Anthracnose Top Dieback Prevalent Across NY, September 2018

Jaime Cummings, NYS IPM Program

Figure 1. Anthracnose top dieback symptoms. Photo: Agrigold.

Many of us are familiar with Anthracnose leaf blight and Anthracnose stalk rot, but many of us were caught off guard this year by another form of disease, Anthracnose top dieback, caused by the same fungal pathogen Colletotrichum graminicola.  Reports of this disease have been received from all parts of the state in the past week.  It affects silage and grain hybrids and is readily identified by its typical symptoms of death of leaves and stalks in the upper 1/3 of the canopy (Fig. 1).  It’s important to note that top leaves my die from a number of factors, including corn borer, drought and other environmental stresses.  Therefore, accurate diagnosis is important when suspecting this disease.  Symptoms initially involve purpling or yellowing of flag leaves, and is often more randomly distributed in a field than top dieback caused by abiotic stresses.  Anthracnose top dieback is the result of the fungal stalk rot occurring on upper internodes, which restricts upward movement of water and nutrients, thus resulting in necrosis of leaves, tassels and stalks above the point of infection.  The easiest way to identify Anthracnose stalk rot and top dieback is to look for signs of the fungal pathogen.  Examine stalks for the typical black anthracnose lesions on the stalks, and peel back the leaf sheath to look for the black fungal fruiting bodies, called acervuli (Fig. 2).  A hand lens is helpful in identifying these spiny fruiting bodies, which may be full of pinkish, wet spore masses under moist conditions (Fig. 3).  Split stalks will reveal rotten or disintegrated pith tissue at the point of infection (Fig. 4).

Figure 2. Anthracnose stalk rot lesions on stalks. Photo: Ohio State University.
Figure 3. Colletotrichum fungal fruiting bodies called acervuli. Photo: Cornell University, Nelson lab.
Figure 4. Anthracnose stalk rot internal stalk symptoms. Photo: APS Press.

This pathogen overwinters in corn residues and spores are transmitted via wind and rain and can infect corn plant roots or stalks.  Insect feeding damage may enhance infection by this pathogen.  Since this pathogen is more prevalent in fields with high corn residues, crop rotations can significantly reduce this disease.  Hybrid resistance is available for anthracnose stalk rot, and hybrids with good foliar disease resistance often reduce stress overall, resulting in less susceptibility to stalk rots in general.  The IPM approach to managing anthracnose top dieback in your fields would involve crop rotations, planting resistant hybrids, and cultural practices to ensure minimal plant stress (balanced fertilization, adequate plant populations, and proper drainage).

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Sudden Death Syndrome and Soybean Cyst Nematode in Soybeans

By Jaime Cummings – NYS Integrated Pest Management Program

Sudden Death Syndrome (photo by Jaime Cummings)

It has been an optimal year for sudden death syndrome (SDS) in some parts of New York State.  Reports and diagnoses have been received in western and northern NY fields.  This disease is favored by cool, wet spring conditions, followed by hot and dry weather.  The infection occurs very early, at germination and emergence, but symptoms rarely appear before reproductive stages and pod filling.  Symptoms are most obvious as interveinal chlorosis on the leaves, and can be confused with other diseases that have similar foliar symptoms, including brown stem rot and northern stem canker.  Splitting the stems of an SDS infected plant will reveal a white pith with discoloration of the vascular tissue of lower stems (see photo).

Few varieties adapted to our region are available with moderate resistance to this disease, and rotation is not very effective since the pathogen can survive for many years in the soil and on other crop debris.  The ILeVO seed treatment has shown good results in trials from other states, and may be your best bet for managing SDS in fields with a history of the disease.  Improving drainage and compaction and delaying planting until soils have warmed up, in addition to planting moderately resistant varieties (where available) with seed treatments, are good IPM practices for fields affected by this disease.

It’s also important to note that there is a synergistic effect of SDS and the soybean cyst nematode (SCN).  If you have a field with a history of SDS and lower yields, this would be a good candidate for SCN testing.  We are approaching the optimal time to take soil samples for SCN testing.  There are many public and private labs available for SCN testing.  The Cornell plant diagnostic clinic offers this service, and there are a number of labs and clinics that specialize in this service and accept out of state samples.  The most highly recommended testing facilities include the University of Missouri SCN Diagnostics lab, the University of Illinois Plant Clinic, and Midwest Laboratories.  Please see a complete list of testing labs and other information on SCN provided by the SCN Coalition:

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NYS IPM Weekly Field Crops Pest Report: August 31, 2018

NYS IPM Weekly Field Crops Pest Report – August 24, 2018

2018 New York Conditions Favorable for Downy Mildew in Soybeans

by Jaime Cummings, NYS Integrated Pest Management Field Crops and Livestock Program Coordinator

Yellow flecking on the upper surfaces leaves with purplish sporulation on the lower surface are obvious symptoms of downy mildew (photo by Gary Bergstrom).

The weather has changed from hot and dry to warm and wet in many parts of the state, and that has changed our expectations for soybean diseases this year.  Many of us are seeing downy mildew in soybeans across the state, ranging from low to high incidence and severity, and some are wondering what, if any, management options are recommended.  As a general rule, we have never recommended spraying fungicides for downy mildew because this disease is typically more of a cosmetic issue which doesn’t tend to result in noticeable yield loss.  Though, there have been reports from other states indicating 10-15% yield losses from very severe downy mildew epidemics.  We have no established thresholds for when to pull the trigger for downy mildew fungicide management in New York State, and have no fungicide efficacy data to provide strong recommendations.  And, keep in mind, most of our foliar fungicides available for soybeans are not labeled for downy mildew and would have very limited effect, if any, because downy mildew is an oomycete and is not in the same category as most of the rest of our foliar fungal diseases that are well controlled with many fungicides.  There is limited research-based evidence that strobilurin fungicides may have limited efficacy against downy mildew, but, again, many aren’t actually labeled for downy mildew in NY.  However, Aproach Prima is labeled for downy mildew in soybeans in NY, and can be applied at a 5 – 6.8 fl oz/A rate, (http://www.cdms.net/ldat/ldBA3003.pdf).  Given the general lack of efficacy data from NY or other states, it is unclear whether or not these applications will be cost effective, and should be reserved only for the most severely affected fields.

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NYS IPM Weekly Field Crops Pest Report – August 3, 2018

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NYS IPM Weekly Field Crops Pest Report – July 27, 2018

Corn and Soybean Surveys Alert NNY Farmers to Disease Trends

White mold discovered in soybeans in NNY in 2017; photos: Mike Hunter, CCE

As Northern New York farmers scout corn and soybean fields for any diseases that may impact crop health and yield, they can use five years’ worth of survey results as a guide to newly-emerging and common crop pathogens in Clinton, Essex, Franklin, Jefferson, Lewis and St. Lawrence counties.

The corn and soybean disease survey project is funded by the farmer-driven Northern New York Agricultural Development Program. In addition to identifying current areas of concern and trends, the project provides regional farmers with the expertise of Cornell Cooperative Extension specialists who scout 12 sentinel fields of corn and 21 sentinel fields of soybeans. These fields on Northern New York Farms represent different soils and growing conditions, and a variety of cropping practices.

Fields are assessed at various stages of crop growth. The Bergstrom Lab at Cornell University in Ithaca, N.Y., has cultured and analyzed field samples since 2013.

“Multi-year surveys better capture variations in weather from year-to-year, from a wet spring to drought in the past five years. The data helps farmers make more informed corn and soybean variety selections, evaluate soil and crop debris for potential problems, and plan management strategy,” said project leader and Cornell plant pathologist Dr. Gary C. Bergstrom, Ithaca, N.Y.

This disease survey project was started in 2013 as the first systematic assessment of corn and soybean diseases conducted in Northern New York in recent decades.

Results of the most recent NNY corn disease survey by county is online at https://fieldcrops.cals.cornell.edu/corn/diseases-corn/corn-disease-survey/.

A statewide soybean disease survey is online at https://fieldcrops.cals.cornell.edu/soybeans/diseases-soybeans/soybean-disease-survey/.

For more information, contact Cornell Cooperative Extension North Country Field Crop Specialists Kitty O’Neil, 315-854-1218, and Mike Hunter, 315-788-8450.

Funding for the Northern New York Agricultural Development Program is supported by the New York State Senate and administered by the New York State Department of Agriculture and Markets. Learn more at www.nnyagdev.org.

 

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Fusarium head blight commentary on winter barley and wheat

Gary Bergstrom, Extension Plant Pathologist, Cornell University
This is a critical week for management of Fusarium head blight (FHB) in winter malting barley.  Some winter barley fields in New York are fully headed now and many more will head out this later week.  Even though we have had frequent rains, the Fusarium Risk Assessment Map (http://www.wheatscab.psu.edu/riskTool.html) shows mostly low risk of Fusarium infection in New York because temperatures have been considered too low for spore production in many areas. A moderate to high risk of FHB is indicated for areas of the Southern Tier, southern Hudson Valley, and Long Island.  Maximal suppression of FHB and grain contamination by deoxynivalenol (DON) mycotoxin results when fully emerged heads of winter malting barley are sprayed with full label rates of Caramba or Prosaro fungicides. A heads emerged spray with these triazole fungicides also helps protect upper leaves against fungal leaf blotches, powdery mildew, and rust.  Foliar sprays of Caramba or Prosaro up to seven days after head emergence may still result in significant FHB and DON suppression.   Fungicide products containing strobilurins should not be applied to headed wheat or barley as they may result in increased levels of DON in grain.
Winter wheat is generally a week or more behind in development from winter barley planted on the same fall date.  Winter wheat in New York varies from stem elongation to flag leaf visible stages.  We should reach the critical fungicide application window for winter wheat over the next two weeks.  The triazole products Caramba and Prosaro are the most effective fungicides for suppression of FHB and DON contamination when applied at flowering (emergence of anthers on heads).  A flowering application of triazole fungicide should be based on Fusarium head blight (FHB) risk as well as the risks of powdery mildew, rusts, and fungal leaf blotches in the upper canopy based on scouting of individual fields.  There is an application window of approximately 7 days from the beginning of flowering in which reasonable FHB suppression can be expected.   Check the Fusarium Risk Assessment Tool (http://www.wheatscab.psu.edu/) and your local weather forecast frequently as your winter wheat crop approaches heading and flowering.
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