What’s Eating You?

If you're wondering what's eating you, then consider this: According to the Royal Horticultural Society (RHS), there are ten pests, nine of which are insects that have made it their sole mission in life to devour your crops before you can get them to your customers. The tenth generally creates a mess of your tidy garden.

This may leave you somewhat disconsolate; but you're deceiving yourself if you pretend that they don't exist and refuse to take steps to control them.

How can you tell what's eating you?

How do you identify your unwanted guests?


Slugs and snails

Slugs and snails top the list. They love to munch, and so you're likely to see where they have been by the holes they make in the foliage of your plants.

How can you control them?

A quick search on the Web reveals tens of thousands of results. It seems that everyone has an opinion and that there is an abundance of products you can buy which allegedly will make the job easier. The effectiveness of these suggestions, however, seems to depend largely on the luck of the draw. Some "solutions" are cost prohibitive, have side effects, are labour-intensive or all three; and those who want to grow organically will have fewer choices than everyone else.

Many small animals, such as newts, hedgehogs, and birds are predators of molluscs, but such fauna are unlikely to be found in greenhouses. For one thing, there isn't a logical way for them to get in or out and, for another, the supply of food for them is less reliable than if they're left to roam freely outside.

So you have to pretty much choose whichever one you prefer or try several until you find one that works for you. It's worth mentioning that these animals will come back to you if you simply gather them up and transport them elsewhere.


Mice & voles

Mice and voles like to dig holes. (The poetry is accidental.)

You may see places where they've dug in the ground to get down to the bulbs you so carefully planted. You may also discover seedlings scattered on the surface or small piles of partially eaten fruit.

Voles leave the tell-tale sign of little mounds of earth on the grass. If they get into your glasshouse, they can reek havoc in a single night.

These rodents can reproduce rapidly. A single female vole can give birth to as many as 60 young in a year, and one mouse can breed at least that many in a similar period of time.

Due to health and safety concerns, supermarkets have insisted that all growers use bait traps to control these animals. Some growers bury finely-meshed chicken wire to keep out rabbits as well.

Controlling them can be very challenging, but fortunately there are a number of animals that prey on them naturally, including your domestic cat. Just remember that it may bring home one or two trophies to prove that's doing its job.


The rest

The remaining eight horticultural pests are insects: vine weevil, cushion scale, lily and rosemary beetle, aphid, leaf miner, Tortrix moth caterpillar, and ants. How can you tell which of these is eating you?

Not all insects can fly. Some, such as the vine weevils, cushion scales, and beetles  are "soil-borne". Leaf miners and moths can fly. Aphids float on the wind, and ants can squeeze through the tiniest cracks. No matter what you do to keep unwanted pests out, you can bet that many of them will still find a way to get in.

Vine weevils

Vine weevils are active the year 'round. The immature grubs go after the roots during the autumn and winter, and it's this that can kill your plants. Adults eat the foliage above ground, but it is rarely bad enough to cause permanent damage.

Vine weevils like plants in containers.

The easiest way to determine if you have a problem is to periodically inspect your plants. Adults are just over a half an inch long with a "dirty yellow mark on the wing cases". The white grubs will be among the roots. Obviously you can't dig up your plants all the time to see if they're there, but you can check when you transplant from one size pot to another.

Once you have identified a vine weevil problem, you need to stay on top of it. Just because you get rid of them doesn't mean that they won't return. Be vigilant.


Cushion Scale

Cushion scale is easy to identify. For one thing you'll only find it on evergreen plants. For another, the black mould on the top of the leaves and eggs in what look like scales are unmistakable.

The risk for Cushion Scale is present all year. The mould will gradually fall off as the weather warms up, or you can wipe it off. Chemical or organic pesticides will be needed to deal with it on large plants.


Lily & rosemary beetles

These beetles are not native to the UK, but they are now well-established. Both have distinctive markings. The lily beetle is fire brigade red, as are its eggs. Its grubs are black. The rosemary beetle is green with purple stripes and may look quite attractive. Both beetles consume the plants and those in the families after which they're named.



Aphids may be one of the most "feared" insects among gardeners. There are about 4,000 varieties. They are also very small and generally leave a sticky mess wherever they go.


Leaf miner

This industrious chap eats all the goodness between the veins of the leaves. All that remains when its licking its chops is the skeleton of the leaf.


Tortrix moth caterpillar

These critters are active all year in glasshouses. You'll know straightaway if they are part of what's eating you because you'll see tiny strands which bind the leaves of your plants together.



The presence of ants is noted by the fine, granular soil that they leave in their wake. They tend to infest cracks in concrete footpaths. More than anything else, ants simply disturb the appearance of your plants by disturbing the soil around them; but they eat aphids, which makes them something of a mixed blessing. If they're not really bothering you, then it's best to leave them alone, after all - they may actually do you some good.


It seems that no matter what you want to grow, there's an animal or an insect just waiting to eat it before you get the chance.


A remedy

Insect Screen

Insect Screens


One way to mitigate the problem is to use insect screens. These can be especially effective on warm days when the roof windows need to be fully open. They allow the maximum flow of air while minimizing the chances that insects will fly in on their own steam or be transported by the wind into your glasshouse. Fewer bugs mean less pesticide, too; and that means lower costs.

In recent years, insects have become more resistant to chemicals. Their continued use will hasten the day when they are no longer effective. That's because these bugs are constantly modifying themselves, such that they are becoming immune to their influence.

The insect screen shown in the picture, enables you to control how much of the roof windows are open at any one time - anything from a little to a lot.

Of course, ventilation is somewhat restricted by screens. The insects who might otherwise fly out are also prevented from doing so when they are in use. It can be a delicate balance. That said, if you choose one that's appropriate for the type of greenhouse you're using, then you shouldn't have any problems.

Screens for greenhouses are made from a soft, but strong polyethylene weave. If you're not sure which type of screen is right for you when your glasshouse is constructed, then you can install it after the fact; but if your budget allows, then you should plan to have it included in the build from the outset.

One last thing.

Simply choosing the cheapest screen available can cause more problems than it solves. It's essential that you use one that is made from the most suitable materials for the job and is of the specification you need.

You don't want to be "penny wise, but pound foolish".



What do you think?