Info Sheets Home - Polytunnels & Greenhouses - Community Allotments - Planting Guides - Organic Food Growing - Pests & Diseases
Unfortunately however vigilant or experienced someone is veggies at some point will come under attack from pests and/or disease. Making sure your plants have enough nutrients and water will help reduce the possibility of attacks. Some pests and diseases will be plant specific while others will be less selective, e.g. slugs and whitefly will affect a number of plants.
You need to watch for signs and take precautionary measures if you believe your veggies are at risk, the rotation system is a good example of a prevention technique(s – delete). And just remember don’t be down hearted if you lose some veggies or even a whole crop! It happens to everyone and you’ve just got to get back out there and have another go!
I’m going to run through the most common pests and diseases that you are most likely to encounter with your veggies and some solutions for these. I’m only going to suggest organic remedies to these problems which in some cases may seem a bit more work but you have to remember that any chemicals you use will have a negative effect on other essential wildlife e.g. bees, which we need to pollinate our crops! Plus consider whether you’ll want to eat them once you’ve seen the chemicals that have been sprayed on them.
Often called green or black fly depending on colour. They attack a host of plants but for the black bean aphid watch for them on broad beans. Heavy infestations will kill a plant
Try to tolerate them on non-important plants as they will act as a food source for predators that will spread and eat the aphids on your veggies. Try to create an area where natural predators e.g. earwigs, ladybirds, spiders etc will thrive which is basically an undisturbed area of logs and plants. Once leaves have started to curl any sprays will be ineffective as aphid will be protected by the leaf. Avoid too much Nitrogen in fertiliser as this will create lots of succulent soft shoots which the aphids love. In broad beans, once they have reached 2 ½ ft pinch off the top cluster of leaves, this is the bit black fly always go for.
A common disease caused by bacteria living on plant debris. Susceptible plants include Brassicas, turnip, swedes, leeks, parsnip, and potato. You’ll see swollen areas of the plant either in the stem, leaf base or tuber. This will then start to emit a foul odour and then slimy brown stuff – nice!
Try to drain the land as much as you can either by a pond or ditches. Stick to the rotation system and clear any plant debris from growing areas. Control wound forming predators, such as slugs as these allow the bacteria into the plant. Once infection has set in there is not cure. Dig up and remove from site (Don't put it in the compost)
This is a fungal disease spread by the wind, insects and rain-splash. Brassicas are most susceptible. You’ll start to notice small white blotches on leaves. These white spots will become powdery. It soon spreads to the rest of the plant.
It’s a tricky one this best to pull up infected plants straight away and destroy. Stick to the rotation plan
Another fungal disease which thrives in damp overcrowded conditions. Spores can overwinter in plant debris. Susceptible plants are mainly broad beans. Symptoms include brown spots appearing on leaves, stems, and bean spots. Areas of the plant that have completely been covered will die back
Space your plants giving ample room between each one. Drained soil will help prevent this problem. Also check if there is a potassium deficiency in the soil, if so add some to the soil.
Again a fungal disease that loves damp conditions which is spread by insects, rain splash, animals and lives on plant debris. Broad beans and peas are susceptible plants. If you look on the under side of the leaves of these plants you’ll notice rusty-brown pustules. They seem horrible but rarely do the plant too much damage.
Once you’re done with the plant remove all of it to the compost. Also when watering try to water the base of the plant rather than through the leaves.
A major bug bear (pun intended) for all cabbage growers. There are 2 types of butterflies that like laying eggs on your cabbage leaves. Both are white in colour and are prevalent at different times of the year. The first lot lay clusters of orange eggs and the caterpillars are bright yellow and black which have up to three generation through the year. The next batch to look out for are orange eggs laid singularly under the leaves and the caterpillars are green in colour, again there are 3 generations of these critters.
Be vigilant! Cover plants with a fleece (usually called cosy grow in shops) or a very fine mesh to keep the butterflies out. However some somehow get through. Keep checking plants all through the summer, squish any eggs and caterpillars you see. It can be squeamish work to begin with but once you’ve seen a few of your lovely cabbages shredded by these things you’ll be squishing away!
This fly is quite large and resembles a horsefly. It lays eggs in the soil very near to the root of the host plant. Damage is worse in late spring and early summer. Brassicas, turnips and swedes are usually the worst affected. Young plants will wilt and be easy to pull up but adult plants may show no symptoms although some damage may make a few inedible
Place a fine mesh or fleece over the area and make sure the edges are buried beneath the soil so nothing can crawl under. Alternatively place what’s known as a collar around the base of each plant. You can make one of these yourself with cardboard or rubber matting, it needs to be 5” square with a slit on one side to allow getting it around the base of the plant. You can also plant into a little hollow. These measures will hopefully prevent the fly laying any eggs near your plant. If the plants are attacked then earth up around the base to encourage new growth.
As the name suggests these are white coloured flies which are very small and gather on the underside of Brassica leaves. If there is a major infestation then the growth of the plant may be stunted.
Once you have cropped the last of your plants, especially if growing over winter remove all traces of plant and bury deep in compost. As soon as whitefly is spotted remove infested leaves, and place again deep in compost. Spraying with a good blast of water will remove some of the pests. You can use a organic pesticide called Insecticidal soap. Use weekly for 3-4 weeks
These are small shiny black flies, and they lay eggs in the soil near susceptible plants. Their young are small white maggoty looking pupae and can over winter in the soil. As the name suggests carrots are most susceptible bit also parsnip and celery. Very young plants may be killed by this pest and adult plants will be stunted. The roots of the plants will have little tunnels chewed into them. Basically your carrots will be ruined!
If possible delay sowing the seeds until June when the first attack is usually over and make sure you have removed all traces of the plant by autumn. Some varieties of carrots are less susceptible e.g. ‘Sytan’ and ‘Flyaway’ But ‘Autumn king’ is more susceptible. When sowing try to do so thinly so as to avoid the need to thin out seedlings, as the carrotfly is attracted by the smell of bruised carrots. If you do thin out then remove all thinnings and water straight away.
This is a soil borne fungal disease which can live in the soil up to 20 years. Its loves acidic soil and damp conditions. The disease is easily spread on plant foliage, tools, boots etc. It will attack Brassicas. You may notice your plants wilt during the day but recover at night. Look out for swellings on the roots which is where the name ‘club root’ comes from. Plant growth and crops will be severely reduced.
Improve drainage on plot or grow in raised beds with ‘clean’ soil. If buying small seedlings get them from a reliable source or grow your own. Test the pH of the soil and if it’s less than 7 lime the soil to increase alkalinity. As soon as disease is spotted remove the plant and do NOT compost. If it becomes a common problem then stop growing in ground and grow in containers with new soil.
This a collective name for a range of fungal diseases. All plants are susceptible to this and mostly at seedling stage and when grown indoors. The seeds will either fail to germinate or the seedling will turn black at the level of the soil and wilt and die. It may also attack adult plants most noticeably potatoes which will have a watery interior.
When seeding into pots make sure you have cleaned these pots with a disinfectant, such as, Citrox. Use clean soil when seeding into trays or pots and ensure they have good drainage and don’t over crowd the seedlings. Don’t over water and try to water plants in early morning before the heat of the day.
These are tiny worms invisible to the naked eye. You will only know you have them when you take a magnifying glass to your plants. Most susceptible are potatoes and tomatoes. The plants will begin to yellow and die back prematurely. When you dig up the potatoes they will be riddled with holes.
Try not to bring in soil on tools and feet from invested sites, use only certified potato seed and if you have had the problem before buy resistant seed, such as, ‘Kestrel’. Feed the soil with manure to increase the natural predators of this worm.
Potatoes will fall foul of this bacterial disease. It is harboured in the soil or plant debris. It causes the stems to become waterlogged, brown and mushy and the leaves to curl, blister and wrinkle. The potato itself can turn into a mushy mess….
Drain the soil and buy less susceptible potato seed, such as, ‘Cara’. Dig up plants in dry weather to reduce the risk of spreading the problem and never save any infected potatoes for next year’s growing.
As it suggests potatoes and tomatoes are affected by this fungal problem. It loves damp conditions and will spread easily and quickly to other plants once present. It will live in the soil and last year’s potatoes so you must thoroughly dig over the potato patch after harvesting to remove all traces of the plant. In potatoes you will notice black brown blotches appear on leaves, around the tips and edges and on the stems. The plant may collapse quickly and the potatoes will develop dark lesions. In tomatoes symptoms are similar except the fruit will dry and become leathery.
Grow good seed potatoes from a known source and try to get resistant varieties, such as, ‘Cara’ and ‘Stirling’. Smooth the side of the ridges where potatoes have been planted to remove cracks in soil where bacteria can get through. Once infection has been noticed on foliage remove all affected leaves and if it continues cut back foliage to ground level. Dig up crop THREE WEEKS after this to avoid spreading the problem. Most of the potatoes will be edible just eat ASAP as they will not store. Throw away all plant material do NOT compost. Stick to the rotation system.
Both these creatures will happily munch through a whole host of plants. You’ll notice large chunks or whole plants disappearing and a slimy trail left around the plants.
This problem is not an easy one to solve. There are many ways to get rid of them but please do so organically. Many of the pellets you can buy will also kill wildlife or your own pets if the pellets or slug and snails are eaten. You can buy organic ones that do not harm other animals and cause the slug to bury under ground where it cannot be eaten. You can also place sharp material around the edges of growing areas such as, egg shell or ashes from fires. Beer traps are very good. Simply fill a old marge tub with beer and place into soil so the rim is just below the soil level. Slugs and snails will just fall in and … die.
You can also buy Nematodes (specific for slugs and snails) which are very effective but expensive if you are treating a big area. Encourage wildlife into your plot/ garden like hedgehogs, frogs and toads as these will love to eat the pesky slugs and snails. Just leave a corner untouched with some stacked bricks or logs, if possible a small pond and a good amount of plant cover and hopefully you will have your own slug and snail killing army!
A particular hate of mine! Weevils are little beetles with what looks like a snout. There are many types which affect different plants but once they’re in there will soon be loads of them! They will eat all parts of the plants but you will notice very neat scallop shaped damage appearing on the leaves of plants and if your plants suddenly start to die check the roots as they’ll be eating those too. The vine weevil particularly like plants in pots and the pea weevil will go for your peas and beans.
Now you can, like I tried, just keep squishing them! Check under pots, gently pull out plants in pots and check roots. But you could be killing up to 30 a day and then there’ll be another 20 the next day etc. So although expensive, Nematodes (specific ones for weevils) are the way to go. They wiped out the weevils that were attacking our plants in days and have never been back. They come in what looks like white powder which you mix with water in a watering can and then just water the whole area that’s affected. That’s it, the nematodes do the rest and they will seek out the weevils themselves. Marvellous!