Soroka, J. J., Dosdall, L. M., Olfert, O. O. and Seidle, E. 2004. Root maggots (Delia spp., Diptera: Anthomyiidae) in prairie canola (Brassica napus L. and B. rapa L.): Spatial and temporal surveys of root damage and prediction of damage levels. Can. J. Plant Sci. 84: 1171-1182. The levels of infestation and damage to canola taproots caused by crucifer-feeding root maggots (Delia spp.)(Diptera: Anthomyiidae) were determined through surveys of commercial crops across the canola growing regions of western Canada. Canola root damage caused by Delia spp. maggots was measured at the end of the season by determining the percentage of plants infested (PPI) per field and estimating average damage levels (DL, on a scale of 0 to 5) to taproots. Over the course of the survey, 2890 canola fields were sampled. Infestation by root maggots occurred wherever canola is grown in western Canada. In the study, 96% of the fields surveyed in Manitoba and Saskatchewan and 99.8% of the fields in Alberta showed evidence of root maggot feeding, with PPI much higher than in provincial surveys of a decade previously. Geographical ecoregion significantly affected both PPI and DL. The greatest amount of damage over the largest area was found in western and northwestern Alberta, although localized areas with severely damaged roots occurred along the northern edge of the entire Parkland ecoregion. Over the entire survey area, Brassica rapa L. roots had greater PPI and DL than B. napus L. roots, although species differences were not significant in Saskatchewan or Manitoba. Data from the survey were correlated with weather variables to develop a model predicting the levels of damage inflicted by root maggots to canola roots. Of the weather variables investigated, temperature, especially the average temperature in the preceding July and August, had the greatest influence on PPI and DL. The warmer the temperatures of the preceding July and August, the lower the PPI and DL in the current year. Likewise, previous year's July and August precipitation influenced PPI and DL negatively. Other weather parameters had little consistent influence on PPI and DI. The predictive model for PPI and DL, developed from the 1995-1998 survey data, incorporated canola species, ecoregion, previous July-August and September-October temperatures and precipitation. The validity of the model was assessed using a set of survey data collected in Alberta from 1981 to 1983. Regression equations of predicted results on actual results were significant. However, r 2 values for the regressions were low, in part because of the few ecoregions surveyed and the lack of canola species data recorded in the earlier survey, and because of the large increase in infestation levels since the earlier data were collected. The study is a first step in forecasting the effects of root maggots across a wide geographic area featuring many different canola production practices. For personal use only.

Effect of swathing on alternaria black spot in Brassica rapa canola in Saskatchewan. Can. J. Plant Sci. 79: 299-302. From 1990299-302. From to 1997, experiments were conducted comparing the effect of swathing versus straight combining on seed infection by Alternaria species and on quality of harvested seed. This was done at several locations in Saskatchewan using a number of cultivars of Brassica rapa and B. napus. The level of A. brassicae in harvested seed was significantly higher in straight-combined than in swathed treatments. Green seed count and seed weight were not affected by treatment. Seed germination was reduced, but not always significantly, with straight combining compared to swathing. This data support the recommendation for swathing at the optimal time to reduce alternaria black spot when the potential for disease development is high. Swathing reduces the time for disease development because it reduces the time of ripening compared with straight combining. Le pouvoir germinatif des graines était moins bon, quoique pas toujours significativement au plan statistique, après moissonnage-battage qu'après andainage. Ces observations viennent conforter la recommandation d'andainer au stade de maturité optimale de façon à réduire l'infection de la tache noire à un moment où ses possibilités de développement sont particulièrement fortes. L'andainage, en effet, laisse moins de temps à la maladie de se développer du fait qu'il raccourcit la durée de maturation par rapport au moissonnage-battage. Mots clés:Tache noire, Alternaria brassicae, canola, andainage Alternaria black spot, caused by Alternaria brassicae (Berk.) Sacc. and A. raphani Groves & Skolko, is found worldwide and is endemic in the northern canola growing areas of the Canadian prairie provinces, where it can cause substantial yield reductions of up to 36% (Rude et al. 1994;Verma and Saharan 1994;Seidle et al. 1997;Duczek et al. 1998). This disease also reduces seed quality by increasing the green seed count, reducing seed weight, and decreasing the percent germination in harvested seed. Alternaria alternata (Fr.) Keissl. is also frequently isolated from seed but it is considered nonpathogenic. Because plants are most affected by this disease late in the season Vanterpool (1963) recommended swathing, which hastens the ripening process, as a means of control. The purpose of this study was to determine the effect of swathing on alternaria black spot. MATERIALS AND METHODS Time of SwathingThe test was conducted in commercial fields of Brassica rapa canola at Medstead, Saskatchewan, and relied upon naturally occurring inoculum for infection. Seeding occurred on 26-28 May, on different dates each year, using a press drill with 15-cm row spacings. The cultivars were AC Parkland in 1995, Tobin in 1996, and AC Boreal in 1997. A randomised complete block design with four or five replicates was used. Each plot was 3 m long by 1.2 m wide with 1 m of crop on either side to serve as a guard. On each swathing date, eight rows of plants from the centre 2 m o...