Managing mealy bugs : Dec 2020 / Jan 2021
The basics of biology and control Table grape producers have good reason to take issue with mealy bugs. These troublesome insects damage vines and fruit while also spreading grapevine leafroll-associated viruses. By Anna Mouton
Growing market resistance to pesticides is limiting chemical options for control. So, what can producers do to combat this pest?
Bug biology basics
The vine mealy bug is the most common economically important mealy bug in South African vineyards. Other species occur sporadically. Mealy bugs cause immediate damage when feeding. They also secrete honeydew on which sooty mould grows, attracting ants and other insects. Applied entomologist Dr Jeanne de Waal of Corteva Agriscience stressed the importance of monitoring to stay on top of mealy bug infestations. Monitoring can include visual scouting and the use of traps. “It’s sensible to follow an integrated control programme,” advised De Waal. Chemical and biological control should be combined with cultural practices. The latter includes the management of ants, weeds and dust. Bark stripping increases the efﬁcacy of dormant sprays. “There are naturally occurring organisms that will help to suppress mealy bugs,” said De Waal. “There are also commercially available species that are commonly used.” Fungal applications to control mealy bugs are under research and could offer producers additional treatment options in future.
The pesticide predicament
“It’s very important to acknowledge that, yes, there are chemical solutions, but
these chemical solutions have limitations,” cautioned Liaan Janse van Vuuren, technical business developer for Viking. Janse van Vuuren pointed out that, although there are many active ingredients registered for use against mealy bugs, market requirements signiﬁcantly reduced the selection available to producers. “Regardless of the active ingredient you use, you need a strategy that not only controls mealy bugs, but also meets market requirements.” One way that growers can keep up to date on product registrations and market requirements is by consulting the Agri-Intel database at www.agri-intel.com. The Agri-Intel website offers access to registration and other information for crop protection products registered in SA. Information is searchable by various categories, including active ingredients, registration holders, and crop and use. “Market and export requirements are ever-changing, which makes it difficult for growers to export. Agri-Intel is a tool to help growers navigate all these changes,” said Chana-Lee White, the manager of Agri-Intel. Agri-Intel is available free of charge for CropLife SA members, and at a fee for others. Luigia Steyn is responsible for minimum residue limit and preharvest interval information at Agri-Intel. She compiled the data in table 1 in the presentation, which illustrates how growers can stay informed about market requirements using Agri-Intel. Chemical applications should be part of a systems approach. Growers must determine their strategy for the season, but adapt to changes in mealy bug populations within a season. Reducing mealy bug populations during winter is important. New infestations and hot spots are managed with an integrated program during the season. Spray applications after harvest should not be neglected. “Monitoring plays a key role to ensure that you know where your hotspots are, and that you know when flights of male mealy bugs are peaking,” stressed Janse van Vuuren. “This is all part of a complete system for controlling mealy bugs.”
Correct application is critical
Mechanical Engineer Kosie Human of Rovic Leers listed five application factors to keep in mind: optimal droplet size; balance of air momentum and forward speed; volume in litres per hectare; final sprayer adjustment; and maintenance.Human recommended droplet sizes of 50 – 175 micron for low volume applications, 100 – 175 micron for high volume applications, and 200 – 250 micron for dormant sprays. Droplets that are smaller than 150 micron are better able to penetrate bunches and canopies. “When it comes to the balance between air momentum and forward speed, ensure that you allow sufficient time for the air to carry the water to the target,” explained Human. “But, if you move too slowly, the air stream will blow off the target.” Maintenance has a big effect on accurate spray application. “I often encounter cases where maintenance hasn’t been done correctly,” recounted Human, “fan belts not set correctly, nozzles that are worn out. Make sure that everything on the sprayer is correctly maintained.” Human highlighted insufficient mixing in the spray tank, blocked filters and incorrect power take-off speed as common problems. Mealy bugs are here to stay. In spite of a shrinking pesticide arsenal, table grape producers can get the upper hand by following an integrated mealy bug control strategy.