Researches on the determination of prevalences, densities of weed species in important onion (Allium cepa L.) production areas in turkey with germination biology and weed control of some of them

This study aimed to determine the weed species, their incidence and density (plant/m2), the fungal agents on the weeds, the 3 weeds, which are the main harmful ones, in the onion production areas of Ankara, Çorum, Amasya and Tokat provinces, which are in the top ranks in terms of planting and production. The study was carried out in 2019-2021 with the aim of determining the seed biology and control possibilities of the weed species. In the survey studies, 135 fields were sampled in 4 provinces and Convolvulus arvensis L, Amaranthus retroflexus L. and Xanthium strumarium L. were found to be important weeds. Fungal disease agents on weed species collected from the same sample points were determined. Within the scope of germination biology, dormancy breaking, germination temperatures (minimum, optimum and maximum) and depth studies were carried out for the seeds of these weeds. Laboratory studies were carried out in Adana BMAE, Ankara ZMMAE, Tokat GOP University Plant Protection Department Phytopathology and Erciyes University Plant Protection Department Herbology Laboratory. Field trials were established at Gölbaşı İkizce Research and Application Farm, affiliated to Ankara TBMAE. As dormancy breaking, the best results for 0-month-old seeds of A. retroflexus, compared to the 'Control', were in hot water bath (40 oC 60 min) with 86.63%, and for 4th month seeds were the application of keeping in sulfuric acid (5, 3, 15 min) with 68.3%, 65.8% and 60.78%, respectively. The best dormancy breaking method of C. arvensis was the tip breaking method with 95.8% germination rate for 0-month seeds and 100% germination rate for 4-month-old seeds. It was determined that there was 4.95% germination for 0-month-old X. strumarium established with fruit with two seeds inside, and 22.43% germination for 4-month-olds and 72 hours of standing in stagnant water. The minimum germination temperature for A. retroflexus was determined as 15 oC, the optimum temperature was 35 oC, the maximum temperature was 40 oC, the minimum temperature for C. arvensis was 10 oC, the optimum temperature was 35 oC, and the maximum temperature was 40 oC. No germination was obtained at the specified temperatures in the seeds of X. strumarium established with its fruit. Optimum germinations were found at 2 cm with a germination rate of 78.64%, at 5 cm with a germination rate of 23.96% for A. retroflexus; at 2 cm with a germination rate of 47.96%, at 5 cm with a germination rate of 39.94% for C. arvensis; at 2 cm with germination rate of 100%, at 5 cm with germination rate of 74.65% for X. strumarium. Within the scope of chemical control, chemical control+mechanical control combination studies, for A. retroflexus weed; it has been determined that Glyphosate+Oxyfluorfen, Pendimethalin+Oxyfluorfen, Mesotrione+Nicosulfuron and Oxadiazon+Tepraloxydim (*Bentazone+2 hand hoe) applications provide 100% effect. The most effective application for C. arvensis has found, respectively; weed-free control plot (90.33%), 3 hand hoeing (88.66%) applied on the 20-40-60th day after emergence, Glyphosate isopropylamine salt+Oxyfluorfen (81.66%) application and Pendimethalin+Oxyfluorfen (74.50%) application and statistically no difference were found among them. For X. strumarium weed, it was determined that weekly weed intake and 3 hand hoe applications on the 20-40-60th day after emergence of the cultivated plant were with 100% effective. In yield studies, the best yield was obtained from weed-free parcels in 2020 and 2021. The ones that give the best results after weed-free plots are 3 hand hoe (on the 20th, 40th and 60th days) after emergence in 2020, Pendimethalin before emergence+Oxyfluorfen after emergence, Bentazone+2 hand hoes after emergence (on the 20th and 40th days), 3 hand hoe after emergence (on the 20th, 40th and 60th days) and Pendimethalin before emergence+1 hand hoe (on the 20th day) in 2021; and there was no statistical difference between them. The average highest onion diameter (5.78 cm) and plant height (52.5 cm) were obtained from the weed-free plots. The weed-free plot was followed by 3 hand hoes with the highest onion diameter (5.21 cm) and plant height (50.46 cm).