Efficacy of Stagonospora cirsii S-47 against perennial sowthistle in potato crops

Potato ( Solanum tuberosum L.) is a crop that needs biological control of perennial weeds (for example, perennial sowthistle Sonchus arvensis L.) due to the insufficient assortment of post-emergent chemical herbicides. The fungus Stagonospora cirsii J.J. Davis from the VIZR culture collection (All-Russian Institute of Plant Protection), being a producer of herbicidal metabolites, is able to infect Sonchus arvensis plants. In the present work, the possibility of using strain Stagonospora cirsii S-47 to control perennial sowthistle in small-scale field experiments was shown for the first time. The aim of the study was to evaluate the effectiveness of the use of Stagonospora cirsii S-47 in the form of chopped mycelium against perennial sowthistle on potato plantings in small-scale field trials. The trials were conducted during the growing seasons of 2020 and 2021 at the experimental field of the All-Russian Institute of Plant Protection (VIZR, Leningrad Province). Experiments were conducted on plantings of potatoes ( Solanum tuberosum L.) of Nevsky variety belonging to the medium-early group. Soil of the experimental site is sod-podzolic, loamy, with a humus content in the arable layer of 3-4 %, pH 6.3. The soil was ploughed in the autumn, and in the spring, the site was disked, cultivated, and furrows were cut. The planting rate of tubers was 25 per ha. Fertilizers were not applied. To exclude the influence of non-target objects on the results of the experiments, the treatment of the experimental plots with the herbicide Gezagard (2.0 l/ha) (OOO Syngenta, Russia) was carried out before the emergence of potato plants. The starter inoculate of Stagonospora cirsii S-47 was obtained by culturing the fungus for 3 days in liquid sucrose-soybean meal nutrient medium. The biomass was grown in a glass fermenter with a working volume of 5 l (Applikon Biotechnology, the Netherlans). The fermentation medium (4.8 l) was inoculated with 200 ml of the starter culture. After 6 days, the raw biomass was separated from the culture liquid by centrifugation (4000 rpm, SL40, Thermo FS, USA) and weighed. A 0.01 % solution of Tween 80 was added to the raw mycelium to a concentration of 50 g/l, and the mycelium was chopped with a blender (MaxoMixx, Bosch, Germany) for 1 min. Potato plantings were treated using a Mesto RESISTENT 3610 manual knapsack sprayer (MESTO Spritzenfabrik Ernst Stockburger GmbH, Germany) in accordance with the experimental scheme. The herbicide Agritox (1.2 l/ha; Nufarm GmbH & Co. KG, Australia) containing 500 g/l MCPA (2-methyl-4-chlorophenoxyacetic acid) in the form of a mixture of dimethylamine, potassium and sodium salts was used as a standard. We used the treatments: 1 - S. cirsii S-47 (50 kg/ha; working fluid consumption was 1000 l/ha), 2 - S. cirsii S-47 (100 kg/ha; 2000 l/ha), 3 - S. cirsii S-47 + Agritox (50 kg/ha + 0.6 l/ha; 1000 l/ha), 4 - Agritox (0.6 l/ha; 300 l/ha), 5 - Agritox (1.2 l/ha; 300 l/ha), 6 - untreated control. During the treatments, the height of potato plants was 10-15 cm, and perennial sowthistle plants were in the stages from rosette to stalking, not exceeding 10 cm in height. The counts were performed on day 14 and day 28 after treatment by quantitative weight method. Biological efficacy (BE) was calculated vs. untreated control. Potato tubers were harvested manually from each plot to quantify the yield. In the absence of extreme weather conditions, the application of 50 kg/ha of S. cirsii mycelium significantly (by 53.9-59.2 %) reduced the weight of perennial sowthistle plants. However, the fungus did not completely eliminate the weed and was less effective than the herbicide Agritox at a dose of 0.6 l/ha. A twofold increase in the rate of application of S. cirsii led to an increase in its effect on the number of perennial sowthistle by 13 % on average. The use of S. cirsii in combination with Agritox (0.6 l/ha) improved treatment efficiency by an average of 15 % compared to the use of the herbicide alone. This made it possible to reduce the amount of the applied chemical by half without reducing the effectiveness of perennial sowthistle suppression. In 2020, the use of microbiological and chemical products contributed to an increase in crop yield by 4.7-10.1 %. The statistically significant (р function show_eabstract() { $('#eabstract1').hide(); $('#eabstract2').show(); $('#eabstract_expand').hide(); }