Sub-sampling plants to monitor tomato-potato psyllid (Bactericera cockerelli) and associated insect predators in potato crops.

Sub-sampling of potato plants was assessed as a practical tool for monitoring Bactericera cockerelli, tomato-potato psyllid (TPP) and other key pests and their predators at Pukekohe. The total numbers of the key insect species and all their life stages on: (1) the bottom leaf; (2) a middle leaf (the bottom leaf on the top half of the stem); (3) the bottom half of the stem; and (4) the top half of the stem, were compared with numbers on the whole stem. Assessing the top half of the stem was the most reliable sub-sampling method for the three main insects sampled, while assessing a middle leaf also gave a reliable estimate for two out of the three insects. A crop scouting protocol for monitoring TPP infestations based on sampling 100 middle leaves off 50 randomly selected plants in a crop is now recommended by the potato industry in New Zealand.