What's Cropping Up? Blog

Articles from the bi-monthly Cornell Field Crops newsletter

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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