What's Cropping Up? Blog

Articles from the bi-monthly Cornell Field Crops newsletter

April 5, 2019
by Cornell Field Crops
Comments Off on What’s Cropping Up? Volume 29, Number 2 – March/April 2019

What’s Cropping Up? Volume 29, Number 2 – March/April 2019

February 21, 2019
by Cornell Field Crops
Comments Off on Western Bean Cutworm and Mycotoxins in Corn Silage

Western Bean Cutworm and Mycotoxins in Corn Silage

Joe Lawrence, Gary Bergstrom, Jaime Cummings, Elson Shields, Ken Wise, Mike Hunter

Mold and mycotoxin development in corn ears and stalks, and the resulting corn silage continues to be a major concern for dairy producers.  Mycotoxins can result in a range of problems for livestock throughout the year as they are ingested with the feed.  The presence of mold does not always have a strong correlation to mycotoxin development but it does present the chance for incidence to occur.

A number of factors influence the prevalence of molds from year to year. Conducive weather conditions for mold and mycotoxin development are outside the control of management options.  But hybrid characteristics and physical damage to the ears can be managed through the selection of hybrids and pest resistance traits in the hybrids.

WBC larvae beginning to feed on tip of corn ear prior to silage harvest. Photo by Joe Lawrence

Western Bean Cutworm (WBC) is a pest of corn (as well as dry beans) and its territory has been expanding eastward over the last 10 to 15 years with pockets of high populations now found in New York and Ontario, Canada. The moth emerges near the time of corn tasseling and lays its eggs near the ear leaf of a pollinating corn plant. When the larvae hatch they enter the corn ear, often opening a wound in the husk, and feeding on kernels. Unlike other earworms, which are cannibalistic, you can find multiple WBC larvae feeding on one ear, increasing the chances for significant ear damage.

Where WBC populations are high, the corresponding ear damage from WBC feeding can leave wounded corn ears more susceptible to pathogen development, but a clear relationship between ear damage and mycotoxin development has not been documented. A number of mold species may develop on corn ears though relatively few of these produce mycotoxins. Principal concern in New York is with the mycotoxins deoxynivalenol (DON or vomitoxin) and zearalenone (ZON), both produced by the fungus Fusarium graminearum. Infection by this fungus also occurs in roots and stalks and leads to Gibberella stalk rot and the accumulation of DON and ZON in stalk tissues. Much of the toxin loading in 2018 corn silage in New York was contributed by contaminated stalks as well as ear tissues.

While WBC damage to corn ears can be significant and may have detrimental effects on corn grain yield and quality, the economic impact on corn silage is less understood. For corn silage growers, understanding whether or not this pest significantly impacts the yield or quality of the forage is critical to their decision making for managing this pest.

Since the Cry1F protein, which has most commonly been utilized for protection against numerous corn insect pests, has been found to be ineffective against WBC, producers are left with limited management options.  Currently, the Vip3A trait in select corn hybrids in combination with a scout and spray program is the best option for WBC management in areas where the pest is prevalent.

With the increased population of WBC in NY, the Commercial Corn Silage Hybrid Evaluation program conducted by Cornell University in collaboration with the University of Vermont and the Northeast dairy industry offers a good opportunity to evaluate numerous hybrids for ear damage from WBC and mycotoxins. This was done in 2017 and 2018 with financial support from both the New York Corn Growers Association and the Northern New York Agricultural Development Program.

Each hybrid is planted (in triplicate) at two locations in NY and one location in Vermont (VT), with the locations each hybrid planted at based on hybrid relative maturity (Table 1).

Mycotoxin screening was limited to the NY locations based on funding available. In 2017, composite whole plant silage samples (3 replicates combined) were taken for each hybrid at two locations; Madrid in Northern NY and Aurora in Central NY. In 2018, a slightly different strategy was used with individual replicate samples taken on a subset of hybrids at each location.

Both seasons, each plot was scouted prior to harvest to assess WBC feeding damage to the ears. At harvest a whole plant silage sample was collected and submitted to the Dairy One forage laboratory for a mycotoxin screening package which included aflatoxins B1, B2, G1, G2, vomitoxin, 3-acetyl DON, 15-acetyl DON, zearalenone, and T2 toxin.

Through the New York State Integrated Pest Management (NYS IPM) WBC Pheromone Trapping Network, WBC populations were monitored at each location.  Though it should be noted that as the traps only attract male moths, they help in understanding geographic differences in WBC population but may not be representative of the population of egg laying females.

The results of the WBC and mycotoxin screening project revealed large differences in the pheromone trap counts and the number of plots damaged by WBC (Tables 2a and 2b). There was also wide variation in the prevalence of samples testing positive for mycotoxins, particularly in 2018.  However, there was a lack of correlation between WBC damage and incidence of mycotoxins in both years (Table 2a and 2b).

Additionally, despite the damage to corn kernels inflicted by WBC, in plots with up to 60% of ears showing some level of WBC damage, the WBC feeding did not correlate to any negative impact on silage yield or forage starch content in this study.

The most prevalent species of mycotoxin-producing mold found in the screening was Fusarium graminearum.  This fungal pathogen can also infect corn ears through the silk channels at the time of pollination during favorable weather conditions and result in contamination of the grain and silage with the mycotoxins DON, 3-ADON, 15-ADON, or zearalenone. A review of the weather data from both years (despite very different overall weather patterns) showed wet conditions at silking conducive to this type of infection. As expected for New York, no aflatoxins were detected.

While there aren’t many in-field management options to reduce the chances of mycotoxin development (note that controlling plant diseases and mycotoxins are not the same thing), harvesting corn silage at the proper whole plant dry matter is helpful. Based on numerous field observations, and notable at the 2018 Aurora location in this study, a whole plant dry matter in the high 30’s or above appears to increase the risk of mycotoxin development.

While there are numerous ways in which molds can establish themselves in forages, this study reflects a common challenge researchers face while attempting to document the conditions where mycotoxin development is likely. These results, over two growing seasons, provide no evidence that WBC damage is an added risk factor for corn silage growers who are worried about deoxynivalenol and zearalenone in their silage. In areas of the country where other toxins are more prevalent the impact of WBC and other insect pest may differ. It is important to note that these results do not reflect what may occur in corn harvested for grain because the time between silage harvest and grain harvest offers additional opportunities for infection and growth.

Growers should continue to scout for this pest and weigh the cost of control with the potential for damage.  However, it does not appear that controlling WBC should be viewed as a significant management consideration for reducing the risk of mycotoxin development in corn for silage.

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October 4, 2018
by Cornell Field Crops
Comments Off on What’s Cropping Up? Volume 28, Number 4 – September/October 2018

What’s Cropping Up? Volume 28, Number 4 – September/October 2018

September 12, 2018
by Cornell Field Crops
Comments Off on Soybean White Mold Variety Trial – Genesee County, 2018

Soybean White Mold Variety Trial – Genesee County, 2018

Jaime Cummings, NYS Integrated Pest Management Program

Figure 1. White mold infection on soybean in the variety trial (photo by Jaime Cummings)

White mold, or Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum is the most economically important and difficult to manage disease of soybeans across NY State (Figure 1).  This disease is so undermanaged because the pathogen survives for a long time (>10 years) in the soil, making crop rotations a challenging management option.  Fungicide trials in other states have shown great promise for a number of products (https://www.ag.ndsu.edu/Carringtonrec/plant-pathology/fungicide-efficacy-testing-results-2013-soybeans), but application timing and canopy penetration is critical and may require multiple applications during a highly conducive season, which may not be economical.  Genetic resistance to this devastating disease should be a viable option, but many commercial varieties lack even modest levels of resistance.

A large-scale, non-replicated strip field trial was established in Genesee County to evaluate 24 soybean varieties for resistance white mold.  The trial was organized by WNYCMA and planted on 5/1/18 in a field with a long history of white mold infection.  The varieties evaluated in this trial included entries from five seed companies, and were representative of maturity groups 0.7 – 2.8.  The trial was rated for white mold severity on 9/5/18 by Jaime Cummings of the NYS IPM Program and Dr. Gary Bergstrom of Cornell’s field crops pathology program using a 1 to 9 rating scale, where 1 = resistant, and 9 = susceptible.  The disease was well established consistently across all strip plots at the time of rating, despite it being rotated out of soybeans since 2014.  The disease ratings are summarized in Figure 2.

Figure 2. White mold disease severity ratings of 24 soybean varieties in a non-replicated field strip trial, rated on a 1-9 scale, where 1 = resistant and 9 = susceptible.

The ratings for all varieties ranged between 4 and 7, meaning that all varieties were classified as moderately resistant (3.6 – 5.9) or moderately susceptible (6.0 – 7.5) at the time of the rating.  However, the disease would most likely progress in these plots over time, which would likely add one or two points to each rating, pushing many of them into the susceptible category (7.6 – 9).  Even though none of the varieties evaluated showed strong resistance, it is good to note that there are noticeable differences among varieties.

New York soybean growers do have options for selecting varieties with some moderate levels of tolerance to this disease, and should know to avoid planting the most susceptible varieties in fields with a history of the disease.  An integrated management plan which includes crop rotation, canopy management, foliar fungicides and planting tolerant varieties is the best approach to managing white mold in NY.

 

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August 7, 2018
by Cornell Field Crops
Comments Off on What’s Cropping Up? Volume 28, Number 3 – July/August 2018

What’s Cropping Up? Volume 28, Number 3 – July/August 2018

August 3, 2018
by Cornell Field Crops
Comments Off on Soybean Soilborne Diseases Appearing Across the State

Soybean Soilborne Diseases Appearing Across the State

Jaime Cummings
NY State Integrated Pest Management Field Crops and Livestock Program

Reports, photos and samples have been pouring in with regards to dying soybeans from western and central NY counties.  Some people report general chlorosis and wilting, and others are finding swaths of dead plants.  The drought conditions experienced in some parts of the state this year may have lulled some of us into thinking that we might be spared from some of our typical soybean diseases.  And, it’s true that foliar diseases have been nearly non-existent this season.  But, some of our important soilborne diseases are now rearing their ugly heads, and some of us are scratching our heads to figure out which is which.  Since many of these diseases tend to have similar general symptoms, especially early on, it’s important to get an accurate diagnosis to make any management decisions for both this season and future variety selections.  Thus far, I have confirmed Phytophthora root and stem rot, northern stem canker and Fusarium wilt in a handful of fields, but these problems are likely more widespread and we’ll probably continue to see more samples.

Managing these soilborne diseases can be challenging, and requires an integrated approach.  When a soilborne disease is identified in a field, you may need to implement multiple tactics, including resistant varieties, crop rotations, residue management, field drainage improvement, alternate weed host management, seed treatments and foliar fungicides where applicable.  Below is more information on some of the diseases of concern identified, thus far, this season.

Phytophthora Root and Stem Rot

Phytophtora root and stem rot stem lesion extending up from the soil line (photo by Mike Hunter)

Phytophthora root and stem rot, caused by Phytophthora sojae is a complicated soilborne disease of economic concern in soybean production areas of NY.  It has been confirmed in at least nine counties in NY, and it is likely more widespread throughout the state.  As with most of the soilborne diseases, occurrence depends on favorable conditions, including cool and wet conditions and compacted soils at planting time.  The disease is exacerbated by flooding of fields after seeding has occurred.  The 2018 growing season has been ideal for this disease in some parts of the state, given our prolonged wet spring and recent heavy rain events causing saturation in some fields.  The pathogen survives long-term in the soil as hardy oospores.  These oospores germinate to produce sporangia that release the swimming zoospores which infect the soybean roots or are splashed up into the canopy.  Infection of seedlings often results in damping off.  Symptoms of infection of older plants include lesions beginning at the soil line and extending up the stem, yellow/chlorotic leaves, wilting, reduced vigor, reduction in root mass and death.   We are currently seeing these symptoms in plants in various reproductive stages.  Over 70 races of this pathogen exist, making management with resistant varieties challenging without knowing which races occur in a particular field.  However, varieties with partial resistance (also called field tolerance), which adds some level of protection against all races, are available and highly recommended.  Improving soil drainage, reducing compaction, utilizing seed treatments, genetic resistance, and crop rotation are good tools for managing Phytophthora root and stem rot.

Phytophthora stem rot internal symptoms (photo by Jeff Miller)

Phytophtora root and stem rot in a section of a field in Oneida County early August, 2018 (photo by Jeff Miller)

Northern Stem Canker

Northern stem canker inside stem (photo by Jaime Cummings)

Northern stem canker, caused by the fungus Diaporthe caulivora, is a disease of economic concern that was first identified and confirmed in NY in 2014.  Since the initial confirmation, it has been discovered to be fairly widespread throughout many soybean production areas in NY, though usually only at moderately low incidences.  We are starting to see it in western NY this year, and expect to find it more widespread as favorable weather conditions continue.  The pathogen survives on infected soy residue, and infection often occurs during vegetative growth stages, but symptoms don’t appear until reproductive stages.  Foliar symptoms include interveinal chlorosis, followed by necrosis, and is indistinguishable from the foliar symptoms of other soilborne diseases including sudden death syndrome and brown stem rot.  Initially, small reddish-brown lesions appear, often near nodes on the lower stems, which expand into distinctive ‘cankers’ with slightly sunken, grayish-brown centers and reddish margins.  Large cankers may girdle stems completely.  Splitting stems longitudinally may reveal a browning discoloration of the vascular tissue and pith, often more pronounced near the nodes on the lower stems, similar to what is observed with brown stem rot.  In severe cases with large cankers, the entire pith may be brownish-red.  The disease reduces the number and size of seeds produced, and could result in yield losses of up to 50% in a severe epidemic.  It is important to note that there are two forms of stem canker; 1) northern stem canker, and 2) southern stem canker. Southern stem canker has not been identified in NY.  Each disease is caused by a different pathogen, and controlled by separate resistance genes.  Because northern stem canker was dismissed as a disease of minor importance in the 1950s, most seed companies do not provide disease ratings specific for northern stem canker in their catalogs.  Most ‘stem canker’ ratings in commercial seed catalogs are for southern stem canker (unless noted otherwise), which is a disease of great importance to many soybean production areas of the U.S., but have no relevance to northern stem canker resistance.  Foliar fungicide applications for management have shown inconsistent results, and may not be cost effective.  Tillage practices to bury infected residues and rotation with non-host crops, including small grains or corn, are recommended for highly infested fields if varieties with resistance specific to northern stem canker are not available.

Northern stem canker foliar symptoms of interveinal chlorosis and necrosis (photo by Jaime Cummings)

Northern stem canker lesions on stem (photo by Jaime Cummings)

Fusarium Wilt

Internal discoloration of vascular tissue of lower stems caused by Fusarium wilt (photo by Jaime Cummings)

Fusarium wilt, caused by a number of Fusarium species, is a fungal soilborne disease of concern in soybean production areas of NY, particularly in years with drought, like we are experiencing in 2018.  Though it has only been confirmed in a few counties, it is likely much more widespread, but is difficult to diagnose or differentiate from other diseases or stresses.  It’s easiest to rule out other diseases, like Phytophthora root and stem rot, northern stem canker, charcoal rot and brown stem rot to arrive at an accurate diagnosis.  Infection is favored by cool temperatures and wet soils during early vegetative growth stages.  Plants are infected during early vegetative stages, but symptoms appear later in the season during reproductive stages, and are exacerbated by hot, dry weather, when infected plants begin to wilt.  In addition to wilting, symptoms include brown discoloration of the vascular system in the roots, crowns and stems, and foliage may become generally chlorotic and defoliation may occur.  Sometimes, the general wilting and chlorosis are overlooked as heat stress, and the full extent of the disease in a field doesn’t become evident until many plants in a field die.  Reducing soil compaction, delaying planting until soil temperatures are favorable for seed germination, crop rotation and seed treatments applied to high quality seed are good management practices for minimizing losses to Fusarium wilt.

Fusarium wilt in a field in Livingston County in early August 2018 (photo by Mike Stanyard)

Fusarium wilt in a field in Livingston County in 2018 (photo by Mike Stanyard)

There can be a lot of overlap in symptoms among many soilborne diseases of soybeans.  Be sure to arrive at an accurate diagnosis before making any decisions.  And, remember, when scouting and collecting samples for submission for diagnosis, the diagnosis you receive is only as good as the sample you submit.  Be sure to collect whole plants, with roots, and ship them overnight to ensure they arrive in good condition.   Information on how to submit specimens for diagnosis is available on the Cornell Plant Disease Diagnostic Clinic website http://plantclinic.cornell.edu/pddcforms/submissionform.pdf, and a submission form is available at http://plantclinic.cornell.edu/pddcforms/submissionform.pdf.  And, for more information on soybean diseases in NY, please visit the soybean disease survey portion of fieldcrops.org (https://fieldcrops.cals.cornell.edu/soybeans/diseases-soybeans/soybean-disease-survey/).

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