their abdomen. 
ISU Extension Entomologist, Erin Hodgson has a good article on Japanese beetle thresholds and management in corn and soybean, which can be found here. Be careful not to confuse Japanese Beetles with another similar looking beetle called a chafer

Bean leaf beetles: The first of the first generation bean leaf beetles will soon be emerging and showing up in soybean fields again. The next generation (2nd) will likely be of most concern for potential feeding in soybean fields, but those emerging in July can be monitored to give us an indication of what to expect for late August and September. Here's a good resource from 2016 on scouting for these pests.

Potato Leafhoppers: For those with alfalfa, don't forget to continue to keep scouting for Potato Leafhopper. The dry conditions can often magnify feeding injury from potato leafhoppers. Here's a good resource for scouting and managing for potato leafhoppers. 

Herbicide drift in soybeans


I'm just starting to get the first phone calls on suspected herbicide drift (dicamba) in soybeans. Thankfully, most cases I've investigated so far have not been from drift onto soybeans but rather "cases of mistaken identity." The University of Wisconsin has developed a nice fact sheet on identifying dicamba injury that you can find here.

Common symptomology known as "cupping" associated with dicamba physical drift, volatility, misapplication, or tank contamination. These show several different ways the injury may present from typical upward cupping, to a crinkle and strapped appearance, to a much slighter puckering/cupping of the leaf. This injury is usually symmetric on leaves (all three leaflets affected similarly).

Common symptomology from POST applications of HG 15 products applied to soybean fields (Warrant, Outlook, Dual, etc.). We often refer to this as "drawstringing" as it looks like the leaf veins at the tips of the leaves stop developing or even appeared pulled back toward the center of the leaf (heart-shaped). This is often not perfectly symmetric.

If you believe you have herbicide drift on your crops, please do not hesitate to call me to discuss the issue. If you need someone to document evidence for a possible settlement, consider hiring a professional agronomist (crop consultant, certified crop advisor, or other well trained agronomist). ISU Extension is in the business of education, but we do not assess entire field situations or get involved with settlements (we are not available as hired expert witnesses). Practical Farmers of Iowa has a really nice pamphlet regarding how to prevent drift and steps to take if you suspect your property or crops have been drifted on.

You can also reach out to the Iowa Department of Agriculture and Land Stewardship Pesticide Bureau at 515-281-8591 to report the drift. The pesticide bureau has a group of employees who investigate drift and their website has several helpful resources for those who are interested, including FAQ about pesticide drift, information about enforcement and investigations, and a list of private labs who do pesticide residue testing in Iowa

Another thing to be aware of is that while the Pesticide Bureau can test for herbicide in plant material or you can send in material yourself for testing, dicamba is often no longer detectable in plants within a few weeks after application. So not detecting the chemical during an investigation does not mean that there was no drift. Be sure to document physical signs of problems as soon as possible after an event is noticed. Do the same with agreements between both parties as to where yield checks in fall should be made; and if drift was on home gardens, consider all produce to no longer be viable for those crops not labeled for a dicamba application.

In the end, communication is key to both preventing and resolving issues, so be a good neighbor and don't be afraid of having the discussion about pesticide applications or potential drift to resolve issues quickly.


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