Kale is a highly nutritious, cool-weather vegetable that is a favorite for many home gardeners, but its open leaves and tender texture make it a prime target for various insects. Successfully growing kale requires a proactive strategy that combines physical protection with environmentally sound intervention methods to keep the plants healthy and the leaves intact.
Identifying the Specific Pests Attacking Kale
Effective pest management requires accurately identifying the culprits, since different insects require different control methods. The most common pests are the caterpillars, which cause significant chewing damage on the leaves. These often include the imported cabbageworm, the velvety green larva of the small white butterfly, and the cabbage looper, a pale green caterpillar that moves with a distinct inchworm motion. Both of these chewing pests leave behind large, irregular holes and ragged edges, sometimes skeletonizing the leaves completely.
The flea beetle is a small, shiny black or bronze insect that jumps readily when disturbed. These beetles feed on the leaves, leaving behind a characteristic “shotgun” pattern of numerous small, round holes. Aphids, particularly the gray-green cabbage aphid, are soft-bodied, sap-sucking insects that cluster on the undersides of leaves and on tender new growth. Their feeding causes the leaves to curl, twist, and turn yellow, often leaving behind a sticky substance called honeydew.
Non-Chemical Physical and Cultural Barriers
Prevention is the most reliable method for protecting kale, and physical barriers are highly effective at stopping pests before they reach the plants. A floating row cover, made of fine mesh netting or a lightweight agricultural fabric, creates a physical shield that excludes egg-laying butterflies, moths, and flea beetles. The cover must be draped over the plants immediately after planting and secured tightly on all sides to the ground with soil, rocks, or metal hoops to ensure insects cannot crawl underneath.
Cultural practices reduce the likelihood of a severe infestation. Rotating crops annually breaks the life cycle of pests that overwinter in the soil and prevents the buildup of pest populations in one area. Adequate spacing between plants ensures good air circulation, which reduces the moist conditions that favor certain pests and diseases. Removing and discarding lower yellowing or heavily infested leaves prevents the spread of pests like aphids and keeps the garden area clean.
When pests are already present, mechanical removal offers immediate control without the use of sprays. For soft-bodied insects like aphids, a strong, direct jet of water from a garden hose can physically dislodge them from the leaves. Caterpillars and harlequin bugs can be easily hand-picked from the plants and dropped into a container of soapy water for disposal. This method is useful for small gardens or when infestations are first noticed.
Strategic companion planting helps to confuse and deter common kale pests. Highly aromatic plants, such as alliums like chives or garlic, release strong scents that mask the appealing odor of the kale, making it harder for pests to locate their host. Dill and sweet alyssum attract beneficial insects, such as hoverflies and parasitic wasps, which prey on or parasitize pests like aphids and caterpillars. Nasturtiums can act as a trap crop, drawing aphids away from the kale leaves.
Organic Sprays and Targeted Treatments
When preventative measures are not enough, organic spray treatments can control established pest populations. Bacillus thuringiensis subspecies kurstaki (Bt) is a naturally occurring soil bacterium that is highly specific for caterpillars. When the caterpillars ingest the treated leaf material, the bacteria produce a toxin that paralyzes their digestive system, causing them to stop feeding and die within a few days. It is safe for beneficial insects, birds, and mammals, but it must be applied thoroughly to all leaf surfaces, including the undersides, where caterpillars feed.
Neem oil, extracted from the seeds of the neem tree, works as an anti-feedant, a repellent, and a growth disruptor for a wide range of insects. For kale, it is effective against aphids, flea beetles, and harlequin bugs. The oil must be diluted with water and a small amount of insecticidal soap, which acts as an emulsifier to allow the oil and water to mix, and should be applied to the entire plant. Application should occur in the early morning or late evening, avoiding direct sunlight and high temperatures, which can cause leaf burn.
Insecticidal soap is another treatment option that works on contact against soft-bodied pests like aphids, thrips, and whiteflies. The soap works by breaking down the insects’ protective outer layer, leading to dehydration and death. For maximum effectiveness, the spray must directly hit the pests, so thorough coverage of the leaf undersides is necessary. Always use a commercial insecticidal soap product, as household dish detergents contain harsh additives that can damage kale leaves. Always follow label instructions carefully and wash all harvested kale leaves thoroughly before consumption.