Organic seed treatments with essential oils to control ascochyta blight in pea

Ascochyta blight is the most important disease worldwide for pea (Pisum sativum L.) and a major threat for its cultivation, especially in organic farming. Laboratory tests and field trials in two sites (Lodi and Rome, Italy) were carried out on three cultivars for two consecutive seasons to develop organic seed treatments with essential oils against the ascochyta blight fungal complex. Tea tree, thyme and clove oils were applied to artificially infected seeds by either submersion or spray treatment, the latter adding pinolene as a natural film coating. Oil phytotoxicity and fungicide activity were tested in the laboratory by recording the number of germinated and infected seeds, respectively. Plant establishment was recorded in field trials. No effect of the inoculation/treatment process was observed on laboratory seed germination during the first season, and only slight effects in the second one. Laboratory results indicated significant activity of the oils in reducing fungal infection on seeds. The submersion treatment showed more consistent efficacy across the two seasons than the spray application. The spray treatment, instead, gave better results in field trials in terms of established plants compared to the submersion treatment. Some damage of seed coats due to imbibition might have been a side effect of the latter treatment. The essential oils appear to be an interesting tool for developing environmental-friendly seed treatments to control ascochyta blight in organic pea cultivation, without substantial differences between the tested oils in each season. Pinolene was a feasible addition to enhance the effectiveness of oil application in spray treatments.