Pycnidia of Stagonospora nodorum, and pseudothecia of Phaeosphaeria nodorum and Pyrenophora triticirepentis occurred in greater numbers after one overwintering period on residues of wheat and barley stored on the surface of the soil than on residues from the previous fall. Conidial numbers of Bipolaris sorokiniana and Drechslera teres on residues of wheat and barley, and pseudothecia of Pyrenophora teres on residues of barley decreased over one winter but these pathogens continued to sporulate at low levels after two winters. With residue from the soil surface, Drechslera teres and B. sorokiniana conidia occurred in greater numbers on lower parts of the plants. Drechslera teres occurred primarily on leaf and sheath areas and B. sorokiniana, on sheath and stem areas, while P. teres sporulated mainly on stems. Numbers of conidia of D. teres may have declined because the pathogen occurred mainly on leaves, which disintegrated after one winter. The wheat pathogen Stagonospora nodorum was able to sporulate on barley residue. Since sporulation occurs on residue in spring, this could lead to early infections on seedlings. To control these diseases, wheat should not follow wheat or barley, and barley should not follow barley or wheat. This study indicates that a minimum of 2 years between wheat crops is required to prevent septoria leaf spot, but 1 year between wheat crops may be sufficient to control tan spot. Barley should not be grown within at least 2 years of a previous barley crop, and possibly even more time should be allowed between barley crops to control net blotch. Résumé: Après un hiver, il y avail plus de pycnides du Stagonospora nodorum, et de pseudothèces du Phaeosphaeria nodorum et du Pyrenophora tritici-repentis sur les débris de blé et d'orge en surface du sol que sur les débris de l'automne precedent. Les quantités de conidies du Bipolaris sorokiniana et du Drechslera teres sur les débris de blé et d'orge, et de pseudothèces du Pyrenophora teres sur les débris d'orge ont diminué après un hiver, mais ces champignons pathogènes ont continue a faiblement sporuler après deux hivers. Avec les débris en surface du sol, les conidies du D. teres et du B. sorokiniana étaient plus nombreuses sur les parties basses des plantes. Le D. teres était présent surtout sur les feuilles et les gaines, et le B. sorokiniana sur les gaines et les chaumes, alors que le P. teres a sporulé surtout sur les chaumes. La quantité de conidies du D.teres peut avoir diminué a cause de la presence prépondérante sur les feuilles qui se sont désagrégées après un hiver. Le champignon pathogène du blé, Stagonospora nodorum, a pu sporuler sur les débris d'orge. Étant donné que la sporulation a lieu au printemps sur les débris, ceci pourrait causer des infections précoces des semis. Pour contrer ces maladies, le blé ne devrait pas suivre du blé ou de l'orge, et l'orge ne devrait pas suivre de l'orge ou du blé. La présente étude indique qu'une rotation d'au moins 2 ans est nécessaire entre les cultures du blé pour prévenir la tache septorienn...

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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...