By Top Crop Manager
Aug. 6, 2013, Saskatoon, SK — Weather is playing an important role in the spread of Goss's wilt in Manitoba.
While Goss's wilt remained isolated to eastern Manitoba in 2012, 2013 has already seen some intense storm systems that could cause it to emerge as a problem for corn growers in southern Manitoba as the disease continues to move.
"This disease can overwinter in the soil and crop debris for a few years, so if growers have had a problem before, it could be an issue again this year," says Wilt Billing, DuPont Pioneer area agronomist.
Historically, infections in Western Canada have been limited to the Red River Valley in Manitoba. Depending on weather conditions and hybrid susceptibility, the disease may cause only minor problems or it may result in devastating damage, such as yield losses approaching 50 per cent.
Several conditions must be present for Goss's wilt to produce significant damage. If the bacterium is already present in the field and a susceptible hybrid is planted in the field, the next main contributing factor is severe weather. Wind, sandblasting and hail create wounds for the bacteria to enter. Wet weather and high humidity are also needed for escalation of disease development.
"It's important to scout for Goss's wilt throughout the season to see if your fields suffer from the disease and to manage against it over the long-term," explains Billing. "This disease can also look like normal environmental stresses such as sun scald and drought stress, which makes scouting for it even more vital."
While the systemic wilt phase is less common than the foliar phase, scout early for Goss's wilt. Early season infections can result in discolored vascular tissue within the stalk. Those cases show a buildup of bacteria in the vascular bundles that inhibits the plant's ability to transfer water. Stunted growth and wilting as if drought stressed is another symptom to watch for.
Mid-season signs and symptoms include distinct dark green to black "freckles" within or just outside of leaf lesions. Shiny or glistening patches of dried bacterial ooze on the lesions, similar to a thin layer of varnish, can also be observed. Other signs of infection are water-soaked streaks accompanied by tan-to-gray lesions that run lengthwise on the leaves.
In-season management choices for Goss's wilt are very limited, so understanding your options is vital. "A fungicide application will not work on bacterial diseases such as Goss's wilt. The best strategy is prevention in the off-season with selection of a hybrid containing native resistance to the disease and incorporating crop rotation and tillage to minimize survival of the bacteria," says Billing.
Reducing corn residue through crop rotation or tillage is another management practice that helps combat this disease. One practice that can increase prevalence of Goss's wilt is corn-on-corn acres where the bacteria can overwinter in the remaining residue. Good weed control is very important because weeds such as green foxtail or barnyard grass are hosts for this bacterium. Billing also suggests harvesting and tilling infected fields last and then cleaning equipment to help avoid spreading the pathogen to uninfected fields.