Here in North Yorkshire, Stockbridge Technology Centre (STC) is hard at work investigating the efficacy of UVC light for incorporation into existing Integrated Pest Management strategies primarily for the treatment of Basil Downy Mildew (caused by the fungal pathogen Peronospora belbahrii), but also delving into the effects of UVC light on Botrytis and both pests and beneficials.
STC has utilised a static system to dose the crop with UVC light, with the dose determined by both the distance from the light fixture and the length of time the light is illuminated. Firstly, we determined a non-phytotoxic range of UVC doses in the treatment of basil across a range of growth stages with a focus on night-time treatments (Fig. 1). It was found that doses up to 67 mj/cm2 caused no observable phytotoxicity nor effect on relative leaf chlorophyll content suggesting maintenance of photosynthetic capability. Doses of 167 mj/cm2 and above, however, caused observable phytotoxicity (Fig. 2). Interestingly, initial data has suggested that basil treated at a younger stage is more tolerant to a higher dose of UVC.
Further experimentation was conducted to determine the effect of UVC light in the treatment of Basil Downy Mildew. Initial experimentation tested the effect of UVC light treatment at a range of non-phytotoxic doses and growth stages following artificial inoculation of the crop.
The selected range of doses was firstly assessed for efficacy, dosing plants with UVC once a week. The disease came through following treatment across the dose range within 14 days of having received two doses of UVC. The data is currently being analysed to determine if there was any statistical effect between the doses on disease levels. Work is also on-going to test the treatment of the artificially infected crop twice and three times a week across the different growth stages.
A small in vitro non-replicated detached leaf assay laboratory experiment was also conducted directing the non-phytotoxic doses directly to the underside of basil leaves (Downy Mildew sporulates on the underside of the leaf), applying doses once, twice and three times a week. Following UVC treatment Basil Downy Mildew continued to sporulate in vitro (Fig.3).
Throughout the coming months, we will continue to investigate the effects of non-phytotoxic UVC light doses on botrytis, pests (Fig.4) and beneficials, and on crop protection spray residues in basil crops.