Establishing the extent of direct and indirect damage caused by fruit flies in wine grapes

Project Number

Project title
Establishing the extent of direct and indirect damage caused by fruit flies in wine grapes.

Project leader
Baard, C W L

FruitFly Africa

Team members
Baard, C W L
Barnes, B N
De Waal, J
Addison, P
Van Schalkwyk, H
Visser, H

Completion date

Project description
It is internationally accepted that the best way of mitigating risks associated with mobile insectpests is through the implementation of area-wide integrated pest management programs. Fortrue area-wide management (and thus best risk mitigation results) of a pest ALL crops need tobe subject to control measures. Unfortunately, this is not the case especially in mixed cropproduction regions. Thus, we deemed it necessary to investigate fruit fly population and damage caused by these pests. We examined the extent to which fruit flies damage wine grapes (WG). Furthermore, we attempted to determine crop losses due to fruit fly damage in WG as well as correlate the occurrence of botrytis infection with fruit fly infestation.
Fruit fly populations densities were assessed for 3 consecutive seasons in 2 regions in the Western Cape, namely Robertson and Paarl/Wellington from October 2015-May 2016, December 2016-May 2017 and November 2017 – April 2018, with three treatments per area in 4 cultivars (Chardonnay, Chenin Blanc, Pinotage, Shiraz). Thirty grape bunches per cultivar/treatment/replicate/region were picked before harvest to determine the number of flies that emerged per bunch. Bunches were also inspected for Botrytis. Damage assessment as well as bait application only took place in the first and 3rd season but not during 2016- 2017.
Fruit flies were trapped in all 4 cultivars, across the 3 treatments for both regions. There were no significant differences in population levels between treatments or cultivars in both regions. Fly emergence differed amongst cultivars for both Robertson and Paarl, within treatments there were varying results. No correlation was found between fruit fly infestation and Botrytis infection.
Fruit flies were present in all cultivars and treatment blocks, thereby indicating that wine grapes provide a suitable habitat for adult fruit flies (through creating adequate shelter, water and food supply). Although infestation levels varied greatly between seasons, it was evident that with high enough population numbers fruit fly damage was present in WG and that fruit flies can complete their lifecycle in WG berries. WG are a suitable host for fruit flies and growers should thus apply the necessary control measures, especially for mixed crop growers.

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