Herbs are very rarely bothered by pests. They are more likely to suffer from poor growing conditions such as over watering or not watering them enough. However they can be subject to the odd infestation, so it’s important to know how to deal with the problem should one arise.
The main pests that are likely to attack your herb crops are aphids and red spider mite. Aphids are attracted to luscious leafy growth and can affect herbs such as basil and coriander. The most common aphids are greenfly or blackfly. They form clusters at the top of plants and around areas of new growth. They suck the sap from the plants and secrete a sticky sweet solution. Ants love to drink this solution, so you will often see them ‘farming’ aphids on plants and harvesting the sweet secretions.
If aphids attack your herbs the easiest way to remove them is to rub them off with your fingers or spray the infestation with a jet from your hose. If the infestation is small, it’s a good idea to leave it there. This will provide food for valuable predators such as hoverfly larvae, lacewings and ladybirds. Never use pesticides on plants you are going to eat. These are damaging to the plant and will end up on your plate!
Another pest to watch out for is red spider mite. Red spider mite can cause damage in very dry weather and is a particular problem in the greenhouse. The adult and young mites feed on plant tissue. They pierce the cells on the underside of the plants’ leaves and suck out its contents, which causes yellowy white spots to form on the upper leaf surface. Heavy infestations can cause the leaves to wither and fall off. Eventually the plant will weaken and die if the pest is not dealt with.
Red spider mites are quite difficult to spot on plants. During the summer months they are actually yellow (they only become red towards the autumn). Look out for webs and fine silk threads, which are produced around the tips of the stems, and leaves becoming mottled and dry.
If you suspect red spider mite has infested your herbs you should act quickly. They thrive in hot, dry weather so regularly misting the plants with water will slow down the spread of the infestation. If you are growing your herbs in a greenhouse, move them outside. The colder, wetter conditions should stop the pests from being a problem.
Companion Planting Herbs With Vegetables
Herbs have very strong smells during the summer, and are often used as companion plants to vegetable crops. This is because their smell can confuse pests. Carrot root fly can detect the smell of its favourite food from up to a mile away, but if you plant a row of strong smelling basil or coriander next to the row, the carrot root fly will have difficulty locating the carrots.
Companion planting can also be used to help herbs. Planting flowers such as candytuft, sunflower and echinacea nearby will attract predators such as ladybirds, lacewings and hoverflies into your garden. They will be nearby to eat up any aphids that attack your herbs.
Pest infestations on herbs are very unlikely, especially on perennial herbs such as rosemary and sage. In rare instances when they attack your annual herbs, you may find burning the crop and starting from scratch is the best option. Luckily most annuals (such as basil and coriander) take only a few weeks to mature from seed. Regularly inspecting your plants for signs of attack can prevent them from becoming a problem.