Insurance against hailstorm-inflicted losses to potato crops is crucial for producer risk management. Insurance providers need regionally specific information on which to base estimates of hail damage. The objective of the research reported here was to determine the effects of a range of simulated hail defoliation treatments, low (33%), medium (66%), and high (99%), relative to an untreated control (0%) on yield and grower economic returns from one medium- and one late-maturing potato variety ('Russet Norkotah TX278' and 'Ranger Russet,' respectively) at three growth stages (tuber initiation, early bulking, and late bulking) in the Columbia Basin of Washington. Plants within the 33% and 66% treatments were defoliated by sweeping a garden rake with 16 solid, curved tines through the canopy of each treatment row several times until plants exhibited the desired defoliation level. Tuber initiation and early bulk plants within the 99% treatment were essentially mowed to ground level. Intensity of defoliation and stage of growth had significant, interacting effects on grower returns. Gross return and yield for both varieties at each growth stage were significantly reduced by 99% defoliation; these effects were mediated by the effects of defoliation on tuber size distribution. Total yield and gross return experienced the largest declines at early bulk compared with tuber initiation and late bulk defoliation in both varieties. When 99% of the early bulk foliage was removed, Russet Norkotah TX278 gross return and yield were reduced to 14% and 38%, respectively, of the values for the non-treated control, and Ranger Russet gross return and yield were reduced to 30% and 51% of control values, respectively. Defoliation of 99% at all growth stages significantly reduced overall market yield compared to controls for both varieties. However, tuber size distribution was most affected by 99% defoliation at early bulk. Severe defoliation (99%) at tuber initiation significantly delayed vine senescence in both varieties. The results of this study suggest that insurance adjusters should take into account the combined influence of growth stage and defoliation level when hail damage occurs.
