Finding broccoli leaves riddled with holes or seedlings severed at the base is a common frustration for brassica growers. This destruction occurs because several garden pests prefer to feed under the cover of darkness. Identifying the culprit feeding on your leaves or stems is the first step toward protecting your crop. Successful identification requires understanding which pests operate nocturnally and examining the distinct signature of their damage.
Identifying the Primary Nocturnal Culprits
Slugs and snails are the most frequently encountered nighttime garden feeders, requiring moist conditions to move and survive. These herbivores emerge from cool, damp hiding spots once the sun sets to feed on tender foliage. Because they move slowly and graze with a rasping mouthpart called a radula, they leave behind irregular holes and ragged leaf edges.
Cutworms are another major group of nocturnal pests, representing the larval stage of several species of moths. These plump, grayish-brown caterpillars spend their days curled up just beneath the soil surface near the base of plants. They emerge after dark to feed, often wrapping around the stem of a young plant to chew through the base, hence their name.
Earwigs are a common nocturnal pest that can cause significant damage to broccoli leaves. These insects seek out dark, tight, and moist crevices during the day. They climb plants at night to feed on the leaves, especially new growth, and their populations can quickly overwhelm a small planting area.
Recognizing Specific Damage Patterns
The most definitive sign of slug or snail activity is the presence of a shiny, silvery, dried mucus trail left on the leaves, stems, or soil. Their feeding often results in large, irregular holes within the leaf interior or along the margins, which can look shredded. Since they prefer moisture, damage is typically most severe after rain or heavy watering.
Cutworm damage is highly specific, usually involving the sudden disappearance of a young plant or a stem cleanly clipped off near the soil line. If you find a seedling lying on the ground, examine the base of the stem for a sharp, horizontal cut. Sometimes the cutworm drags the severed plant part slightly beneath the soil to continue feeding.
Earwig damage can be confused with slugs, as both cause irregular holes and jagged leaf edges, but earwigs do not leave a slime trail. Their feeding often leaves smaller, more scattered holes, and they sometimes chew directly into the growing points of the plant. If you suspect earwigs, going out an hour after sunset with a flashlight is the best way to catch them feeding.
Immediate, Non-Chemical Control Strategies
For slugs and snails, one effective strategy is setting out simple beer traps, which use the yeast in beer or a mixture of water, sugar, and yeast to attract them. Bury a shallow container, such as a tuna can, level with the soil surface, fill it with the liquid, and the pests will crawl in and drown. Another barrier method involves placing a ring of copper tape around the base of plants, as the copper reacts with their slime to deliver a mild, unpleasant electric shock.
To protect young broccoli plants from cutworms, use physical collars made from cardboard, plastic cups, or aluminum foil. Push the collar a couple of inches into the soil and ensure it extends a few inches above the soil to block the caterpillar from wrapping its body around the stem. Handpicking is also possible; locate the cutworm by gently digging a few inches deep near the base of a freshly cut plant, where it will likely be hiding in a characteristic C-shape.
Earwigs can be managed with simple traps, as they seek dark, moist places to hide when morning arrives. Laying out rolled-up newspapers, short sections of bamboo, or garden hoses overnight will attract them, and you can collect the traps in the morning to dispose of the earwigs in soapy water. You can also sprinkle diatomaceous earth in a ring around the plants; this fine powder causes dehydration in insects but must be kept dry to remain effective.