Grasshoppers are common insects known for their powerful hind legs used for jumping. They are generalist herbivores, meaning they feed on a wide variety of plants and are found in nearly every terrestrial ecosystem. While a few grasshoppers are a natural part of a healthy garden, serving as a food source for predators, their populations can rapidly multiply under favorable conditions. When numbers increase significantly, these insects transition from harmless visitors to serious agricultural and garden pests capable of inflicting substantial harm.
Assessing the Threat: Signs of Grasshopper Damage
The distinct, ragged feeding patterns they leave behind on foliage confirm the presence of grasshoppers. Unlike smaller insects that might skeletonize a leaf or bore a clean hole, grasshoppers use their chewing mouthparts to create large, irregular holes. This defoliation can quickly reduce a plant’s photosynthetic capability.
In severe infestations, the insects consume almost all the soft leaf tissue, leaving behind only the tough, fibrous stems and leaf veins. Grasshoppers are indiscriminate feeders, and while they may prefer lush plants like lettuce, corn, and beans, high populations will readily attack ornamentals and even the fruit itself.
The extent of the damage determines the threat level. Young, tender plants are particularly vulnerable and can be entirely consumed or “mowed down” to the soil line. Plants with a high water content, such as onions, carrots, and the growing tips of alfalfa, are highly susceptible targets, while plants like squash and tomatoes are less preferred.
Understanding Grasshopper Behavior and Life Cycle
Grasshopper populations tend to spike during periods of hot, dry weather, which increases egg survival and speeds up nymphal development. Most pest species overwinter as eggs deposited in the soil, often in undisturbed areas like weedy patches and ditches. Eggs are laid in clusters within the top few inches of soil during late summer and early fall.
Hatching typically occurs in the spring, and the newly emerged young, called nymphs, are wingless. These nymphs are often the most destructive stage because they are concentrated in their hatching beds and must feed immediately to survive. They go through five developmental stages, or instars, before reaching adulthood, a process that takes five to six weeks.
Adult grasshoppers can migrate into gardens in July and August. This migration is often triggered when surrounding vegetation, such as pastures or field crops, dries out or is harvested, forcing the insects to seek fresh, green food sources. Understanding this timing is essential, as control measures are most effective when applied to the concentrated, wingless nymphs.
Effective Control and Prevention Methods
Effective grasshopper management relies on an Integrated Pest Management (IPM) approach that combines multiple strategies to disrupt the insects’ life cycle. Cultural and physical controls focus on prevention by eliminating preferred egg-laying and feeding habitats.
Cultural and Physical Controls
Fall tilling of untilled ground, such as garden borders or adjacent weedy areas, helps disrupt egg pods by exposing them to harsh winter conditions, desiccation, and predators. Keep garden perimeters and nearby ditches mowed or weed-free, as tall, weedy growth provides a sheltered environment for young nymphs to develop.
For high-value plants, physical barriers like fine mesh row covers or cheesecloth can be draped over vulnerable crops to create a barrier against feeding insects. These covers must be secured tightly to the ground to prevent grasshoppers from crawling underneath.
Biological Controls
Biological controls offer a selective, long-term solution that avoids harming beneficial insects. Encouraging natural predators, such as insectivorous birds, parasitic flies, and ground beetles, can suppress populations.
A highly targeted microbial control is the protozoan Nosema locustae, which is applied as a bait, typically on wheat bran. When ingested, Nosema locustae infects the grasshopper, causing a disease that reduces appetite, decreases mobility, and ultimately leads to death, often spreading through cannibalism among the insects. The success of this biological agent is greatest when applied early in the season, targeting young nymphs when they are still less than three-quarters of an inch long and concentrated in their hatching areas.
Chemical Controls
Chemical control should be considered a last resort for severe infestations, and the application must be highly targeted. Baits containing a chemical insecticide, applied to non-crop areas like borders, are preferred over broad-spectrum sprays because they are ingested by the grasshoppers themselves. Focusing application on the borders of the garden, where grasshoppers migrate from, is more effective than treating the entire yard.