The “pickle bug” is a common name for the pickleworm (Diaphania nitidalis), a significant garden pest of cucurbit plants like cucumbers, squash, and melons. This article provides information on identifying pickleworms, recognizing the damage they cause, understanding their life cycle, and implementing effective prevention and control strategies to protect harvests.
Understanding the Pickleworm
The pickleworm undergoes complete metamorphosis, appearing as a moth, larva, pupa, and egg. The adult pickleworm moth has a wingspan of about 1 to 1.2 inches (2.5 to 3 cm) with iridescent purplish-brown wings featuring a semi-transparent yellow splotch. These nocturnal moths often rest in wooded or weedy areas during the day.
The destructive stage of the pickleworm is the larva, or caterpillar. Newly hatched larvae are very small and nearly white. As they grow, their color can vary, ranging from off-white, yellowish, or green, depending on their food source. Mature larvae can reach about 1 inch (2.5 cm) in length and may turn a pinkish or coppery color before pupating.
Identifying Pickleworm Damage
Pickleworms primarily target cucurbit crops such as summer squash, winter squash, cucumbers, melons, and gourds. Summer squash is particularly preferred.
The most significant damage occurs when the larvae bore into the fruits, rendering them unmarketable. Evidence of pickleworm activity includes small, perfectly round holes in fruits, often accompanied by soft, wet, sawdust-like excrement, known as frass, extruded from the entry points. Beyond fruit damage, larvae also feed on flowers, buds, and shoots, which can severely reduce fruit set. In some cases, tunneling within vines can lead to wilting and stunted plant growth, potentially killing the plant if the infestation is severe. Cantaloupes, with tougher rinds, may show external scarring from surface feeding.
Pickleworm Life Cycle
The pickleworm completes its life cycle from egg to adult in approximately 30 days, depending on environmental conditions. Adult female moths lay eggs singly or in small clusters of two to seven. These eggs are initially white but turn yellow within about 24 hours. Eggs are deposited on actively growing parts of the host plant, such as new leaf buds, flowers, and shoots. Egg hatching usually occurs within three to four days.
The newly emerged larvae then begin feeding, progressing through five larval stages, or instars, over about 14 days. After completing their larval development, the caterpillars pupate, typically in a leaf fold or in plant debris on the ground, forming a flimsy cocoon. The pupal stage lasts for approximately 8 to 9 days. In warmer regions, pickleworms can produce multiple generations per year, often two to four, allowing populations to build up throughout the growing season. They overwinter in frost-free areas like southern Florida and Texas, with moths dispersing northward as temperatures rise each spring.
Effective Prevention and Control
Managing pickleworms involves a combination of cultural practices, physical barriers, and targeted treatments. Planting early-maturing varieties can allow for a harvest before pickleworm populations become significant, as infestations are often worse on later-planted crops. Selecting resistant cucurbit varieties, such as certain types of winter squash like ‘Butternut 23’ or ‘Golden Hubbard’, can also help reduce damage.
Physical barriers, such as floating row covers, provide an effective defense by preventing the nocturnal adult moths from laying eggs on plants. These covers should be applied at dusk and removed in the morning to allow for pollination by bees. Maintaining garden sanitation by promptly removing and destroying infested fruits, damaged plant parts, and crop residue can help disrupt the pest’s life cycle and reduce overwintering sites. Tilling the soil in the fall can also destroy pupae.
For biological control, the bacterium Bacillus thuringiensis (Bt) is an organic option that targets caterpillar pests. Bt must be ingested by the larvae, so it is most effective when applied to plant surfaces where young larvae are feeding, before they bore into the fruit. Some entomopathogenic nematodes can also control pickleworms, particularly in plants with enclosed flowers. In cases of severe infestation, chemical insecticides may be used, but timing is crucial; applications are most effective against young larvae before they enter the fruit where they are protected. When using insecticides, it is important to consider pollinator activity and apply products with low residual activity in the late evening to minimize harm to beneficial insects.