As we enter the new soybean season, Brazilian agronomists are warning about the potentially significant threat of Asian rust in Mato Grosso this year.
Populations of voluntary soybeans have been high in the north and west of Brazil's top-producing soy state, probably nurtured by uncharacteristic rains in late August and early September, according to the Mato Grosso Soybean and Corn Growers Association (Aprosoja-MT).
These voluntary plants allow the fungus to survive the 90-day prohibition of soybeans in the state and allow the spores to propagate quickly during the next season.
According to Jose Tadashi, a phytopathology specialist, and Eduardo Vaz, an Aprosoja analyst, germinating soybeans were identified across the north and west.
According to Tadashi, the voluntary plants create an environment for spores that are carried on winds from southern Brazil, as well as Paraguay and Bolivia.
"The message for all is that they must pay special attention (for signs of rust) at the start of planting," said the specialist.
While pressure from caterpillars and other insects has grown in recent years, Asian rust remains perhaps the biggest threat to the soybean crop. The fungus causes lesions on the leaves of soybean plants, which impede the formation of the bean and can result in massive yield losses. In more extreme cases, the fungus can kill the plant.
Brazilian farmers have learned to manage the fungus' threat since it arrived in the first half of the last decade by spraying on the first reports of cases in their region rather than waiting for the telltale yellow mosaic to appear on their own plants. But control requires great vigilance and large outlays on fungicides.
With margins tighter than in recent years, the concern is farmers may try to skip applications, allowing the fungus to spread early.
On the other hand, despite the early September showers, more substantive spring rains are expected to arrive late to Mato Grosso this season, which will inhibit the spread of rust.
Brazilian soybean planting is expected to rise by 2% to 5% in 2015-16, with the U.S. Department of Agriculture forecasting a crop of 97 million metric tons. Mato Grosso is responsible for approximately a third of that production.
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