Lawn Armyworm (Spodoptera sp.)
Posted on Feb. 25, 2024 / Plant Pests, Turf, Golf Courses / Subscribe 0
By: Alberto Ricordi, Hannah Lutgen, Zhiqiang Cheng
The most common insect pests of turfgrasses in Hawaii are “lawn caterpillars,” the larvae of lepidopterous insects (moths and butterflies), including lawn armyworm and others. All of Hawaii’s turfgrasses are susceptible to attack by these pests, although some of these insects prefer a particular type of turf. This article highlights key information about lawn armyworms from existing literature, includes tips to monitor lawns for insect damage, and provides a list of resources available to identify and manage pests, and obtain information about pesticides.
Biology and Life Cycle:
Armyworm adult moths reproduce and lay their eggs in fuzzy clusters on trees, leaves, or building walls & ceilings near lights. The young larvae are small green caterpillars that feed on grass blades during the night and day. As the caterpillars age, they turn brown with pale stripes that mainly feed at night and hide in the thatch during the day. Mature caterpillars excavate and pupate in the soil: developing a hard red-brown case (pupa) and emerging into a gray-brown moth. In Hawaii, lawn armyworms complete their life cycle in 43 days and may produce 8 generations per year (Deputy & Hara, 2020).
Figure 1. A mature lawn armyworm caterpillar is brown with stripes. Photo credit: Allison Wright, Island Plant Company.
Hosts & Symptoms:
Armyworms prefer Bermudagrass lawns but will also feed on sedges, sugarcane, seashore paspalum, and goosegrass. As they feed on grass the leaf blades appear clipped, skeletonized, and damaged, so look for circular or scattered patches of discolored turf grass with distinct borders between damaged and undamaged turf. Heavy infestations of armyworms can destroy about 1 foot of grass each night (Deputy & Hara, 2020).
Figure 2. Armyworm feeding damage. Photo credit: Allison Wright, Island Plant Company.
Monitoring:
Landscape professionals utilize the following simple and easy tips to scout for armyworms and other lawn pests.
- Look for bird activity. Birds often migrate to lawns to feed on insect larvae or grubs. If birds are consistently there or concentrate in damaged areas of the lawn this could indicate an armyworm infestation.
- Place a piece of plywood or cardboard with weights on the lawn in an area of grass along the edge or transition zone between healthy and damaged grass for 1-2 hours. Mature armyworms are most active and feed at night or during dark periods. So, these armyworms will think it’s nighttime and crawl out from the soil and thatch, and you will see them.
Figure 3. To scout for pests, landscape professionals put a piece of plywood along the edge of damaged turfgrass areas and leave it for 1-2 hours to trick armyworms into thinking it is night. This encourages caterpillars to crawl out from the soil and thatch. Photo credit: Allison Wright, Island Plant Company.
Figure 4. Mynah birds feed on armyworms and/or other turf grass pests. Photo credit: Allison Wright, Island Plant Company.
Identification and Management:
Proper pest identification is the first step prior to management. To accurately identify armyworms and other lawn pests, please refer to this CTAHR Extension publication. In CTAHR's publication “Destructive Turf Caterpillars in Hawaii”, Jay Deputy and Arnold Hara describe several types of “lawn caterpillars” to help landscape professionals better understand the different turf pest species, their life cycles, and their identification. Also included is a list of insecticide’s active ingredients that were effective against caterpillars at the time of the publication (2000).
Because the list of products labeled for control of caterpillars in lawns is extensive and evolving, the following resources may be used to find the trade names and labels of current products in Hawaii. Contact your local distributor to verify what products are available and always read and follow the label to ensure that a product is approved for the application. In response to the needs of the local turfgrass industry, Dr. Zhiqiang Cheng of CTAHR is planning a research project to identify effective control measures (low-risk insecticides and/or biological control) against lawn armyworm in 2024. Research updates on this project will be provided.
List of Databases for Pesticide Information:
Hawaii Department of Agriculture licensed pesticides- refer to this website to find licensed pesticide products in Hawaii.
National Pesticide Information Retrieval System
Always follow the label when using a pesticide. The label is the law. Contact your county extension agent if you need assistance.
Disclaimer: Mention of a trademark or proprietary name does not constitute an endorsement, guarantee, or warranty by the University of Hawaiʻi Cooperative Extension or its employees and does not imply recommendation to the exclusion of other suitable products.
References:
Deputy, J. and A. Hara, 2000. Destructive Turf Caterpillars in Hawaii. University of Hawaii at Manoa. College of Tropical Agriculture and Human Resources (CTAHR). CTAHR Extension Publication IP-5. Available at https://www.ctahr.hawaii.edu/oc/freepubs/pdf/IP-5.pdf
Brennan, B., Swfit, S., and C. Nagamine. 2016. Turf and Ornamental Pest Control A guide for Commercial Pesticide Applicatiors. University of Hawaii at Manoa. College of Tropical Agriculture and Human Resources (CTAHR). Available at Tuf and Ornamental Pest Control (hawaii.edu)
Alberto Ricordi, Department of Tropical Plant and Soil Sciences, Cooperative Extension, Oahu County, CTAHR, University of Hawaii at Manoa. Hannah Lutgen, Extension Faculty, Department of Tropical Plant and Soil Sciences, Maui County Cooperative Extension, University of Hawaii at Manoa CTAHR. Dr. Zhiqiang Cheng, Professor and Extension Specialist, Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa CTAHR.
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