Published on 03/01/07

Georgia farmers eyeing new pests in soybean 'boom'

By Brad Haire
University of Georgia

It's been a decade since Georgia farmers figured to plant as many soybeans as this year. With much more now at stake, experts are watching to see if the state's weather and a helpful predator can keep two new soybean saboteurs (a disease and an insect) at bay.

Growers are expected to grow more than 300,000 acres of soybeans in Georgia this year, says Nathan Smith, a Cooperative Extension agricultural economist with the University of Georgia College of Agricultural and Environmental Sciences. That's double the acreage of last year.

Soybean prices are around $8 a bushel now, he said, $2 higher than last year and the five-year average.

The sharp price increase is largely due to corn prices' being pushed up to $4 a bushel on the rabid demand of the U.S. ethanol boom. Buyers are offering more to make soybeans look as sweet as corn economically this year.

A potential problem with the acreage upsurge is Asiatic soybean rust, which has already been confirmed in seven places in five southwest Georgia counties this year.

Caused by a fungus, the disease has caused billions of dollars in damage in Brazil and other tropical countries for years. It was first found in the United States in 2004, most likely catching a ride from South America on a late-season storm.

Freezing temperatures kill this disease, and even south Georgia freezes. But the rust can overwinter on protected kudzu that isn't killed in winter, says UGA Extension plant pathologist Bob Kemerait. That's where it's been found so far this year.

The good news is that even though it can overwinter, the disease must be introduced anew to commercially grown Georgia soybeans each year. This has happened later in the summer when soybean plants have developed pods, Kemerait said. In Brazil, it's always around and can destroy fragile blooms.

Georgia's notoriously hot and often dry summers also keep the disease from spreading as it does in Brazil. There, it can travel hundreds of miles in a day.

Before the disease, Georgia farmers rarely sprayed fungicides to protect soybeans. It wasn't economical. But over the past two years, they've sprayed at least half the crop, and the disease still has caused some damage.

Due to the increase in acreage and expected higher value this year, Kemerait said, growers need to be ready to apply timely fungicides to protect the crop if the disease spreads early.

Another soybean pest now lives in north Georgia. The Asian soybean aphid was first discovered in the U.S. in Wisconsin in 2000, says Bob McPherson, a UGA research entomologist. It has since spread to more than 20 states, hitting Georgia in 2002.

Left untreated, the 10th-of-an-inch insect can multiply quickly and cut yields by 40 percent in some northern states, he said.

These aphids like Georgia's winter weather and overwinter easily, he said. But they don't like the hot, dry summer, particularly in south Georgia, where most soybeans are grown.

Lady beetles, however, do like Georgia's weather year-round. And they're found in high numbers statewide. They don't hurt plants, McPherson said. But they love to eat aphids, particularly soybean aphids. They can be found munching on them in north Georgia.

The Asian soybean aphid will likely never reach a population able to damage Georgia soybean yields, he said. But they will continue to be monitored.

"They're still rascals that are good at adapting like all insects," he said. "I have seen some insects once under control adapt, and here we go again."

Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.