6.21
CULTURAL AND CHEMICAL CONTROL OF FUNGAL ROOT ROTS AND ROOT MAGGOTS IN COLE CROPS

KF CHANG1, SF HWANG2, RJ HOWARD1, P RAGAN1, LM DOSDALL2 and B CHOBAN3

1Crop Diversification Centre South, Brooks, Alberta, Canada, T1R 1E6; 2Alberta Research Council, Vegreville, Alberta, Canada, T9C 1T4; 3 Crop Diversification Centre North, Edmonton, Alberta, Canada T5B 4K3

Background and objectives
Cole crops, the major group of vegetables grown in Alberta, often incur heavy losses from infestations by Rhizoctonia solani and root maggots [1]. Infested stands appear thin or spotty and often require replanting. Root maggots (Delia radicum and D. floralis) emerge from overwintered puparia in mid-May to early July and lay eggs at the base of the stem. Larval feeding on taproots causes disruption of water and nutrient flow to the upper portions of the plant, and the subsequent invasion of these wounds by pathogenic fungi further weakens the root system. The objectives of this research were to investigate the effects of cultural and chemical practices for the control of root rot and root maggot infestations in cole crops.

Results and conclusions
Response of cauliflower cultivars to root rot disease: significant differences in stem lesion length occurred between inoculated and non-inoculated plants; however, head weight did not differ significantly between these two groups. Lesion length varied significantly among cultivars, with cv. Yukon having significantly longer lesions than cvs Minuteman, Bur-Queen, Cashmere, Bishop and Snowball. Head weight was significantly lower in cvs Vio-Queen and Bur-Queen than all other cultivars.

Fungicide trial: while no significant differences in disease severity or lesion length were observed between control and inoculated plots, average weight per head and total cauliflower production per plot were significantly greater in control than in inoculated plots. Overall, plants in fungicide-treated plots had shorter lesion lengths and lower disease severities than those in non-treated plots. Similarly, total weight per plot was significantly higher in the fungicide-treated plots than in the non-treated plots. Average weight per head was significantly greater for the Terrachlor and Bravo treatments than for the non-treated control. Lower disease severities were observed in plots treated with Benlate than those treated with Zineb.

Fungicide and insecticide trial: inoculation did not produce significantly lower head weights in the insecticide study. All treatments significantly reduced lesion lengths and disease severities, and increased total harvest and individual head weights. Diazinon and Lorsban, when combined with Benlate, resulted in significantly shorter lesions than when Benlate was used alone.

Mortality of cauliflower and cabbage seedlings was affected by planting method, whether by transplanting or direct seeding. On average, twice as much mortality occurred in direct-seeded cauliflower as in transplants. In cabbage, transplantings produced less mortality than direct seeding. Evidently, early transplanting of cole crop seedlings is advantageous for reducing the mortality caused by pathogens and pests.

References
1. Hwang SF, Chang KF, Deneka BA et al., 1997. Canadian Journal of Plant Pathology 19, 325.