Category: Disease Management

Jaime A. Cummings¹, Gary C. Bergstrom¹, David M. Thurston^1,2, and Xiaohong Wang^1,2
1School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology Section, Cornell University; and ²USDA-ARS

In coordination with a statewide soybean disease survey, soil samples were collected from soybean fields from 17 counties throughout New York beginning in 2013 to search for the presence of the soybean cyst nematode (SCN) (Fig 1).  Surveys were enabled with support of the Northern New York Agricultural Development Program, the New York State Corn and Soybean Growers Association Soybean Check-off Program, and USDA-NIFA Hatch and Smith Lever funds.  After four years of intensely surveying field soils from western through northern NY counties, the nematode has now been identified and confirmed in Cayuga County.  The survey was coordinated by Cornell University’s Field Crops Pathology program under the direction of Dr. Gary Bergstrom and Research Support Specialist Jaime Cummings in collaboration with numerous Cornell Cooperative Extension Educators and countless soybean growers throughout the state.  Nematode extraction and initial identification was performed in Dr. Xiaohong Wang’s USDA ARS nematology lab at Cornell. Confirmation of the nematode’s identity as Heterodera glycines was made via microscopic examination by Dr. Zafar Handoo and via DNA sequence analysis by Dr. Andrea Skantar, both of the USDA-ARS in Beltsville, MD.

The soybean cyst nematode is considered the single largest cause of soybean yield losses nationwide and its occurrence has been confirmed in much of central and eastern North America (Fig. 2).  Identifying and diagnosing SCN damage can be challenging, because aboveground symptoms, including stunting and chlorosis, may be vague and also caused by other abiotic stresses.  Belowground symptoms include discoloration or necrosis of roots and reduced nodulation.  The female nematodes may be visible on roots as very small white or yellow lemon-shaped cysts, and are easily distinguishable from nodules (Fig. 3).  This pest was expected to be found at some point in New York soils, as it has been documented in areas of Canada adjacent to Niagara, St. Lawrence, Franklin, and Clinton Counties.  However, low levels of the pest can be difficult to identify in soil samples, and may require multiple years of sampling before the pest population reaches a detectable level.

We should be vigilant in our continued search for the likely more widespread distribution of this potentially devastating pest throughout NY.  Systematic research survey efforts through CCE collaborators will continue in 2017.  Soil sampling for SCN analysis is recommended for growers who suspect infestation, and this service is available through the Plant Disease Diagnostic Clinic at Cornell University and other state and commercial laboratories (Fig. 4).  Because the nematodes are very persistent in the soil, and have a complicated race structure, an integrated management approach is recommended.  Management practices include crop rotation, planting race-specific, resistant varieties, nematicidal seed treatments, and cultural practices that reduce plant stress and optimize plant health and yield.

The results of this ongoing survey are now available in the soybean disease section of Cornell’s fieldcrops.org extension website https://fieldcrops.cals.cornell.edu/soybeans/diseases-soybeans/soybean-disease-survey.  The website, updated annually, outlines the progress of the survey and the counties included in the survey.  New York soybean growers can use this new tool to find information on which diseases/pests have been identified in their respective counties, along with information on each disease including epidemiology, diagnostic characteristics for in-field identification, and management options and recommendations.

Save

Jaime A. Cummings and Gary C. Bergstrom
School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology Section, Cornell University

Surveys of soybean diseases in New York were initiated in 2012 with support by the Northern New York Agricultural Development Program (2013-2016) and the New York State Corn and Soybean Growers Association (2013-2015). The survey was coordinated by Cornell University’s Field Crops Pathology program under the direction of Dr. Gary Bergstrom and Research Support Specialist Jaime Cummings in collaboration with numerous Cornell Cooperative Extension Educators and countless soybean growers throughout the state.  The purpose of the surveys was to gain a better understanding of the occurrence and distribution of soybean diseases affecting NY growers and to document and monitor the expansion of diseases to new areas.  All distribution maps are based on a positive laboratory diagnosis of the causal microorganism associated with observed symptoms.  Actual ranges of disease occurrence may be wider than appears on these maps but have not yet been confirmed through vigorous laboratory diagnoses. The results of this ongoing survey are now available in the soybean disease section of Cornell’s fieldcrops.org extension website https://fieldcrops.cals.cornell.edu/soybeans/diseases-soybeans/soybean-disease-survey.

Through the efforts of this survey, a total of seven diseases previously undocumented in NY were discovered and confirmed.  These diseases included charcoal rot, Fusarium wilt, sudden death syndrome, brown stem rot, northern stem canker, bacterial wilt and powdery mildew.  The soilborne diseases identified are of particular concern to growers.  Knowing where these diseases have been confirmed will aid growers in making decisions on selecting varieties with resistance and other management options for diseases of potential importance in their areas.  Multiyear surveys better capture the reality of disease occurrences in the region due to the variation in weather from year to year, because each disease may be favored by specific weather conditions.  We will continue the soybean disease survey in 2017 to expand our database and knowledge of which soybean diseases occur throughout NY.

The website, updated annually, outlines the progress of the survey, including the locations included in the survey, the number of samples diagnosed and the primary diseases identified each year.  New York soybean growers can use this new tool to find information on which diseases have been identified in their respective counties, along with information on each disease including epidemiology, diagnostic characteristics for in-field identification, and management options and recommendations (Fig. 1).

Save

Save

Save

Jaime A. Cummings and Gary C. Bergstrom, School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology Section, Cornell University

A potentially yield-reducing disease called ‘brown stem rot’ (BSR) was confirmed for the first time in New York soybean fields in 2013, and was found again in 2014.  It showed up in some plants from soybean fields in Cayuga, Herkimer, Niagara, and Yates Counties collected by Cornell Cooperative Extension Educators Kevin Ganoe, Keith Severson, Michael Stanyard, and Bill Verbeten, with support from the New York Soybean Check-off Program.  The disease was diagnosed in the Field Crops Pathology Laboratory at Cornell based on characteristic symptoms and the laboratory isolation of the causal fungus and confirmation of a portion of its signature DNA sequence. So far, BSR has not been detected outside of the four counties mentioned above.  It is noteworthy that BSR was not detected in soybean fields in northern New York scouted in 2013 and 2014 by CCE Educators Michael Hunter and Kitty O’Neil, with support from the Northern New York Agricultural Development Program.

Brown stem rot is caused by the fungus Cadophora gregata (syn. Phialophora gregata) and occurs in most soybean production regions of the US, but this is, to our knowledge, the first confirmation in New York or the northeastern U.S.  Reported yield losses in the Midwest have ranged from minor to in excess of 25%, so the presence of the pathogen is considered a significant factor for soybean production. Yield loss is often a function of the relative susceptibility of varieties that are planted; varieties vary from susceptible to resistant.  BSR is a disease of priority to soybean seed companies.  Resistant varieties are widely available, and most seed catalogs provide resistance ratings for BSR.  If BSR becomes more prevalent in New York, selection of resistant varieties may become more important for New York producers.

The foliar symptoms of BSR are similar to those of other soilborne diseases that restrict the movement of water and nutrients to the leaves.  So BSR can be confused with northern stem canker and sudden death syndrome, all of which result first in yellowing and then browning of leaf tissues between the veins during pod-filling stages.  However, not all soybean varieties exhibit foliar symptoms when infected with the BSR fungus.  What is distinctive about BSR is the browning of the internal tissues of infected plants (Figure 1).  This discoloration is often most obvious near the nodes when stems are split lengthwise.  Dead leaves may remain attached to the plant. Stem discoloration symptoms may be confused with those caused by white mold, northern stem canker, or Phytophthora stem rot.

Infection by the fungus occurs early in the season, through the roots, from where the fungus continues to grow throughout the plant’s water-conducting tissues.  Temperature has the greatest impact on disease development, and is favored by temperatures between 60 – 80F.  But, temperatures above 80F may halt BSR development and spread.  Because infection occurs at early stages (around the three leaf stage) of the crop, foliar fungicides applied during flowering and pod-filling stages will not be effective in suppressing BSR.

The fungus survives on soy residues and in the soil in the field for many years. Luckily, the pathogen survives on few other plant species, and in severely infested fields, a rotation of at least 3 years out of soybean and deep plowing of infected soybean residues would reduce the incidence of BSR in a subsequent soybean crop.

The most important thing that a New York soybean producer can do at this time is to learn to recognize the symptoms of BSR and other soilborne diseases and to get a diagnosis of problems that they observe in their fields.  If BSR or other soilborne diseases are confirmed, producers should talk to their seed supplier and order soybean varieties with appropriate levels of resistance for the soilborne diseases observed on their farm.

Acknowledgements: This research received financial support from the New York Soybean Check-off Research Program, the Northern New York Agricultural Development Program, and Cornell University Hatch Project NYC153473.