Potassium silicate and salicylic acid effects on onion thrips population density and some growth indices of onion cultivars

Thrips tabacci Lind. (Thysanoptera: Thripidae), the onion thrips, is one of the most damaging pests to onion fields. By using biotic or abiotic stimuli or growth regulators, it is possible to induce resistance, which activates the plant's natural defense. The effect of foliar application of two growth regulators, salicylic acid and potassium silicate, separately and in combination, on onion thrips population density, fresh weight, dry weight, chlorophyll concentration, and height of onion cultivars was investigated in the Jiroft region between 2016 and 2017. The experiment was conducted as a factorial design with 12 replications. Two onion cultivars (Gardesco and Milky Way F1), salicylic acid (0, 0.25, 0.5 mM), and potassium silicate (0, 1, 2 cc. lit-1) were used in three different concentrations. The analysis of variance revealed that the effect of biological fertilizer on thrips population density, fresh and dry weight, chlorophyll concentration, and the effect of onion cultivar on plant height and thrips population density were all statistically significant (Pvalue£0.01). Additionally, the interaction between fertilizer and cultivar was significant only for the pest population density parameter at the 1% level. The treatment with potassium silicate (2 cc. lit-1) resulted in the highest fresh and dry weight values, 363.29 and 120.25, respectively. Milky Way F1 plants were taller (41.16 cm) than Gardesco plants (37.10 cm). These findings indicate that salicylic acid and potassium silicate have the potential to significantly reduce the T. tabaci population