In the past week, West Placer, Roseville and Lincoln, have received an increase in reports of unusual grasshopper activity. The Placer County Agricultural Commissioner in collaboration the UC Urban and Community Integrated Pest Management Area Advisor, the UC Master Gardeners of Placer County, Placer Mosquito and Vector Control District, and the cities of Roseville and Lincoln, worked together to answer some frequently asked questions.


What species of grasshoppers are being found in Roseville and Lincoln?

The grasshoppers being found in West Roseville and Lincoln have been identified as short-horned Melanoplus spp. grasshoppers.

The young grasshoppers (called “nymphs”) emerge from the soil in late spring, commonly in pastures or field environments. Melanoplus grasshoppers are general feeders and consume a wide variety of plants. They prefer young green plants and enjoy consuming lettuce, beans, corn, carrots, onions, and some annual flowers. They dislike tomatoes and squash, so your tomato plants are safe unless there are no other food options nearby. The nymphs molt (shed their skin) five times over about two months before developing into winged, flying adults. 


Has the county ever experienced something like this before?

In most years, these grasshoppers go unnoticed, but when conditions are favorable such as warm, moist springs when abundant food is produced, populations may increase dramatically. Adult or nymphal grasshoppers may migrate into surrounding areas in search of more food. Severe outbreaks only occur every eight to ten years and can last a couple of years. When wild food becomes depleted (i.e. grasses dry up in rangelands), grasshoppers migrate into neighborhoods and landscaped areas in search of food. Landscape plants can be a desirable food source for grasshoppers. Luckily, garden damage is usually limited to a few weeks in early summer, immediately after rangeland plants dry up.


What can we do to help with the grasshopper activity and mitigate impacts to our yards and plants?

Unfortunately, once large numbers of grasshoppers are present in residential landscaping, control options are very limited. Individual plants may be protected by covering them with screens or cloth. However, grasshoppers will eat through cloth or plastic screen if hungry enough. Metal window screen is resistant to grasshopper mouthparts. A successful screening strategy could include screening your most desirable plants and leaving other plants available for grasshoppers to eat. Grasshopper populations may be reduced by manually removing insects through sweeping or raking and bagging for disposal. However, physical removal may not be effective for large grasshopper populations and will require ongoing removal to control.

The optimal time for insecticide application is when grasshopper nymphs are in fields because control with insecticides becomes difficult after grasshoppers have migrated into the garden. Insecticides are generally ineffective against grasshoppers in the landscape because of low residual activity of only a few days. Read the product label to determine the allowable frequency of application. Irrigation or rain can wash away insecticides and further reduce the effectiveness. Insecticide application endangers bees and other beneficial insects; therefore, it is important to ensure insecticides are not sprayed on pollinator plants. Grasshoppers’ natural predators are birds, blister beetles, and robber flies.

For more information visit UC ANR IPM website.

How long is the grasshopper infestation expected to last?

There is no expected time frame on how long this grasshopper infestation may last.


Who is responsible for the issues that are caused to yards and plants due to the grasshopper infestation?

The Placer County Master Gardeners track pest problems and keep residents informed of new developments in pest control. Although, they cannot make any control treatments, they can provide advice and track reports. They can be reached at (530) 889-7388 their hotline or by submitting a question form through their website.