Fungicide usage is increasing: don’t forget to rotate fungicides

Non-Peer Reviewe

Pathogenic variability of Ascochyta rabiei in Saskatchewan

Non-Peer ReviewedForty isolates of Ascochyta rabiei collected in Saskatchewan Canada and 18 obtained from other countries were assessed for pathogenicity on eight chickpea differential lines/cultivars under controlled conditions. Each assessment was repeated once. Based on the differential by isolate interactions, 15 distinct pathotypes were identified among the isolates from Saskatchewan. This demonstrates that many races of A. rabiei are present in Saskatchewan. Formation of new virulent races through gene recombination is possible. This will have large impact on Ascochyta blight development and its control. Plant breeders should anticipate a highly diverse A. rabiei population with a high potential for change

Effect of seed damage and metalaxyl seed treatment on seedling blight of field pea

Non-Peer ReviewedWhen cool, wet conditions occur at seeding, soil-bone diseases can severely reduce stand establishment in field pea. Seed that has been damaged by rough handling (augering or dropping) is particularly vulnerable to injury from Pythium spp. Field trials were conducted over 3 yr to assess the impact of seed rot, damping-off and seedling blight on seedling establishment and seed yield from damaged field pea seed. The effect of fungicide seed treatment was also examined. Mechanical damage to the seed reduced seedling emergence and seed yield. Seed treatment with metalaxyl (Apron) reduced the impact of seed damage, but did not always restore emergence and seed yield to the same level as from undamaged seed. Differences among cultivars were small relative to the effect of seed injury. This study showed that planting fungicide-treated, high quality field pea seed was an effective means to maximize emergence and stand establishment for commercial field pea production

Evaluation of biofungicides for control of clubroot on canola

Non-Peer ReviewedClubroot of canola, caused by the protist pathogen Plasmodiophora brassicae (Pb), is an emerging threat to canola production in western Canada. Effective/practical control options are currently lacking. This study was initiated to assess registered microbial fungicides for control of clubroot on canola. Selected biofungicides were initially applied as a soil drench and the fungicides Allegro and Ranman were also included for comparisons. Selected products were further evaluated at varying concentrations, soil drench volumes, and for seed treatment. At moderate disease pressure, the biofungicides Serenade and Prestop, as well as synthetic fungicides Allegro and Ranman were highly effective as a soil-drench treatment, reducing clubroot severity by 85–100% in controlled conditions. Biofungicide concentration appeared to be important while soil-drench volumes may be reduced. All products, however, were significantly less effective or ineffective under extremely high disease pressure. All products were less efficacious in trials using infested field soils, a circumstance that may be related to treatment timing. Results from seed-treatment trials were too variable to draw a conclusion but there was a strong indication that this approach be successful though more research is required on microbial formulations. Serenade, Prestop, Allegro, and Ranman should be further evaluated under field conditions for clubroot control

Use of cultivar resistance and crop rotation with Bacillus subtilis for clubroot control in canola

Non-Peer ReviewedThis study was conducted to assess additional strategies potentially complimentary to cultivar resistance or biocontrol in control of clubroot. New granular Bacillus subtilis formulations and a seed dressing method were developed to facilitate biofungicide delivery in field trials. The granular formulations were applied in furrow during seeding at 50 kg/ha to a clubroot resistant (CR) and susceptible (CS) canola cultivar, respectively, in three field trials. The seed dressing applied approximately 1×105 to 5×106 cfu/seed doses of the biocontrol agent, and was evaluated on the CS cultivar seeded to different crop-rotation scenarios where the plots had a 1-year, 3-year, or 11-year break from last canola crop. Clubroot disease pressure was high at all trial sites with disease severity indexes (DSI) ranging from 69% to 98% on the CS cultivar. None of the granular formulations reduced clubroot substantially, whereas the CR cultivar showed a high effect, reducing DSI to below 15% and doubling the yield over that of CS cultivar. Plots of varying rotation showed a pattern of clubroot pathogen pressure, with those of 1-year break from canola being the highest. The DSI for all rotational scenarios was high, reaching 100% in short-rotation plots. Biofungicide seed dressing did not reduce DSI, but longer crop rotation often reduced gall size slightly, showed much milder above-ground damage, and increased the yield significantly relative to short rotation in two separate trials. Even a 3-year break from canola was highly beneficial, with the yield doubled as opposed to that with only 1-year break from canola

Impact of crop management on plant diseases

Non-Peer Reviewe

Influence of plant age on resistance to Ascochyta rabiei in chickpea cultivars

Non-Peer ReviewedAscochyta blight of chickpea, which is caused by the fungal pathogen Ascochyta rabiei, can cause severe losses in yield and seed quality. When environmental conditions favour blight development, even resistant cultivars may become heavily infected (Nene and Reddy 1987). Plant age has no impact on disease reaction in susceptible cultivars (Trapero-Casas and Kaiser 1992). However, two previous studies of the reaction of resistant cultivars as the plants mature had conflicting results, with resistance increasing in one study and declining in the other (Hafiz 1952, Sattar 1933). The objective of this study was to investigate the impact of plant age on Ascochyta blight severity in partially resistant and susceptible chickpea cultivars adapted for western Canada

Tillage and rotation have minimal effect on diseases of lentil and wheat in diverse rotations

Non-Peer ReviewedThe current trend towards reduced tillage practices was expected to increase losses due to plant disease relative to conventional tillage; increased diversity in crop rotation was expected to reduce these losses. To test these widely-accepted hypotheses, diseases (incidence and severity) were monitored on spring wheat, lentil, and field pea grown in diverse crop rotations under zero and conventional tillage at Indian Head, SK from 1992-1995. Crop rotation and tillage practice had little effect on lentil diseases, but epidemics of Ascochyta blight [Ascochyta lentis] and botrytis blight [Botrytis cinerea] were most severe in the treatments with the densest plant stands. Leaf disease severity on wheat grown under zero tillage did not differ from wheat under conventional tillage, but root disease severity was lower. The importance of individual root pathogens of wheat changed under zero tillage, with Fusarium spp. increasing while Bipolaris sorokiniana decreased. Rotation did not affect disease severity or the incidence of pathogens causing root disease. However, leaf disease severity on spring wheat was slightly higher in the most diverse rotation than in two other diverse rotations. Regardless of the tillage or crop rotation practices used, the annual environment was the most important factor limiting the severity of disease and the losses incurred

Reaction of lines of the rapid cycling brassica collection and Arabidopsis thaliana to four pathotypes of Plasmodiophora brassicae

The clubroot reaction of five Rapid Cycling Brassica Collection (RCBC) lines (Brassica carinata, B. juncea, B. napus, B. oleracea, and B. rapa) and 84 lines of Arabidopsis thaliana to pathotypes 2, 3, 5, and 6 of Plasmodiophora brassicae (as classified on William's system) was assessed. Also, the reaction of the Arabidopsis lines to a single-spore isolate of each of pathotypes 3 and 6 was compared with that of a field isolate. Seedlings were inoculated with resting spores of P. brassicae, maintained at 25 and 20\ub0C (day and night, respectively), and assessed for clubroot incidence and severity at 6 weeks after inoculation. Several lines of A. thaliana and RCBC exhibited a differential response to pathotype but none of the lines were immune. Among the RCBC lines, B. napus was resistant to all of the pathotypes; B. oleracea was resistant to pathotypes 2, 3, and 5; B carinata and B. rapa were resistant to pathotypes 2 and 5; and B. juncea was susceptible to pathotypes 5 and 6 and had an intermediate response to pathotypes 2 and 3. Line Ct- 1 of A. thaliana was highly resistant to pathotype 2, Pu2-23 was highly resistant to pathotype 5, and Ws-2 and Sorbo were highly resistant to pathotype 6. These results indicate that the lines of RCBC and A. thaliana have potential for use as model crops for a wide range of studies on clubroot, and could be used to differentiate these four pathotypes of P. brassicae. The reaction of the RCBC lines to pathotype 6 was highly correlated with response under field conditions but the reaction to the single-spore isolates of pathotypes 3 and 6 was not strongly correlated with reaction to the field collections in the Arabidopsis lines. \ua9 2013 Department of Agriculture and Agri-Food, Government of Canada.Peer reviewed: YesNRC publication: Ye