Grasshopper Control

Grasshoppers can be garden pests

Bill Sevier: Ask a Master Gardener  

Saturday, August 15, 2015

Q: Grasshoppers are eating all my flowers and vegetables. What is the best way to control them? J.W., Claremore

A: If you rate the difficulty of insect control from one to 10, grasshoppers will be an eight or nine. They are a challenge, but there are several ways to deal with them — including insecticides and landscape alterations

There is excellent detailed coverage of grasshoppers and strategies for control in OSU fact sheet EPP-7322, “Grasshopper Control in Gardens and Landscapes” available online.

Oklahoma has more than 130 species of grasshoppers, but only a few are pest problems. They are more prevalent in rural sites close to pastures or in urban areas which have land overgrown with weeds or other vegetation nearby. This is because grasshopper eggs are deposited in the soil under the cover of vegetation.

The eggs hatch in spring and look like tiny versions of the adult. They then go through five levels of development, called instars, and are mature 1-2 months after hatching. The small instars have no wings and stay close to the hatching area. However, the adults have wings and can fly for miles if the local food supply is depleted.

Grasshoppers feed on ornamentals and vegetables, as well as grass. They can be destructive, eating large amounts of foliage, when found in large numbers. Evidence of their destructiveness may be found in the biblical and current descriptions of “locust plagues.” The locust in these plagues are not locusts but grasshoppers and continue to be a significant problem in Northern Africa, the Mid-East and Australia.

Several insecticides are recommended for use when grasshopper damage rises to the level when treatment is needed. A list of insecticides, their characteristics and effectiveness are listed in the OSU fact sheet mentioned. It is clear that the small instar grasshoppers are sensitive to these insecticides but the mature adults less so.

One of the problems with insecticides is that most of them are degraded by heat and sunlight, so there is no prolonged effect. Once the current crop of grasshoppers is killed, many others may move in from local weed patches and thrive due to degradation of the insecticide.

Other strategies include closely inspecting the surrounding weed patches looking for concentrations of young grasshoppers, then dealing with them. You may have to get cooperation from you neighbors for this to be effective.

Floating row covers can be used as a barrier to the insect, especially with vegetables (unless the vegetable needs pollinators).

Lastly, there is biological control, a fungus lethal to grasshoppers, which is available as a bait. It has 3 percent to 40 percent effectiveness at best.

Garden tips

During peak heat of summer is a bad time to use post-emergent broadleaf weed killers such as those containing 2,4-D. Weeds need to be growing to be susceptible to these chemicals. Weeds will start to grow when it cools.

The birds need a handy source of water, as well as food. Put out a big saucer of water and watch them not only drink, but also take baths to cool off and remove parasites. Another saucer of water filled with stones and sand will be a watering hole for butterflies and other beneficial insects.

If you are seeing scattered tips of limbs on trees turning brown with some falling to the ground appearing to be broken off, this is likely cicada damage. We experienced a hatch of 17-year cicadas earlier in the summer (the larvae have been in the ground for 17 years). The adults dig into the bark of a stem about 6 inches from the tip and lay eggs. The limb tip usually dies and may fall to the ground. It commonly involves oaks but others as well. The amount of damage is so low to be of little consequence.