Weapons of precise destruction

Vine weevils. Just hearing the words makes me shudder. Small yucky white grubs in the soil and adult grey-black beetles that eats unsightly marks on the leaves on many types of garden plants. Have you had any in your garden? Do you even know if you have any? You might have some, without it representing an infestation.

Last summer I had a particularly bad attach of vine weevils it seems, although all I saw was the result of the adult beetles munching away on my plants. Well, that in itself is not devastating harm to a plant, but on evergreen plants it is rather unsightly, my rhododendrons have still got the same leaves with the same notches and holes. I have tried to remove some of the worst leaves the last few months, hoping the evergreens will produce some new leaves when they discover the missing ones. I can’t remove all the ones with damage, that would be too stressful for the plants I think.

The leaf damage is just part of the vine weevil problem and to be fair, is more of a cosmetic problem, what goes on underground is much more devastating. Each female beetle lays 1.500 eggs every summer, which all becomes larva and those are the real threat to the plants. They stay between the roots of the plants, eating away the whole root system of a whole range of plants, especially plants in containers and pots , but also plants in open ground. With an infection big enough, a gentle tug at the crown of the plant will usually pull it away from the soil surface, as there is no root system left. Sometimes the first clue that something is wrong is when the plant blows across the garden like a ball of tumbleweed with all roots having been munched through. An exploratory dig around the planting area usually reveals the larvae about 2-5cm down, in what was left of the plant roots.

Here comes a solution - hence the title of this post! “Nematodes are naturally occurring microscopic worms, already present in our soil in the UK. Beneficial nematodes attack and kill targeted garden pests. They are environmentally friendly, safe for children, pets and wildlife. Research scientists have isolated the nematodes that kill specific garden pests including slugs, vine weevils, chafer grubs, leatherjackets, caterpillars, codling moth and various others. Millions of nematodes are bred to be easily applied by gardeners. When nematodes can no longer find prey they will die back to their original numbers. The nematodes in the Nemasys Range are naturally occurring so you are only boosting existing populations and not adding anything new to the environment.  They are effective in controlling pests without the restrictions associated with chemical controls.” (info from the nemasysinfo.co.uk)

I bought my nematodes on Amazon, but you can get them from many places including garden centres. If you live outside UK I am sure there are similar products in your country. Nematodes is a live product and have an expiry date of around 3 weeks from purchase and they need to be kept in the fridge until the day you want to use them. I carefully read information about this product before making my order, and one of the most important thing is that the soil need to be above 5 degrees for this particular product to work (some need even higher), or the nematodes will die. So when is the soil above 5 degrees C then? And does it need to be above 5 degrees both day and night? With the weather we have had this spring I have waited and waited and waited – normally this product is applied in March, but we were in the middle of deep arctic winter in March! And in April we were still having frost nights. Finally, last week of April I sent off an email to the company and asked some questions. Basically what they said was: "Generally air temperature during the day needs to be twice that of soil, so above 10 degrees C air temp applications should be fine and it needs to be that for the duration of the application period, 10-14 days. This particular type of nematode is a cold tolerant nematode and should not be affected by any light night frosts, provided well watered in."

So two days ago I went ahead with it. According to the instructions, the pack I have bought should be more than enough for my garden, covering up to 100 sqm, but the dilution method seemed a bit tricky: divide the batch of nematodes in 8 portions, mix each portions with 8 litres of water in a watering can. To me that sounded very difficult - to manage to spread this solution all over my garden and on every pot using only 8 watering cans. It would not be much on each plant, just a quick pass by, how would I ensure every plant actually got some of the solution around the base of the plant? The website said: drench pots or infected soil with nematodes. Drench? I have around 200 pots and containers from the smallest to the largest, in addition to my whole garden – how can I drench with only 8 watering cans? I asked about that too in my email, their answer was to dilute it more, they said: “Mix pack with 5 litre of water. Mix 500 ml to 10 litre of water.” 

Since my watering can only took 7 litre I used 350 ml of solution and mixed with 7 litre of water. That became around 15 watering cans of the standard 7 litres. So to recap:

One 100 sqm pack of nematodes in a bucket of 5 litres of water, then 350 ml of that solution into each full 7 litre watering can of water until all solution is used up. I am glad I asked them, I think I would have struggled to spread only 8 watering cans evenly on my whole garden, even though I don’t have a full 100 sqm garden as the pack was intended for.

The first thing to do was to give the garden a really good watering, even though we are in the spring, it hasn’t rained much and the nematodes need a moist ground to move so to be sure it was wet enough I gave the whole garden and all the pots a good soak. Here is what the nematodes looked like out of the box. I must admit I was fully protected with gloves when I opened it, not really knowing if the nematodes were going to spring out in the air once I removed the plastic film – but I needed have worried, they all stayed together. When I tipped it out in to the water it looked like a piece of old cheese someone had long forgotten about at the back of the fridge (not that I have ever had that kind of things on my fridge, no!) The block of nematodes just floated around on the top of the water so...

...after a good stir it looked like this. I had to keep stirring it throughout the process, as the product kept separating, so in the end I just left the stick there and gave it a good stir every time I filled up a new watering can. This solution seems very opaque, but mixed again with the right amount of water it simply looks like water. You could not see at all that there was anything added to the water, and crucially, the day after, there was no residue on any of the plants either, as some pesticides and fertilisers leave, very annoying when you come out the next day and find greyish blotches on all the leaves. There was no sign of any residue at all here, could not tell at all that I had added anything.

So here is what I needed in order to treat my whole garden: A bucket and a bamboo stick, a small measuring jug, a 7 litre watering can with a rose, access to water and a stool to sit on when filling the watering can (optional).  In hindsight there is one more thing I would have liked to have had; someone young, tall and strong who could have carried all those 15 watering cans for me, it became a struggle in the end, but I did finish it – the whole thing took me just over an hour. And what is an hour’s work if it can save my garden this summer from those pesky things?! After I had treated the whole garden I gave the garden another good splash of water, just to make sure the solution was going to get down in the ground and that all areas were thoroughly wet.

Now, this is an experiment, I hope it will be successful, but only time will show. However, the treatment I have done now is only half of it, to ensure to minimise the population I will have to repeat this treatment in the autumn, before soil temperature goes below 5 degrees, and possibly again next spring too. And as my garden is not in a sterile glass bubble, nothing is stopping vine weevils from next doors gardens from making a visit to my garden for breakfast, lunch and dinner. Future treatments might be necessary.

Have you used vine weevil nematodes before? I would love to hear what success you had with them, if any. And have you used any other beneficial nematodes in your garden? Please share with us! I am not sure when I will be able to share my success rate with you all, I suppose it depends whether I’ll get any attacks or not this summer. Last year the first attack happened in May, but with everything being so late this year, many insects have hardly woken up yet. I will get back on this topic at some point I suppose.

And finally, slightly off topic, but staying with the issue of insects just woken up. I found this one in my garden yesterday and I don’t think I have ever seen it before. Not sure though, because I don’t tend to study the creepy crawlies in my garden too closely, and anything that flies I tend to duck for or wave away, depending on what it is. But this one was just sitting there on a leaf, completely still. I went inside to get my camera, assuming it would be gone by the time I was back but it wasn’t – still there. Getting a photo means identification is so much easier. I found it on Google, after a bit of searching. It’s nothing unusual, but like me you might never have heard about it before? It is a bee-fly, a fly that mimics a bee, this particular one is called Bombylius major, since it is a ‘large bee-fly’. It is a parasitic fly, the eggs are flicked by the adult female toward the entrance of the underground nests of solitary bees and wasps. After hatching, the larvae find their way into the nests to feed on the grubs. Hmm, the world of insects is so cruel. On the other hand, this Bombylius is also a pollinator, along with all other bees, so it has its rightful place there, however, the larvae limit the population of other pollinators. Cruel world indeed.

OK, enough about creepy crawlies and flying things. It’s May Bank Holiday in Britain, usually a wash-out and although it rained for a few hours today, tomorrow seems much better and Monday we might get as much as 22 degrees and full sun here in London. When did we last have a May Bank Holiday Monday when it didn’t rain?? Must be many years ago, I can’t even remember. This one is very welcome! Until next time, take care.