Last week I cleared out the remains of my crop of kale, the success of which might be a factor of the mild winter.
In the space of five sq ft of raised bed I harvested four or five leatherjackets (colloquially known as Torry worms).
These are the larvae of the crane fly or daddy longlegs (Tipula spp) and the first I’ve recorded in this garden. They can cause a lot of damage to plants.
The mild winter will have helped a number of such soil-borne pests to come through comparatively unscathed.
I was not surprised therefore to read that there is a general warning going out to farmers that this could be a bumper year for Leatherjackets causing potato farmers in particular much anguish – just one more problem to cope with.
Gardeners are most likely to find leatherjackets in the lawn.
The first sign is the development of yellowish brown patches in the grass concurrently you might be aware of crows, rooks and starlings busily poking holes in the turf because they just love leatherjackets!
How do they know they’re there?
Do they notice the Crane flies laying their eggs the previous summer/autumn and mark the spot, licking their lips in anticipation?
One of nature’s great mysteries.
These pests can also cause serious damage to crops, seedlings and young plants but potatoes in particular where they eat into the developing tubers, creating sites where fungal organisms can thrive.
The grubs are about 30mm long, fat, tubular and greyish brown in colour. Whilst the birds will do their bit to reduce the population, there are two other methods of control available to gardeners.
Firstly, especially suitable for lawns – after heavy rain, cover the worst affected sections of lawn overnight with black polythene.
When you strip it off in the morning, you can sweep up the larvae that have come to the surface.
No rain forecast – problem getting worse – give the lawn a good soaking with the hosepipe and then cover as suggested.
The alternative is to use biological control, using the relevant Nemasys product.
It can be expensive, especially if you don’t stick to the instructions.
Apart from the cost, the crucial element is soil temperature. The treatment will NOT work if the soil temperature is below 12 deg C.
Another subterranean pest that is likely to crop up is the so-called Cutworm.
It is NOT a worm but the caterpillar stage of night flying moths, for example the Turnip Moth and it gets its name from the type of damage caused i.e. the first evidence will be to find the odd young plant collapsed.
Closer examination will show that the stem has been nipped through at or just below ground level.
These moths lay their eggs in June/July, the resulting larvae overwinter in the soil and become active in spring as plant growth commences.
Fully grown they are at least 2.5mm long, colours vary, depending on moth species – grey, brown, greeny yellow, some with longitudinal stripes.
They are very slow moving and like Vine Weevil larvae tend to curl up in a foetal position when disturbed.
Control is not easy, though they may spend most of the winter at depth, they do come close to the surface in spring as growth starts and therein lies one of the simplest control methods.
Firstly make sure that bare ground is not allowed to become weedy, in other words denying them sustenance and secondly cultivate the ground regularly to expose the beasties to the local bird population. (This technique will also help control Leatherjackets infesting open ground).
This is our main planting out season for many classes of vulnerable plants, not just vegetables like broad beans, brassicas, lettuce and so on but young herbaceous and bedding plant material.
It is said that the plants can be protected with barrier collars of cardboard – redundant loo rolls come to mind as a source of suitable material.
The collars have to be sunk into the ground to a depth of about 2.5cm.
Somehow I can’t imagine that to be a popular or even feasible thing to do. I did learn that sprinkling coffee grounds around the neck of vulnerable plants is a successful deterrent. I have never tried it and therefore cannot endorse the idea.
Where you do lose a plant, pick it up immediately and dig down and around the immediate vicinity and you will find the culprit. That has to be the surest way of solving the problem.
And then there is the wireworm – that one can wait for another day!