The intricacies of managing vine mealybug

By Dr. Gulu Bekker Head Technical | Western Cape

As within the rest of the world’s vine growing regions, Planococcus ficus or vine mealybug (hereafter VMB), is a key pest on vines (wine and table grapes) in South Africa. In the Western Cape, VMB was first recorded as a pest in 1930 (Joubert, 1943), and is a significant pest as it can cause direct and indirect damage to grape vines, as listed in Table 1 below.

In order to make an informed decision regarding the management of vine mealybug, one needs to have enough information regarding the current state of the population, in order to be confidant in the decision you make. Horgan 2017 and Möhring et al 2020 suggest that uninformed decisions are probably made due to the fact that a lot of the integrated pest management decision-making is based on cumbersome threshold methods, which can confuse growers, leading them to favour more user-friendly and convenient options (i.e. calendar-based sprays). However, for VMB, very simple monitoring protocols have been developed to inform management decisions (Walton et al, 2003; Millar et al, 2002).

The following monitoring protocol is suggested:

• Bait a yellow delta trap with a sticky pad and a VMB male lure. This trap should be hung at or above the cordon at a density of 1 trap per ha at the end of September, beginning of October, and checked every two weeks until harvest and every month after harvest.
• The action threshold (when action should be taken) for VMB is 2% infestation, which has been found to be equivalent to 65 males/trap in a two week trap cycle (Walton, 2003).
• Once 65 males/trap/2 weeks have been caught, visual scouting should be initiated.
• The visual scouting entails monitoring 20 plots (1 plot = 5 vines) per block (noting whether a vine is infested or un-infested), preferably evenly distributed throughout the block/vineyard.
• When grapevines have an infestation of less than 2%, it is advisable to purchase and release beneficial insects. This is a prevention strategy, to ensure that populations don’t build up exponentially, making the reliance on synthetic chemicals less.
• There are many natural enemies associated with VMB that has been recorded, please refer to Walton & Pringle 2004 for a complete list. However, the most common natural enemies occurring in the Western Cape includes the parasitoids, Anagyrus, Coccidodoxenoides perminutus and Leptomastrix dactylopii, and the predatory beetles, Nephus bineavatus, N. angustus and N. quadrivittatus

The seasonal population dynamics and phenology of VMB is mostly driven by history of VMB infestations within a block and most importantly temperature. In South Africa Kriegler (1954) and Walton (2003), recorded between 5 – 6 generations per year. Vine mealybug have overlapping generations and can over-winter in any of its life stages (Figure 1) (eggs to adults), however, mostly the instars are found located under the bark at the graft union, on trunk pruning wounds and below the base of spurs, in winter. However, eggs, instars and adults have also been found over-wintering under the bark, within developing buds and on roots. Upward movement from their over-wintering sites begins as temperatures increase after winter, this normally coincides with the onset of spring (end of September beginning of October). Populations normally peak in January or February after which the numbers decline. The individuals within the vine canopy, after harvest, forms the core of the overwintering populations.