Lettuce Drop Research Articles

Survival of sclerotia of Sclerotinia sclerotiorum and effects of cultivation practices on disease

The effect of burial on survival of sclerotia of Sclerotinia sclerotiorum and production of apothecia was studied in the Bairnsdale and Mildura districts of Victoria. The effect of origin of sclerotia (within bean stems or exposed) on their survival was studied at Bairnsdale. More sclerotia survived at the soil surface than when buried at Bairnsdale (6%) and Mildura (32%). Tests on survival of sclerotia from beans (Bairnsdale) and lettuce (Mildura) at both Bairnsdale and Mildura showed that 50% more sclerotia survived in the Mildura environment. Burial of sclerotia increased the production of apothecia by 40% at Bairnsdale compared to sclerotia on the soil surface, and decreased the production by 61% at Mildura. Sclerotia formed within or outside bean stems were tested for survival when protected or unprotected by bean straw. The most (11%) sclerotia survived when protected in bean straw or when the sclerotia had originated from within stems. In addition the effects of cultivation practices and benlate on white mould of beans and drop of lettuce were studied in the Bairnsdale and Mildura districts. The simulation, with wheat grain, of effects of cultivation on distribution of sclerotia in soil showed that harrowing left grain at 0–5 cm whereas ploughing buried grain at 15–20 cm. Ploughing and benlate each reduced disease in lettuce by 20% compared with either harrowing or unsprayed plants. The combined effect of ploughing and benlate reduced disease by 37%, which suggests that additional control of lettuce drop can be achieved by growers who use this combination of disease management practices rather than chemical control alone.

Sclerotinia minor on lettuce: progress of an epidemic

SUMMARYAnalyses of disease progress curves of lettuce drop, caused by Sclerotinia minor, indicate that early infected plants sometimes provide inocula for later secondary spread within the crop, there sometimes being evidence of plant‐to‐plant spread. It is suggested that primary infections are attributable to aerially dispersed ascospores, produced by germinating sclerotia which are soil‐borne, and that secondary plant‐to‐plant spread is associated with mycelial inocula.