Sherri Roberts PAg Crops Extension Specialist, Weyburn
Are your normally dense, well-seeded flax fields showing gaps in the rows and large open spots within the field? It may not be due to the spotty emergence issues that we have been seeing in other crops this year.
As one drives around the province this year, you may notice that there are many flax fields showing signs of poor emergence and possible improper planting techniques. Is this really the cause? Closer examination of the fields, including lab analysis of the affected plants, is revealing Rhizoctonia solani has attacked many of these fields.
R. solani is a plant disease that causes fungus with a host range comprised of more than 165 different host plants, including various weed species. R. solani survives as a composite of strains that differ in host range and disease-causing ability. Strains attacking sugar beets and legumes such as alfalfa and field peas also attack flax. R. solani attacks flax at an early stage of development, destroying the root and causing thinning or, in severe infection, death of seedlings. It also causes root rot symptoms, which appear in plants after the flowering stage.
According to the Flax Council of Canada, seedlings with inadequate vigour tend to be negatively affected by the previous season's growing and harvest conditions, as well as by soil pathogens. Seedlings produced from damaged seed may germinate very slowly and may also have injured root tips, broken or cracked cotyledons, split hypocotyls, twin radicles, radicles trapped inside the seed coat and roots that are blunt, broken, long and spindly, or gnarled and distorted. To reduce the risk of R. solani infection, have your seed vigour tested.
Improper seed handling can increase a flax crop's susceptibility to R. solani infection. The flax seed coat is fragile and can be damaged mechanically when flax is threshed at excessively high cylinder speed, low concave clearance, combined when seed is too dry, or from a combination thereof. Large-seeded varieties may be more prone to cracking than small-seeded varieties. Proper combine adjustment at harvest can reduce this factor. Yellow-seeded varieties are more prone to cracking, which renders them more susceptible to seedling blight and root rot than brown-seeded varieties. Differences in susceptibility of flax cultivars has been seen in studies conducted in Egypt.