Tag Archives: drill and drop

Don’t forget your roots

Having discussed the Triffid-like rhododendrons that infest parts of Ardnamurchan and the tools needed to clear them, here’s a further instalment showing how to ensure they don’t re-grow.

Rhododendron (Rhododendron ponticum) are relatively shallow-rooted woody shrubs. They can spread by wind-dispersed seed and by suckering. Suckers are more correctly termed basal shoots and emerge from the root system.

Dense rhododendron growth with no understorey

Dense rhododendron growth with no understorey

Each of these suckers essentially has the ability to form a new plant.

If you cut a rhododendron to near ground level – leaving just enough of the woody stump to trip over 🙁 – it will usually produce new growth.

Even if it doesn’t produce growth from the stump, it will almost certainly generate suckers from which large new plants will eventually grow.

Consequently, simply cutting rhododendrons to the ground and leaving the roots untouched results in dense multi-stemmed thickets forming.

Multi-stemmed rhododendron from suckering

Multi-stemmed rhododendron from suckering

Therefore to ensure the rhododendron does not re-grow you must kill the roots of the plant. There are a variety of methods that can be used to achieve this, some faster than others.

Environmentally friendly methods – efficacy unknown

You can cut and clear the rhododendron and then periodically return to the stumps and, using something like a hammer, smash down the re-growth. Over a period (perhaps a long period) the stump will be killed.

There is an approach called the ‘lever and mulch’ method in which the shrub is cut down and the amputated top growth is used to cover the stump, effectively starving any new growth of light.

I’ve not tried either of these methods – I don’t have the time and want the site cleared – and so cannot comment further on them.

Environmentally unfriendly methods

A very common approach is to cut down the plant and then return after it has re-sprouted to spray with a systemic weedkiller such as glyphosate (in commercial products Roundup or Gallup).

Spraying requires a dry relatively calm day. If it’s wet and/or windy the weedkiller will either be less effective or may damage other plants.

Ardnamurchan has fabulous weather but it’s not always suitable for spray treatment 😉

I’m also not keen on the relatively indiscriminate application of weedkillers so have not used this method.

Drill and drop

What’s needed is a method that applies a weedkiller such as concentrated glyphosate in small amounts precisely where it is needed.

This can be easily achieved using stem injection.

The method is simplicity itself. A 10mm hole is drilled near the base of the trunk and 1-2ml of strong weedkiller is applied directly into the hole. The weedkiller is transported throughout the plant and, over a period of weeks or a few months, the plant is killed.

Once the plant is dead it can be cut down and burnt.

For pretty-obvious reasons this method is known as drill and drop.

Birds-eye view of a multi-stemmed rhododendron drilled for glyphosate application

Birds-eye view of a multi-stemmed rhododendron drilled for glyphosate application

Notice the holes an inch or two above the leaf litter in all the major stems. Why, if ‘… the weedkiller is transported throughout the plant …’ does every stem have to be drilled?

That’s because I oversimplified the method. The weedkiller appears to only kill the top growth and root of the individual sucker. It’s not entirely clear why. I presume that the new growth establishes its own root system over time (some of these stems are 2-3″ in diameter and 15-18 feet long) and that the weedkiller only spreads systemically within this new growth.

Consequently every stem must be drilled … and some will be missed 1.

Therefore, there is another method that can be used …

Drop and drill

You cut the plant down first, drill the remaining stump and apply the weedkiller. This approach has the advantage of immediacy. There’s no waiting for the rhododendron to die. It also has the advantage of thoroughness. Since you’ve cut all the top growth down you cannot inadvertently miss any of the stems.

Drop and drill

Drop and drill

The additional advantage is that you are generally drilling from the top into the stump. It’s easier to generate a clean hole and there’s even less chance of spilling weedkiller.

Driller killer

A battery-powered portable drill with a 10mm wood bit is needed. If the rhododendron growth is very dense or very extensive or – in my case – very dense and extensive 🙁 then it’s worth having a spare charged battery or two so you aren’t forced to stop just as you’re beginning to have fun.

The hole needs to be 2-5 cm deep. It is best drilled at an acute angle to reduce the chance of excess weedkiller running down the stem onto other plants. One hole is generally sufficient, even for the largest stems.

Stems as narrow as 2 cm in diameter can also be drilled. Choose a place where the growth is horizontal – close to the original stump – and drill a 1 cm deep hole, filling it with weedkiller to just below the brim.

Choose your poison

The weedkiller I use is Gallup glyphosate. Bought in bulk this costs about £20 for 2 litres. Because you’re applying a very small amount to a single, potentially very large, plant it needs to be used quite concentrated. I’ve used it at 20-25% i.e. mixed 1 in 4 or 1 in 5 with water.

Prepare a stock solution in a well-labelled plastic bottle. Don’t make up much more than you need as I’ve read it degrades over time and so loses efficacy. I make up 250ml which is enough for a very rewarding afternoon of rhodo-poisoning.

Trickle 2 container for delivery of glyphosate

Trickle 2 container for delivery of glyphosate

Administering 1-2 ml to a small hole in the base of a drilled stem requires a steady hand and a bottle with a nozzle that doesn’t drip or leak. I’ve used what a beekeeper would know as a Trickle 2 oxalic acid bottle. These probably have a proper name, but I’ve no idea what it is.

The bottle has a 100 ml reservoir and a small upper chamber that takes 5 ml. It has a twist-lock nozzle and doesn’t drip. It needs to be refilled every 50 or so stems. Remember you’re probably using it on your hands and knees in dense undergrowth. A refill is a welcome opportunity to stand up and stretch.

Drill and drop vs. Drop and drill

In practice I’ve found I have to use a mix of the two approaches. Each has advantages and disadvantages, but both are usually needed.

Drill and drop is great because the killed shrubs are much lighter to cut down, easier to transport and burn faster. It takes about 3 months for the plants to die – the upper growth withers and finally drops off.

The disadvantage of drill and drop is that you need to get to the base of the stems in very heavily-overgrown areas. Almost inevitably this means crawling about, working in confined dingy spaces and involves encounters with brambles, wasps nests and sharp pointy things.

Wear safety glasses.

New growth retrospectively drilled and killed

New growth retrospectively drilled and killed

Almost inevitably you’ll miss some stems. Drop and drill has the advantage of immediacy. You cut the plant down and then drill and poison the stump. You gradually work your way through a dense thicket, but the drilling and glyphosate delivery is done in an already cleared area so is much easier.

Slash and burn

I prefer to drill the plants, let them die back, cut them all down and return to ‘mop up’ the remainders I missed the first time round. I usually carry a pen to mark stumps cut down ‘live’ that need retrospective treatment 2. This avoids double-dosing.

If you cut the trunk near but below the previously drilled site the woody interior of the stem is usually stained distinctively, so you can avoid re-dosing it.

Waiting for the inferno

Waiting for the inferno

The side branches and top growth are removed with a billhook, stacked up and subsequently burnt.

Towering inferno

Towering inferno

The main stems are cut up and dried for firewood.

Something for the winter

Something for the winter

That lot is about half what I prepared from the 1600 m2 (i.e. 40 m x 40 m) area I’ve cleared so far.

Glyphosate – mode of action and toxicity

Glyphosate is a broad-spectrum (i.e. indiscriminate) weedkiller that inhibits the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase. This enzyme is critical for the synthesis of the aromatic amino acids tyrosine, tryptophan and phenylalanine. Production of these amino acids is important during plant growth which explains why glyphosate only kills growing plants.

Glyphosate was discovered by Monsanto, given the trade name Roundup and first used for agricultural purposes in 1974.

It is adsorbed through the leaves, through drilled or cut stems but only poorly through the roots. Stem drilling, or stem injection, is a much more effective way of administering glyphosate than simply painting it onto a cut stem; there is less wastage and much less potential for collateral damage.

Glyphosate has low acute toxicity and a half-life of about 47 days in soil.

Glyphosates and cancer

Glyphosate is extremely widely used. Consequently, residual amounts are sometimes found in food products. The levels are very low, with over 99.5% of nearly 7000 food products tested in 2016 having less than the maximum allowed residue levels.

However, the very widespread use and potential long-term exposure to low levels of glyphosate mean that it has repeatedly been associated with causing human cancers. Monsanto (now Bayer) have recently lost a court case when sued by a an individual who had developed non-Hodgkin lymphoma, claiming it was caused by long-term exposure to high levels of glyphosate while working as a gardener. Monsanto is appealing against the decision.

The scientific evidence (a very different level of ‘proof’ to a law court) supporting glyphosate being a carcinogen is very limited and equivocal.

A long-term (decades) study of 55,000 people showed that there was no increased risk of cancer in those exposed to higher levels of glyphosate.

Very recentlymeta-analysis (a statistical study of other studies) has linked exposure to very high levels of glyphosate to non-Hodgkin lymphoma. Despite the headline figure being a scary 41% increased risk 3 of developing non-Hodgkin’s lymphoma the absolute risk was only about 0.5%. And this was only for people exposed to very high levels over a very long period.

The headline 41% figure sold some newspapers, but the coverage was probably distorted and ignored or selectively over-interpreted much of the scientific evidence.

There’s wasa good account of this subject on the More or Less podcast recently.

Nevertheless, I always take care when using glyphosate. I wear disposable nitrile gloves and safety glasses. I administer small doses (1-2 ml) to the drilled holes, avoid spilling it and wash my tools and hands carefully after use.

A blank canvas

Before

Ardnamurchan or Borneo?

Ardnamurchan or Borneo?

After

Cleared and ready for native tree planting

Cleared and ready for native tree planting

There’s still more to do (measured in acres not m2) but after a bit more clearing this area will be planted up with native trees in the 2019/20 winter.


 

 

Triffids

Ardnamurchan has an unwanted squatter, an evergreen cancer spreading inexorably along the shores of Loch Sunart and – triffid-like – extending its tentacles up the steep, narrow valleys leading up onto the hills.

The invasion is particularly bad around Glenborrodale, the northern bulge of Morvern and the Salen area across the loch, Resipole, Ardery and – further North – Kinlochmoidart and the area to the east of Castle Tioram.

Forestry Commission rhododendron control areas

Forestry Commission rhododendron control areas

I am, of course, talking about rhododendron. More specifically – as there are many varieties of rhododendron – I’m talking about Rhododendron ponticum.

Rhododendron invasion

Rhododendron is not a native plant to the UK, at least not since the last ice age. Its natural range includes Spain and Portugal, Bulgaria, Turkey and a large swathe of central Asia (Himalayas, Afghanistan, Northern Pakistan, India and Kashmir). Genetic evidence indicates that the plants in the UK originated from the Iberian peninsula. 

The specific name, ponticum, refers to the Pontus area south of the Black Sea where it was first identified by the botanist Joseph Pitton de Tournefort at the beginning of the 18th Century. It was introduced to Britain in 1763 via Gibraltar as an ornamental shrub and was popular in Victorian country estates.

Glenborrodale Castle

Glenborrodale Castle

How and where it first appeared on Ardnamurchan is unclear. It is well established in the Glenborrodale area, particularly around the castle, so it may have been introduced when Glenborrodale Castle was built and the grounds landscaped (1898-1902). Its spread east along the loch would have then been aided by prevailing westerly winds.

What does rhododendron do?

Rhododendron is highly invasive and spreads widely by seeds and suckering, thriving in the damp conditions of Ardnamurchan as well as other areas of western Scotland, Wales and Ireland.

It forms evergreen spreading bushes 2-8m high that quickly outcompete other flora by casting dense shade under the long, dark green, glossy leaves. In Spring it bears lilac, light or dark purple flowers that can appear very dramatic when it covers entire hillsides.

But don’t be seduced by this brief spectacle. Where rhododendron is out of control – as it is on Ardnamurchan – it has dramatic and damaging effects on habitat structure and native biodiversity.

This includes eliminating native plants that are unable to compete for light and the consequent loss of native animals.

The CABI Invasive Species Compendium states that “where R. ponticum is introduced in an area all plant species are threatened”.

One thing rhododendron does not do is ‘poison the soil’ as is often reported. There is no good evidence that rhododendron is allelopathic. James Merryweather has written a comprehensive article on why this piece of folklore probably became established.

Rhododendron has no natural predators. The leaves, flowers and nectar are toxic due to the presence of diterpines, known as grayanotoxins. Therefore the foliage is unpalatable to herbivores and insects. Honey produced from rhododendron flowers contains grayanotoxins and is known as ‘mad honey’. I’ve recently written about mad honey, the mechanism of toxicity and the symptoms in humans on my beekeeping website, The Apiarist.

Rhododendron control

We’ve got a lot of well-established rhododendron on our land. The evergreen leaves provide a sort of semi-attractive, year-round verdant appearance to the site. However, I can’t ignore the damage they’re doing to the flora and fauna.

One day all this will be under rhododendron

One day all this will be under rhododendron

The bushes above are not yet encroaching on the view of Loch Sunart. However, they’re ‘only’ about 3-4m tall at the moment. They will get bigger.

They have to go.

I’m going to write separately on how to control rhododendron once I’ve worked out a reliable way that works best for me. Essentially methods are either manual or chemical, or the double-whammy of both.

Manual methods include mechanical flailing with a modified tractor, so-called ‘Lever and Mulch’ or simply cutting them down with a machete or chainsaw. Chemical methods usually involve glyphosate or similar weedkillers.

The disadvantage of manual methods is that the roots will reshoot unless they are killed or removed. The disadvantage of many chemical methods is that it involves widespread use of rather indiscriminate weedkillers. The local flora is struggling already … I don’t want to make it worse.

I currently favour the ‘drill and drop’ combination of tightly focused topical application of glyphosate, followed by the tightly focused application of my Trusty Husky chainsaw 😉

Or, of course, ‘drop and drill’ which is exactly the same in reverse.

The Day of the Triffids

Triffids are a fictitious tall, mobile, prolific and highly venomous plant species from John Wyndham’s 1951 novel The Day of the Triffids. Of course, rhododendron are not triffids …

The Day of the Triffids movie poster

The Day of the Triffids movie poster

… or are they.

Rhododendron are tall, they’re mobile 1, they’re highly prolific 2 and – although they’re not venomous – they are toxic.

So perhaps the name is appropriate.

I’ve already described how they damage local flora and fauna, but are they a threat to humans?

Well, probably not, though there are several recent cases where tourists or hill walkers have become trapped in dense rhododendron ‘forest’ in the Republic of Ireland.

I’m off to do battle with this lot … if you hear shouting call the emergency services 😉

Rhododendron jungle

Rhododendron jungle


Notes

A brief but thorough account of the damage that rhododendron do to the environment can be found here.

The Day of the Triffids is the 1951 post-apocalyptic science-fiction novel by John Wyndham, a pseudonym of John Wyndham Parkes Lucas Beynon Harris (1903-1969). The novel was made into a film of the same name in 1962. The story is well known, involving a blinding meteor shower, the eponymous carnivorous plants, survivalist groups, the Isle of White and – of interest to a beekeeper – the disablement of an armoured car by pouring honey into the fuel tank.