By Steven Poindexter, Michigan State University Extension
Aphanomyces cochlioides can significantly reduce yield and quality of sugarbeets in Michigan and Ontario.
Aphanomyces root rot in the Great Lakes growing region can occasionally be a significant factor in reducing sugarbeet yields and quality when weather conditions are warm and wet. This disease can occur in two distinct stages. Infections during the seedling stage will cause a constricted black hypocotyl. These seedlings appear to hang on by a thread and often result in plant death. Chronic root rot can develop in plants affected during the seedling stage or anytime from June until harvest. Under severe situations, plant death can occur, but more often plants survive with a scabby or wrinkled constricted root (see photo).
The severity and impact of the Aphanomyces disease will depend on sugarbeet growth stage, favorable environmental conditions and genetic tolerance. It is not uncommon with early season seedling infections that significant stand loss will occur. Infections at a larger plant size often cause scaring on the roots. Sugarbeets that survive will have reduced tonnage and quality. Research that was conducted by Michigan State University Extension Sugarbeet Advancement looked at the impact of scarred roots (not rotted) on sugarbeet quality. These sugarbeets are the survivors (healed sugarbeets) of an earlier Aphanomyces attack.
Scarred and healthy sugarbeets were collected for sugarbeet quality sampling. Each quality sample contained 10 sugarbeets. Samples were mixed in 20 percent increments from no diseased sugarbeets to 100 percent of the roots having scarring. Results indicated (tables below) that Aphanomyces scarred roots will significantly affect sugarbeet quality as heavier concentration occurs. Recoverable sugar per ton was reduced up to 22 pounds per ton and 1.5 percent in sugar when all sugarbeets in the sample had significant scarring.
0% - No Beets had Significant Scarring
10% of Beets had Significant Scarring
20% of Beets had Significant Scarring
40% of Beets had Significant Scarring
60% of Beets had Significant Scarring
80% of Beets had Significant Scarring
100% of Beets had Significant Scarring
Percent of Aphanomyces scarred sugarbeets in sample
In Michigan, significant Aphanomyces may not occur every year because it is very environmentally dependent. Early planting under cool soil condition will greatly minimize the disease. Seed treated with Tachigaron will also help safeguard against early seedling infections. Selecting varieties with good Aphanomyces tolerance is very important for season long control and can pay good dividends when later season infections occur.
Source : msu.edu