Mustard bugs are a common garden pest that can significantly affect plant health. Understanding how to identify and manage them is key to maintaining a thriving garden.
Identifying Mustard Bugs
The pest commonly referred to as the mustard bug is actually the harlequin bug, scientifically known as Murgantia histrionica. These insects are easily recognized by their striking coloration, featuring a glossy black body adorned with vibrant orange, red, or yellow markings in a distinctive shield shape. Adult harlequin bugs typically measure approximately 3/8 inch long and are often found on the undersides of plant leaves or along stems.
Harlequin bug eggs are barrel-shaped, white with two prominent black bands, and are typically laid in clusters of 10 to 15 on the undersides of host plant leaves. Nymphs, the immature bugs, are smaller than adults and vary in color, often appearing red and black, or green and yellow with black bands. They progressively darken as they mature through five developmental stages.
Understanding Mustard Bug Damage
Harlequin bugs damage plants by inserting piercing-sucking mouthparts into plant tissues to extract fluids. This feeding disrupts the plant’s internal systems, leading to symptoms like stippling, which appears as small, light-colored spots, or larger white and yellow blotches on leaves.
Heavy infestations can result in wilting, stunted growth, and browning of plant foliage. Young plants are vulnerable and may experience deformed growth or plant death if the infestation is severe. Harlequin bugs primarily target plants in the Brassicaceae family, including cabbage, broccoli, cauliflower, kale, collards, mustard greens, radishes, and turnips. If preferred hosts are scarce, they may also feed on other plants like beans, squash, and tomatoes.
Effective Control Strategies for Mustard Bugs
Prevention
Cultural practices can help prevent harlequin bug infestations. Practicing crop rotation disrupts their life cycle, reducing populations. Removing plant debris and crop residue, especially in fall or early spring, eliminates overwintering sites. Controlling weeds, particularly wild mustards and other Brassica-family weeds, removes alternative food sources and breeding grounds.
Physical barriers like lightweight floating row covers can exclude bugs from susceptible plants. Another strategy involves planting “trap crops” such as mustard or radishes slightly earlier than main crops. These attract bugs away from desired plants, and once bugs congregate, the trap crop can be removed and destroyed to reduce the pest population.
Physical/Mechanical Control
Physical intervention is effective for managing harlequin bug populations, especially in smaller gardens. Hand-picking adult bugs and nymphs from plants and dropping them into soapy water reduces their numbers. Regularly inspecting the undersides of leaves for egg masses and crushing them or removing the infested leaf section prevents new generations from hatching.
Biological Control
Natural enemies can help manage harlequin bug populations, though their effectiveness is limited by the bugs’ chemical defenses. Parasitoid wasps target and parasitize harlequin bug eggs, reducing hatching nymphs. Generalist egg predators, such as minute pirate bugs and lacewings, also feed on eggs. Birds consume adult harlequin bugs and nymphs, contributing to natural pest suppression.
Organic Solutions
Several organic solutions are available for infestations.
Insecticidal soaps kill harlequin bugs on contact by disrupting their outer layer.
Neem oil, derived from the neem tree, works as an anti-feedant and growth disruptor, interfering with the bugs’ life cycle.
Diatomaceous earth, a fine powder, can be sprinkled on plants to abrade exoskeletons, leading to dehydration.
Some pyrethrin-based sprays, approved for organic use, provide contact control.
Applying kaolin clay as a spray creates a physical barrier on plant surfaces that deters feeding.
Chemical Control
For severe harlequin bug infestations, chemical pesticides may be considered for immediate and widespread control. Select products specifically labeled for harlequin bugs and the plants being treated. Always follow label instructions precisely regarding application rates, timing, and safety precautions to ensure effectiveness and minimize risks.