Crown rust on oats
Control options for crown rust include cultural practices and strategic use of fungicides
According to the National Agricultural Statistics Service, about 60,000 acres of oats were planted across Michigan in 2010 with an average yield of 68 bushels per acre. Using a “marketing year average” price of $2.45 per bushel, the state-wide oat crop had a value of just under $10 million. The top five oat producing counties in Michigan include Sanilac, Huron, Montcalm, Presque Isle and Ogemaw, accounting for 12,300 acres. Oats harvested in the northern lower and Upper Peninsula totaled 22,100 acres. Oat acreage in Michigan exceeds barley (10,000 acres of barley harvested in 2010), but is small compared to wheat at 510,000 acres harvested in 2010. Primary uses of oats include companion crop for new forage seedings, livestock feed, grain and seed.
Oats are susceptible to a variety of plant diseases including fungal, viral and bacterial pathogens. The most common disease with economic significance is crown rust, also known as leaf rust. This disease is caused by a fungus in the genus Puccinia. Spores are air-borne and can originate in southern states, or come from nearby buckthorn, an alternate host that allows the disease to overwinter. Wheat, barley and rye are not susceptible. Symptoms include small, oval, orange pustules on leaves. Pustules may also appear on leaf sheaths, stems and panicles.
The disease spreads from leaf to leaf as pustules release spores. Under conditions ideal for the disease, new pustules can form in 7 to 10 days. Damage to the oat plant is due to leaf damage, especially the flag leaf, or top leaf on the plant. This results in decreased photosynthesis and interference with grain fill. Moderate infection can reduce yields by 10 percent. As the severity increases, losses will increase, with crop failure possible if a susceptible cultivar is grown and conditions are ideal for the disease.
Selecting an oat variety resistant to crown rust is an important control consideration. However, given enough time, the crown rust fungus is able to overcome resistance bred into oat varieties. Plant breeders continually screen potential new varieties for crown rust resistance. A properly timed fungicide application can provide protection against crown rust. Spraying should take place at flag leaf emergence. If pustules have already formed on the flag leaf, it is too late. Fungicides labeled for crown rust in oats are protective, that is, they can prevent the disease from entering the plant. However, once the pathogen is inside, a protective fungicide won’t help.
In 2011, fungicide trials on oats will be conducted with assistance from staff at MSU’s Upper Peninsula Research Center in Chatham.
For more detailed information about fungicide application to control crown rust in oats, read page 168 in the University of Minnesota Extension’s Impact of Foliar Fungicides to control Crown Rust in Oats in 2009.