Carrot (Daucus carota L.) cultivar resistance to carrot rust fly (Psila rasae Fab.) with a note on the seasonal history of the adult and its distribution in Newfoundland

Hooper, Laura R. E. (1997) Carrot (Daucus carota L.) cultivar resistance to carrot rust fly (Psila rasae Fab.) with a note on the seasonal history of the adult and its distribution in Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The role of adult host preference as a mechanism of carrot (Daucus carota L. cultivar resistance to carrot rust fly (Psila rosae F. [Diptera: Psilidae]) attack was examined via an ovipositional preference study in the laboratory and a damage assessment in the field. Laboratory studies were conducted to determine if P. rosae had a propensity to oviposit on a specific cultivar. Cultivar pairs were exposed to adult P. rosae for seven days to two weeks in controlled temperature chambers and were examined for the number of eggs deposited by P. rosae through floatation and filtration of the samples. There was a significant difference (P = 0.0015) between the number of eggs found on cv. Danvers Half Long 126 and on cv. Flyaway. There were no significant deviations from the expected 50:50 ratio in the tests comparing oviposition on Danvers and Nantes, Danvers and Chantenay, Nantes and Chantenay, and Nantes and Flyaway. -- The resistance of the same four carrot cultivars to carrot rust fly attack was investigated in field studies at two sites in 1995 and 1996. Four carrot cultivars were planted in mid-June at two sites (Memorial University of Newfoundland Botanical Garden (BG) and Agriculture and Agri-Food Canada Research Centre, St. John's (RC)), in a randomized block design, and assessed for the damage caused by P. rosae larvae. At the BG site in 1995, significant damage was found on cv. Danvers Half Long 126 (1.2%), Nantes Half Long received 1.1% damage, Chantenay had 0.9% damage and Flyaway received 0.3% damage. No significant damage was found at this site in 1996 or at the RC site in 1995 or 1996. -- Adult carrot rust flies were monitored with marigold-yellow sticky traps at home gardens and commercial sites in the St. John's area from mid-June to November in 1995 and 1996. One distinct period of adult activity was observed in 1995 whereas two distinct periods were observed in 1996. This reflects the occurrence of one generation per year typically and the possibility of another generation depending upon the season. Two-year means for cumulative air degree-days (DD) above 3°C after 1 April for first, 10%, maximum, and 90% trap catch of the overwintering generation were 308,418,590, and 752 DD, respectively. -- Adult carrot rust flies were trapped in carrot production areas in the regions surrounding Conception Bay, Placentia Bay, Bonavista Bay, Notre Dame Bay, and Bonne Bay. However, even though traps were placed in field in the area around St. George's Bay and in Labrador, no flies were trapped. -- Damage caused by the larvae of the carrot rust fly was reduced in areas exposed to wind compared to more sheltered areas thus it is possible that carrot rust fly damage can be reduced by planting the carrot crop in exposed areas of the garden or field where the adult will have difficulty flying. -- The study of the seasonal history and distribution of the carrot rust fly in Newfoundland provides valuable information to producers because it has alerted producers to a potential pest in their production area. The information will provide the farmer with the tools required to understand the activity of the carrot rust fly in the field and consequently accurately time controls. Although many studies have investigated the activity of the carrot rust fly in other parts of Canada and the world, the pest has never been studied in a climate similar to that found in Newfoundland.

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