The effects of water steam on weeds and fungal diseases in the stands of onion

Abstract

The yield of common onion bulbs in our study ranged from 4.06 to 5.41 kg m-2. A statistically significantly higher yield of onion bulbs was produced in the treatment where steaming had been applied all over the plots compared with the hand-weeded plots. The experiment was conducted in the fields of farmers in Kaunas (in 2012), Vilkaviškis (in 2013) and Rietavas (in 2014) districts, Lithuania. The aim of the study was to ascertain the effects of water steam as a weed and fungal disease control method in the common onion (Allium cepa L.) stand. The trials were carried out according to the following design: 1) weeds were hand-weeded three times: the first hand-weeding was performed after mass emergence of weeds, 9–11 days after planting of onions; the second and third hand-weeding operations were carried out after emergence of weeds at a 2–3 leaf growth stage of weeds; 2) thermal weed control using water steam was carried out twice per growing season with the duration of weeds and onions exposure to steam of 2 seconds; thermal weed control was applied on the entire experimental plot, i.e. all over the plot, without protection of onion plants against exposure to steam; 3) thermal weed control using water steam was carried out twice per growing season with the duration of weed exposure to steam of 2 seconds. Thermal weed control was applied only in the inter-rows at a seedling stage of weeds. The impact of water steam on the onion bulbs was partial. The findings of the current study suggest that the application of water steam all over the trial plots, twice per growing season gave the most effective control of weeds in the stands of onion. Water steam treatment was found to reduce the occurrence of fungal diseases in the onion stand. The severity of downy mildew in the plots treated with water steam decreased by 52.5–739%, compared with the control plots. The steam treatment all over the trial plots reduced the severity of white rot of onion by 43.5–46.9%. Steaming all over the plots diminished the onion neck rot infection level on onion plants by 68.0–86.1%, while inter-row steaming reduced the disease pressure by 33.3–83.7%.