Date of Award

2007

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

Renae Moran

Second Committee Member

David Handley

Third Committee Member

Mark Hutton

Abstract

The response of red raspberry (Rubus idaeus) plants to the loss of flower buds through the feeding and oviposition activities of the strawberry bud weevil (Anthonomus signatus), and the potential impact of this bud loss on fruit yield and quality, was studied through greenhouse and field experiments. With two cultivars of raspberry (‘Killarney’ and ‘Encore’) grown in a greenhouse, manual clipping of flower buds to simulate strawberry bud weevil (SBW) damage demonstrated that the impact on yield is dependent upon the number of buds lost, their position on the inflorescence and cultivar. In a 2006 greenhouse study, removal of primary flower buds resulted in an increase in fruit size from secondary buds for both varieties, suggesting yield compensation. However, removal of secondary or tertiary buds did not result in any increase in the size of fruits from primary flower buds. Removal of two secondary flower buds from every lateral on a cane did not have a significant impact on total yield (weight). Clipping all buds except the terminal cluster reduced total yields by 76%. Clipping all of the buds except the primary bud on each lateral decreased the total yields by up to 93%. When all buds other than primary buds were removed, size of fruits from primary flower buds increased slightly for ‘Encore’ but not nearly enough to compensate for the loss of yield compared to the control (no buds removed). Flower bud clipping treatments in a field experiment were not characterized by any significant impact on yield in ‘Reveille’ raspberry. Up to 31% of the flower buds were removed from canes without significantly affecting fruit weight, fruit number or fruit size. However, wide variation within treatments as a result of environmental factors, including winter injury and shading, seemed to have more of an impact on the treatments than clipping buds. Also, the buds were all clipped on the same day, which is not representative of actual SBW damage in the field and may, therefore, not have produced a response characteristic to SBW damage. In two sequential field surveys of fourteen commercial raspberry fields in Maine, up to 22% and 59% damage to flower buds was found in 2005 and 2006, respectively. Flower buds on raspberry plants were concentrated near the base of the cane, whereas damage caused by SBW was distributed over the canes; there was more damage present where there were more buds. The data suggests that SBW is an important pest in raspberries in Maine. The most effective scouting method for estimating actual bud damage in the field was visual estimates of clipped buds. Other scouting methods, such as the sticky traps, pheromone traps, sweep nets and beat cloths to monitor live clipper, were not effective at predicting actual bud damage. These studies have shown the need for development of effective monitoring methods for SBW in raspberry fields in Maine, and a better understanding of the ability of the raspberry plants to compensate for bud damage.

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