Happy New Year! I should really start a new year of six on Saturday posts with something inspirational and uplifting but I’ve been meaning to write about this subject for a while, so this is what you are getting. But gardening isn’t all positive and we roll with punches. We have ups and downs and by sharing the negatives I may help someone else in future.
1. RHS pests and diseases
I have started the process of revising for my next RHS exams. In the next round of exams, I am taking two exams. The first on soil and composting, the second on plant health, pests and diseases. I purchased the RHS pests and diseases in preparation for my revision and I have found myself browsing it in odd moments for the many ways our plants can be attacked. The book is a good guide to promoting plant health and while it does list chemical solutions it largely pushes more nature-friendly methods of promoting plant health. My current garden concern is vine weevil which I will spend the rest of my six looking at in more detail.
2. Vine weevil
Vine weevil are a fairly common pest. They are more of an issue for plants in pots which I think is where my problem started. I had two pots of heuchera that I discovered a few months back were infested. I disposed of these pots but there have been signs that they are in the ground too. So far the problem seems to be just in the front garden and the back seems to be unaffected. I could dig up the plants affected but this may mean removing almost everything and even then any new additions could still be attacked again. So I am trying several approaches to tackling them.
Vine weevil are a beetle Otiorhynchus sulcatus. The larvae are plump, white, legless grubs with brown heads that can be found around the roots of plants. While I have an interest in most aspects of nature you will find few positive odes to the vine weevil grub. Most people would describe them as repulsive. Knowing what they are they are not a welcome sight. They live in the soil where they nibble through the roots of your plants. In some cases, this will just stunt growth. In more extreme infestations they will cause the death of the plant.
I knew I had vine weevil when moving a pot I moved the plant and it came away in my hand. The larvae had eaten the whole of the stem and roots detaching the crown. It is possible to clean these off and re-pot but I didn’t want to take the risk so I disposed of the plants in pots. If you would like to read how to clean off infested plants read Plantsagogo advice. They attack a wide range of plants but heuchera are a particular favourite with hostas, hydrangea and cyclamen being on the list of vine weevil diet. Pretty much the list of what I grow in the front garden.
The larvae mainly cause damage through autumn and spring. The adults emerge late spring and summer. They are about 9mm long with dull black bodies and antennae that form a right angle. They are slow-moving and eat notches out of the leaves. They are flightless so you can set up barriers around your pots. If you grow plants in pots you can keep them in a saucer of water as the vine weevil don’t swim. The adults will lay many hundreds of eggs over a couple of months.
3.Non-chemical control-nematodes and predators
There are a handful of chemical controls for vine weevil but many of these pesticides are unsuitable to infestations in the ground. The pesticides can be applied as a compost drench but all the products I have looked at involve neonicotinoids which will kill more than just the vine weevils. Instead, I have used nematodes. These are natural predators that will attack the vine weevil larvae. They are delivered as a powder that you mix into a solution that you add to a watering can to water over the area. I gave the front garden a treatment in autumn and then again late on.
I have also encouraged natural predators of vine weevil to try and control the numbers further. The front garden does get frogs visiting despite no pond. There are a number of dark damp spots such as under the water butt where they can hide. I have been intending to look at making a mini-pond for the front garden to encourage them further but this is probably a job for spring now. I have also put a fat ball feeder in the front garden to encourage a few more birds in. I feed the birds with many different feeders in the back garden but I don’t really bother in the front as there isn’t much cover around for them. Once we get to late spring I will start to check the plants in the evening to see if I can remove any of the adults myself.
4. Encouraging healthy plants
The nematodes may not prove effective enough though as they don’t work as well as the temperature gets colder. They stop working at temperatures below 5 degrees. I applied the last dose about 2 weeks before the temperature dropped to this point. So I have taken a dual approach of looking at biological controls but also looking at promoting the health of the plant. Back in autumn, I gave the front garden plants a scattering of bone meal. Bone meal is a good autumn feed as it encourages plants to toughen up for winter and root well. As vine weevil mainly cause issues with roots I want the plants to be in as good health as possible. The bone meal is sprinkled on the surface and lightly forked in.
5. Mycorrhizal fungi
Mycorrhizal fungi are beneficial fungal that form associations between roots and plants to give the plants better access to nutrients. The RHS profile page partly dismisses them as the use of lots of fungicide and other fertilisers can disrupt the process. However, as we learn more about the effect these fungi the more gardeners are seeing the benefit of using this funghi. We still know relatively little about how these relationships work but they are truly astounding. I am reading Merlin Sheldrake’s entangled life and it is fascinating reading all the things fungi are capable of doing. Empathy sells many different mycorrhizal products for the gardener aimed at many different functions. They have products aimed at acid lovers, roses, evergreens but I went with the general rootgrow product. This is ideally spread on the roots when planted but as I have already got the front garden planted up the plants received a sprinkling around and it was forked in around some. So this will, hopefully, allow the plants attacked by vine weevil manage to grow back strong enough to survive any future attacks.
Mulching may not seem to have much to do with vine weevil but let me explain how this may potentially help. The front garden is heavy clay. So heavy you can sculpt with it. Bricks were made locally from it. I have discussed my efforts to improve the soil previously here. Nematodes do not work as effectively on heavy soil in part because the temperature drops colder. So in order to make sure I get the most from the nematodes I need to improve the soil. I am using a no-dig approach of applying top dressings. The soil organisms will gradually take it into the soil improving the structure of the soil. I have used Dalefoot clay buster which I can get delivered free locally. This is a lovely product for enriching the soil. Not cheap, but it feels and looks beautiful. Most gardeners will appreciate this while any of the non-gardeners reading this will think I’m crazy. As well as improving the conditions for nematodes, the mulch can also help improve the drainage while also helping water retention which may seem contradictory. It also provides the plants with some additional nutrition. Clay soil is rich in nutrients but it is not always accessible to plants. All of this should improve the health of the plants to make them more resilient to vine weevil and other problems.
I hope you have found some of this of interest. We’ll see next month if vine weevil come up on my exam. If they do I feel pretty prepared for answering a question on them. The one time I’ll actually be wanting vine weevil to appear.