The effect of N:K relationship was evaluated when applied through fertigation, on two-spotted-spider mite, Tetranychus urticae, infestation and on the yield of two strawberry cultivars. Strawberry plants received weekly doses of N and K (g/plant) by drip irrigation: 0.27 and 0.13; 0.27 and 0.50; 0.27 and 0.76 and control (water+micronutrients). Fruits were collected twenty two times during crop cycle. Marketable, non-marketable fruits and other yield parameters were evaluated. Leaf nutrient content analysis was performed to determine the nutritional condition of the plants. Population density of T. urticae was evaluated weekly. A significant interaction between K doses and pest population was observed. Higher doses of the nutrient reduced the number of eggs and active forms of the pest population and the cultivar Diamante showed the smallest pest density. K and P showed negative correlation with both variables, but N showed a positive one. No effects were observed of fertilization on yield parameters due, probably, to the high mite infestation (>40 individuals per leaflet) in all treatments during most of the crop cycle. Solely the use of different N:K ratios on the strawberry fertilization management at this specific experimental condition, was not sufficient to control two-spotted spider mite nor to reduce losses caused by that pest.
Tetranychus urticae; Fragaria x ananassa; nutrient balance; plant nutritional status; pest control
