Time of Tuber Infestation and Relationships Between Pheromone Catches of Adult Moths, Foliar Larval Populations, and Tuber Damage by the Potato Tuberworm1,2

J. Econ. Enlomol. 72: 599-601 (1979) Time of tuber infestation by Phthorimaea operculeLla (Zeller) was markedly affected by the type of irrigation system employed. Tuber infestation under furrow irrigation was above 25% for 4 wk prior to vine senescence while sprinkler irrigated potatoes sustained less than 5% damage during this period. After irrigation was terminated, infestation increased rapidly in sprinkler irrigated plots. Tuber infestation continued to increase in all irrigation blocks late in the season, but rows which were hilled and rolled sustained less damage than ones which were only rolled. Larval populations in the foliage and moth counts in pheromone traps increased during the season and were significantly correlated. Under furrow irrigation, pheromone trap catches and larval counts in the foliage were significantly correlated with tuber damage. Experiments were conducted in 1978 at the University of California's Moreno Field Station, Riverside Co., with spring planted (Mar. 27) 'Kennebec' potatoes. This cultivar was used since it is a shallow-setting variety with high susceptibility to potato tuberworm. Rows were on 0.81-m centers, and the soil type was uniform sandy loam. Standard commercial cultivation practices were utilized, except that no insecticides were used to control the potato tuberworm. A 2.39-ha rectangular, experimental area was subdivided longitudinally into 3 blocks. Blocks were oriented Several approaches are available for the development of an integrated pest management system for the potato tuberworm, Phthorimaea operculeLla (Zeller), on potatoes. Traynier (1975) demonstrated that eggs are preferentially laid in the soil at the base of plants and suggested this site as useful in relation to control. A number of foliar insecticides are used against the potato tuberworm, but control of foliage infestation does not always prevent tuber infestation (Bacon 1960, Foot 1974). In the absence of pesticides, natural controls constitute an important mortality factor, particularly in fall plantings (Oatman and Platner 1974). Cultural controls that utilize deeper seed planting and hilling of rows also help to prevent tuber infestation (Langford 1933, Foot 1976). Irrigation practices can reduce tuber infestation with sprinkler irrigation significantly reducing damage when compared to furrow irrigation (Shelton and Wyman 1979). Following the identification of the potato tuberworm sex pheromone (Roelofs et al. 1975, Persoons et aI. 1976) and the development of an effective trapping system (Kennedy 1975, Bacon et aI. 1976), a new tool for evaluating tuberworm field populations became available. To facilitate commercial utilization of this pheromone, we conducted studies to determine when tuberworm infestation occurs under different irrigation systems, as well as the relationship between pheromone trap catches and foliar larval counts, and their relationships to tuber damage. Materials and Methods I Lepidoptern: Gelechiidae. , Received for publication Feb. 12. 1979. © 1979 Entomological Society of America in a N-S direction because potato tuberworm moths normally move into the area from the south. Each block received one of 3 common irrigation practices: furrow (one 24-h set/week); sprinkler IX (one 18-h set/week); and sprinkler 3X (three 6-h sets/week). Sprinkler laterals were spaced 12.2 m between uprights and 2A-mm nozzles were used. Six sampling areas (plots) were established in each block and buffered by 12.2 m on N-S sides and 19.5 m on E-W sides. Each plot was subdivided into 4 rectangular subplots (44.6 m2 each) positioned within the plot so that, together with border areas, they formed a rectangle (267.6 m2). In the center of each plot, a UC/Davis water trap (Bacon et al. 1976) was placed at ground level and baited with a rubber septum that was impregnated with potato tuberworm sex attractant (trans-4, cis-7-tridecadienyl acetate, Zoecon Corp., Palo Alto, CA). Trap pans were filled to within 2 cm of the top with water that contained one ml of detergent/3.8 liters of water. A onem area around each trap was cleared offoliage. Trapping was initiated 76 days after planting when moth populations began to increase, and traps were monitored weekly for 7 wk. Two plants and 5 tubers from each of the plants were removed weekly from each subplot at random, beginning 76 days into the growing season. Weekly subsampIes were combined to make a total of 8 plants and 40 tubers from each plot. Tubers and plants were returned to the laboratory and examined for potato tuberworm infestation. Tubers were characterized as either infested or noninfested, and the lower half of each potato plant was dissected to detect potato tuberworm larvae which were found in both foliage and stems. Infested tubers were expressed as a percentage of the total harvested per plot per week, larvae as the mean no. per plot per week, and adult moths as the mean no. per trap per night for weekly periods. Most vine senescence occurred between 108-118 days after planting; the last foliage sample was taken and irrigation was terminated at III days. At 118 days, remaining vines were rotochopped, and beds in half of each plot were rolled while beds in the other half received an additional hilling before being rolled. Two ad· ditional weekly tuber samples were taken after vine re-