Özet:

There are many biotic and abiotic factors that affect the yield and quality in onion production areas. One of the biotic factors is weeds. It has been reported that crop losses due to weeds are between 20-100%. In order to develop effective and economical weed control methods in onion, which has weak competition, weeds must first be identified. This study was carried out in 2019 in order to determine the troublesome weed species, their densities and frequency of occurrence in the onion production areas of Amasya and Tokat Provinces. Surveys were conducted in a total of 57 fields, 33 in Amasya and 24 in Tokat. Surveys were conducted in different directions of the fields and at least 3 km away from each other. Counts were made randomly at each sampling point by placing 1 m2 qadrat at 4, 6, 8, 12 and 16 points respectively for fields of 1-5, 5-10, 10-20, 20-60 decares and larger fields. As a result of the surveys, 70 weed species, one of which was parasite, belonging to 25 families and 59 genera, were determined in the onion fields of Amasya Province. When evaluated on the basis of families, the families containing the most species were listed as Asteraceae (12), Poaceae (7), Fabaceae (7), Apiaceae (6), Polygonaceae (4) and Solonaceae (4). Considering the density of weeds per m2, Amaranthus retroflexus (0.82 plants/m2), Convolvulus arvensis (0.78 plants/m2), Xanthium strumarium (0.69 plants/m2), Cynadon dactylon (0.69 plants/m2), Cyperus rotundus (0.67 plants/m2) was found to be the most dense 5 species. C. arvensis (87.87%), Euphorbia prostrata (75.75%), A. retroflexus (63.63%), X. strumarium (60.60%), Chenopodium album (51.51%) were in the top five ranks according to the frequency of occurrence. 61 weed species, one of which is parasite, belonging to 26 families and 52 genera, were determined in the onion cultivation areas of Tokat Province. The families including the most species are listed as Asteraceae (9), Poaceae (8) Apiaceae (4), Polygonaceae (4), Fabaceae (4). Considering the density of weeds per m2, the 5 most common weed species are C. arvensis (1.59 plants/m2), A. retroflexus (1.53 plants/m2), C. rotundus (1.27 plants/m2), Xanthium spinosum (0.92 plants/m2), C. album L. (0.61 plants/m2). Species in the top five ranks according to the frequency of occurrence are determined as C. arvensis (83.33%), A. retroflexus (66.66%), C. album (50.00%), X. strumarium (45.83%), X. spinosum (41.66%). A total of 88 weed species belonging to 30 families were found in onion fields. As a result of the surveys, it is thought that it is necessary to investigate effective control methods against these weeds, which are problematic in terms of frequency and density.