1a. Objectives (from AD-416):
Develop integrated pest management for insects vectoring diseases in Pacific Northwest potato crops.
1b. Approach (from AD-416):
Determine susceptibility of different potato plant growth stages to BLTVA phytoplasma under field conditions using leafhopper exclusion and exposure studies. Determine susceptibility of different potato plant growth stages to BLTVA phytoplasma under field conditions by timing applications of selected insecticides targeted against the beet leafhopper. Assess the impact of the timing of BLTVA infection on the potato yield, tuber processing quality, and phytoplasma transmission rate in daughter tubers. Develop treatment (action) thresholds for the beet leafhopper to reduce incidence of purple top disease in Columbia Basin potatoes.
3. Progress Report:
The work summarized in this progress report relates to objectives number 1 and 2 in the Project Plan for 018-00D: 1. Develop new knowledge of behavior, genetics, physiology, and ecology of wireworms, aphids, secondary potato pests, and their natural enemies, that provides opportunities for new and improved biorational control of potato insect pests. 2. Develop monitoring methods and techniques that reduce grower risk from wireworms that improve predictability of threats to potatoes; and objective number 2 in the Project Plan for 020-00D: 2. Develop bio-intensive methods to manage insect vectors of zebra chip and purple top diseases. Several insects, including aphids and beet leafhopper, transmit viruses and phytoplasmas that cause diseases to potato crops in the Pacific Northwest. Information on the biology and epidemiology of these pests and diseases is required to develop effective integrated pest management programs for these potato pests. To address this issue, we conducted research on the pathogen BLTVA phytoplasma that causes potato purple top disease and the beet leafhopper, its insect vector: 1) determined potato plant growth stages susceptibility to BLTVA phytoplasma infection and the relationship between beet leafhopper density and purple top development; 2) determined timing of insecticide sprays targeted against the beet leafhopper; 3) assessed the impact of the timing of BLTVA infection on the potato yield, tuber processing quality, and phytoplasma transmission rate in daughter tubers; and 4) determined treatment thresholds for the beet leafhopper to better manage purple top disease in Pacific Northwest potatoes. It was determined that younger plant growth stages of potato are more vulnerable to BLTVA phytoplasma and insecticide applications targeted against the beet leafhopper should mainly be made early in the season. In addition, it was determined that as few as one BLTVA-infective beet leafhopper per potato plant is enough to cause purple top disease and significant yield loss, suggesting that this insect pest should closely be monitored. Furthermore, it was discovered that, contrary to previous beliefs, BLTVA phytoplasma is transmitted to daughter tubers at a relatively high rate, thereby threatening potato seed quality. Information from this research will help growers in developing effective management strategies to better control beet leafhopper and reduce incidence of purple top disease, in addition to reducing insecticide use in Columbia Basin potatoes.