Horticulture and Crop Science Department
BS in Crop Science
Michael J. Costello
Vitis vinifera L. cv. Chardonnay vines were fertilized to approximate baseline, low, medium, and high grape-leaf potassium contents, relative to viticultural target values. From those vines, twelve replicates of leaf-discs were made per fertilizer treatment. The leaf-discs were populated with individuals of Willamette spider mite, Eotetranychus willamettei (McGregor) and maintained in a plant growth chamber (25°C, 14L:10D h). Data pertaining to maturation time (days), pre-oviposition period (days), lifetime fecundity (eggs / ♀), and longevity (days) of E. willamettei was recorded daily. Petiole analysis revealed that the grape-leaf potassium contents were greater than target values. Respective to fertilizer treatment, the actual grape-leaf potassium contents were: 3.43%, 6.28%, 7.39%, and 8.06%. Treatment differences in mean values of maturation time, pre-oviposition period, lifetime fecundity, and longevity of E. willamettei were tested for significance by one-way analysis of variance, alpha = 0.05 and were short of statistical significance. However, novel information about several life-history traits of E. willamettei was recorded (mean ± SE): maturation = 6.7 ± 0.2 days, pre-oviposition period = 1.5 ± 0.2 days, fecundity = 37.3 ± 3.5 eggs per adult female, and longevity = 22.3 ± 1.7 days.