A hot, wet December was just what the soybean crop in Brazil's top-producing center-west region needed. And that's what it is getting.
But the humid conditions are also promoting the spread of the deadly Asian rust fungus
The first confirmed cases among commercial crops were reported in Mato Grosso and Goias at the start of the month and instances are now expected to multiply quickly as the crop hits the later stages of development.
In total, Brazil has registered 47 cases so far this season, up from 27 at the same stage last year. So far, many of the cases are in voluntary plants.
Now the task is to control the fungus
"We know from 10 years' experience that we can limit the impact of rust. But farmers have to monitor crops closely to treat before it takes hold," said Luiz Nery Ribas, technical director at the Mato Grosso Soybean and Corn Growers Association (Aprosoja).
The rust fungus, or Phakopsora pachyrhizi, 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.
It is virtually impossible to prevent rust's arrival as the fungal spores are carried on the wind. However, it can be controlled by fungicide.
In 2012-13, rust cut yields by as much as 10% in Mato Grosso, according to the Mato Grosso Agricultural Research Foundation (Famato-MT).
The concern among researchers is that farmers will not be as diligent in monitoring for rust as in the past because they are so worried about a new threat -- the Helicoverpa amigera caterpillar, or corn earworm, which devastated crops in Bahia last year and has spread across Brazil's farm belt.
"We want to make sure that producers don't forget about rust, which is potentially much more dangerous," said Ivan Pedro, a Famato researcher.
Especially as while the rainy conditions are conducive for rust, they increase the efficiency of pesticide in tackling corn earworms.
The cost of controlling rust, and other pests and diseases, has risen this year.
At the start of December, chemical costs for soybean crops in Mato Grosso were, on average, 22% higher than last year, although many farmers bought earlier in 2013 when prices were lower, according to the Mato Grosso Agricultural Economics Institute (Imea).
Mato Grosso farmers will apply fungicide an average of three times this year, according to Aprosoja, although the number varies greatly from farm to farm.
"Farmers who monitor hard and act quickly as the first sign of rust will end up spraying less," said Aprosoja's Ribas.
Brazilian soybean planting is now virtually complete with approximately 60% of the crops in the germination phase, 25% in the flowering phase and 7% in pod filling.
Alastair Stewart can be reached at email@example.com
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