Close up of a group of aphids on a lettuce leaf
Organic control of aphids on lettuce
Controlling aphids on lettuce crops can be a real problem as they tend to end up hidden deep within the heart of the plant. They can also be well camouflaged coming in several colour forms ranging from green to orange and even pink in colour. Aphids are a well-known pest insect that can quickly colonise the soft tissue parts of your plants. They damage and weaken the plant by sucking the sap out of pressurised parenchyma cells just below the leaf cuticle especially on the soft, young growth.

Adult ladybird eating blackfly on a stem
Organic control of aphids on lettuce
Symptoms: Lettuce aphid likes to feed deep inside the plants, preferably toward the centre on the new leaves. In head lettuce types such the crisphead and butterhead varieties, aphids are found almost exclusively at the heart of the plant.

On the looser leaved varieties, such as Cos and Butterhead, just tease out some of the younger, central leaves. Clusters of these small insects are readily recognised and in severe cases, the infected leaves can begin to wither due to the quantity of sap being removed from that area. The foliage can become sticky due to honeydew and may show signs of a harmless black mould called sooty mildew.

Treatment: As an edible crop you should avoid using chemical controls however there are a number or organic solutions that can be very effective. If you are prone to aphid attack then you can pre-empt an infestation by growing under plastic cloches. For early infections you can try blasting the pests off with a hose but this can end up as a weekly task if you are using no other control methods. Keep down weeds in the local areas as these can be breeding grounds for more aphid attacks, and if you want to use a spray to knock them out then make sure that it is organic.

Consider plants that will attract the predators of aphids (see links below) such as a combination of basil and asparagus to attract ladybirds, or provide companion plants that help to deter aphids away from your lettuce crop. Chives, dill, fennel and peppermint have all had some proven success in repelling aphids. Alternatively or even in conjunction with companion plants you can consider making your own organic insecticide sprays.

Two of the most popular homemade aphid sprays are tomato leaf and garlic oil. Tomato leaf spray is made by chopping up one or two cups of tomato leaves and soaking the overnight in 500 ml or 1 pint of water. Let it steep overnight. Strain out the leaves using a cheese-cloth or a fine strainer. Add the subsequent tomato leaf liquid to another 500 ml or 1 pint of fresh water and then pour it into a spray bottle. Be aware that some people can show sensitivity to this liquid so take precautions when preparing and applying.

To make garlic oil spray mince or finely chop three to four cloves of garlic, and then add them to two teaspoons of mineral oil, also known as paraffin oil which can be easily purchased online. Allow the mixture to rest for 24 hours before straining out the garlic pieces. Add the resulting liquid to one pint of water, then add one teaspoon of washing up liquid soap.  Test the spray it first on an inconspicuous part of the plant and if after a couple of days there is no sign of yellowing or leaf damage then continue using the spray. If damage does occur then dilute the spray further with water and test spray once more.

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