Vine Weevil

Trigger points for Black Vine Weevil control solutions 

The Black Vine Weevil gets a lot of bad press – which is well deserved. One of the most problematic pests of ornamental horticulture, with the loss of thiacloprid – which could be conveniently incorporated in to growing media – its presence is being felt by many UK nurseries. Encouragingly, growers implementing a full IPM approach to controlling this potentially devastating pest are reporting good results.   

Here, Technical Area Sales Manager – Peter Robinson – explains what to look out for and provides practical tips on prevention before moving on to the trigger points for action. 

What you need to know  

Outdoors, the adult beetle is active from spring to autumn, before overwintering – generally as larvae (grubs) in growing media.  

Nocturnal feeders, the beetles rest during the day, hiding in sheltered places – classically under pots and pot rims or beneath Mypex, benches or staging.  Beetles are asexual, and each one is capable of laying 600-800 eggs.   

The classic calling card of the adult beetle is highly visible notching on leaf edges – they are incapable of making holes.  However, the root-feeding larval stage is the most destructive stage and can easily initially go undetected – with the grubs hidden in the growing media.   

In heated structures, above 12°C, all life cycle stages can be present at the same time.  

Prevention  

Before moving on to discuss the triggers for crop protection strategies, it is worth taking a moment to address some basic guidelines to help reduce population pressure.  Prevention is the first step in any good IPM approach.  

• Good nursery hygiene is essential. Identify larvae infected pots and dispose of them away from the nursery. Heaps of old plants/growing media out the back are not a good idea! 
• Keep resting places for adult weevils to a minimum. Pot and tray storage areas are ideal for adult weevils so check thoroughly before introducing them to the nursery! 
• Inspect bought in stock – preferably on the supplier’s nursery. If infected plants with grubs reach your nursery, reject or quarantine them and treat the batch immediately with beneficial nematodes (being mindful of temperature tolerances for nematodes).  

• A week prior to potting, it is worth considering treating all plants with a nematode drench.  
• Be aware the flightless beetles can walk a reasonable distance – covering the whole nursery in a single season.  

Triggers to crop protection solutions 

Regular monitoring is fundamental to IPM programmes.  Sticky and conical traps are now available for detecting vine weevil adults. These traps should be regularly checked – alternatively, simply go out with a torch at night and shake plants over a large piece of paper and see what falls out!   

Pitcher GR targets vine weevil eggs  

Outdoors adults typically emerge late-spring and within a couple of weeks start egg laying. If adults are detected, 2-3 weeks later it is advisable to apply our award-winning garlic based biorational – Pitcher GR to help control the egg stage.   

Rather than apply as a blanket treatment across the whole nursery, applications can be targeted at species the Vine Weevil are particularly attracted to – such as Begonias, Bergenias, Cyclamen, Fuchsias, Heuchera, Polyanthus, Primulas, Sedums, Succulents and Saxifrages.                  

C-shaped grubs  

Regular crop inspections can reveal signs of larval damage, such as poor performance or wilting.  To monitor effectively, knock out some pots and inspect the growing media – particularly in the root ball.  Again, it makes sense to focus monitoring activities at plant species that vine weevil prefer.   

Beneficial nematodes target grubs   

As soon as adults or grubs are observed, plans should be put in place to apply nematodes with repeat applications every 2-3 months – depending on the severity of the infestation.   

Nematodes species are temperature sensitive, so it is important to selecting the correct product and apply at the appropriate time of year.   It is important to note that Pitcher GR is incompatible with beneficial nematodes – so timing of applications of different products is crucial*. 

New bioinsecticide – Lalguard M52 GR targets grubs  

Growing media incorporated, this highly efficacious new Metarhizium-based (fungal) bioinsecticide helps to control vine weevil grub populations – while exerting some control on eggs, pupae and adult life stages. Lalguard M52 infects on contact and is highly compatible with existing biological and chemical crop protection products.  

The decision to use Lalguard M52 needs to be made before growing media is ordered.  As it is temperature sensitive, timing is crucial to achieve the best results.                                                    

*Plant Health Planner – here to help  

So, as with many pests, when it comes to Black Vine Weevil prevention is definitely better than cure. While that is easier said than done, any actions taken to reduce the population will be repaid many times over.   

For nurseries where the pest is detected, our Plant Health Planner is an extremely useful and practical tool for planning and plotting a targeted IPM programme involving biorationals, bioinsecticides and beneficial nematodes.