How to Deal with Garden Pests and Diseases

We put some common garden pests and diseases under the microscope and learn how to deal with them.

It can sometimes feel like you have to battle on many different fronts in the vegetable garden, with pests attracted to all different crops and diseases becoming prevalent in certain weather conditions. However, there are often simple steps you can take to keep your plants safe and sound – and without causing harm to the environment. Here, we share some tips and tricks to get on top of common garden pests, diseases, and other problems, easily and in an eco-friendly way.

Cabbage Caterpillars
The larvae of cabbage white butterflies and cabbage moths can all be a problem. Inspect brassica plants regularly for signs of caterpillars and eggs, and pick them off if you see any. Large white butterfly larvae are up to 5cm long with hairy yellow bodies and black markings, while cabbage moth caterpillars are 3.5cm long and green or brown without obvious hairs, and small cabbage whites are green, 3.5cm long and have a covering of short hairs. Consider growing your crops under insect-proof mesh or trying a biological control to help avoid problems.

Slugs
A real menace to growers, these gastropods love nothing more than munching on our precious crops – from leaves, stems, and fruits to brand-new seedlings just emerging – and everything in between! There are plenty of ways to prevent losing all your veg, but many methods are debated as to whether they work effectively. Therefore, one of the best ways to get on top of these pests in your garden is to attract predators, such as hedgehogs, which will patrol the plot for you and guzzle slugs like there is no tomorrow! Nematodes are another environmentally friendly solution.

Blossom End Rot
This isn’t technically a disease, but a problem that develops from growing conditions. At risk are aubergines, chillies, cucumbers, squash, melons, and tomatoes. The blossom end of the fruit gains a darkened patch that develops into a sunken, rotten area. The main cause is a lack of water flow preventing calcium from reaching the fruit. Therefore, crops grown in containers are usually most likely to suffer from irregular water supplies. It can’t spread from plant to plant, but if fruits are affected, pick and discard. Consistency with watering is key to avoiding this issue.

Blight
This is a problem that impacts growers of tomatoes and potatoes. From early summer onwards, plants are susceptible to this fungus-like organism – symptoms of which are leaves shrivelling and going brown, and fruits being affected by brown patches. It spreads rapidly in damp or humid environments, and unfortunately there is no cure, so affected plants should be removed from the site and destroyed. You can now purchase blight-resistant varieties if the disease is common in your area. Again, good plot hygiene helps minimise the risk of blight developing.

Clubroot
This is a fungal infection affecting brassica roots. Signs of infection include stunted growth, wilting in hot weather, purplish foliage, reduced yields and even plant death. Fine roots are lost and a massively distorted and swollen main root can be seen. On rotting, the swollen roots release resting spores that can contaminate soil for up to 20 years. Clubroot is reduced (but not eliminated) by raising the soil pH level. This can be done by adding lime, ideally while also improving drainage. Destroy all infected roots before they rot and release spores. There are no chemical controls but resistant types are available.

Rust
This issue impacts mint, marjoram, savory, leeks, garlic and chives. The symptoms to look out for are raised orange pustules which appear on leaves; these spots mature to brown/black and eventually, leaves shrivel. Rust likes mild, wet weather, so is worst in damp summers. Herb plants are best lifted out and thrown away (not composted) to get rid of the issue. Plant at wide spacings and avoid high-nitrogen feeds which can increase the problem.

Damping Off
This is a problem that affects young seedlings. It can take hold before seedlings even emerge, causing patchy germination – or no germination at all. But it’s probably more easily identified in seedlings which collapse and sometimes become covered in white mould. Damping off is caused by fungi and other fungi-like organisms that thrive in pots and trays which are overwatered, poorly ventilated and overcrowded. It can wreak havoc on your fresh sowings at any time of the year, but it’s most common in spring when light levels and temperatures are lower, and under glass, where there’s less air circulation. Try sowing seed thinly, don’t overwater, and keep the area well-ventilated. Like all fungi, damping off organisms love cramped, humid conditions – so don’t give it to them! Also, make sure any pots and trays you use haven’t housed crops that have been affected by damping off before.

Bolting
This is a term which describes crops running to seed too early, before they can be harvested. It’s a survival mechanism – when unpredictable conditions strike, usually like sudden changes in the weather or day length, the plants mature quickly and begin to produce seed for the next generation. In essence, any conditions that put the plant under stress can trigger bolting. There are several measures you can take before planting to ensure there is less chance of your crops bolting. If you’re sowing direct outdoors, try to wait until fluctuations in temperature are less likely. If you do sow during unpredictable weather seasons, cover your sowings with cloches or horticultural fleece to protect them from harsh changes in temperature or weather conditions. Better yet, sow seed indoors and plant them out when temperatures are warmer, making sure to harden them off first.

Powdery Mildew
This issue is a common fungal disease which affects a wide range of edible crops. The fungus is visible as a dusty white powder which covers the surfaces of foliage, flowers, and sometimes fruits. Dispose of fallen infected leaves in the autumn and remove any infected shoots. Ensure there is good airflow around vulnerable plants, which should not be planted too close together – this disease, like many others of the fungal kind, loves humid conditions, so ensuring a good level of ventilation is key. Planting away from walls is therefore another good tactic.

Cucumber Mosaic Virus
Don’t be fooled by the name, because cucumber mosaic virus actually infects a wide range of plants, including other cucurbits, lettuce, spinach, celery and many flowers. It’s a common problem on the plot. Distortion is the most obvious symptom, along with mottled yellow leaves and stunted growth. The foliage may also curl downwards and edibles will produce significantly less fruit if they are suffering from this problem. This virus is transmitted via ‘vectors’ as they have no means of self-dispersal – aphids are the main example of this when they feed on an infected plant and then move onto a healthy one, but unclean tools and hands can also cause this to happen. It’s vitally important to practice good hygiene on the plot to stop this issue from spreading across a large number of your crops. Unfortunately, there are no direct forms of control available to treat cucumber mosaic virus. Stopping aphids from infesting your plants could stop one of the many ways of transmitting the problem, but this is very difficult to achieve. The best form of prevention is to grow resistant varieties.