The Prairie Farm Rehabilitation Administration (Anon. 1993) has reported that leaving more standing stubble on crop land and reducing fall tillage are becoming more popular among farmers in Alberta and Saskatchewan. From 1988 to 1993, the percentage of cereal fields with >1000 lbs/acre of crop residue increased from 70 to 90%. During the same period the amount of summerfallow decreased by 8%. Accompanying this trend towards increasing adoption of conservation tillage is the continued popularity of rotations with cereal following cereal in Alberta and Saskatchewan (Bailey et al. 1994). The combination of increased adoption of conservation tillage and the continued popularity of rotations where cereal follows cereal may increase the potential impact of residue-borne diseases like net blotch and scald of barley.

During the summer of 1995, a survey of commercial barley fields under conservation and conventional tillage systems was conducted. The goal of the survey was to assess the impact of conservation tillage on net blotch and scald of barley. We asked for the cooperation of Alberta Agriculture, Food and Rural Development (AAFRD) Cereal/Oilseed Specialists to produce a large sample size that would make the information more useful on a province-wide basis. In June of 1995, sampling kits and survey sheets were sent to cooperators who indicated interest in collecting samples during the summer. In the fall, samples were returned from 12 of the 18 potential cooperators. Samples then were shipped back to Lacombe for assessment of foliar disease severity.

A total of 99 barley fields were surveyed during the summer. The leaf samples collected were rated for the percentage leaf area covered by scald, the net-form of net blotch, and other leaf spots. Disease and survey data then were entered into the computer and tabulated. Fields were classified according to tillage regime, variety resistance to scald and net blotch, and rotation. Some fields could not be classified according to these categories because survey information was incomplete or unclear. Data from unclassified fields were excluded from the summaries for particular categories. Disease assessments and data entry were completed in December 1995; data tabulation was completed in January 1996.

Using information supplied on the survey sheets, fields were grouped into three tillage categories: conventional (more than two tillage operations before seeding including cultivation or discing), minimum tillage (up to two tillage operations before seeding using a cultivator, no discing), and zero tillage (no tillage operations before seeding). Harrowing before seeding was not considered a tillage operation. Of the 99 fields that were sampled, 39 were classified as conventional, 17 as minimum, and 38 as zero tillage.

Scald severity remained low in most fields, with mean severity less than 3% for both the flag and flag-1 leaves. Nevertheless, severity levels of more than 30% were observed in some fields. Consistent trends among the tillage regimes were not evident, perhaps due to low scald levels. Similar levels of scald were observed for the three tillage regimes.

The level of net blotch was higher in those fields sampled during the summer of 1995. Mean disease severity was above 5% for both flag and flag-1 leaves. In a few fields, maximum net blotch severity was over 40%. More consistent trends for net blotch were observed among the tillage regimes. Disease levels were lowest for those fields under conventional tillage, highest under zero tillage, and intermediate under minimum tillage. A similar trend was observed for the maximum levels of net blotch found in sampled fields.

Disease resistance appeared to have an influence on scald severity. Although mean severity levels were low, fields sown to varieties classified as susceptible or intermediate tended to have the highest disease severity, while fields sown to resistant varieties had the lowest mean and maximum severities.

Variety also appeared to have an influence on net blotch severity. Much higher mean and maximum severity levels were found for fields sown to varieties classified as susceptible compared with intermediate varieties. Currently, no commercially available barley varieties are classified as having a resistant reaction to net blotch (Varieties of Cereal and Oilseed Crops for Alberta - 1996, AGDEX 100/32).

The influence of rotation on disease severity was examined for the data collected during the summer of 1995. Fields were classified based on the presence of barley or a non-host (wheat, canola, peas, summerfallow, chemfallow, etc.) in 1993 and 1994. Of the 93 barley fields classified according to rotation in 1994; 65 had a non-host in 1994, while 28 fields had barley in 1994. Seven fields had continuous barley from 1993 to 1995. No distinct trends in scald severity on the flag or flag-1 leaves were observed based on rotation, although slightly higher overall mean levels of scald and other leaf spots were observed for those fields that had barley in 1994 compared with a non-host.

Trends in net blotch severity associated with rotation were more pronounced. Higher disease levels on the flag and flag-1 leaves were observed when barley in 1995 was preceded by barley in 1994 compared with a non-host. Disease levels were highest when barley in 1995 was preceded by barley in 1994 and 1993.
 
 

Fields were classified according to 1995 tillage regime and to the 1994 rotational crop (barley versus non-host). No consistent trends in scald or other leaf spot severity were observed. Consistently higher mean and maximum levels of net blotch were found when barley in 1995 was preceded by barley in 1994 for fields that were under minimum or zero tillage in 1995.

Trends in scald and net blotch severity were evident based on tillage and variety resistance. Scald severity tended to be slightly higher for susceptible and intermediate varieties grown under all three tillage regimes. This trend was even more pronounced for net blotch severity. For example, under zero tillage the susceptible varieties had 14% of the flag-1 leaf affected by net blotch compared with 0.61% for intermediate cultivars. For both scald and net blotch, much higher maximum disease levels tended to occur in those fields sown to susceptible varieties for all tillage regimes.

Caution must be exercised when using the results of the current survey to draw conclusions based on tillage, variety and rotation. The trends observed in the survey represent data from one year. In addition, the survey was an observational study and it may be inappropriate to infer any cause and effect relationships. Nevertheless certain trends were evident based on the data from the summer of 1995. These trends may provide some insight concerning the impact of conservation tillage on barley foliar diseases in Alberta.

Net blotch severity tended to be highest for those fields under minimum and zero tillage. The severity of scald and net blotch tended to decrease as the level of disease resistance increased. Disease severity was increased when barley in 1995 was preceded by barley in 1994, especially for net blotch. Differences in disease severity observed among the cooperators probably reflected variation in weather conditions. Overall, net blotch was more severe during the summer of 1995, although significant levels of scald did develop in certain fields.

Results from the 1995 survey suggest that the increase in disease severity observed under zero or minimum tillage may be reduced by planting a non-host between barley crops rather than continuous barley cultivation. Furthermore, the use of more resistant varieties may also help to counteract any increase in disease levels observed under conservation tillage. Environmental variation among, fields, regions, and years may also have a large impact on disease development regardless of tillage regime.
 
 

Anonymous. 1993. Crop residue survey: Land use changes in Alberta and Saskatchewan, 1988 to 1993. Prairie Farm Rehabilitation Administration. Agriculture Canada. 2 pp.

Bailey, K.L., L.J. Duczek, L. Jones-Flory, R. Kutcher, M.R. Fernandez, G.R. Hughes, D.

Kaminski, C. Kirkham, K. Mortensen, S. Boyetchko, P. Burnett, and D. Orr. 1994. Saskatchewan/Central Alberta barley disease survey, 1993. Can. Plant Dis. Surv. 74: 62-66.