The interaction of two-spotted spider mites,Tetranychus urticaeKoch, with greenhouse-grown radish plants was analyzed in terms of the importance of soil moisture levels and applied fertilizers that differed in nitrogen level and the ratio of nitrogen to phosphorus and potassium. Low soil moisture levels produced both smaller plants and lower total mite populations, although the same mite intensity (number per g of foliage) was attained regardless of moisture level. Fertilizer composition had no effect on the dry weights of uninfested plants or on mite population size, but the highest intensities were associated with fertilizers that had high N to P and K. Mite infestation of the foliage caused a large reduction in the dry weight of the storage and root tissues but did not consistently reduce foliage or total plant dry weight. Radish plant response to mite infestation was consistently influenced by the composition of the applied fertilizer when soil moisture was adequate.