Cause Clover yellow vein virus (CYVV) is transmitted by the green peach aphid, pea aphid, black bean aphid, and clover aphid. Two or three subspecies of Trifolium repens (white clover) are the principal virus reservoirs in western Oregon. Clover yellow vein virus and strains of bean yellow mosaic virus often are in the same field.
Symptoms First, the terminal leaf rolls down and turns brownish. Following terminal death, stem and leaf tissues die from the terminal down. Within 4 to 7 days, the upper part or the entire plant may turn dark brown and die.
Cultural control
- Use resistant varieties if available.
- Where feasible, eradicate white clover from border or pasture areas near fields used for bean production. Instead, grow red clover, alsike clover, other hardy clovers, birdsfoot trefoil, or other agronomically suitable legume species.
- If white clover eradication is not feasible, select fields for bean production that are at least 100 yards from white clover stands. This small degree of isolation will substantially reduce losses from the bean necrosis disease.
- When possible, locate bean fields upwind (toward the prevailing summer breeze) from clover fields or pastures containing clover. This further minimizes infection due to aphid flights from clover to beans.
- Avoid planting beans in fields that contained white clover the previous year.
Chemical control Insecticides to control black bean aphid or other species in June and July may be beneficial. Sprays should include field border areas containing numerous white clover plants. See the PNW Insect Management Handbook for details.