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9 th EWRS Workshop on Physical and Cultural Weed Control 44 Samsun, Turkey, 28 – 30 March 2011 Effects of cover crops on weed populations in hazelnut (Corylus avellana L.) Husrev Mennan 1 , Dogan Isık 2 , Emine Kaya Altop 1 , Unal Budak 1 1 Department of Plant Protection, Agriculture Faculty, Ondokuz Mayis University, 55139 Samsun, Turkey 2 Black Sea Agricultural Research Institute, Samsun, Turkey The cultivated hazelnut (Corylus avellana L.) is native to the Black Sea coast of northern Europe, and Turkey is one of the few countries in the world with a suitable climate for its production. The relatively high rainfall and fertile soils of hazelnut orchards in the Black Sea region favour establishment of a wide range of annual and perennial weed species. Weed management in hazelnut orchards is necessary to eliminate competition, conserve nutrients for the trees, and improve hand harvesting efficiency. Weed management in hazelnut is a major production challenge, with glyphosate being the main herbicide used. Weed control without the use of herbicides is an expensive and time-consuming task in orchard management. Mechanical weed control methods are thought to be environment friendly and could help to prevent public pressure to reduce herbicide use in hazelnut orchards. Orchard floor management practices such as the use of cover crops either alone or combined with mechanical methods, could have significant effects on weed management in hazelnut production. Field trials were conducted from 2009 to 2010 to evaluate effects of cover crops on weed populations. The cover crop treatments consisted of Lolium perenne L., Vicia villosa Roth., Medicago sativa L., Onobrychis sativa L., Brassica napus var. oleifera L., and Brassica rapa L. Cover crop seeds were broadcast and incorporated into the soil with a shallow cultivation. All cover crops or weeds growing in the fallow plots were killed mechanically by mowing on April 24, 2010. To determine the suppressive effects of the cover crops during growing season, weed species, weed density, and total weed dry biomass were assessed at 14, 28, and 56 DAI from all plots using a 50 by 50-cm quadrat placed randomly in the plots. Additionally, visual estimates of seedling emergence were conducted at 28 and 56 DAI using a scale of 0 to 100%, where 0% represents no weed control (fallow treatment) and 100% complete weed control. After 56 DAI the entire experiment was hand weeded to eliminate further weed competition. Biomass (kg ha-1) 4000 3500 3000 2500 2000 1500 1000 500 0 L. perenne V. villosa M. sativa O. sativa B. napus B. rapa Cover crops Figure 1. Biomass production (kg ha -1 ) of cover crops prior to incorporation in 2009 and 2010. Vertical lines represent standard errors of the means. 2009 2010
9 th EWRS Workshop on Physical and Cultural Weed Control 45 Samsun, Turkey, 28 – 30 March 2011 All cover crops established well and L. perenne biomass was the greatest in both years (Fig. 1). In 2009, L. perenne, V. villosa, M. sativa, O. sativa, B. napus and B. rapa produced 2.812, 2.345, 2.143, 2.435, 2.450 and 2.158 kg ha -1 biomass, respectively. Similar results were obtained in 2010 about biomass production. When compared with the bare soil system, the cover crops reduced weed density, number of weed species that emerged, and total weed dry biomass. All cover crop treatments resulted in a decrease in the number of weed species compared to the bareground. The number of weed species was lowest at 14 DAI then increased at 28 and 56 DAI. Residues from the cover crops suppressed Urtica urens L., Convolvulus arvensis L., Chenopodium album L., Lapsana communis L., and Poa annua L. Weed dry biomass was significantly reduced in the cover crop treatments at 14 days after desiccation. Our findings indicated that cover crops suppressed many weed species in hazelnut orchard during early summer, but should not be used as the only weed control method. References Mennan, H., M. Ngouajio, D. Isık, and E. Kaya. 2006. Effects of alternative management systems on weed populations in hazelnut (Corylus avellana L.). Crop Prot. 25:835–841. Ngouajio, M., Jr, M. E. McGiffen, and C. M. Hutchinson. 2003. Effect of cover crop and management system on weed populations in lettuce. Crop Prot. 22:57–64. Ngouajio, M. and H. Mennan. 2005. Weed populations and pickling cucumber (Cucumis sativus) yield under summer and winter cover crop systems. Crop Prot. 6:521–526. Putnam, A. R., J. DeFrank, and J. P. Barnes. 1983. Exploitation of allelopathy for weed control in annual and perennial cropping systems. J. Chem. Ecol. 9:1001–1010. Reddy, K. N. 2003. Impact of rye cover crop and herbicides on weeds, yield, and net return in narrow-row transgenic and conventional soybean (Glycina max). Weed Technol. 17:28–35.
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