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Goss's wilt arrives in Alta. cornfields

On Prairies, bacteria previously seen just in southern Manitoba

Alberta corn growers have been advised to look again at their variety choices for 2014 now that a potentially yield-destroying bacterial disease has been spotted in the province.

Speaking to farm writer Helen McMenamin in the Sept. 2 issue of Alberta Farmer, provincial plant pathologist Mike Harding, based at Brooks, said the disease has been confirmed in only two Alberta fields so far.

"It doesn't seem to have caused significant yield losses in those fields but we're looking to see if it's in other fields as well," Harding said in the farm newspaper, without giving the fields' location.

Historically, Goss's wilt infections were limited to western Nebraska and eastern Colorado, but in recent years the disease has been on the move, spreading as far east as Indiana and, on the Prairies, into southeastern Manitoba's Red River Valley.

This year, according to corn seed and biotech firm DuPont Pioneer, growers elsewhere in southern Manitoba have already seen storm systems that could further the disease's spread there.

"This disease can overwinter in the soil and crop residue, so if growers have a problem, they should look at disease ratings prior to purchasing corn for 2014 as it could be an issue again next year," Nicole Rasmussen, an agronomist with DuPont Pioneer, said in a release Tuesday.

Depending on weather conditions and hybrid susceptibility, the disease may cause only minor problems or could lead to yield losses nearing 50 per cent, DuPont Pioneer said.

If the bacteria are already present in a field and a susceptible hybrid is planted there, the next contributing factor for more severe losses is severe weather, including wind, sandblasting and hail, which create wounds for the bacteria to enter. Wet weather and high humidity are also needed for the disease to further develop.

Manitoba corn saw significant yield damage from Goss's wilt in 2009. In 2011, about 80 per cent of crops showed some symptoms of the disease.

Fungicides won't work on bacterial diseases such as Goss's wilt, Rasmussen said, so growers' best bet is to seek out corn hybrids with native resistance to the disease, and to cut down the survival rate of the bacteria through crop rotation and tillage.

"Genetic resistance is the primary management strategy, and therefore affected growers should contact their seed providers about resistant corn varieties," Manitoba's agriculture department warned when Goss's wilt symptoms were spotted in corn fields in August 2012.

Goss's wilt can become more prevalent in corn-on-corn acres, where the bacteria can overwinter in the remaining crop residue. Weed control is also important, DuPont Pioneer said, because weeds such as green foxtail or barnyard grass can also host the bacteria.

Harvesting and tilling infected fields last, then cleaning equipment to help avoid spreading the pathogen to uninfected fields, is also advised.

The challenge for growers when scouting, Rasmussen said, is that Goss's wilt can look like normal environmental stresses such as sun scald or drought stress.

The disease's systemic wilt phase is less common than the foliar phase, the company said, but growers should still scout early for Goss's wilt. Early-season infections can result in discolored vascular tissue within the stalk. Stunted growth and wilting, as if drought-stressed, is another symptom.

Signs and symptoms at mid-season include dark green to black "freckles" within or just outside of leaf lesions, Pioneer said. Shiny or glistening patches of bacterial ooze on the lesions, appearing like a thin layer of varnish, can be observed, as can water-soaked streaks with tan-to-gray lesions that run lengthwise on the leaves. -- AGCanada.com Network


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