Jaime Cummings (NYS IPM), Joe Lawrence (PRO-Dairy), and Josh Putman (CCE)
Reports of Southern Corn Leaf Blight, have been confirmed by our neighbors near Erie, PA this past week. This is on our radar, because that area shares latitude with some of our corn acreage in our southern tier and Hudson Valley region. Therefore, you may want to keep an eye out for atypical corn foliar disease symptoms as the season progresses.
Most corn growers are unfortunately familiar with many of our common foliar diseases, including northern corn leaf blight, gray leaf spot, and eyespot. Sure, at first they all look alike as all young lesions start out as small chlorotic spots. But, as the disease progresses, and as the lesions mature, each disease has fairly distinctive lesion types that a trained eye could possibly identify even from the window of the truck on a drive-by scouting effort. But, throw an unfamiliar leaf spot into the mix, and it might get a little more confusing.
Southern Corn Leaf Blight (SCLB), though not common in NY, was confirmed in 2018 on Long Island, and may be appearing again in 2019. Suspicious samples have been submitted for ID. SCLB lesions may not be as distinctive or easy to identify, because they are somewhere intermediate in size and shape between gray leaf spot and northern corn leaf blight, and they also resemble lesions of the northern corn leaf spot disease. With so much overlap in symptoms, it’s best to get an accurate diagnosis before making any management decisions.
SCLB typically appears on corn leaves between VT and R4 growth stages as irregular tan lesions with vaguely reddish margins. Lesion shape and size may vary among hybrids. There are different races of this pathogen (races T, O, and C), but race O is most common in North America and is restricted to leaf infections. However, race T also exists in the US, and can infect leaves, stalks, and ears. As with most of our corn diseases, the fungus overwinters on corn debris, and can be further disseminated by wind or rain within and among fields in subsequent seasons (Fig. 1). There can be multiple cycles of this disease in one season if conditions are favorable (warm and wet). However, this hasn’t been a major disease of concern since the 1970’s, and we don’t anticipate it to be a chief concern here in NY compared as compared to our regional issues with northern corn leaf blight and gray leaf spot.
As with all corn foliar diseases, the incidence and severity of the lesions and the level of epidemic in the field will determine its impact on yield, because all foliar diseases affect photosynthesis and may leave plants more susceptible to stalk rots. The first and best option for managing SCLB is through genetic resistance. However, since this is such an uncommon disease in NY or other northern production areas, resistance ratings specifically for this disease may not be widely available in seed catalogs when making hybrid selections. And, as for many of our common foliar diseases, an integrated management approach will work best. Reducing primary inoculum through residue management and crop rotations, in combination with genetic resistance and use of fungicides only when necessary will successfully minimize losses from southern corn leaf blight. Please remember, research has shown that fungicides are most cost-effective with a single application at VT/R1 when disease pressure is >5% throughout the field, and when the disease reaches at least the ear leaf by tasseling on susceptible hybrids when the weather is expected to be conducive for the disease to spread (Fig. 2).
To help Northern New York farmers be alert to newly emerging field crop diseases and trends, the farmer-driven Northern New York Agricultural Development Program funds an annual field crop diagnosis and assessment project. The data produced by the survey is critical to farmers locally and statewide.
The annual evaluations, revived in 2013, provide farmers with real-time alerts in the current growing season, and add to multi-year data tracking that identifies trends and indicates emerging and re-emerging challenges.
“Northern New York farmers are increasingly faced with important management decisions that require real-time knowledge of plant diseases. The regional survey provides data to help them select crop varieties with disease-resistance and plan management practices to most cost-effectively and efficiently respond to the current-day threats and year-to-year variability,” says project leader Michael E. Hunter, a Cornell University Cooperative Extension Regional Field Crops Specialist.
Hunter and Cornell University Cooperative Extension Regional Field Crops and Soils Specialist Kitty O’Neil collaborate with Cornell University Plant Pathologist Gary Bergstrom, Ph.D. to respectively detect potential issues and collect crop samples in the fields, and analyze them at the Bergstrom Lab at Cornell University in Ithaca, N.Y.
Thirty-two farms located across the six-county Northern New York region that includes Clinton, Essex, Franklin, Jefferson, Lewis and St. Lawrence counties participated in the most recently-completed survey.
The NNYADP-funded survey also includes 19 sentinel cornfields and 18 sentinel fields of soybean, chosen to maximize the diversity of environments and cropping practices that can impact disease potential. In 2018, across the NNY survey area, seven corn diseases and six soybean diseases in total were identified and diagnosed.
“We are seeing an increasing number of growers using an integrated approach to managing field crop diseases on their farms. There are growers that are now paying closer attention to disease-resistant crop varieties, crop rotations, tillage practices, soil fertility management and fungicide selection based on the crop diseases identified in this regional survey,” Hunter notes.
The results of the 2019 field crops disease diagnosis and assessment survey will be posted on the Northern New York Agricultural Development Program website at www.nnyagdev.org and disseminated to growers, crop consultants, agribusiness and extension field crops educators at crop meetings and field days locally and statewide.
Funding for the Northern New York Agricultural Development Program is supported by the New York State Legislature and administered by the New York State Department of Agriculture and Markets.
By Jaime Cummings of NYS Integrated Pest Management, and Janice Degni of Cornell Cooperative Extension
We had an interesting report from Janice Degni (CCE, SCNY dairy and field crops team leader) this week. While out scouting and measuring alfalfa stands in Onondaga County, Janice noticed some wilting plants. Upon closer inspection, she found sclerotia, the tell-tale sign of white mold on the alfalfa stems (Fig. 1). Though this disease can be found in alfalfa and clover stands, you are likely more familiar with white mold on soybeans. Two different species of this pathogen can be found on alfalfa. Sclerotinia trifolium is the one most commonly identified on alfalfa, but the same species found on soybean, Sclerotinia sclerotiorum, can also infect alfalfa.
Remember that these pathogens overwinter and survive many years in the soil as sclerotia. Sclerotia are the black structures you’ve likely seen on infected soybean stems. These two different fungal pathogen species are difficult to differentiate, but the trend is that S. sclerotiorum tends to infect in the spring and summer, while S. trifolium typically infects in the fall. Regardless of the species, the symptoms, epidemiology and management are similar.
The symptoms of Sclerotinia crown and stem rot in alfalfa include rotting crowns, cottony growth on stems and crowns, and wilting and rotting stems. Infected crowns tend to die-off, and may be confused with winterkill, if not for the tell-tale sign of sclerotia in the dead tissues. Infection in first-year stands is most problematic. Just like in soybeans, this disease can spread quickly through a field, either by spores or via fungal mycelium spreading among plants during a cool, wet spring. This can potentially thin a stand out rather quickly, and can leave plenty of those sclerotia behind as inoculum for future years.
This prolonged cool, wet spring we’ve been experiencing has provided ideal conditions for this disease that we infrequently encounter in our alfalfa fields. An integrated management approach is the best solution. Since this disease is most prominent in first year, fall-seeded fields, you may consider future spring plantings in fields where you find it. Or, get your fall seedings in as early as possible so that seedlings have a chance to establish before the sclerotia germinate and produce spores in the fall. Tillage buries the sclerotia, which can reduce the number of spores released and may decrease infection in the field. But, as in soybeans, this disease is difficult to manage. Dense stands and weedy fields create perfect conditions for this pathogen to thrive. However, a few alfalfa varieties exist with moderate resistance, and may be considered in fields with a history of this disease. Research in other states has shown that some fungicides are efficacious against this disease when applied in the fall (Table 1). We have limited options for fungicides labeled for white mold on alfalfa in NY, including Pristine and Endura. However, fungicide applications for this disease may not be cost-effective (always follow label instructions, restrictions, and pay attention to post-harvest intervals). Herbicides, such as Paraquat, have also been used to reduce weeds and open up the canopy to increase air-flow lessen disease development.
Once the weather warms up and fields dry out, this disease will likely halt, and some infected stands may recover and produce sufficient yields in subsequent years. But, keep in mind that those sclerotia will remain in the soil for many years waiting for perfect conditions to start the disease cycle again.
Interested in keeping up to date with pest and disease issues identified statewide by CCE and IPM staff? Subscribe to the NYS IPM Weekly Pest Report.
With spring underway, our fall planted wheat, barley, rye and triticale crops have woken up and are in early developmental stages, and some spring planted barley, oats and rye are emerging. By now, you’ve already assessed plant stands for winterkill or other weather-related damage and weed pressure. But did you look for signs of diseases?
Fungicidal seed treatments protect our small grains crops from soilborne pathogens that cause damping-off, and foliar fungicides may be warranted for many of our common early-season foliar diseases. Early epidemics from these pathogens may spread throughout the canopy as the season progresses, given favorable weather conditions, resulting in potential yield reductions. An integrated approach for managing these diseases involves crop rotation, residue management, planting pathogen-free seed of resistant varieties, proper fertility and canopy management, and foliar fungicide applications where necessary. Susceptible cultivars benefit most from fungicide applications for reduction of diseases. While scouting, keep an eye out for some of our most common early season diseases:
Powdery Mildew can be commonly found lower in the canopy of all small grain crops, and is easily identifiable by its white, fuzzy fungal growth on both the upper and lower leaf surfaces (Fig. 1). This pathogen overwinters on straw residues which provide inoculum in the spring to blow into growing wheat stands. Cultivars vary in their levels of resistance to powdery mildew, and resistance is the most cost-effective method of defense. Should you find high levels of powdery mildew in your field, you may consider a triazole foliar fungicide application at flag leaf emergence.
Septoria and Stagonospora Leaf Blotches are two other very common foliar diseases you may encounter in NY wheat fields. Though caused by two different pathogens, the leaf spot symptoms can be somewhat similar and difficult to differentiate for scouts (Fig. 2). Both fungal pathogens overwinter on crop residues, and initial infection often occurs on seedlings emerging in the fall, but may also occur in the spring. Many commercially available cultivars are available with varying levels of resistance to these pathogens. But if you notice high levels of leaf blotches in your field, you may consider a foliar application of a strobilurin or triazole fungicide at flag leaf emergence to protect yield.
Leaf Rust, or brown rust, can occasionally be found early in the season, though it often appears later as the spores migrate on winds from the south. Leaf rust is easily identified as bright orange pustules on the upper leaf surfaces throughout the canopy of all small grain crops (Fig. 3). Rust fungi are obligate pathogens, which require a living host, and therefore must either over-winter on alternate hosts, or arrive on wind currents from the south. Planting resistant cultivars is the most cost-effective management tool, and a flag leaf application of a strobilurin or triazole fungicide also offers effective control of leaf rust on susceptible cultivars.
Scald is another fungal leaf spot that easily identified on winter malting barley by its distinctive lesions that can be found on any above-ground plant tissue (Fig. 4). The fungal pathogen can over-winter on residues or can be seed-transmitted. On susceptible cultivars and under favorable environmental conditions, scald can spread quickly throughout the canopy and field, resulting in significant yield loss. Pay attention to scald resistance ratings when selecting malting barley cultivars to plant, as they vary drastically in susceptibility. Susceptible cultivars will benefit from a triazole fungicide application at flag leaf, or even earlier to protect yields.
When deciding whether or not to spray a fungicide, there are many points to consider. Not least of all, cost. Use the following information as a guide from the Cornell Integrated Guide for Field Crop Management for making fungicide decisions in small grains:
Activity Worksheet: Economical Analysis of Thresholds in Wheat:
Does the crop have a reasonable yield potential?
Assess the crop in early May (stem elongation stages) for adequate stand (density of approximately 30 strong stems per foot of row for 7-inch rows on good soils) and plant vigor. If the stand is sparse or plants are not vigorous or show widespread virus symptoms, fungicide application should not be considered further. ____ Yes ___ No
Have foliar diseases been observed before flag (last) leaf emergence?
Assess upper three leaves for symptoms and signs of powdery mildew, leaf spots, or leaf rust in early to mid-May, before flag leaf emergence. If disease (any amount) is observed on approximately 50 percent of main tillers, averaged across the field, a spray should be considered now. This threshold is exceeded in less than 50 percent of location/year situations in New York, so there is a significant risk of making an unnecessary fungicide application. ____ Yes ___ No
Have foliar diseases been observed during head emergence?
Assess upper two leaves for foliar diseases in late May to early June; if disease (any amount) is observed on approximately 50 percent of main tillers, a spray should be considered now. Fungicide applications made after early June may control some diseases but are unlikely to produce significant yield benefits. ___ Yes ___ No
Are climatic predictions conducive for further disease development?
Powdery mildew development is reduced dramatically once the average daily temperature rises above 70˚F; this disease often disappears by June. Severe leaf spot development is favored by extended periods of wet weather; it may be insignificant if dry weather persists in May and June. Listen for regional advisories on the threat from leaf rust; rust inoculum often builds up in areas to the south and west of New York and is deposited here by thunderstorms in June or July. In addition to disease observations, use long-range local weather forecasts in making your spray decision. What is your short to medium term weather conditions?
Have I selected fungicides appropriate for the disease spectrum and have I read the label carefully?
Be sure that the materials you spray will be effective against the range of diseases found in your field; e.g., some products effective against powdery mildew are ineffective against leaf spots or vice versa. Check in the Cornell University Guide for Integrated Crop Management.
Is the spray decision consistent with my perception of risk?
A simple formula for evaluating the relative economics of a fungicide spray is: Relative Profit = (Grain Yield Increase x Grain Price) – (Cost of Fungicide + Application Costs). If ground spray rigs are used, the yield lost to wheel traffic should also be factored in. Each of these variables influences the relative economics of fungicide application. At a grain price of $4, producers will need to see approximately a 5 bu/A yield increase to break even on the added costs of fungicide application. Because disease occurrence is erratic over years and locations, fungicide application cannot be expected to result in a 5-bushel or greater yield increase every year. Spray decisions should be tied closely to disease scouting information. When considering your economic risk, also be aware that foliar fungicides will not protect potential yield components that may be diminished by scab disease (fungus that infects heads at or following flowering), viral diseases (wheat spindle streak mosaic and yellow dwarf), soilborne diseases, or several other environmental factors.
Relative Profit = (Grain Yield Increase x Grain Price) – (Cost of Fungicide + Application Costs)
Since its first confirmation in Cayuga County in 2016, New York soybean farmers have a new pest to be leery of, the Soybean Cyst Nematode (SCN). SCN is considered the number one pest of soybeans globally, causing yield losses of approximately 100 million bushels annually across the U.S. alone. These high yield losses are due to the rapid and highly productive life cycle of SCN (Fig. 1). It’s true that those yield loss estimates don’t relate directly to our current situation in NY at the moment, but the best way to avoid these potential losses is to gain a better understanding of SCN populations statewide.
Fortunately, a network of pathologists and nematologists across the US who have been dealing with this potentially devastating pest for years have come together to fight as a unified front as an organization called the SCN Coalition. Their website is full of useful information, resources, recommendations and much more, including proper sampling techniques, which labs you can send soil samples to for testing, and best management practices.
We highly recommend that NY soybean growers take a proactive approach at identifying and managing SCN while populations are low. And, now is the best time to get out and take your soil samples for SCN testing. Just because it’s only been officially confirmed in one county doesn’t mean it isn’t more widespread, or possibly even in your own fields. And, once established in a field, management can be tricky because this pest has been developing races that have been overcoming the most widely deployed sources of genetic resistance incorporated into the majority of the commercial soybean varieties. Check out this short video for more information on the SCN resistance issue.
Since SCN populations are likely low in fields across NY at this time, it’s important to focus your soil sampling for testing on fields with a long history of soybean production, and in areas of those fields that are most likely to harbor populations. The most high risk areas for finding SCN in your fields include compacted areas such as entryways, areas that are frequently flooded, areas where you have found sudden death syndrome, sections with high pH, or areas of fields that you notice are consistently low-yielding (Fig. 2). Despite your focused soil sampling efforts, you may get zeros as your test results. This doesn’t necessarily mean that your fields are SCN-free though, because it can be challenging to detect SCN at low population levels due to the way cysts are distributed in the soil (Fig. 3). Zeros are good, but it doesn’t mean you shouldn’t continue to sample annually.
Although SCN management is getting more challenging as resistance is breaking down, we recommend an integrated management approach. This would involve annual testing of your fields to know your numbers (and eventually your races of SCN), rotating SCN resistance sources in your soybean varieties, crop rotation with non-host crops (corn, wheat), and utilization of nematicidal seed treatments (Fig. 4).
Now is the ideal time for you to collect soil samples for SCN testing. Focus on high-risk areas outlined above, and collect 15-20 1-inch-diameter core samples, 8 inches deep from within soybean rows near the roots. Mix the cores well and send to an SCN testing lab, following specific packaging instructions from individual facilities. Many options are available for SCN testing facilities, including public and private labs. Testing prices on average are around $25-$28 per sample at most SCN testing labs. The Cornell plant disease diagnostic clinic offers this service, or you may consider one of the most highly recommended facilities which focus entirely on SCN, such as Midwest Laboratories, SCN Diagnostics, or University of Illinois Plant Clinic. Most private and public testing facilities accept out of state samples.
For anyone interested in further, in-depth information on SCN, please check out this hour-long training webinar on the biology and management of SCN from Iowa State Nematologist Greg Tylka.
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 Colletotrichumgraminicola. 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).
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).
By Jaime Cummings – NYS Integrated Pest Management Program
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: