Preparing for the future: vine weevil control

While many UK growers are bemoaning the imminent loss of Exemptor, Karl Ducker of Mr Evergreen hedging and screening plants is already in a strong position - committed to nematode alternatives, he already has many years’ experience using them under his belt.

While studying at Pershore College in the 1980’s, Karl undertook a project exploring biological solutions to vine weevil. Since embarking on a career in production horticulture, he has put his trust firmly in beneficial nematodes, which target the grub stage, and has not looked back.

“In the 80’s it was obvious the then ‘go to’ vine weevil control – the organochlorine insecticide Aldrin - was not going to be around much longer,” he recalls. “In my first commercial job, in 1988, I began trialling commercially available nematodes and found they did a great job.  

“Back then, nematode controls were quite costly.  Keen to get the biggest ‘bang for my buck’, I spent time getting the application rates and timings right, routinely monitored for signs of adults and grubs. I was working with nursery stock in 2-10litre pots grown under protection and the nematodes were applied through spray irrigation – the resulting control was very good.”  

Large evergreens

In 2014 Karl set up Mr Evergreen, based at Efford Nurseries, producing quality large evergreens outdoors in 12-50litre pots, supplying professional horticulture, landscapers and the construction industry.   

“Arguably the vine weevil control challenges are greater as we’re dealing with fluctuating outdoor temperatures and need to ensure good nematode distribution within large pots,” says Karl – factors he has been addressing working with ICL’s Andrew Wilson.

“Knowing the growing media temperature in the pot is crucial for nematode efficacy and can have an important bearing on cost,” explains Andrew. “Nematode control products that are cold tolerant - such as Vine Weevil Seeka CT containing Steinernema kraussei – are efficacious at a lower temperature, from 5°C. This offers benefit of performing well earlier and/or later in the year. However, this species is more expensive to produce.   

Switching to cold tolerant species

“As soon as temperature rise to at least 12°C, it’s more cost-effective for growers to switch to products containing Heterorhabidits bacteriophora, such as Vine Weevil Seeka.  This robust nematode happily works in temperatures up to 30°C.”

As part of its programmed approach to vine weevil control, ICL has issued Efford Nurseries with a temperature probe and data logger. “This takes the temperature guess work out of the equation,” explains Andrew. “I’ve found growers are always quite surprised how different air temperatures are compared to those in a pot, or indeed a field.

“The temperature probe is positioned within a pot, or field, and the data logger can be attached to a bamboo cane with cable ties. The temperature data is downloaded on to a laptop, although our new loggers are bluetooth enabled so data can be collected without disturbing the sensor. An easy to use App makes downloading data to apple or android devices simple.”

Each year different

“The data shows that in spring the growing media temperature rises quickly and - even when the nights are cold - remains much more stable than we expected,” says Karl. “Each year is quite different, there are clear anomalies.  This data is helping us make informed decisions.”

The nematodes are efficiently applied through the dripper irrigation system – two drippers per pot.  The production team is careful to remove the filters so the nematodes can pass through the system unharmed.  The stock tank is fitted with an air agitator, to ensure good nematode distribution, while a hydraulic injector releases them into the irrigation system.    

“Even though we are surrounded by woodlands, I’m please to say we don’t have an established vine weevil population on the nursery,” says Karl. “The nematodes give us effective control.” 

As with all pests, the production team remain vigilant.  “From time to time, I still tip out pots and look for grubs,” says Karl.  “Occasionally I even come out in the evening with a torch and look for the nocturnal adult beetles.

Good nematode distribution key

“When I set up Mr Evergreen, one of my initial concerns was getting good nematode distribution in our large, 33cm diameter, pots.  While control levels have been good, I am always looking for way to optimise nematode performance.  I’m considering using the new penetrant - Transporter - to enhance water, and hence nematode, distribution in the growing media.  I plan to use it when treating species particularly vulnerable to vine weevil.”

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