Scouting

Tar Spot of Corn in Ohio Again this 2019

Source:  Pierce Paul, Felipe Dalla Lana da Silva, OSU Extension

Tar Spot, a new disease of corn caused by the fungus Phyllachora maydis, was reported for the first time in Ohio at the end of the 2018 growing season. At that time, it was found mostly in counties close to the Indiana border, as the disease continued to spread from the middle of country where it was first confirmed in 2015. Over the last few weeks, there have been several new, confirmed report of Tar Spot in Ohio, this time not only in the northwestern corner of the state, but also from a few fields in central and south-central Ohio. As was the case last year, disease onset was late again this year, with the first reports coming in well after R4. However, some of the regions affected last year had more fields affected this year, with much higher levels of disease severity. It could be that Tar Spot is becoming established in some areas of the state due to the fungus overwintering in crop residue from one growing season to another. This is very consistent with the pattern observed in parts of Indiana and Illinois where the disease was first reported. We will continue to keep our eyes out for Tar Spot, as we learn more about it and develop management strategies. You can help by looking for Tar Spot as you walk fields this fall, and please send us samples.

What does it look like? Even though corn is drying down, if Tar Spot is present, you can still detect it on dry, senescent leaves almost as easily as you can on healthy leaves. So, please check your fields to see if this disease is present. “Symptoms of tar spot first appear as oval to irregular bleached to brown lesions on leaves in which raised, black spore-producing structures call stroma are formed… giving the symptomatic areas of the leaf a rough or bumpy feel to the touch… resembling pustules on leaves with rust. Lesions … may coalesce to cause large areas of blighted leaf tissue. Symptoms may also be present on leaf sheaths and husks.” As the name of the disease suggests, symptoms look like the splatter of “tar” on the leaves. In some cases, each black tar-like spot may be surrounded by a necrotic halo, forming what is referred to as “fish-eye” lesions.

What causes Tar Spot and how damaging is it? In the past, the greatest impact of this disease in terms of yield loss were observed when P. maydis-infected plants were co-infected with a second fungus called Monographella maydis. In other words, the damage tended to be much more severe when the two fungi worked together to affect the plant. So far, only the first fungus, P. maydis, has been reported in the US, but based on work done in Illinois, this pathology alone is capable of causing substantial yield reduction on highly susceptible hybrids when conditions are favorable and infections occur early.  

Where did it come from and will it survive and become established? At this point it is still unclear as to how Tar Spot got to the US in the first place and how it continues to spread. The fungus is not known to be seed-borne or infect other plant species, so corn seeds and weeds are unlikely to be the sources of inoculum. However, the fungus can survive and be moved around on fresh and dry plant materials such as leaves and husks. In addition, since spores of the fungus can be carried be wind, it could be blowing in from neighboring states/counties/fields. Although not yet confirmed through survival studies, it appears that the fungus could be overwintering in infected crop stubble between growing seasons.

What should I do if I find Tar Spot? If you see anything that fits the description of, or resembles (Picture) Tar Spot, please inform your state specialist, field specialist, or county extension educator, but most importantly, please send samples to my lab (1680 Madison Ave, Wooster, OH) for confirmation. We will also be using your samples to study the fungus in order to develop effective management strategies.

Read more about Tar Spot of Corn at:

https://cropprotectionnetwork.org/resources/articles/diseases/tar-spot-of-corn

https://www.extension.purdue.edu/extmedia/BP/BP-90-W.pdf

 

Stalk Quality Concerns

Source: Peter Thomison, Pierce Paul, OSU Extension

2019 may be an especially challenging year for corn stalk quality in Ohio. Stress conditions increase the potential for stalk rot that often leads to stalk lodging (Fig. 1).  This year persistent rains through June caused unprecedented planting delays. Saturated soils resulted in shallow root systems. Corn plantings in wet soils often resulted in surface and in-furrow compaction further restricting root growth. Since July, limited rainfall in much of the state has stressed corn and marginal root systems have predisposed corn to greater water stress.

Continue reading →

Fall Herbicide Treatments – Even More Important This Year?

Source: Dr. Mark Loux, OSU

If you have never applied herbicide in fall to burn down winter annuals, or done it only infrequently, this might be the year to make an investment in fall herbicides.  Fall treatments are an integral component of marestail management programs.  They also prevent problems with dense mats of winter annuals in the spring, which can prevent soil from drying out and warming up, interfere with tillage and planting, and harbor insects and soybean cyst nematode.  2019 was a generally tough year for weed control, leading to higher end of season weed populations in some fields.  A number of acres were never planted, and growers got to experience the difficulty in obtaining season-long control in the absence of a crop.  Reminds us all how important the crop canopy and shading of the soil is during the second half of the season.  Bottom line – there was substantial production of weed seed in some fields, and a replenishment of the soil seedbank by both winter annual and summer annual weeds.  The seed of winter annuals and marestail lacks dormancy so above-average weed seed production can lead to an immediate increase in fall-emerging weeds.  Applying herbicides this fall can compensate for increased weed populations and make life easier in the spring.

We have published information on fall herbicides fairly frequently, and our suggestions for fall treatments have not really changed much.  There is plenty of information on fall herbicide treatments in the C.O.R.N. newsletter archive and on other university websites.  Our philosophy on this has not changed much over the past decade.  A few brief reminders follow:

1.  When to spray?  Anytime between now and Thanksgiving will work, and possibly later.  We have applied into late December and still eventually controlled the weeds present at time of application.  Once hard freezes start to occur, there is usually a substantial change in the condition of certain weeds, such as dandelion and thistle, that renders them less sensitive to herbicides.  We discourage applications during periods of very cold weather which can occur starting about Thanksgiving, and also (obviously) when the ground is snow-covered.  The generally dry conditions we are experiencing have limited weed emergence so far this fall.  We anticipate that rain occurring now that leads to some sustained soil moisture near the surface will likely result in germination and emergence of the weeds that have been missing until now.  Our recommendation is to wait for rain and the additional weed emergence before applying any herbicide this fall.  The risk in this is that the weather turns wet, making it difficult to apply herbicide.  So it’s also possible to apply now and include a residual component to help with later fall emergence (which is the exception to the “no residual” recommendation in #4 below), such as simazine, a low rate of metribuzin or Canopy, or a Sharpen rate higher than 1 oz.

2.  What about all of the crop residue on the ground after harvest – won’t that cause problems?  We have not worried about this, and the herbicides seem to work regardless.  Most agronomists I have asked have the same impression.  On the other hand, it probably wouldn’t hurt to wait a while after harvest to let the residue settle down, and the weeds to poke through.  Dense crop residue usually prevents marestail from emerging anyway. Continue reading →

No Pigweed Left Behind – Late-Season Scouting for Palmer Amaranth and Waterhemp

Source: Dr. Mark Loux (edited)

Remain vigilant!  We have Palmer and Waterhemp in Knox County!! Now is an excellent time to scout for these weeds, especially in bean fields. If you would like help with identification call John at 740-397-0401.

If you don’t already have to deal with waterhemp or Palmer amaranth, you don’t want it.  Ask anyone who does.  Neither one of these weeds is easy to manage, and both can cause substantial increases in the cost of herbicide programs, which have to be constantly changed to account for the multiple resistance that will develop over time (not “can”, “will”).  The trend across the country is for Palmer and waterhemp to develop resistance to any new herbicide sites of action that are used in POST treatments within about three cycles of use.  Preventing new infestations of these weeds should be of high priority for Ohio growers.  When not adequately controlled, Palmer amaranth can take over a field faster than any other annual weed we deal with, and waterhemp is a close second.  Taking the time to find and remove any Palmer and waterhemp plants from fields in late-season before they produce seed will go a long way toward maintaining the profitability of Ohio farm operations.  There is information on Palmer amaranth and waterhemp identification on most university websites, including ours –  u.osu.edu/osuweeds/ (go to “weeds” and then “Palmer amaranth”).  An excellent brief video on identification can be found there, along with an ID fact sheet.  The dead giveaway for Palmer amaranth as we move into late summer is the long seedhead, and those on female seed-bearing plants are extremely rough to the touch.  We recommend the following as we progress from now through crop harvest: Continue reading →

The Ohio Noxious Weed Law – A Tool in the Prevention of Waterhemp and Palmer Amaranth

Source: Dr. Mark Loux

Waterhemp and Palmer amaranth are both now listed on the Ohio noxious weed law, which means that landowners must take steps to control infestations and prevent further spread.  Since these are annual weeds, preventing spread is achieved by preventing plants from reaching maturity and producing seed.  This is the basis for our “No pigweed left behind” effort, for which the goal is to create an understanding that the only way to beat these weeds is to prevent seed.  Prevention needs to occur in any area that might be subject to infestation, such as roadsides, parks, conservation seedings, parks, etc, in addition to agricultural fields.  The entities managing these areas are responsible for recognizing and controlling infestations of waterhemp and Palmer amaranth, but this does not always occur.  Not everyone involved in crop production or land management is aware of the waterhemp/Palmer problem to begin with, and many managers are busy enough that preventing noxious weed problems has low priority.

Our advice is to pay attention to what’s happening in your area or in the areas that you farm, with the goal of becoming aware of new infestations early enough that plant maturity and seed can still be prevented, regardless of where they may be occurring.  We recommend as a first step contacting the land manager or owner to explain the issue, make them aware that they have an infestation, and request that action be taken.  However, where it’s not possible to have this conversation, or there is a refusal to take action, the Ohio noxious weed law can be used to try to force action.  A two-page summary of the noxious weed law that can be found here on the OSU Ag Law Blog, and also links directly to the law itself.

The basic idea here is that following an unsuccessful attempt to work with a landowner or manager, noxious weed issues should be reported to township trustees, and this must be done in writing.  The trustees then have the responsibility to deal with the issue, and the method for doing so varies depending upon what the land is used for and who is managing it.  If it’s necessary to use the noxious weed law, be sure to start the process early enough in summer, well before potential seed production.  There is a need to allow time for all of the steps in the process to occur, and for notifications to be received and acted on (or not).  Our experience is that not all landowners and managers will take action upon first notification, and in addition to action, their response to notification can include minimal response of protesting their need to act.  Waiting too late to start the process can result in lack of resolution of these issues in time to prevent plant maturity and seed production.  The noxious weed law has been used several times within the last two years to force managers to control Palmer amaranth, and could be used to accomplish the same for waterhemp, which was recently added to the list.  Consider the law a tool to prevent the establishment and spread of these weeds when other methods are ineffective.

You can search this blog for a complete description and pictures of all the weeds on the Ohio Noxious weed list.

No pigweed left behind

No pigweed left behind

Noxious Weeds in Cover Crop Seed and Seed Germination

Source: Alexander Lindsey, Laura Lindsey, Mark Loux, Anne Dorrance, Stan Smith, John Armstrong, OSU Extension

Seed quality is key to establishing a good crop (or cover crop). Some of the critical components of seed quality are percent germination, mechanical analysis for purity (% other crops, % inert, and % weeds), and a listing of noxious weeds identified by scientific/common name and quantity found. As producers are looking for seed sources to provide living cover on acreage this year that was previously earmarked for corn or soybeans, it is important to pay attention to the quality. These tests may also be required on seed lots for use in some relief programs as well. Commercial or certified seed used for cover crops should have a seed tag that shows variety and the seed quality measurements above. However, if the seed is sourced from out of state, the noxious weeds listed (or NOT listed) on the tag by name may differ from those had the seed been sourced from Ohio.

Only the noxious weeds for the state where the seed was originally going to be sold are required to be listed on the tag by name and quantity (Federal Seed Act, part 201.16). Each state determines which species are included on this list, and can differ from state to state. If seed is outside of Ohio for use on-farm, producers may want to have the seed tested for an “all state noxious-weed exam” prior to planting if this was not done previously on the seed lot. Only 1.1-1.2 lbs of seed is needed for the test, but it is critical the sample is representative of the lot to ensure quality test results. This test would screen the seed sample supplied for the weed contained in this list: https://www.ams.usda.gov/sites/default/files/media/StateNoxiousWeedsSeedList.pdf, and may serve as a more comprehensive exam than was conducted at the time of initial seed lot labeling. One service provider that can conduct this exam is Central Ohio Seed Testing (a subsidiary of the Ohio Seed Improvement Association; https://ohseed1.org/about-our-lab/). Samples can also be sent to ODA for an Ohio noxious weed exam (https://agri.ohio.gov/wps/portal/gov/oda/divisions/plant-health/grain-warehouse-feed-and-seed/). Depending on the source of seed and the planned use, a seed lot may be eligible to be tested for free through ODA between June and December (up to three per farmer). Conducting a noxious weed exam could help slow the movement of problematic weeds throughout the state and minimize future weed problems.

Another issue to consider is the quality of seed in storage that was not planted this year due to weather. Storing seed in an environment where the temperature (in F) plus the % relative humidity are less than 100 (Harrington’s rule) helps to minimize the rate of seed deterioration (or loss in germination and vigor). Seed germination is an important consideration for determining seeding rate to ensure the critical final stand for yield is achieved for crops like corn and soybeans. Most seed germination percentages on a seed tag for agricultural seeds (like corn and soybeans) are valid for 12 months from the last date of the month in which they were completed, with the exception being cool season grasses which are valid for 15 months beyond the month of testing (Ohio Revised Code, Chapter 907.07). Be sure to check the seed tag for both the date of the test as well as the germination when planning seeding rates.

You can search this blog for a complete description and pictures of all of the weeds on the Ohio Noxious weed list.

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.

 

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 →