Institut für Phytomedizin

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/14

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Enhancing weed suppression in plants by artificial stress induction
(2025) Merkle, Michael; Petschenka, Georg; Belz, Regina; Gerhards, Roland
Various plant species from the Poaceae, Cannabaceae, and Brassicaceae families are used as cover crops to suppress weeds and volunteer crops through competition and allelopathy. This study examined the effects of artificially induced stress on the physiological processes, total phenolic content (TPC), and allelopathic potential of the plant species Avena strigosa, Cannabis sativa , and Sinapis alba at an early growth stage with the aim to increase their weed suppression abilities. Stress was induced at the 3–4 leaf stage in greenhouse-grown plants via harrowing, methyl jasmonate (MeJA) application, insect stress simulation, or a combination of insect stress and harrowing. Maximum quantum yield of photosystem II and shoot dry matter in the three plant species were only minimally or not affected a few days after treatment (DAT). Insect stress caused visible symptoms on treated leaves in all plants. The TPC in the shoot extracts of combined stress-treated C. sativa and insect-stressed S. alba was significantly higher by 1.7 and 1.9 times, respectively, five DAT compared to the shoot extracts from untreated control plants. Additionally, laboratory bioassays with aqueous shoot extracts from the untreated and treated plants were conducted to identify changes in allelopathic potential within the shoot tissues. The application of shoot extracts from MeJA-treated C. sativa and S. alba resulted in the lowest seed germination rates for the two weed species Alopecurus myosuroides and Stellaria media , as well as for the volunteer wheat Triticum aestivum , which were up to 65% lower 10 DAT compared to seeds treated with shoot extracts from non-stressed plants. However, the root-suppressing effect of the shoot extracts on weeds was not influenced by the stress treatments. This study reveals that artificial stress induction can be a suitable management strategy to enhance weed and volunteer cereal suppression in plants in an early growth stage but may vary between stress types and plant species, and requires further optimization and field testing.
Sensor-guided mechanical weed control in transplanted lettuce and cabbage
(2025) Gerhards, Roland; Spaeth, Michael; Heyn, Alexandra; Saile, Marcus
Effective weed control is extremely important in vegetable production because weeds affect yield and quality of vegetable crops. Usually, only combinations of preventive and direct weed control methods can sufficiently suppress weeds. Therefore, costs for weeding are much higher in vegetables compared to most arable crops. Due to restrictions for herbicide use in vegetables, alternative and efficient direct weeding methods are urgently needed. Six field experiments with transplanted cabbage and lettuce were conducted in Southwestern Germany to quantify the weed control efficacy (WCE) and crop response of sensor-guided mechanical weed control methods with different degrees of automation. A camera-guided inter-row hoe with automatic side-shift control alone and combined with intra-row finger weeders and a camera-guided intra-row hoeing (robot) were compared to standard mechanical weeding, a broadcast herbicide treatment and an untreated control. Weed densities prior to treatment averaged 58 plants m −2 in cabbage and 18 plants m −2 in lettuce. Chenopodium album, Amaranthus retroflexus, Thlaspi arvense, Solanum nigrum and Digitaria sanguinalis were the dominating species. Until harvest, 80% weed coverage was measured in the untreated plots of cabbage and 28% in lettuce, which caused 56% yield loss in cabbage and 28% yield loss in lettuce. The highest WCE was achieved with the robot (87% inter-row and 84% intra-row) The broadcast herbicide treatment achieved 84% WCE for both inter-row and intra-row areas. Conventional inter-row hoeing had the lowest WCE of 73% inter-row and 35% intra-row. Camera-guided inter-row hoeing increased inter-row WCE to 80% and intra-row WCE to 56%. Finger weeding increased intra-row WCE in lettuce and cabbage to 54% with conventional hoeing and 62% with camera-guided hoeing. Camera-guidance reduced crop plant losses by 50% (from 9.1 to 4.5%) and increased crop yield by 13% compared to conventional hoeing. This study highlights the benefits of camera-guidance, AI-based weed detection and robotic weeding in transplanted vegetable crops.

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