Assessment of Susceptibility to Zebra Chip and Bactericera cockerelli of Selected Potato Cultivars under Different Insecticide Regimes in New Zealand

Tomato-Potato Psyllid (TPP) Bactericera cockerelli was first identified in New Zealand in 2006 and has caused major problems for the potato industry, particularly in the North Island. TPP and Zebra chip (ZC) resistance are now major priorities in Plant & Food Research’s potato breeding programme. ZC is caused by a liberibacter associated with the TPP. Twelve potato lines, including most of the more widely grown potato cultivars in New Zealand, were assessed in main-crop yield trials at Pukekohe under three insecticide levels: FULL (pre-plant plus 13–15 foliar insecticide applications through the season), REDUCED (4–5 foliar applications) and NIL (no insecticide), over two consecutive seasons’ harvest (2010 and 2011). In both years work there was a consistent substantial yield reduction from the FULL to the REDUCED insecticide to the NIL insecticide treatment. In most cases a similar trend was seen in dry matter and tuber size. ZC severity recorded in crisp slices before and after frying tended to be highest in the NIL insecticide treatment and lowest in the FULL insecticide treatment. The fresh market cultivar ‘Nadine’ had very little ZC in any raw tubers of any of the insecticide treatments in either season. Despite this the marketable yield of Nadine with NIL insecticide was almost half that of the FULL insecticide treatment in 2010 and about 60 % of the intensive insecticide level in 2011. There was no real indication that any of the other cultivars in the trial had any effective resistance to TPP or ZC.