Identify and control vine weevil – adults & larvae
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What are Vine Weevils?
I have worked in garden centres for over 20 years, and one pest we have always had trouble with is vine weevils. More importantly, the larvae of vine weevils. I would go as far as saying they are the one pest that could cause enough significant damage that can actually kill a plant. With plants particularly that are being grown in pots and containers they can become a real problem, causing catastrophic results.
This is because significant damage can be done (which is detrimental to the plants) before you even realise there is a problem. Basically, this is caused by the vine weevil larvae. These said larvae are white in colour with light brown heads, they are maybe 10mm long and U-Shaped, and you will often find them eating the roots of your plants.
How to recognise Vine Weevil damage
The adult vine weevils (as shown in the picture above) eat the leaves of your plant, happily nibbling away from the edges of the leaf inwards or leaving holes in the middle of the leaf. This in itself is usually not something that causes any real issues and in most circumstances won’t affect the plant’s vigour. Some of the leaves will just look a little unsightly. The real issue comes from the young larvae that live in the soil because they can eat (and significantly damage) the roots. Unfortunately, you often won’t notice this is happening until it’s too late.
Often, the first indication you have vine weevils is that the leaves have the edges eaten away. This damage is caused adults and I personally don’t usually worry about this too much because the damage is usually limited. However, it’s my first warning sign there is an infestation. If you don’t notice this, then the next thing you will notice, usually in autumn and winter, is the foliage wilting with no signs of recovery, no matter how well you water them.
Now, the young vine weevils live in the soil and they cause the greatest problems for plants that are growing in pots or containers because the root systems and available roots for them to eat it limited. Whereas, with plants being grown in the ground, it’s not usually as significant a problem because there is plenty of other roots for them to eat amongst the flowerbeds and borders, so they don’t usually cause enough damage to just one plant.
They are usually a big problem with plants grown in pots only, and the good news is that the vine weevil larvae are actually easier to treat when the plants they are attacking are grown in pots.
What can you do about them?
Preventing vine weevils
The easiest way to try and prevent vine weevil in the first place is to try and control the adults before they manage to lay their eggs. It’s worth noting that each adult can lay up to 300 eggs, which can then be 300 vine weevil larvae. It only takes a handful of vine weevil larvae feeding on the roots of a pot grown plant to kill the plant.
I check susceptible plants frequently to remove the adults. There are two ways I have found to be successful, the first is to lay sticky traps around the base of the plant or inside greenhouses. I usually do this after seeing evidence of vine weevils eating the edges of leaves. Another more proactive way is to go out a couple of hours after dark with a torch (in spring and summer on mild days) and remove them by hand as they feed on the leaves and dispose of them. It is also worth looking underneath pots and greenhouse staging for plants grown inside a greenhouse.
Finally, do your part to encourage natural predators into the garden such as birds, frogs, and hedgehogs which all feed on the beetles and their larvae.
Treating vine weevils
One way to try and control the larvae in pots and in the ground is to use microscopic insect pathogenic nematodes. A quick search online for ‘nematodes’ should find you what you need. They need very specific conditions for it to work which means applying in August or early September when the soil temperature is warm enough for the nematodes to be effective. I personally don’t use these even though it is organic and a natural control. They are also a good solution for edible and ornamental plants.
I usually use a pesticide that is applied as a soil drench as the problem is usually in pots. This kills the vine weevil larvae before they are established and is best applied in mid to late summer and usually lasts around 4 months. This usually stops the cycle and has proven to be very effective. The pesticide I use is a systemic neonicotinoid insecticide acetamiprid called Bug Clear Ultra Vine Weevil Killer. Don’t use this on edible plants, for this, I always use the nematode only.