A robot prototype for manual application of UV-C in vertical crops was constructed for the development of a control strategy in cucumber. This machine allows us to drive at different constant speeds through the crop, so a correct UV-C dose can be applied.
Two application strategies are optimized to control powdery mildew in cucumber:
- A preventive application to avoid germination of the powdery mildew spores and slow down powdery mildew growth.
- A curative application to destroy the powdery mildew in the greenhouse including highly infected leaves.
To optimize the application scheme, different doses of UV-C and application frequencies were tested.
High doses of 20 and 40 mJ/cm² have shown promising curative effect on powdery mildew, but also some damage on the plant and fruit. When applied for three to five times in a week, these doses result in smaller young leaves and faster yellowing of the old leaves. Also some of the fruit is visibly damaged. Even when applying for only 3 times as a curative treatment, the effect of 40 mJ/cm² is seen on the plant and fruit. In a following experiment, preventive treatments will be followed by only one dose of 40 mJ/cm² to see if the negative effects of the UV-C light are still visible.
Low doses of 5 and 10 mJ/cm² show lesser but still significant effect on powdery mildew, and have no problematic effect on plant or fruit. These doses do not entirely cure powdery mildew in these experiments with high disease pressure, but are potentially very useful to prevent the disease and kill off the spores when there is only a lower disease pressure.
Frequency testing did show a difference between applying 3 or 5 times a week, but the added value of applying 5 times a week is minimal. As one robot will have to treat as many hectares as possible, it is very questionable if the extra effect will cover the extra expenses.