Arugula, often known as rocket or roquette, is a fast-growing leafy green prized for its distinct, peppery flavor. This popular vegetable belongs to the Brassica family, which also includes cabbage, kale, and broccoli. Being a Brassica makes arugula highly susceptible to specialized garden insects drawn to the plant’s unique chemical compounds. Understanding these common invaders and employing a dual strategy of prevention and targeted treatment is the most effective approach to maintaining a healthy, hole-free crop.
Identifying the Primary Arugula Pests
The most immediate sign of trouble is the characteristic damage left by the tiny, dark-colored flea beetle. These insects, typically less than one-eighth of an inch long, jump rapidly when disturbed. Their feeding leaves numerous small, round holes across the leaf surface, frequently described as “shot-hole” damage. Young seedlings are particularly vulnerable; heavy feeding can severely stunt growth or even cause plant death before they establish themselves.
Another common adversary is the aphid, a soft-bodied, pear-shaped insect that can appear in shades of green, black, or yellow. Aphids feed by piercing the plant tissue and sucking out the sugary sap, which leads to distorted or curled leaves and stunted plant development. They tend to congregate in dense, clustered colonies, especially on the undersides of leaves and on tender new growth. As they feed, they excrete a sticky, clear substance known as honeydew, which can eventually promote the growth of black sooty mold on the foliage.
Larger damage is caused by the caterpillars of the cabbage white butterfly and various moths, collectively referred to as cabbage worms or loopers. These larvae chew large, irregular holes into the leaves, sometimes consuming entire sections of foliage. A clear diagnostic sign of their presence is the dark, spherical fecal matter, known as frass, left scattered on the leaves. This feeding and waste contamination can rapidly ruin the harvest quality.
Proactive Cultural Practices to Deter Infestation
Defense against arugula pests begins with implementing physical controls before an infestation takes hold. Using lightweight, floating row covers immediately after seeding or transplanting is highly recommended. This fine mesh fabric acts as a physical barrier, preventing adult pests like flea beetles and cabbage white butterflies from landing on the plants to feed or lay eggs. Securing the edges tightly to the soil ensures that crawling or jumping insects cannot gain access.
Crop rotation disrupts the pest life cycle. Since most arugula pests, including flea beetles and cabbage worms, overwinter in the soil and debris near their host plants, planting Brassica crops in the same location encourages population buildup. Gardeners should avoid planting arugula or any other Brassica in the same spot for at least two to three years to starve out localized pest populations.
Strategic planting times and watering habits reduce pest issues. Arugula is a cool-weather crop; planting it in early spring or late fall helps avoid the peak activity periods of pests like flea beetles and cabbage worms, which thrive in warmer summer months. Ensuring consistent soil moisture is important, as stressed plants are generally more vulnerable to attack. Companion planting, such as using radishes as a sacrificial trap crop, can also divert flea beetles away from the main harvest.
Reactive and Targeted Organic Control Methods
Once an active infestation is identified, physical removal methods are the first step. For larger pests like cabbage worms, regular inspection and hand-picking the caterpillars and their eggs from the leaf undersides is effective for small populations. Aphids, which cluster densely, can often be dislodged with a strong, focused jet of water from a hose. This forceful spray physically removes the soft-bodied insects from the plant, preventing them from climbing back onto the foliage.
For more widespread problems, insecticidal soap is a targeted organic solution that works on contact, primarily against soft-bodied insects like aphids. The soap penetrates and disrupts the insect’s outer cell membrane, leading to dehydration and death. Proper application requires thorough coverage of the entire plant, especially the undersides of the leaves where pests hide, and should be applied when temperatures are moderate to avoid leaf burn.
Neem oil, derived from the seeds of the neem tree, provides a dual-action organic treatment. It functions as an antifeedant, making the leaves unappetizing to pests, and as a growth regulator that disrupts the life cycle of insects like flea beetles and caterpillars. When using neem oil on arugula, it must be applied in the late evening or early morning to prevent damaging the foliage in direct sunlight.
For crawling pests near the soil, food-grade Diatomaceous Earth (DE) can be used as a mechanical control. This fine powder consists of fossilized diatoms, which are sharp microscopic particles that abrade the protective waxy layer of an insect’s exoskeleton. DE only remains effective when it is completely dry, so it should be dusted around the base of the plants and reapplied after any rainfall or overhead watering.