Graduate Thesis Or Dissertation


Chemical Control of Suckers in Hazelnuts (Corylus avellana): Comparing Herbicide Efficacy, Spray Nozzle, and Carrier Volume Public Deposited

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  • Hazelnuts (Corylus avellana) produce a prolific growth in the base of the trunk and roots, known as suckers, which are often removed in order to promote the development of a single trunk tree. Sucker removal facilitates cultural practices and mechanized operations, such as weed management and harvest. Sucker presence can be a source of pest and diseases, impact on fruit/shoot ratio, and reduce hazelnut yield. Thus, the removal of suckers is a crucial practice in hazelnut crop management. Sucker removal can be done manually; however, it is time-consuming and labor-intensive. Chemical control is a cost-effective option, and it is a frequent method used by farmers in Oregon. Although different herbicides are registered for hazelnut sucker control, few studies provide information regarding the efficacy of these herbicides. Also, the available information is outdated. The objective of this study was to compare the efficacy of registered herbicides, alone or in combination, for sucker control in hazelnuts. Two long-term trials and four short-term trials were conducted in 2017 and 2018 in commercial orchards in Western Oregon. Following label recommendations, studies started when suckers reached 15 cm. Fifteen treatments included: 2,4-D, carfentrazone, glufosinate, paraquat, pyrafluflen, and saflufenacil alone and in combination. Long-term trial treatments were reapplied after 28 days, in a total of four applications. In the short-term trials, only one application was made, and trials were terminated after 28 days. Assessments included: visual control, height, biomass, and cross-sectional area. After the fourth application of the long-term trial, treatments containing 2,4-D, glufosinate, or paraquat resulted in 80% or greater sucker control; sucker height was at least 67% smaller, and biomass was 87% inferior compared to nontreated control. Carfentrazone and saflufenacil, alone, reduced sucker biomass by 58 and 67%, respectively, but were not effective as 2,4-D. Short-term studies confirmed long-term results. Results also suggest that multiple applications are needed during the entire growing season, emphasizing the importance of effective herbicides in hazelnut sucker management. Herbicide efficacy can be affected by nozzle type and carrier volume. Frequently, the use of nozzles that produce larger droplets is associated with less coverage and, consequently, decreases of herbicide efficacy. However, the literature has shown that, in some cases, it is possible to keep herbicide efficacy while using a nozzle that produces larger droplets. Nozzles with air-induction technology are used to prevent the off-target movement of herbicide. Growers often increase carrier volume to compensate for the increase in droplet size. The objective of this study was to compare carrier volume and nozzle type for the efficacy of 2,4-D and glufosinate. Six field trials were conducted in Western Oregon, including two long-term trials and two short-term trials. Treatments included: manual removal, 2,4-D at 1,060 g ai/ha, and glufosinate at 1,150 f ai/ha. Two different nozzle types (flat fan and TTI) and two different carrier volume (187 L/ha and 374 L/ha) were tested for both herbicides. Assessments included visual sucker control, height, biomass, and cross-sectional area. Results of long-term trials suggest that no difference was noticed between 2,4-D and glufosinate, and both resulted in excellent sucker control (>90%) after the fourth spray. Also, no difference was noticed between the two types of nozzles or carrier volume. Thus, both herbicides can be used for sucker control, and 187 L/ha is recommended since it can save water and refilling time compared to 374 L/ha. TTI nozzles are preferred over flat fan nozzles since drift risk is reduced while herbicide efficacy is maintained. This study provided relevant information for a more efficient and safer chemical sucker control.
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