6.12
SCALD AND NET BLOTCH OF SPRING BARLEY IN ALBERTA, 1995-97: TRENDS ASSOCIATED WITH TILLAGE, ROTATION AND VARIETY

TK TURKINGTON1, PA BURNETT2, K XI3, GW CLAYTON1, JH HELM3, RI WOLFE1 and P JUSKIW3

1Lacombe Research Centre, Agriculture and Agri-Food Canada, 6000 C&E Trail, Lacombe, AB, T4L 1W7, Canada; 2Lethbridge Research Centre, Agriculture and Agri-Food Canada, P.O Box 3000 Main, Lethbridge, AB, T1J 4B1, Canada; 3Alberta Agriculture, Food and Rural Development, 5030 50 St Lacombe, AB, T4L 1W8, Canada

Background and objectives
The province of Alberta accounts for close to 50% of the total barley acreage in western Canada, which is estimated to be around 2.3 million ha [1]. On average, 36% of producers grow barley on barley with the proportion increasing to 75% in the western parts of central and southern Alberta. Conservation tillage has become a routine practice for many farmers in Alberta. From 1991 to 1996, the amount of summer fallow in Alberta decreased by 19%, while the acreage of zero tillage increased by 215% to 0.8 million ha [1, 2]. The combination of increased adoption of conservation tillage and the continued lack of rotation to non-hosts by some producers may increase the impact of residue-borne diseases like net blotch and scald. In 1995, 1996 and 1997, a survey of commercial barley fields under conservation and conventional tillage systems was conducted to assess the impact of tillage regime, crop rotation, and variety resistance on scald and net blotch.

Materials and methods
Surveys in 1995, 1996 and 1997 were conducted in conjunction with provincial extension personnel located throughout Alberta. Each cooperator was sent a sampling kit and survey form that were used to sample from a maximum of five fields each under conservation and conventional tillage. Leaf samples were collected from barley fields in August and then shipped to Lacombe for assessment of percentage leaf area diseased (PLAD) by scald and net blotch (net-form). Survey forms were used to classify fields according to tillage regime, variety resistance to scald and net blotch, and rotation.

Results and conclusions
A total of 99, 148 and 88 barley fields were surveyed during the summers of 1995, 1996 and 1997, respectively. Average levels of scald on the flag and flag-1 leaves remained below 4% PLAD under zero, minimum and conventional tillage in all 3 years. Net blotch severity on the flag-1 leaf was highest in 1995 (7.5% PLAD), lowest in 1997 (2.5% PLAD) and intermediate in 1996 (4.2%, PLAD). Overall, trends associated with tillage and rotation were limited. In 1996 and 1997, scald and net blotch severity were similar in fields planted to barley the previous year compared with fields planted to a non-host. In 1995, when net blotch severity was higher, disease levels tended to be highest for those fields under minimum and zero tillage. Disease severity was also increased when barley in 1995 was preceded by barley in 1994, especially for net blotch. In all 3 years, substantial levels of both scald and net blotch (>15% PLAD) did develop in fields not planted to barley for the previous 4 years. The most likely source of disease in these fields was seedborne inoculum. Variety resistance did have a consistent influence, where each disease tended to decrease as the level of resistance increased. Survey results from 1995 indicated that increased net blotch levels under zero or minimum tillage may be reduced to levels comparable to those observed under conventional tillage by the use of resistant varieties or by not planting barley in a field previously cropped to barley. Although tillage and rotation may have an influence on barley diseases, other factors such as environmental variation, seedborne inoculum and variety will also have a substantial impact.

References
1. Anon., 1997. Census of Agiculture, Statistics Canada.
2. Anon., 1993. Prairie Farm Rehabilitation Administration. Agriculture Canada.