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Pests and Diseases

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As organic gardeners, one of the biggest problems we have is getting a good balance of wildlife in our gardens. We need to work to encourage those insects which will help us with our crops, and we also need to control or be rid of those which compete with us for our crops.

"But I thought all insects and creepy crawlies were bad and should be exterminated,"  you cry. No, many insects out there are predators of other insects, or pollinators of flowers. In fact, there is a whole range of the good, the bad and the ugly.

Some of the major insect problems come to mind immediately, such as aphids, but others are not very obvious, and you tend to discover them when you have a problem.

One or two of our insect friends are well known, but others you wouldn't instantly recognise.

Make yours an ecological garden....

The best way to make sure you don't have too many problems with pests is to make sure you have an ecological garden. You need to encourage predators, and pollinators, and compost makers, and you won't notice the pests too often.

Lets start by going through the list of foes. I'm not going to make this comprehensive, but I will be quite extensive.

Aphids are probably the first that springs to mind. There are a range of aphids- you probably know them as greenfly, blackfly and whitefly. Different aphids affect different things, and to a different degree.

Greenfly can be a big problem in conservatories and greenhouses, especially when you keep plants going through the winter- we always get a huge greenfly problem in early spring in our conservatory, when we have lots of new tender plants growing, some older plants that have been in there all winter, and also potato tubers chitting. There are also lots of them in mid-late summer in the greenhouse. Infestations on young growing plants can seriously stunt them. Greenfly can also carry plant viruses, which is a more serious problem, especially for potato tubers and tomato and pepper plants.

Blackfly are less of a pest. They are usually found on the tips of broad bean plants, and can also become common on globe artichokes. They don't cause too much problem, as by the time their numbers build up, the plants are usually well grown and cropping.

Whitefly in the greenhouse again tend to be a problem when numbers build up too far, and they start to stunt plant growth and cropping.

There is a second aphid which could be thought of as a whitefly. It is actually called a woolly aphid, and it loves Brassicas (cabbage, broccoli, etc) in mid-late summer. As you brush past the plant, a cloud of them will float up into the air. They are more of a problem from a culinary point of view- they are very difficult to get off the plant, and boiling is the best way I have found to remove them from heads of calabrese or broccoli. They are again not too big a problem for the plant if they don't reach epidemic proportions.

So, what to do about your aphids?

The best way to reduce you aphid population (especially greenfly) is to make sure you have plenty of ladybirds and hoverflies around the place, as the larvae of both and the adult ladybird are master aphid-crunchers. Ladybirds are familiar, but would you recognise their larva, or just squash it as & some other crawly thing that must be harmful? The larva is a grey tube, sort of caterpillar-ish, but shorter, with yellow and black markings on it- look for a group of aphids in summer and you'll quite likely find one there. Hoverflies are small insects that look a bit like bees- they're yellow and stripy, and hover in front of flowers. The larva however, is a very ugly green squishy thing, very caterpillar like. But it is probably the all time champion greenfly muncher. (P.S., its not that fussy, it will munch its way through blackfly infestations as well)

A common form of 'chemical control' for organics is either to spray your plants with a dilute solution of washing up liquid, or to use liquid derris. I find that neither of these is totally effective, but they definitely reduce numbers of aphids.

The thing to bear in mind is that as insecticides, these are not specific to aphids, and will kill any hoverfly/ladybird larva you have around, or anything else for that matter.

A much-talked about whitefly control for greenhouses is to use a biological control called Encarsia. It is an insect which parasitises the aphids. It is claimed to be highly effective, but it is also expensive, and I have never felt the need to try it.

Another much-discussed method of controlling aphids in glasshouses, especially whitefly, is to grow French marigolds in the greenhouse alongside your crops such as tomatoes, cucumbers, etc. the strong scent of the marigold is supposed to deter the whitefly. I have never tried to test this one scientifically, but there is never any harm in having flowers around the veg garden, and they should be an integral part of your friendly-insect friendly garden anyway.

Cabbage butterflies.

One of the other major insect pests with we are all familiar is the cabbage white butterfly. There are actually two butterfly species involved here, the large and the small white, but both can be equally devastating to a brassica patch. The adult butterflies lay their eggs on your cabbage/cauliflower/broccoli plants, and the caterpillars can quickly turn you crop into a set of stems rather than a fine crop of plants.

The best deterrent would be to stop the adults gaining access to your Brassicas, which would require extensive fine netting, but this can be difficult if you have plants dotted around rather than in a block. It is also quite unattractive, and can be expensive if you have a large area to cover. A reasonable strategy is to let the local bird population eat them- if you live in a rural area, this will often happen. One of the best strategies is just to remove the caterpillars as you find them- not a pleasant task if you have to squash lots. Derris can be used, but bear in mind that it is a non-specific insecticide.

Rootflies.

Rootflies are another group of insect pests- carrots, parsnip and related plants get them, as do onions, turnips- each crop has their own type. Again, a companion planting approach is one which can be tried, where rows of carrots and onions are interplanted to confuse the enemy- not an entire area of one or other crop.

In general, this can be a very effective means to reduce the impact of any insect in a garden, as a monoculture of any vegetable crop is always a large feast to the insect. One or two other pests which you don't always read about in the pests and diseases handbooks.

The first of these is one we have personally had quite a few problems with, but has a relatively simple solution. This is a grub called Cutworm. It is the larva of a beetle, and it lives in grassland. If you are in the situation where you are converting an area of grass (old lawn for instance) into a vegetable plot, you will have problems with this beasty. You've cleared an area of grass, and you have just planted out a crop of small lettuce plants, for instance. The following morning you go out to see how you young plants are doing, and one plant in the row is completely wilted, but intact. When you handle the plant, it comes away at soil level. This is the favourite pastime of the cutworm. If you gently dig down into the soil in that hole, you will probably find a grey grub, about an inch long, with black jaws- that's him- just squash him.

This problem goes away after the first season or two, and the best remedy is to have a few extra plants ready to fill in the gaps.

Fleabeetle is becoming more of a pest that is mentioned in books. It is a small jumping beetle which loves Brassicas, including radishes and the oriental Brassicas which don't usually suffer like our traditional western greens. The only control is exclusion- fleece or enviromesh covering of seedlings are very effective, and also the use of sticky traps- those yellow cards used in greenhouses (of which more in a moment).

If you grow a lot of plants in the house and/or conservatory/greenhouse for planting out later, or for early crops, you may get a problem with Sciarid flies or fungus gnats. These tiny flies look harmless enough, and the adults are, but their larvae are found in soil, and nice moist potting compost, especially the coir-based, peat-free versions, are their favourite. The little grubs will strip the newly-formed root system of seedlings as soon as they form. The most susceptible crops are peppers, aubergines and pumpkin/courgette family. The best solution we have found is to buy the sticky yellow card traps  from garden centres, and place these in the areas where you have most of your seed trays.

I think this has become a problem for us as we nearly always have crop plants as well as houseplants around the house, so there is plenty of moist compost in a warm environment all year round.

Who are our friends?

Your best friends in the garden have been touched upon already - the ladybird and the hoverfly.There are other valuable predators, one of the best is the ground-beetle. This is a shiny black beetle about 1-2 cm long (it has iridescent colours, often violet or green, in sunlight) and is very active. As well as insects, it will also eat small slugs, so this is a creature to be encouraged. If there is plenty of compost or well-rotted manure around the garden, then the ground-beetle is happy. The 'devils coach-horse' is also a black beetle (our biggest Rove beetle). You may think it is very scary - it has a long 'tail' which is often raised in the air; this is actually just the end of its body, and is a deliberate ploy to make things scared. This is also a carnivore- it will eat any dead or live animal remains.

Bees and wasps are a common sight, and are closely related to each other. The honeybee is invaluable - it will pollinate pumpkins and squashes, runner beans, broad beans, and any other insect pollinated crop. Bumblebees are bigger, but are also good pollinators. The problem is, they are very greedy for nectar, and will chew through the base of bean flowers to get to the nectar as they are too big for the flower. This isn't normally a problem, as they do far more good than harm, and none of the bees are as common as they used to be.

Wasps are more of a problem when they start to raid your fruit in the autumn, but during the summer they are doing good work eating other insects, usually those which are more of a problem, for you, so losing a bit of fruit shouldn't be a big deal, although if you have a large nest of aggressive wasps, the best solution is often to have it destroyed by a professional.

There are other crop-specific insect pests out there, such as gooseberry sawfly- again the best solution is removal by hand of the larva- and asparagus beetle, and invaders of other fruit crops. There are a host of things which will chew leaves a bit, such as pea weevils, but don't seem to harm the plant, and others, such as pea moth, whose caterpillars form in the pea pod, which can easily be avoided but using early and late varieties, not maincrops. ( this is also a good strategy for carrot root fly)

If you tried to wipe out all the insects which could be a pest, then your garden would be a poorer place, as few of the colourful and friendly insects would be able to survive, as their food sources would be gone. Also, your soil would not be in as good condition, you wouldn't make very good compost, as many insects are involved in the breakdown of dead plant matter, and your beans and fruit wouldn't get pollinated.

Build up a good ecosystem - leave a patch of nettles somewhere out of the way, leave a bit of dead wood (a small pile of hedge-trimmings will do), and grow lots of flowers.

Nasturtiums, marigolds and poached egg plant are excellent companion plants for you veg plots, and if you use the green manure phacelia, let some flower- the purple flowers are irresistible to bees and hoverflies.

If you have a herb patch, make sure you let your herbs flower, as these are fantastic plants to encourage the predators- hoverflies just cant resist flowering fennel and dill, and thyme and marjoram are the bees favourites.

Onion and leek flowers can be almost as much of a draw for the bees and hoverflies, so why not leave just one or two of your old bulbs in the corner of the plot, and see what a difference it makes.

Not only will you have lots of healthy veg to look at, but lots of bright flowers and a buzz of industrious insects. You won't even have time to spot the few remaining aphids out of the way, as you'll be so fascinated by the antics of the bees, hoverflies and groundbeetles.

Pests & Diseases

Namely, that though all we gardeners suffer from pests and diseases, they're not really a huge problem. Most years, I grow about 24 sorts of vegetable and 8 sorts of fruit crops. Out of these, I would expect 3 or 4 to have problems. This means that we always get a lot of fruit and vegetables, even if the odd one fails. So be encouraged! You can't go that far wrong.

Expectations.

It's good to examine your expectations when considering pests and diseases.

You have to consider what you can control and what you can't. For example, in a dry season, many crops will show signs of distress. This is just a fact of gardening life - you can't control the weather, so there is a limit to what you can do.

How much work are you prepared to put in?

Again, in a dry season, you can water plants. But unless you do it reliably and regularly, it's a waste of time. Many garden problems can be dealt with if you are prepared to put the time in, but if you are busy, maybe you just have to accept them.

Finally, can you cope with slightly marred produce? If you don't mind maggots in apples, or whitefly or a few holes in your cabbages, then you can accept these things instead of trying to wipe them out. Essentially, your commitment in terms of time and energy will determine how much you want to do about pests and diseases. Often, the simplest thing is to ignore the things which aren't serious, and to ruthlessly dig up and burn plants which are seriously affected.

Ground Rules.

The right plant in the right place, adequately nourished and watered, will survive. This means that your energy should be focussed on healthy growing, rather than on 'pests and diseases'.

The mycorrhizal relationship

The early organic movement focussed their attention on the fact that, in a healthy soil, the roots form an association with certain fungi that are able to draw nourishment from humus. That nourishment is then available for the plant to take up. This means that growing is more than just plant roots in soil - it includes fungi too. So when we organic gardeners use compost, manure and other organic materials in our soil, we are nourishing both plant and fungi. This is how our plants are made healthy.

If you want to read more about this, try these books, which you can order from the library:

Soil nourishment and type

You will gather, then, that if you feed your soil with compost, or manure or other organic matter, it will become more and more healthy, and your plants will be healthy.

You also need to be aware of your soil type; acid or alkaline; clay, loam or sandy. There are certain crops which do not thrive in certain soils - these individual preferences can easily be checked in a vegetable growing guide.

Situation

Some plots have full sun, some sun part of the day, some are shady. Some sites are windy. These factors will affect your crops. For example, lettuces in full summer sun bolt more quickly. Onions like the sun, while parsnips and turnips will tolerate some shade. Brussels sprouts in a windy place need staking or they will blow about. Brassicas need liming to prosper on an acid soil.

To sum up, examine you plot and its soil, and note where the sun falls, and where it's shady, and plant accordingly.

Moisture

Some plants need a lot of moisture, some don't. Very few will prosper in a real drought. Again, it pays to know your soil - whether it dries out quickly or not. The more you dig a soil, the more likely it is to dry out, so that, where dryness is a problem, it may be best to avoid digging. You can retain moisture by applying a mulch to the soil. This acts like a blanket to prevent evaporation.

Weather

We often go for periods of weeks when it doesn't rain at all. It can therefore pay to exploit the rain when it comes. For example, if you have plants to transplant, do it immediately after a rainstorm. Don't be tempted to wait. It can also pay to cover new transplants with fleece for a week or so in the summer, to protect from hot sun. This will save them from undue stress and allow them to root.

Above all, know what sort of season it is, and adapt accordingly. If there has been a lot of rain, slugs and snails will prosper. It will pay to go round lifting any cover in the garden (bricks, wood, carpet) and collect and destroy them. In a very damp and humid season you can anticipate potato blight (which also affects tomatoes). Keep an eye out for it, and deal with the first signs. Similarly, in a dry season, onions are more likely to get white rot.

There is very little you can do if the season is too wet or too dry except learn the problems you may encounter and deal with them if you can.

Wildlife

Not all wildlife is good news but a good balance of goodies and baddies can even itself out to some extent. You may get mice, rats, deer, hares, squirrels, wood pigeons (and other things too) which are more of a problem- other gardeners on your allotment site or in nearby gardens will know what the local menace is. For rabbits, hares and deer, you will need to net your crops.

Good Husbandry

Rotation

This is a fundamental tenet of organic gardening. If you don't grow the same plant on the same spot every year, you are less likely to get disease. It means a bit of planning before you plant. Eventually, you need to consider the different families of plants you are growing, and group them together. You then divide your plot into 3 or 4, and put one plant family on each section. The next year, you move the plants round, so that each replaces its neighbour, and the same the following year, so that it is at least three years before each crop (potatoes, for example) return to where they were grown first. It is well worth studying the subject of rotation in one of the organic gardening books.

Hygiene

Don't compost diseased plants - burn them if you can. This breaks the chain of infection. Inspect your plants frequently. If you notice a diseased plant, take it out and destroy it. This may stop the pest or disease spreading. Plants under stress are the most likely to suffer from pests and diseases - you will often see only one broad bean plant in a row has blackfly, the runt of the row - so get rid of it. Try not to let your plants suffer, for example by transplanting when it is very hot. They are more likely to get attacked.

Tour of inspection

This is a good idea. You can dawdle round your plot, admiring your crops and congratulating yourself. If you see a problem early, you are more likely to get on top of it. Learn the predictable things that happen at various times of year: slugs attack seedlings in March and April - look for them and remove them, cabbage white butterflies lay eggs from July to September-pick off the caterpillars as they grow.

Too much and too little

Not everything likes a lot of nitrogen (manure is rich in nitrogen). Too much makes onions store badly. Too much manure on winter brassicas makes them sappy and vulnerable to frost. Too much on carrots and parsnips makes the root fork. Learn which crops like lots of manure, which like compost, which like lime, which hate it.

Some 'diseases' are actually problems of deficiency or overdose, such as chlorosis. This makes the leaves pale in colour and means that the plant needs nitrogen (or has a mineral deficiency).

Resistant Varieties

Some plant diseases are so predictable that vegetable varieties have been bred for resistance. For example, the potato variety Pentland Crown has good resistance to blight, whereas Pink Fir Apple variety does not. Parsnip Tender and True has good resistance to canker, White King less so. It is worth picking varieties with resistance when choosing seeds from the catalogue.

You've got a problem

Where should you start?

Have a really good look at the plant. Turn leaves over to look for insects on the bottom side of leaves. Look for insects deep in the heart of cabbages or cauliflowers. Gain as much evidence as you can.

Identification

You need a good book. I find Hessayon's 'Vegetable Expert' and 'Fruit Expert' very good and cheap. They have pictures for identification, though they are not organic in their remedies. Also good is the RHS 'Encyclopaedia of Gardening' or their pests and diseases volume. Or look in the organic gardening section in the bookshops. Ask your neighbours - they might have the same problem.

Why?

I find it useful to consider why I might have the problem. For example, is it a dry year? If so, they plant is of course under stress. Did I overmanure that plot? That means the onions are very green and sappy. Because it's been raining a lot, there are lots of fungi about - that's why the onions have downy mildew. I'll be more careful next year.

General solutions

I'm a great believer in 'encouragement', so I often spray a sick plant with a feed of liquid seaweed. No-one seems quite sure what seaweed feed does, but it seems to be a sort of tonic, and it makes plants grow better. Sometimes it is enough to strengthen a plant against disease. Always try it, I'm surprised how often it works.

My other tonic is dried blood. It is a nitrogen fertiliser, and will give a lift to plants that have been suffering from slug or flea beetle damage. Try to remove diseased material. See if you can limit its spread. This too works surprisingly often.

After this you have 2 choices - give up, or adopt a remedy from one of the organic gardening books.

Afterword

The important thing about pests and diseases is that, the more you garden, the more you will become your own expert. There are lots of ways of avoiding trouble, and of dealing with it when it occurs. You will learn more and more as you go on. But I will repeat once again my firm belief that no matter how inexperienced you are, you will always get some food from your plot, so concentrate on your successes and don't let the pests grind you down!