Damage potential of Tetranychus urticae Koch to cucumber fruit and foliage: Effect of initial infestation density

Field trials were conducted to assess the damage potential of two-spotted spider mite (Tetranychus urticae Koch) on cucumber (Cucumis sativus Linnaeus). Young cucumber plants were artificially infested with different densities of T. urticae (5, 10, 15 and 20 mites/ grown up leaf) while uninfested plants acted as control. Post infestation, the plants differed in their support to mite density in accordance with initial infestation density and observation period. Grown up leaves were found to be the most susceptible to mite infestation (5.86 mites/ sq. cm leaf). The number of feeding (chlorotic) patches on cucumber leaves significantly increased from 1.38/sq cm at a pre-count of 5 mites per grown up leaf to 1.71/sq cm leaf at a pre-count of 20 mites as compared to no patch recorded in control. Highly significant negative correlation was recorded between mite population and photosynthetic pigments. Total chlorophyll, chlorophyll-a, chlorophyll-b and carotenoids decreased to a maximum of 40, 43.63, 45.45 and 47.27 percent at the highest infestation density as compared to control. Results revealed differences among various treatments in terms of yield attributes of cucumber. The per cent reductions from 6.15 to 12.42 in number of fruits, 0.59 to 1.56 in fruit length and 0.93 to 3.28 in fruit width at different inoculums of T. urticae were recorded over uninfested plants. The cumulative effect led to the ultimate reduction in average fruit weight in the range of 10.16 to 17.19 per cent in the infested plants