The early part of the growing season was drier, meaning that disease pressure had been lower, says Nick Lewis, Commercial Technical Adviser for Bayer in Kent and Sussex.
“Higher temperatures and / or humidity favours Botrytis development, so the recent weather should put strawberry growers on alert,” he says.
In addition, as the season progresses the covers over some strawberries tend to be closed more, similarly creating a more favourable environment for disease.
As with all crops regular monitoring and using risk assessment tools will help judge whether treatment is necessary. “Risk is heavily dependent on where the crops are at in their life cycle,” says Mr Lewis. “For Botrytis the key timings for fungicides are around flowering. Fungicides are more effective when used preventatively rather than curatively, so it is important to use them either just before infection, or in the very early stages.
“So paying attention to which crops are about to flower, as well as the favourability of recent weather for disease incidence will all help decision making. Growers should also make use of predictive modelling tools where available so that they’re best prepared for the need to spray.”
Botrytis fungicide programmes require careful planning to reduce the risk of resistance building up, as well as achieving the necessary level of protection.
Start with a strong protectant, such as Luna Sensation (fluopyram + trifloxystrobin), suggests Mr Lewis. “Although it does have some curative activity on powdery mildew, it works best as a protectant for both this disease and particularly for Botrytis, so timing is important – typically from first open flowers for Botrytis control.”
However, only two applications of Luna Sensation are allowed in one season for resistance management purposes, so it should be alternated with products with different modes of action, such as Teldor (fenhexamid) and the biological fungicide Serenade ASO (Bacillus subtilis strain QST713).
Serenade offers a good break between chemical applications when used in programmes, especially in periods of lower disease pressure, he explains. “The bacillus in Serenade has been specially selected to produce high levels of active biological compounds during production. When applied to the plant, these disrupt the cell membrane of the fungus, preventing spore germination and growth. Because it’s a physical action, this mechanism makes it difficult for fungi to develop resistance, which makes it very useful.”
To get the best effect from Serenade however, it needs careful consideration. “Use Serenade when disease pressures are lower to make the most of its protectant value, saving your conventional chemistry for higher pressure periods. Because it is contact acting only, good coverage on the leaf surface is important, so the use of a spreader or wetter can help.”
Luna Sensation is a combined new-generation SDHI and strobilurin fungicide for protected strawberries.