Alligatorweed Control With Thrips

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picture of alligator weed and its flowering part

Healthy alligatorweed with distinctive white clover-like flowers. Photo by D. Rashash

Article adapted from Dr. Diana Rashash, Area Specialized Agent, Water Quality at
Alligatorweed Thrips for Alligatorweed Control.

There is a new to North Carolina management strategy for alligatorweed control. Alligatorweed (Alternanthera philoxeroides) is an invasive aquatic weed native to Brazil that arrived in the southeastern US in the early 1900s. The plant has opposite leaves, a hollow stem, and a white clover-like flower. It grows very well in our ditches, ponds, and waterways. Healthy alligatorweed has distinctive, white, clover-like flowers and can spread through fragmentation, with each node capable of forming a new plant. This allows for easy transport and spread through activities like mowing or boating, and especially through drainage in ditches and
waterways.

Typical chemical control measures have included the use of glyphosate applied at regular intervals throughout the growing season. From 2006-2015, several counties in eastern NC received Alligatorweed flea beetles (Agasicles hygrophila) in hopes that they would be a useful integrated pest management (IPM) practice. Flea beetles feed on foliage and can do a good job of knocking back alligatorweed. Unfortunately, NC is at the northern edge of their cold tolerance. Despite repeated attempts, strong colonies of the alligatorweed flea beetles were not
attained.

In August 2018, a sample of “sick” alligatorweed from a pond in Onslow County was sent to the NC State University Plant Disease & Insect Clinic (PDIC) and the Army Corps of Engineers lab in Vicksburg, MS. Both laboratories confirmed the presence of alligatorweed thrips (Amynothrips andersoni O’Neill). The adult a. thrips is approximately 2 mm in size, and the larvae are roughly 1.5 mm. This was the first confirmed sighting of alligatorweed thrips in NC. The a. thrips have a broader cold tolerance than the flea beetle. The a. thrips at the Onslow site
easily survived the 10-day freezing spell during winter 2018. This gives us hope that a. thrips will be a good IPM agent.

picture of an immature thrip

Closeup of immature alligatorweed thrips. Photo by D. Rashash

picture of adult thrip

Adult alligatorweed thrips, Amynothrips andersoni O’Neill. Photo by D. Rashash

The a. thrips juveniles and adults only eat alligatorweed, so there is no risk to other plants or crops. Early damage appears as discolored and curled leaves. A high level of predation can completely defoliate a patch of alligatorweed. These are tiny, yet mighty insects!

picture of damage to alligator weed by thrips

Damage by thrips

Since their discovery in NC, the alligatorweed thrips have been provided to the N.C. Department of Agriculture and Consumer Services, Beneficial Insect Lab. NCDA&CS is establishing a breeding population. The Cooperative Extension Service has placed thrips in several locations in Eastern NC, including this year in Pamlico County.

As of July, actively feeding alligatorweed thrips have been found in four locations in Bayboro and Stonewall, approximately 2 two miles from their original locations.

Alligatorweed can clog waterways and drainage ditches, leading to washouts and restricted waterflow. This poses difficulties in use of water resources and often leads to flooding in agricultural fields and residential properties. Hopefully this tiny insect will help to reduce these hazards and limit the continual spread of this invasive plant.

If you would like more information on this topic, please contact Daniel Simpson at 252-745-4121 or daniel_simpson@ncsu.edu.