Avoiding the Arms race……. a multi faceted approach : a case study with strawberry powdery mildew

trawberry Powdery Mildew (Podospheara aphanis) is the most feared disease of Strawberries, causing between 20% and 70% yield loss per annum. A 20% yield loss causes a financial loss of £56,800 million a year. In order to control this disease many growers spray fungicides every 7 to 14 days for 6 months, up to 20 sprays a season. The number of active ingredients available to growers is falling. The ‘arms race’ is generally either between the fungus and the resistance genes in the host, or between the fungus and the fungicides used. Work at the University of Hertfordshire since 2004 shows that a multi faceted approach is important to keep disease levels down to a minimum and prevent either arms race developing, even when disease pressure is high. The disease usually enters the farm on plants from the propagator or, where crops are grown over the winter, the disease overwinters as chasmothecia on dead leaves from the previous season. Both can be controlled by a clean up spray early in the season. Whilst some varieties are tolerant to the disease, the choice of variety is dictated by supermarket preferences rather than disease resistance. Disease conducive environmental conditions develop 8 to 10 weeks into a growing season, and so that the use of a real time decision support system that predicts accurately when spraying is needed enables disease control with fewer sprays reducing the selection pressure on the fungus. Finally the addition of a silicon nutrient in the fertigation tubes throughout the season enhances the passive defence pathway therefore delays the start and build up of the epidemic. This multi faceted approach enables growers to control strawberry powdery mildew with fewer fungicide sprays thus reducing the likelihood of an ‘arms race’ developing.