Adapting Burndown Herbicide Programs to Wet Weather Delays

Source:  Dr Mark Loux, OSU

While it’s not terribly late yet, the wet soils and wet forecast could keep most of us out of the fields for a while.  The questions about how to deal with burndown herbicide treatments in delayed planting situations are rolling in.  One of the most common ones, predictably, is how to kill glyphosate-resistant marestail and giant ragweed and generally big weeds in soybeans when it’s not possible to delay planting long enough to use 2,4-D ester (Enlist soybeans excluded).  While we wrote last week about marestail populations being on the decline, this does not mean it’s gone by any means.  Overwintered marestail plants become tougher to kill in May, and the fact that fall weather was not conducive for herbicide applications makes the situation worse in some fields.  The good news is that we have some additional herbicide/trait options for help with burndown since the last time we wrote an article covering this in 2016, although our experience is that nothing we suggest here is infallible on large marestail.

A burndown of glyphosate and 2,4-D struggles to control marestail in the spring anyway, especially in the absence of fall herbicide treatments.  Our standard recommendation, regardless of when spring treatments are applied, is to either replace the 2,4-D with something more effective, or to add another herbicide to supplement the 2,4-D.  Sharpen has been the frequent replacement/supplement, and we now have the option to use dicamba in the Xtend soybean system instead of 2,4-D.  While it’s possible to use higher 2,4-D rates in the Enlist soybean without waiting to plant, higher rates do not necessarily solve this issue based on our research, although a follow up POST treatment that includes glufosinate or 2,4-D usually finishes off plants that survive burndown.  We also would not expect the addition of Elevore to consistently solve this issue either, and it requires a 14 day wait to plant any soybean.  There’s a list of suitable soybean burndown treatments in our marestail fact sheet, and also below – these are for fields not treated the prior fall.

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Estimating Wheat Yield With Stem Counts

Source: Dr. Laura Lindsey

Between planting in the fall and Feekes 4 growth stage (beginning of erect growth) in the spring, winter wheat is vulnerable to environmental stress such as freezing temperatures with limited snow cover, saturated soils, and freeze-thaw cycles that cause soil heaving. All of which may lead to substantial stand reduction.

However, a stand that looks thin in the spring does not always correspond to lower grain yield. Rather than relying on a visual stand assessment, farmers should estimate the yield potential of their winter wheat crop by counting stems, before deciding whether a field should be destroyed. An alternative method to evaluate wheat stand is fractional green canopy cover (FGCC). Fractional green canopy cover can be used to measure the canopy surface area using the mobile device application Canopeo. The app can be downloaded for free here: http://www.canopeoapp.com.

Figure 1. Measurement tool used to consistently count the number of stems in one foot of row.

Wheat Stem Count Methods: Wheat stems (main stem plus tillers) should be counted at Feekes 5 growth stage (leaf sheaths strongly erect) from one linear foot of row from several areas within a field (Figure 1).

 

 

 

 

 

Figure 2. Winter malting barley image analyzed for fractional green canopy cover with the Canopeo mobile device application.

 

Fractional Green Canopy Cover Methods: Fractional green canopy cover should be measured at Feekes 5 growth stage using the mobile device application, Canopeo (http://www.canopeoapp.com). The camera should be held at a height to capture three rows of wheat in the image (Figure 2).

 

 

 

 

 

After counting the number of wheat stems or measuring FGCC, Table 1 can be used to estimate wheat grain yield. For example, if an average of 51 stems is counted from one foot length of row, the predicted grain yield would be 100 bu/acre. Similarly, if the average FGCC measurement was 35%, the predicted grain yield would be 100 bu/acre.

 

 

 

 

Spring Herbicide Applications on Winter Wheat – Part 2 Labeled Herbicides

Source: Purdue University (Edited)

If weed infestations are severe enough to require a herbicide application, the use of liquid nitrogen fertilizer solution as a carrier is a popular option for applying herbicides and topdressing the wheat crop in a single pass over the field.  Caution should be taken when using a liquid fertilizer as a herbicide carrier as moderate to severe crop injury can result, especially in saturated conditions.  Many post applied wheat herbicide labels allow for liquid nitrogen carriers, but require different rates and types of surfactants than if the herbicide was applied with water as the carrier.  Table 1 includes precautions to be taken when applying wheat herbicides using liquid fertilizer as a carrier; further details and directions can be acquired from the herbicide label.

Another consideration growers should take into account when planning early spring herbicide applications is the plant back restrictions to double crop soybeans.  A large percentage of the herbicides listed in Table 1, especially those with activity on Ryegrass and Brome, have soybean plant back restrictions greater than the typical three month time period between spring applications and double crop soybean planting.  The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double crop soybeans after wheat.  Refer to Table 1 for more specific plant back timing restrictions.Click Here For Complete Table

Tar Spot – A “New” Corn Disease

Adopted from: CPN-2012 Corn – Tar Spot, Crop Protection Network

Initial symptoms of tar spot are brownish lesions on the leaves. Black, spore-producing spots appear later, making the leaf feel rough or bumpy. (Purdue Botany and Plant Pathology photo/Kiersten Wise)

Tar spot is a foliar disease of corn that commonly occurs throughout Mexico, Central America, South America, and the Caribbean. The disease was identified in the United States for the first time in 2015 in northern Illinois and Indiana. As of 2018, it has been confirmed in Iowa, Michigan, Wisconsin, Ohio, and Florida.  During the 2018 growing season, the prevalence and severity of the disease increased dramatically, and in some areas tar spot caused substantial yield losses.

In the United States, tar spot of corn is caused by the fungus Phyllachora maydis. The fungus produces small (0.2-0.8 inch), round to semi-circular, raised black structures called stromata.  In severe cases, stromata may also be observed on leaf sheaths and husks.  Tar spot severity on ear leaves at growth stage R5 (dent stage) can exceed 50 percent in susceptible hybrids when conditions are favorable for the disease.

Corn at any developmental stage is susceptible to infec­tion by the tar spot fungus when conditions are favor­able. Disease symptoms have been observed as early as the third-leaf (V3) growth stage in the United States. P. maydis overwinters on infested corn residue on the soil surface, which serves as a source of inoculum for the subsequent growing season. It is not known if P. maydis overwinters on or infects any other plant hosts in the United States.

Conditions that Favor Disease   In Latin America, cool temperatures (60-70°F) and high relative humidity (greater than 75 percent) favor tar spot development. In addition, disease incidence increases when there is at least seven hours of free moisture on the leaves due to rain, fog, or high relative humidity. However, it is not currently known what conditions favor the disease in the United States. In both 2015 and 2018, warm weather and periods of persistent rain and high humidity during the growing season likely favored the development and spread of the disease.

Continuous corn cultivation with minimum tillage practices, and high application rates of nitrogen fertilizer are also positively correlated with increased disease in Latin America. Although corn lines have been identi­fied in Latin America that have resistance to tar spot complex, U.S. observations indicate that most hybrids grown in the North Central region are susceptible to P. maydis (although they differ in susceptibility).

Yield Losses and Impact   Preliminary data from the Midwest indicate that severe tar spot outbreaks can reduce yield by more than 30 bushels per acre. Yield losses are a function of reduced ear weight, poor kernel fill, loose kernels, and vivipary (a condition in which the seed germinates while still on the cob). Observations also suggest that stalk rot and lodging are increased when tar spot severity is high. Severe tar spot also reduces forage quality.

Diagnosis  You can diagnose corn tar spot in the field by examining corn leaves for the presence of black, tar-like spots. To date, tar spot has been observed most often during mid-to late grain fill (growth stages R3-R6) and usually on leaves below or near the ear leaf. You can observe stromata in green and senesced tissues. Occasionally, you may also observe necrotic brown tissue surrounding the black structures, which produces a fisheye appear­ance.

Management  Most of what we know about tar spot has originated from Mexico and Central America. However, differences in the environments, fungal populations, hybrid genetics, and cropping systems may influence disease development in different areas. Our understanding of this disease in the United States is limited because of its very recent history.

However, several management practices may help reduce tar spot development and severity.

  1. Manage residue. Tilling fields buries infected residue and encourages it to decompose, which may help reduce the amount of overwintering tar spot inoculum.
  2. Rotate to other crops. This will allow residue to decompose and reduce the primary It is not yet known how many years it may take to sufficiently reduce inoculum.
  3. Avoid highly susceptible hybrids.
  4. Investigate fungicides. Some fungicides may reduce tar spot, however, we have little data about application timing that will provide an effective and economical response.  Efforts are underway to understand the biology and epidemiology of this disease, which may help formulate fungicide application decisions in the future.

 

Conservation Tillage Conference: March 5-6 in Ada

A world-renowned scientist will be the keynote speaker on the first day of this year’s Conservation Tillage Conference (CTC) in Ada.  Christine Jones, an Australian Soil Ecologist, will be giving the keynote of the annual event with the topic “Building New Topsoil Through the Liquid Carbon Pathway for Long Term Production and Profit.”  The annual conference is scheduled for March 5thand 6th at Ohio Northern University.  The McIntosh Center and Chapel on campus will once again be the location where about 60 presenters, several agribusiness exhibitors, and approximately 900 participants will come together to learn about the latest topics in crop production.

Farmers will be able to choose from four concurrent rooms that will host a variety of speakers from several land grant universities as well as agricultural agency and industry personnel.  Tuesday, March 5th there will be Corn University; Nutrient Management; Precision Agriculture and Digital Technologies; Cover Crops, No-Till, and Soil-Health speakers in each of these rooms.  Wednesday, March 6ththere will be Cover Crops: Issues and Benefits; New Tri-State Fertilizer Recommendations; Soybean School; Water Quality Research and Best Management Practices; Soil Balancing – Is it Important to Manage the Calcium: Magnesium Ratio in Soils?; and Identity Preserved Crops.

The conference fee is $85 for both days ($65 for one day) if paid online by February 21; registration afterwards and day of the event is $80 for one day or $105 for both days.  Registration includes lunch and break refreshments during the day.  Registration information and a detailed program schedule may be found at http://ctc.osu.edu. The detailed program also includes information on continuing education categories for each presentation.  Certified Crop Advisers (CCA) will be able to receive seven hours of continuing education credits each day.  Hours will be offered in all categories, including hard to get categories of Soil and Water Management and Nutrient Management.

Soybean Seed Quality Considerations for 2019

Source: Carl Bradley, University of Kentucky; Daren Mueller, Iowa State University; Damon Smith, University of Wisconsin-Madison; Shawn Conley, University of Wisconsin-Madison; and Kiersten Wise, University of Kentucky.

Seed quality from the 2018 soybean harvest was below average across the majority of the soybean-producing areas of the United States. Several factors led to poor-quality soybean seed, but some of the most important were wet conditions throughout the fall and subsequent delayed harvest.

The wet conditions delayed harvest and created the right conditions for several seed diseases, including:

  • Phomopsis seed decay (caused by the fungus Diaporthe longicolla, formerly known as Phomopsis longicolla)
  • Purple seed stain (caused by the fungi Cercospora kikuchii and Cercospora flagellaris)

Seeds affected by Phomopsis seed decay can be cracked, shriveled, and have a chalk-white color on the seed surface.

Seeds affected by Purple seed stain are covered in purple blotches, or the entire seed may be purple.

While some areas harvested high-quality soybean seed in 2018, many U.S. seed suppliers have reported that soybean seed for the 2019 crop is frequently testing positive for the Diaporthe fungus that causes Phomopsis seed decay. This is resulting in lower than normal seed germination rates, and could translate to lower than average germination rates in 2019.

While it is impossible to predict 2019 soybean planting conditions, if soil conditions are wet and cool during planting, then it is likely that both seedling survival and plant population will be diminished in fields planted with low-quality soybean seed. This means farmers need to decide now on how to manage low-quality soybean seed to minimize the impact of poor seed quality, low germination, risk for reduced stands, and lower yield in 2019.

Ways to Minimize the Impact of Low-Quality Soybean Seed Continue reading

Achieving Full-season Waterhemp Control in Soybeans

Dr. Bob Hartzler and Meaghan Anderson, Integrated Crop Management News, and Iowa State University Extension and Outreach.

Although there are many ways weeds escape control in crop fields, one of the leading causes of waterhemp control failures is emergence of plants following postemergence herbicide (POST) treatments.

Waterhemp requires more than twice as many growing degree days to reach 50% emergence as giant foxtail or velvetleaf (Figure 1), resulting in much of the population emerging after mid-June.

The layered residual system is one of the best ways to reduce late-season waterhemp escapes in soybean. It involves a split application of herbicides with residual activity – the first application is made at or near planting, and then additional residual is included with the POST application (Figure 2). The additional residual herbicide extends activity later into the season than a single application, and is especially beneficial in years with heavy rains following planting.

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Extensive Spread of Corn Toxin Could Affect 2019 Crop

A wetter than normal summer and fall in Ohio led to the worst spread of a toxin on corn in at least a decade, according to a grain disease expert with The Ohio State University.

And next year’s crop may be at risk as well. The fungus that produces the toxin can survive the winter, particularly if stalks or other plant material from the 2018 corn crop are left on the surface of the soil, said Pierce Paul, an Ohio State University Extension specialist in corn and small grain diseases. OSU Extension is the outreach arm of the College of Food, Agricultural, and Environmental Sciences (CFAES).

The extent of vomitoxin across Ohio and the rest of the Corn Belt led some farmers to receive a lower price for their crop, Paul said.

High moisture levels spur the spread of vomitoxin, which can cause people and animals to get sick. The rainy summer and fall in the state and across the Midwest not only left more moisture in fields, but also delayed some farmers from harvesting.

And any corn left standing in wet fields becomes more susceptible to vomitoxin, Paul said.

Gibberella ear rot, a fungal disease that produces vomitoxin, also sucks nutrients out of corn, leading to smaller and lighter kernels, which can reduce yields and what farmers earn for the grain.

“I know there were farmers who had problems with price discounts, and some had their grain completely rejected,” Paul said.

Vomitoxin can cause animals, particularly pigs, to vomit or simply refuse to eat the tainted corn. If contaminated grain or grain products are consumed, this toxin can also make people ill, which is why the U.S. Food and Drug Administration has set strict limits on the amount of vomitoxin allowed in grain for human and animal consumption.

Moldy corn still can be used to produce ethanol. But the byproduct of ethanol production, typically a rich source of nutrients for animals, cannot be given to them because it will have a high concentration of vomitoxin, Paul said.

Vomitoxin can also contaminate wheat and barley. However, in Ohio, both of these crops were harvested by the first few weeks of July and were out of the fields before the persistent rains came, Paul said.

Not every cornfield had a problem with vomitoxin, because rainfall amounts are never uniform across the state.

The fields that were tainted with vomitoxin could still be a problem next season if the same or another susceptible hybrid is planted, Paul said.

Gibberella ear rot can survive in a field through winter and potentially harm the new crop if wet weather occurs, and “there’s nothing you can do after the fact” to control the disease, Paul said.

As a result, it’s important for farmers to choose corn seed that’s resistant to the fungus, he said. No corn hybrid is totally immune to Gibberella ear rot.

So, buying a hybrid that resists the disease is akin to people getting a flu shot. The hybrid does not guarantee that the crop will not get the disease, but it reduces the odds of that happening. If the crop does get infected, the damage is less extensive.  

In a field contaminated with vomitoxin, burying the stalks and other plant material that remain will help reduce, but won’t eliminate, the spread of the fungus in next year’s crop, Paul said.

Symptoms of Gibberella ear rot include pinkish mold. But it can be easy to overlook if a growing crop has been tarnished by the fungus because the husk covers up where the damage occurs, on the ear of the corn.  

“A lot of farmers are caught off guard,” Paul said. “After you harvest the grain or when you take it into the grain elevator, that’s when you start seeing weird stuff and realize you have a problem.”

For more information on vomitoxin, see go.osu.edu/vomitoxinfacts

Developing a long-term comprehensive weed management system – Part 2

Source: Iowa State University, (Edited)

Post 2 of a 4 post series.

As the end of the year approaches and we reflect on the 2018 growing season we need to look at what changes or improvements we need to make in our production plans for 2019.  Herbicide resistant weeds are continuing to create problems.  New, very invasive and harmful weed species (Palmer Amaranth and Waterhemp) are now prevalent in Knox County.  Therefore, a review of the effectiveness of your herbicides program is definitely in order.

To effectively battle these new weed problems, creating a comprehensive, all-encompassing weed control strategy is essential in today production agriculture.  Over the next 4 weeks I will share information developed by Meaghan Anderson and Dr. Bob Hartzler at Iowa State University on developing a long-term weed management system.

Last week’s post:   Herbicide program development: Using multiple sites of action

This week’s post: Herbicide program development: Using effective herbicide groups

After you’ve started working on a program that contains multiple herbicide groups (sites of action), you need to make sure you’re using multiple herbicide groups that will be effective against your target weeds. For most people, the target weed will be waterhemp. Others may have problems with giant ragweed, horseweed/marestail, or other weeds. Waterhemp is the target weed in my example, but consider what your most problematic weeds are to run through this exercise for yourself.

Things to consider when determining whether a herbicide is effective against your target weed include (1) whether the herbicide is labeled to control the weed and (2) whether your target weed is resistant to the herbicide group.

Let’s look at herbicides as if waterhemp is the weed that causes us the most issues. Here’s a table of herbicide groups used in Iowa crops.

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