Lincoln, Nebraska
June 23, 2005
While Asian soybean rust could enter Nebraska
this summer, it's uncertain whether this fungal disease poses a
threat to dry edible and snap, or green, beans in the state, a
University of Nebraska-Lincoln
plant pathologist said.
Depending on storm movement and wind currents, soybean rust
spores could move from southern states to the Midwest and High
Plains in the coming months, said James Steadman, plant
pathologist in the university's Institute of Agriculture and
Natural Resources.
If environmental conditions are favorable, it could become
established in commercial dry edible or snap beans. The disease
does best between 65 and 80 degrees and requires moisture for
development.
"With its wide range of host plants, including legume weeds like
kudzu and some edible legume crops, the disease could pose an
unknown but potentially serious threat to future crops of
soybeans and possibly common beans (dry edible and snap),"
Steadman said.
Soybean rust was first detected in the U.S. last fall in several
southeastern states. Soybean rust defoliates soybean plants and
can reduce yields up to 90 percent in untreated fields.
However, scientists don't know how susceptible dry edible beans
are to soybean rust, said Loren Giesler, another UNL plant
pathologist.
"With soybeans, you know it is susceptible. With dry edible
beans, the producer may have a crop that's not susceptible and
make an unnecessary and expensive fungicide application,"
Giesler said. "This makes management much more difficult."
The long-term survival of this tropical disease in temperate
climates, such as in Nebraska, is another unknown, Steadman
said.
Tests at U.S. Department of Agriculture quarantine greenhouses
in Maryland and bean plots in South Africa and Brazil suggest
that dry bean varieties vary in their reaction to soybean rust
and are not affected as severely as soybeans, Steadman said.
In addition, preliminary observations suggest that infection
severity of susceptible dry beans is lower if they were located
more than 10 feet from infected soybeans, he said.
"The potential impact on dry edible and snap beans is of more
concern if dry edible beans are planted with or contiguous to
soybean fields," he said.
Steadman said some dry edible beans could be planted near
soybeans in the northern Sandhills, but where dry edible and
snap beans are planted each year varies across the state.
He added gardeners' green beans should be safe.
"First of all, snap beans usually aren't grown in the heat (of
the summer) and are finished producing by mid-summer," he said.
"Even so, gardeners may want to keep watch for symptoms if they
plant a fall crop of snap beans in August."
If soybean rust hits Nebraska, it most likely would be later
this summer.
Steadman said USDA and industry research is under way to
determine whether soybean rust in other bean species could be a
potential problem.
"Right now, we really have no idea if this is going to be a
problem, but we have sentinel plots and, hopefully, this will
give us a better idea of how soybean rust affects other types of
beans," he said.
Soybean rust symptoms include tan to dark brown or reddish
lesions one-twelfth to one-sixteenth of an inch in diameter and
are most abundant on the underside of leaves in the lower to
mid-levels of plant canopies. The disease starts at the bottom
of the plant and moves up.
Producers need to carefully scout fields to detect foliar
infection as early as possible.
Several fungicides are labeled for use on soybean rust. For more
information about soybean rust and dry edible beans, visit Crop
Watch, extension's crop production newsletter, at
http://cropwatch.unl.edu/archives/2005/crop05-14.htm#rust.
For information about fungicides and the latest information
about soybean rust throughout the growing season, visit UNL's
Targeting Soybean Rust Web site at
http://soybeanrust.unl.edu. |