The impact of non-chemical weed control methods on the disease occurrence in the organically grown winter oilseed rape crop

Abstract

Oilseed rape cultivation under organic farming conditions presents a high risk of increased incidence of weeds, pests and diseases, resulting in low rapeseed yielding capacity. The current study aimed to estimate the effects of non-chemical weed management methods: thermal, mechanical and self-regulation (natural weed/crop competition), on the incidence of fungal diseases in winter oilseed rape (Brassica napus L.) stands and on rapeseed yield in the organic production system. A field experiment was conducted in 2014–2017 at Aleksandras Stulginskis University’s Experimental Station. The soil of the experimental site is Endocalcaric Endogleyic Luvisol (LV-can.gln). Under less favourable conditions for the occurrence of phoma stem canker, both thermal and mechanical weed control methods were shown to inhibit the spread of the disease in the oilseed rape crop compared with the self-regulation weed control treatment. However, under the conditions conducive to the spread of phoma stem canker, only mechanical weed control method in combination with the bio-preparations proved to be effective. In 2015 and 2016, the lowest incidence of the verticillium wilt was recorded in the oilseed rape plots where weeds had been managed by steaming. In 2017 significantly, from 2.3 to 3.3 times lower number of verticillium wilt-affected stems was determined in the mechanical weed control plots as compared with that in the plots where other weed control methods had been applied. Application of bio-preparations decreased the number of verticillium wilt-affected stems by on average 11.1– 15.6%. The lowest incidence of dark leaf and pod spot was established in the plots where weeds had been controlled by water steam and no bio-preparations had been used. The bio-preparations were found to increase the severity of dark leaf and pod spot on oilseed rape siliques by on average 13.1–79.4%. Significantly the highest rapeseed yield in 2015 and significantly higher compared with self-regulation in 2017 was recorded in the mechanical weed control treatment, while in 2016 the highest rapeseed yield was established in the self-regulation treatment applied with the bio-preparations. In 2017, the verticillium wilt severity in the winter oilseed rape crop was found to negatively, strongly and statistically significantly correlate with rapeseed yield (r 2 = 0.69, P < 0.05).