Invasive Species

 

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Himalayan Balsam

 

One of the greatest threats to our native ecosystem and domestic gardens is the arrival of pervasive and invasive species. Anyone who has taken a walk along local riverbanks, which are frequently clothed in Himalayan balsam, can see how these can become a real pest.  Himalayan balsam, or Impatiens gladulifera, is a relation of the popular summer bedding plant, busy lizzie. This has colonised huge tracts of river banks, suffocating native plants which our native wildlife depends on for food and nesting. The summertime is when it is most difficult to get in amongst garden plants to weed and sneaky species can get a foothold, so autumn, when you are clearing and cutting back is a good time to look for evidence of unwanted species and dig them out before they become a problem. There are a three categories of invasive plants; the first are the common weeds we all know and battle against year in year out like dandelion, daisy and buttercups. The second category are garden plants like Japanese anemones and Echium that have self-seeded to such an extent that they have become a nuisance, but cause no real damage.  The third category are species which were introduced by horticulturalists as curiosities but quickly naturalized and spread throughout the countryside.  The latter category causes real ecological and structural damage by escaping from our gardens and into the countryside beyond. A classic example of such a pest is Horsetail or Equisetum arvense. This plant has creeping rhizomes which can go down 2m below the surface, making them almost impossible to eradicate by digging. Even when using a pesticide persistent applications are necessary, you may need to call in specialist help. Japanese Knotweed, or Himalayan Balsam, was introduced from Japan in the nineteenth century and since its introduction it has spread nationwide. It can destroy the foundations of houses as it can grow through concrete and tarmac. It also blocks wildlife corridors and clogs up watercourses.

Removal and control of invasive species causes millions of euro a year. Other pests include Bamboos – Philostachys species which form impenetrable thickets, block out native plants and spreads rapidly, again popping up through hard surfaces with ease.

 

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Japanese knotweed

Obviously the best way to fight invasive species is not to plant them in the first place so here are some tips to keep these thugs out:

  • Check a plants habit before you buy it and see if there is a non-invasive alternative.
  • If you have been walking along river banks or areas where invasive non-native species have colonized always wash the soles of your shoes thoroughly before wearing them in your garden. Seeds are commonly brought in on the soles of boots or on animal’s coats.
  • Never add any part of an invasive plant to the compost heap.
  • Invasive aquatic plants have caused considerable problems to our waterways and it is important to stop their spread. Avoid swapping cuttings or fragments from friend’s ponds. Otherwise you may end up with an invasive species in your pond.
  • Wash the roots of plants you buy too – I have a dreadful duck weed problem in my pond which came in on a plant bought from a very reputable garden centre.
  • Learn to recognise seedlings of invasive plants. Dig out seedlings as soon as you see them in spring and before they establish.
  • When weeding out mature plants make sure to remove all of the roots. Plants with tap roots like dandelion species will generate from every little bit of root left in the soil.
  • Rhizomatous weeds such as couch grass, bindweed and ground elder respond well to glyphosate if treated twice over a two-week period. It is very important to avoid drift so apply on a very still day. To treat bindweed, spray the weed killer onto rubber gloves and run your hands along the plant.
  • To eradicate ivy on trees and old walls cut it back to the ground and dig out the woody stump.
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Horsetail

Vine Weevil Alert!

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A Vine Weevil Grub

Take a look at the pictures  above and below and please excuse the poor quality. This was taken today and it shows one of a number of complete and utter bastards I found in a pot today. This particular little bugger is vine weevil grub – study it closely and take heed – note its curly little white body and its dirty brown mouth and if you see one SQUASH THE LITTLE BLIGHTER IMMEDIATELY.

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The Adult Vine Weevil

I knew something was up when I saw that my old reliable French Marguerite (Argyranthemum frutescens) was looking not just poorly, but utterly defeated. On touching it, it just came away in my hands and I immediately knew what was up. A quick investigation in the soil in the pot revealed a gang of the white wriggly grubs close to the top of the soil and confirmed that I had a serious vine weevil problem,

Vine weevils are dreadful pests, really, really annoying and tend to pick on favourite plants. Container plants are particularly susceptible. Though the adults are troublesome; they chew tell-tale semi-circular bites of out of leaves, it is their grubs that cause the catastrophic damage by eating the roots of plants, sneakily under the soil surface, so it is only when the damage becomes apparent and the plant dies that you notice their presence. By this time it usually too late to save the plant.

Adult vine weevils are curious creatures their Latin name is Otiorhynchus sulcatus – the sulcatus means grooved and you will notice the leathery backs of the vine weevils are indeed grooved. They look like beetles but there are matte and leathery rather than shiny and have little snouts. All of them are female. They reproduce by parthenogenesis –which means virgin creation in Greek, but anything less virgin-like and innocent you would be hard pressed to find. Each female fan produce offspring from unfertilized eggs.

Naturally weevils have no taste for dandelions, common daisies, thistle, bind weed or other pesky plants, instead they prefer ornamental plants and fruits, especially precious container grown specimens. From now – late spring until midsummer the little fat grubs will be feasting, growing fatter and greedier by the day until the time comes for them to sleep and metamorphose into adults and the adults will be busy laying more eggs – each one will lay hundreds in a lifetime, and remember, she doesn’t have to hang around waiting for a Mr vine weevil to mate with.

So how do you control these little creeps? The best way is obviously to stamp on, squash, and crush and give no quarter at all to any live adult weevils or their grubs. Sometimes the odd adult, brazen hussies that they are, will waltz across the floor of the house. You must immediately kill the beast and dispose of the body. When you find an infestation in a pot you must throw away the soil – every bit of it. If you think the plant has a chance of survival wash the roots thoroughly, take off every bit of soil and examine it to make sure there are no grubs (or adults) left on the plant, repot in clean, sterile soil and give it a good water and feed.

As I do with slugs, the best way to find the weevils is to get out in the evenings and hunt them down. If you suspect and infestation or see the tell-tale chunks bitten out of the leaf margins of plants like bergenia or rhododendron, lay some newspaper underneath the plants and give them a good shake to see if you can knock any weevils that might be hiding off their perches. Regularly check pot plants for signs of weakening, look underneath them and dig your fingers into the soil to see if you can spot any white grubs.

The best control for vine weevils is by encouraging gardener friendly wildlife into the garden such as hedgehogs, frogs and birds who will eat the grubs. A biological control is readily available, a nematode worm. The nematode is a tiny little creature which loves to feast on the baby grubs. When you buy the nematodes they come in a packet and you mix what looks like dry powder into water and pour it onto your plants. The down side to nematodes is that they only work in warmer weather.

If you are non-organic and have just had enough you can go for the scorched earth solution and try acetamiprid – a chemical insecticide. You can’t use this on any edible plants and you also run the risk of killing bugs that really don’t cause any harm at all.