Michael R. Fulchera, Gary C. Bergstroma, Mark E. Sorrellsb, and David Benscherb
aPlant Pathology and Plant-Microbe Biology Section and bPlant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY
Crown rust is a continuing threat to oat production in New York, and recent epidemics have cast a spotlight on this disease. To better advise growers on crown rust management, we examined the impact of crown rust on oat grain yields and the disease resistance of available and soon to be available varieties.
The fungal pathogen that causes this disease, Puccinia coronata var. avenae, is widespread in New York and often found on susceptible oat varieties. Characterized by bright-orange, blistering pustules, this disease can be seen from June through August (Figure 1). Once established in a field, disease progresses quickly as the spores of the fungus are dispersed by the wind. The spores are blown to new leaves, different plants and even other fields. Older crown rust lesions develop a black rust spore stage, and these spores can infect the alternate host, common buckthorn, providing early inoculum for oat infections in fields adjacent to infected buckthorn in the following May.
The pathogen requires living plants to survive so it rarely persists through the winter on oat in New York. However, viable crown rust spores from maturing oat crops in states to our south arrive in New York on wind currents each spring to commence annual epidemics. Some overwintering can occur in New York when the fungus moves back and forth between oat and common buckthorn (Figure 2).
Management of crown rust is best achieved through careful selection of an oat variety. Few options exist to combat the disease after plants are in the field. Some fungicides are labelled for crown rust control in New York, and some growers have realized a return in investment from a timely fungicide spray at or prior to panicle emergence. Crown rust significantly impacts the yield of susceptible varieties and in extreme cases may cause crop failure. Even slight visual symptoms around the soft dough growth stage can translate to yield loss (Figure 3). Rust pathogens are known to evolve quickly to overcome resistance, but based on several years of observation we have identified the varieties that currently are most resistant in New York (Table 1). If you are considering a spring oat planting, choose a variety with proven resistance to current populations of the crown rust fungus in New York.
Late summer forage plantings are at a higher risk for infection since the spores that cause disease will increase and spread throughout the growing season. When these forage plantings are infected, pathogen overwintering on buckthorn can be increased. This contributes to crop epidemics the following year and may speed the breakdown of oat varietal resistance.
Crown rust will continue to threaten oat yields, but you can reduce the spread of this disease by planting resistant varieties and notifying your local Cornell Cooperative Extension Field Crop Specialist or the Cornell Field Crops Pathology Program if you find the pathogen in your fields.