Why you should target vine weevil larvae now

As autumn rolls around, the risk of serious vine weevil damage to plants increases – warns Sam Rivers, ICL technical manager for controls.

One of the most destructive pests of ornamental plants, the vine weevil larval stage – which feeds on plant roots – causes the most serious damage. During autumn, the larvae nestle down in root balls to overwinter and, if left unchecked, can wreak havoc on plants.

To manage larval infestations and protect plants over winter, September and October are ideal months to act with an Integrated Pest Management (IPM) programme – encompassing natural solutions such as Seeka nematodes.

Vine weevil lifecycle

The lifecycle of this pernicious pest starts in the spring, when adult beetles emerge and begin munching on plant leaves, creating characteristic notched edges. After feeding for a week or two,  they start to lay their eggs.

Over the summer, these hatch into larvae which live in the growing media dining out on plant roots. As summer wanes and temperatures drop, the larvae settle in for the winter – making autumn an ideal time to target them. While helping to minimise damage to plant roots over winter, timely autumn interventions will also help keep the pest population in check – reducing the emerging adult population in spring.

Top Tip: Keep in mind that in protected, or heated, areas – where the temperature stays above 12°C – all stages of the vine weevil lifecycle can be present year-round.

Choose nematode species wisely  

Beneficial nematode products, such as Seeka, are super-effective at targeting the larvae in autumn.  These tiny organisms attack and kill the larvae in the growing media.

To get the best results, it’s important to pick the right nematode for the temperature of your growing media. If the pot temperature is above 12°C, Heterorhabditis bacteriophora (Seeka) is recommended.

Top Tip: For cooler temperatures, below 12°C, Steinernema kraussei (Seeka CT – Cold Tolerant) works better. Effective at temperatures as low as 5°C, Seeka CT is a great option for late autumn and early winter.

Don’t forget Lalguard M52 GR

To strengthen your IPM strategy, Lalguard M52 GR is a great additional tool. This biological pesticide contains Metarhizium brunneum, a beneficial fungus that targets and kills the larvae.

Working best at temperatures between 15°C and 30°C, Lalguard M52 GR is less effective during the colder months of autumn and winter.  So, as autumn progresses nematodes become the go-to option, since they handle lower temperatures better.

However, that said, Lalguard M52 GR can be incorporated to the growing media anytime of the year and remains active for up to 12 months, working well alongside beneficial nematodes – especially in warmer months.

Cultural controls have role to play

Successful IPM plans go beyond just biological controls. Cultural controls, like regular plant monitoring and keeping production areas free from weeds and debris, can also play a part helping to reduce vine weevil pressure on the nursery and should be the first line of defence in any IPM plan.

Top Tip:  It is a good idea to quarantine any new, vine weevil susceptible plants, before bringing them into your main growing area.

So, in short, autumn is a great time to tackle vine weevil larvae.  By adopting a strategy combining nematodes and biopesticides, such as Lalguard M52 GR, you can keep this destructive pest under control all year long.

Helping hand

To help growers plan, simplify and optimise their plant health programmes on their nurseries year-round, we have developed a new digital web-based tool – the ICL Plant Health Planner. In line with the Sustainable Use Directive, our Plant Health Planner is helping growers reduce their reliance on chemical crop protection products.

To find out how the ICL Plant Health Planner can help you, or for more information or to order any of our vine weevil control products, speak to your local Technical Area Sales Manager.