Optimization UV-C strategy to control powdery mildew in strawberry
Complementary biological spray strategies
The investment of a UV-robot is a big step for commercial growers. In autumn 2019 Research Centre Hoogstraten investigated the possibility of complementing the UV-C strategy with biological sprayings so the grower can lower the frequency of UV-C application and use the UV-robot on a larger scale. Weekly application of biological sprayings have been complemented to the UV-C strategy (‘UV-C + Bio’). Next to this we compared this complemented biological spray strategy with the conventional strawberry IPM strategy (‘IPM’), a biological strategy (‘Bio’) and a chemical reference (‘Chem’). Table 1 gives an overview of the spraying scheme for the different objects.
Repetition gives better control than increasing the UV-C dose
The trial consists of three different UV-C dosages. A dose of 110 J/m2 applicated one time a week (Wednesday) or three times a week (Monday, Wednesday and Friday) was compared with a weekly UV-C application of 220 J/m2 on Wednesday.
Figure 1 shows a mildew assessment on strawberry plants. Three times a week UV-C (complemented with biological sprayings) gave better control of powdery mildew in comparison with the weekly UV-C application. So to have good mildew control, it’s important to irradiate the mildew fungus on a regularly base. The effect of weekly UV-C application with a dose of 220 J/m2 is not significantly different from a weekly UV-C application of 110 J/m2. The UV-C strategy (complemented with biological sprayings) outshines the exclusively biological spraying strategy. Application of the IPM strategy or the UV-C strategy equally controls powdery mildew. Solely chemical sprayings gave a mildew control comparable with the three times a week UV-C application of 110 J/m2 complemented with biological sprayings. Important to mention is that the plants from the chemical object were treated with seven different chemical spraying agents. Which leads to a higher amount of active ingredients on the harvested fruits.
UV-C application complemented with biological sprayings leads to better mildew control in comparison with UV-C application without complementary biological sprayings. Treating the plants one time a week with UV-C light (110 J/m2) complemented with biological sprayings is not equally effective as three times a week UV-C application. But differences are small, so maybe two UV-C applications a week complemented with biological sprayings is as effective in controlling powdery mildew in comparison with three times a week UV-C application under high disease pressure.