Squash bugs are a major problem for many home gardeners, often devastating crops like zucchini, pumpkins, and various squash varieties. These persistent insects can quickly destroy a healthy plant, leading to frustration for those relying on a successful harvest. Companion planting offers a natural, non-chemical pest management method by using specific plants to either repel the pest or draw them away from the main crop. This practice leverages plant chemistry and natural insect behavior to protect vulnerable squash plants. Understanding which plants are effective deterrents and how to place them strategically can be the difference between a bountiful harvest and crop loss.
Identifying and Understanding Squash Bugs
The squash bug, Anasa tristis, is the culprit. The adult bug is approximately five-eighths of an inch long, with a flattened, shield-shaped body that is typically dark gray to dark brown. Females lay clusters of small, oval-shaped eggs, which are bronze or yellowish-brown, usually found in the crevices of leaf undersides.
The newly hatched nymphs progress through five instars, initially appearing light green with dark heads and legs, gradually turning a light gray or brownish-gray as they mature. Both the adult and nymph stages cause damage by using piercing-sucking mouthparts to draw sap out of the plant tissue. This feeding action injects a toxic substance into the plant, which prevents the proper flow of water and nutrients.
This disruption initially manifests as yellow spots that eventually turn brown and dry out, a condition sometimes called “anasa wilt.” Young seedlings are particularly vulnerable and may wilt and die quickly, while larger plants can suffer vine collapse and premature death.
Specific Plants Known to Deter Squash Bugs
Plants deter squash bugs through three main methods: strong aromatic repellents, serving as a physical or chemical mask, or acting as an irresistible trap crop. Aromatic plants work by emitting compounds that confuse the insect’s ability to locate its host plant through scent. Herbs like mint, basil, and catnip are effective repellents because their strong essential oils overpower the scent of the squash foliage.
Dill and borage are also known for their repellent qualities and for attracting beneficial insects. Dill, in particular, attracts the parasitic tachinid fly, Trichopoda pennipes, which lays its eggs on adult squash bugs. The resulting larva then burrows into the adult bug, eventually killing it, providing biological control.
Nasturtiums and radishes function as masking plants or decoys. Nasturtiums have a distinct spicy aroma that helps deter squash bugs and may also serve as a trap crop. Radishes, especially the daikon variety, have a sharp, peppery scent that may discourage squash bugs from laying eggs near the main crop.
Trap cropping is a highly targeted strategy using a plant that is significantly more attractive to the pest than the main crop. The most effective trap crop is the Blue Hubbard squash, which contains high levels of the biochemical compound cucurbitacin, making it irresistible to the pests. Planting a few Blue Hubbard plants is intended to draw the entire squash bug population to this single location, where they can be destroyed.
Strategic Placement for Maximum Protection
Effective companion planting requires careful planning regarding the location, density, and timing of the deterrent plants.
Aromatic Herbs
When using aromatic herbs like mint or basil, they should be planted in close proximity to the squash plants so their scent can effectively mask the squash odor. Since mint spreads aggressively, it is often best to plant it in a buried container near the squash to prevent it from taking over the garden bed.
Trap Crops
Trap crops, such as Blue Hubbard squash, require specific timing to be effective. The trap crop plants must be larger and more appealing than the main crop when the overwintering adult squash bugs emerge in the spring. Gardeners should plant the trap crop two to three weeks before the main squash crop is planted, ensuring the Blue Hubbard seedlings are more mature and attractive.
For a small garden, a few trap plants, perhaps six to eight Blue Hubbards, planted at the corners or a short distance away (three to eight feet) from the main crop, can be sufficient. This perimeter planting creates a protective barrier, concentrating the pests in a single area where they can be removed by hand or with targeted treatment. It is important to destroy the squash bugs and their eggs on the trap crop regularly, or they will reproduce and eventually migrate to the main plants.
Intercropping and Rotation
Intercropping involves mixing the deterrents directly among the squash plants, which is common with aromatic herbs and nasturtiums, to create a confusing, diverse canopy. Regardless of the companion planting method used, practice crop rotation by not planting any member of the squash family in the same location year after year. This practice disrupts the pest’s life cycle by eliminating easy access to a host plant in the spring.