Evalution of Exotic Rust Fungi in the United States for Classical Biological Control of Weeds

Abstract

Evaluation and introduction of exotic plant pathogens for biological control of weeds in the United States takes place at the Plant Disease Research Laboratory (PDRL) in Frederick, MD. Pathogens of target weed species collected overseas are sent to PDRL and evaluated in a containment greenhouse for aggressiveness and specificity toward the target weed. Currently, rust fungi (Uredinales) are evaluated at PDRL for control of leafy spurge (Euphorbia esual L. #4 EPHES), musk thistle [Carduus nutans L. ssp. leiophyllus (Petrovic) Stoj. & Stef. # CRUNU (= C. thoermeri Weinm.)], and yellow starthistle (Centaurea solstitialis L. # CENSO). Determination of host range is central to the evaluation of potential pathogens, but some difficulty has been experienced in obtaining propagative material of important plant species, especially if the plant is threatened or endangered. A proposal is made to organize a seed bank to meet this need.