Apple pests stand up to antibiotics

Antibiotic resistance in bacteria may soon force apple farmers to search for a new prescription to fight a deadly tree disease.

Resistance to the common antibiotic streptomycin is sweeping through apple and pear orchards, impairing farmers' ability to fend off fire blight, says Patricia S. McManus, a plant pathologist at the University of Wisconsin-Madison.

Fire blight, a leading killer of fruit trees, is the reason farmers spray more than 11,000 kilograms of streptomycin on U.S. orchards every spring. Streptomycin and the antibiotic oxytetracycline both can keep fire blight in check, although streptomycin does a better job, says McManus.

That may change as two forms of streptomycin resistance proliferate in fire blight bacteria, McManus said at the American Association for the Advancement of Science annual meeting in Washington, D.C., last month. The most common form—caused by a mutation in one bacterial gene—has appeared in orchards in the northweste