Protect your allotment from insects and pests

Written by The National Allotment Society on 8th February 2016

Pests and insects are a perennial headache for any allotment holder. Fortunately, there are cheap and relatively easy steps you can take to help keep the problem at bay – without necessarily resorting to a bottle of chemicals.

Encourage Natural Predators

Careful gardeners who manage their plots in a way that encourages insect predators will benefit from natural biological pest control. A plot with a healthy population of ladybirds, hoverflies, lace wings and their larvae will have some aphids but the natural predators will keep them to manageable numbers. One lacewing larvae can get through more than 100 aphids an hour, they also attack caterpillars and insect larvae, piercing them and sucking out the juice.

Plants that encourage beneficial insects are coreopsis, cosmos, yarrow, goldenrod, Queen Anne’s lace and marguerite daisies. It is also possible to purchase ladybird and lacewing larvae between late April and August and you can encourage them to breed and overwinter by placing insect hotels on your plot.

Insect-Proof Netting

Your aim here is simple: create a physical barrier between insects and your crops. Consisting of a fine, transparent mesh, good quality netting should shield your plants, while ensuring that they get enough light and don’t overheat. Pay special attention to the physical properties of the netting when shopping around for different products. Suitable netting will allow light and air passage of at least 90%.

When applying the netting, lay it flat over your bed while allowing enough slack for the crop to grow. Pegs should be used to bury the edges and make sure there are no gaps. Once in place, you should have an effective barrier against a host of problem insects including cabbage white butterfly, onion fly, cabbage root fly, leek moth and many species of aphids.

For most leaf and root crops, the mesh can stay in place all year round. For crops that require insect pollination (e.g. cucumber and squash), the plant must be uncovered once it starts flowering.

Pheromone Traps

This can be a useful ploy for dealing with very specific insect problems where netting isn’t an option. The trap replicates the scent of receptive female insects to attract males. Once attracted, the insects are stuck to the spot, thus hindering breeding and minimising egg laying in the area you want to protect. Put the trap in place in time for the relevant breeding season (usually April or early May). Products are designed for specific insects, such as plum moth and codling moth in apples.

Biological Pest Control

Biological controls work best in controlled environments such as a greenhouse or polytunnel. Whitefly Control uses a tiny parasitic wasp called encarsia Formosa. These are supplied as pupae on cards and hung in a shady position amongst your tomatoes and cucumbers. Spider mite can be controlled by a predatory mite called phytoseiulus persimilis, that can be used outside if the weather is warm enough. Most biological controls need to be applied at specific temperatures and used as soon as they arrive.

There are also biological controls that we can use out in the allotment plot, the North West region of the Society has just taken part in a trial of pathogenic nematodes to control slugs. There are also nematode treatments for caterpillars, vine weevils and codling moth and a combined treatment containing a mix of nematodes for cabbage root fly, cutworm, onion fly, sciarids, gooseberry sawfly, thrips and caterpillars. Take note – you must only use once the pest is visible or the predator will have nothing to eat and die!

Wire Netting for Rabbits

Rabbits can be a particular issue if your allotment is on a site that adjoins woods, farms or common land. If a rabbit problem is increasing, it’s probably the right time for your allotment holders’ association to think about the erection, renewal or repair of rabbit-proof fences and gates. But even here, all it takes is a couple of weak spots for rabbits to find their way in. Round fecal pellets along with stripped down stems on the likes of lettuces and beets are the signs that you’ve had a visitor.

Wire mesh barriers can provide a useful extra line of defence for particularly susceptible crops. Bear in mind that Rabbits can jump and dig, so the mesh should be pegged in to a depth of 6 inches and a height of 3 feet.

Slug Control

Grow vulnerable seedlings in a controlled environment like a greenhouse until they are strong enough to withstand an attack by slugs. Encourage predators such as frogs, toads and slow worms, which are all partial to slugs, as are ground beetles and creating suitable habitats on your plot will encourage them to stick around.

A small pond will entice a frog population; toads and slow-worms like a drier atmosphere such as the compost heap or pile of stones. Beetles will congregate under wooden boards or slates, which will also attract slugs but if checked regularly the slugs and their eggs can be removed. Certain slug species make a bee-line for potatoes, although some varieties are less susceptible to slug damage than others. Among these, Maris Piper and Cara have a particular susceptibility, whereas Charlotte and Romano are considerably more resilient.

Encouraging Friendly Visitors

A hedgehog can eat its way through an estimated 200g of insects in a single night and slugs are a favoured target. Simply by stacking a small log pile at the bottom edge of your allotment and/or by leaving a bramble bush in situ, you can help create an environment that attracts hedgehogs.

From aphids to snails, a bird population can also be an efficient way of keeping pests in check. Simply by introducing a bird feeder, you can easily encourage this.

More broadly, ‘pests’ can come in other forms too; whether vandals, thieves, and as we’ve been reminded recently, floods. Specialist allotment insurance for your association, club or society is essential to help to shield you against these additional threats, while The National Allotment Society has a host of resources to help you towards a safe and successful growing season.  For further information about the largest risks for allotment owners, check out our latest video guide to ensure you’ve got everything covered in time for spring, or request a callback from our experts today.

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