Postharvest Potato Tuberworm Population Levels in Cull and Volunteer Potatoes, and Means for Control1

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Abstract
Postharvest samples of cull tubers and volunteer plants in commercial potato fields provided a large food resource for Phthorimaea operculella (Zeller) during noncropping periods. In commercial, spring-planted fields sampled in 1977 and 1978, 27.6 and 74.3 surface culls/100 m2 and 1092.9 and 1670.0 subsurface culls/100 m2, respectively, were recovered 2 months after harvest. In 1977 and 1978, 19.7 and 53.8 adult potato tuberworms/100 m2, respectively, were reared from the surface culls, and 880.5 and 2368.1/100 m2 were reared from the subsurface culls, respectively. In 1977, 187.2 volunteer sprouts/100 m2, infested with a mean of 866.8 potato tuberworm larvae/100 m2, were present 3 mo after harvest. Culls and volunteers from the spring plantings harbored potato tuberworm larvae until the following spring planting, at which time potato tuberworm populations increased until host material was no longer available. Maleic hydrazide, a sprout inhibitor, effectively reduced volunteer sprouting. It also reduced the surviving potato tuberworm population, as indicated by larval and pheromone trap counts.