Influence of tomato/clover intercropping on the control of Helicoverpa armigera (Hübner)

Tomato plants, Solanum lycopersicum L., are often infested by the tomato fruit borer (TFB), Helicoverpa armigera (Hubner), in northern Iran. Persian clover, Trifolium resupinatum L., was selected as a companion plant in intercropping with tomato in our experiments, due to a key role in enhancing soil fertility and soil texture, attracting flower-visiting natural enemies by production of numerous flowers, and repelling insects by phenolic compounds secretion. Field experiments were conducted to evaluate the impact of intercropping tomato (T) and Persian clover (C) in the four patterns: 1 T: 2C, 2 T: 2C, 3 T: 2C and 4 T: 2C (row ratios) in comparison with sole tomato on the densities of TFB and natural enemies in tomato plantations during 2016 and 2017 growing seasons in Iran. Moreover, yields of both crops were measured to evaluate yield benefits of intercrops. Results indicated all intercropping patterns significantly reduced the density of TFB eggs and larvae compared with sole tomato in the two growing seasons. Lower densities of TFB eggs and larvae, among intercrops, were recorded in 1 T: 2C and 2 T: 2C in the two seasons. In 2016 and 2017 growing season, the average numbers of predatory bugs, coccinellids and Chrysoperla carnea (Stephans) were higher in intercrops than in sole tomato and their abundance, among intercrops, raised with increasing the proportion of clover/tomato rows. Moreover, the egg and larval parasitism rates were higher in intercrop plots than in the control plots. The highest value of land equivalent ratio (1.29 in 2016 and 1.30 in 2017) was found in 1 T: 2C among intercrop patterns in the two cropping seasons. Therefore, we could conclude that intercropping tomato and Persian clover, especially in 1 T:2C and 2 T:2C patterns are more profitable in TFB management programs.