WINETECH Technical Yearbook 2021

VITICULTURE RESEARCH | MAY 2021

PIA ADDISON 1 , BONGINKHOSI DLAMINI 1 , MESHACK MAGAGULA 1 , JULIEN HARAN 2 & ANTOINETTE MALAN 1 : 1 Department of Conservation Ecology and Entomology, Faculty of AgriSciences, Stellenbosch University, Stellenbosch; 2 CBGP, CIRAD, Montpellier SupAgro, INRA, IRD, University of Montpellier, France KEYWORDS: Weevils, vineyard pests, integrated pest management. Weevils in vineyards – a species-rich assemblage BY PIA ADDISON, BONGINKHOSI DLAMINI, MESHACK MAGAGULA, JULIEN HARAN & ANTOINETTE MALAN THE AIM OF THIS RESEARCH WAS TO INVESTIGATE THE IDENTITY OF THE WEEVIL COMPLEX OCCURRING IN VINEYARDS, TO DETERMINE THEIR SEASONAL CYCLE AND PEST STATUS. FURTHERMORE, WE AIMED TO ASSESS THE EFFECTS OF ENTOMOPATHOGENIC NEMATODES AND ENTOMOPATHOGENIC FUNGI ON THE BANDED FRUIT WEEVIL IN LABORATORY AND SMALL-SCALE FIELD TRIALS. THIS RESEARCH HOPES TO ESTABLISH GUIDELINES AND A SUITABLE STRATEGY TO COMBAT WEEVILS IN VINEYARDS. Weevils in vineyards – a species-rich assemblage I Several other weevil species may be found in vineyards, which may be of economic concern. For example, Sciobius weevil (Figure 1) has been shown to damage de- ciduous fruits, but this weevil, along with some other species, are very sporadic. Not much is known about their seasonal cycle and pest status in vineyards. Due to the weevils lacking wings, they climb up the vine trunks or trellis poles at night, when they are active, and feed on developing bunches, stems and leaves. For this reason, trunk barriers have been recommended for their control. Full cover applications are registered, but are not always c mpatible with an integrated pest management (IPM) programme. Initial research found th t entomopathog nic nematodes (EPNs) and entomopathogenic fungi (EPF) hold promise to supress BFW populations, and could easily be incorpo- rated into an IPM programme. OUTCOMES Weevil complex numbers peaked one month earlier, fol- lowed by the other weevil species, and numbers also decreased after April (Figure 2 and 3). Pest status Damage was monitored by checking leaves and berries for feeding injury (Figure 4) during middle December 2017 and March 2018 (before harvest). It was found that if BFW was excluded from the analysis, the remaining eight weevils’ effect on fruit damage was significant. The same analysis only for BFW was also significant, but the correlation was stronger. This suggests that BFW is likely responsible for the ma- jority of damage in vineyards, but that the other eight species contribute to a lesser extent, probably as their numbers are much less than the BFW (Figure 2 and 3). Biological control EPN THE AIM OF THIS RESEARCH was to investigate the identity of the weevil complex occurring in vineyards, to determine their seasonal cycle and pest status. Furthermore, we aimed to assess the effects of entomopathogenic nematodes and entomopathogenic fungi on the banded fruit weevil in laboratory and small-scale field trials. This research hopes to establish guidelines and a suitable strategy to combat weevils in vineyards. INTRODUCTION The banded fruit weevil (BFW) (figure 1) is a native South African pest, and contributes to damage and crop loss in deciduous fruits and vines, specifically apples, nectarines and grapevines. Previous studies by Brian Barnes has found that the weevils prefer hot- dry summers and larvae develop in the soil, feeding on roots of weeds. BFW has a wide host range of non- commercial plants, including roots of broad-leaved weeds, herbs, woody plants and root vegetables. They are also problematic in the undercover production of blueberries and vegetables. The pupae are also found in the soil, while females lay their eggs on the soil surface or organic material. After hatching, the larvae move deeper into the soil to feed on the roots. The pre-pupal stage constructs a chamber in the upper 100 mm of the soil, with the pupal stage lasting from one to three weeks. BFW have one to two generations FIGURE 1. Weevil species sampled from vineyards in Stellenbosch and Elgin, West rn Cape province, during 2017 and 2018. Weevils were sampled, using double- sided cardboard bands, every two weeks during the growi g s son. Identifications were made by Dr Julien Haran (CIRAD, France) using morphological and molecular m thods. (Images: Julien Haran and Meshack Magagula). INTRODUCTION The banded fruit weevil (BFW) (Figure 1) is a native South African pest, and contributes to damage and crop loss in deciduous fruits and vines, specifically apples, nectarines and grapevines. Pre- vious studies by Brian Barnes has found that the weevils prefer hot-dry summers and larvae develop in the soil, feeding on roots of weeds. BFW has a wide host range of non-commercial plants, including roots of broad-leaved weeds, herbs, woody plants and root vegetables. They are also problematic in the undercover production of blueberries and vegetables. The pupae are also found in the soil, while females lay their eggs on the soil surface or organic material. After hatching, the larvae move deeper into the soil to feed on the roots. The pre-pupal stage constructs a cham- ber in the upper 100 mm of the soil, with the pupal stage lasting from one to three weeks. BFW have one to two generations per year, with a second generation usually only developing in irrigated vineyards. Nine diffe ent weevil species were found to occur in three vineyards in Stellenbosch and Elgin (Figure 1). The cultivars sam- pled included Pinotage and Shiraz, and all three vineyards were irrigated with micro-sprinklers. It should be noted that the 2017/2018 season was characterised by drought conditions, which may well have influenced our results. For example, we sampled Eremnus occatus , which is not commonly found in vineyards, but not E. setulosus or E. cerealis , which were generally regarded as widespread in vine- yards. It is not possible to determine the exact reasons for this. Seasonal cycle BFW numbers peaked during December 2017 and were not detected after April 2018. Eremnus occatus and E. setifer Biological control using EPN can be tar- geted against the soil stages of the weevil, which include the larvae, pre-pupae, pupae and the emerging adult, offering a large window of opportunity for the use of nem- atodes. From laboratory bioassays, there was significant penetration of EPNs on BFW larvae; significant mortality of EPNs on BFW pupae, ranging from 55% to 70%; and significant mortality of BFW adults, ranging from 24% to 95%. Mortality was assessed over two days. Results from the laboratory trials were used to test effective EPNs in a small- scale field trial, whereby BFW larvae were placed at known locations under the soil in retrievable containers and the soil treated with Steinernema yirgalemense at three EPN concentrations. Soil temperatures ranged from between 8°C minimum to 30°C maximum at the time of applications. Steinernema yirgalemense at 40 IJs/cm 2 (78%) gave significantly greater mortality of the BFW larvae than those treated at

Pantomorus cervinus.

Naupactus leucoloma.

Phlyctinus callosus , banded fruit weevil.

Eremnus atratus.

Eremnus chevrolati.

Sciobius tottus , Sciobius weevil.

Eremnus occatus.

Tanyrhynchus carinatus.

Eremnus setifer.

FIGURE 1. Weevil species sampled from vineyards in Stellenbosch and Elgin, Western Cape province, during 2017 and 2018. Weevils were sampled, using double-sided cardboard bands, every two weeks during the growing season. Identifications were made by Dr Julien Haran (CIRAD, France) using morphological and molecular methods. (IMAGES: JULIEN HARAN AND MESHACK MAGAGULA.)

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