Effect of fertilizer and water regimens on insects’ populations in carrots

The nutritional quality of plants is one of the main characteristics of host plant selection by phytophagous insects. Primary macronutrients of plants include nitrogen, phosphorus, and potassium; while secondary macronutrients include calcium, magnesium, and sulphur. The relative availability of those nutrients, as well as the water regimen can affect the growth of plants and the growth and fitness of herbivores. Carrots represent an important crop in the Columbia Basin of Oregon and Washington for the fresh, processing, and carrot seed market. This 2-year study focused on determining if side-dressing applications of calcium nitrate and urea ammonium nitrate, in combination with normal (1 inch/lap under central pivot irrigation) or extra (10% plus) water regimens would influence pests and beneficial populations in carrots. The trial was set up as a split randomized complete block with four replications per treatment. Experimental plots were 3 beds wide x 6 m long, with 2 rows per bed and 60 cm row spacing. Normal commercial production practices were followed throughout the growing season. After plant emergence, insects were collected weekly using a sweep net and an inverted leaf blower to collect insects above ground, and pitfall traps were used to collect insects below ground. Above ground, leafhoppers, thrips, Lygus bugs, aphids, and beneficial insects were collected. Springtails, ground beetles, rove beetles, carrion beetles, and beneficial insects were collected below ground. Whereas the two fertilizers did not affect insect populations, water regimens influenced the population of key insect pests in the areas, such as leafhoppers.