It is not surprising that sclerotinia stem rot disease levels differ from field to field even if fields are in close proximity. Sclerotinia disease level is very dependent on the microclimate within the field. Moist weather conditions (ie. frequent rainfall or high humidity or heavy dews) promote disease development but factors that result in moisture-laden canopies can also promote disease development. Factors that can influence canopy moisture levels and subsequently sclerotinia incidence and severity include:
Variety selection – higher disease levels in varieties that have more leaf area, more branching or are taller or have poor standability; lower levels in genetics with some tolerance to stem rot
High fertility levels – higher nitrogen rates or the addition of manure results in heavier, more dense and thick canopies
Degree of lodging – lodged crops tend not to dry out readily and facilitate disease spread with increased direct plant-to-plant contact or contact with diseased plant debris
Seeding date – influences maturity and can result in flowering stage coinciding with weather conditions conducive to disease infection and development
High plant populations – good for competition with weeds and earlier, more uniform maturity but tend to reach canopy closure earlier resulting in moist canopies; plus thicker plant populations usually result in plants with smaller, weaker stems that are more prone to lodging
Click here to read more information on sclertotinia stem rot in last week’s Watch.