Forage 2025 | Managing Invasive Trees: Tamarisk and Eastern Redcedar Control 

Invasive trees are a threat to rangelands. Early detection is key to rapid response in managing them. 

The tamarisk tree is becoming problematic in the Yellowstone area. According to Megan Hoyer, Invasive Species Education Coordinator for the Montana Department of Agriculture, there are a few characteristics of tamarisk that can help ranchers identify it. The needles have a grayish-green color, and the bark is reddish with distinctive white hash marks. The needles are very salty and leave a long-lasting salty taste in the mouth when licked. In the late fall, tamarisk has flowers that are pink and white plumes. However, this does not help identify the tree during the management window as it is not in bloom. 

In the Missouri River Valley, the eastern redcedar tree is taking over rapidly. Sean Kelly, the South Dakota State University Extension Liason Officer for the Mid-Missouri River Prescribed Burn Association, described the eastern redcedar tree as a coniferous evergreen tree that will become either male or female when it gets about four to five years old. Males have brownish tips on the needles, and females develop purplish-blue, berry-like cones. 

Both trees decrease rangeland productivity as forage will not grow around them. 

Tamarisk can use up to 200 gallons of water, a critical resource in the region, per day. It takes up salt with the water and collects it in the needles. When it drops its needles, the salt deposits in the soil making it hard for plants to grow. Tamarisk also crowds out vegetation as it rapidly grows. 

“It reduces the biodiversity,” Hoyer said. “It just grows out of control.” 

Tamarisk also clogs waterways, causes flooding and changes hydrology.  

While eastern redcedar makes a good shelterbelt with its low-hanging branches, it is a problem when not controlled. This tree is highly invasive, drought resistant and will grow in poor soil conditions. 

“Shelterbelts definitely have their place on ranches,” Kelly said. “I recommend farmers and ranchers who have shelterbelts with eastern redcedar to monitor them and make sure they are not spreading.” 

According to Doug Feltman, a South Dakota rancher, the tree inhibits the growth of vegetation around it. 

“There is a chemical the needles produce, and when they fall, grass cannot grow there,” Feltman said. 

This tree will spread rapidly as seen on Feltman’s ranch where photos taken several years apart show the invasion of eastern redcedar. 

“We found these pictures, and it shocked me how bad it had been and how these have taken over,” Feltman said. 

Medium encroachment can reduce rangeland productivity by 50% to 75%, and heavy encroachment reduces rangeland productivity even further. Additionally, a 1% increase in eastern redcedar canopy cover decreases forage production by 1%. 

Early management of these trees is important, but they have opposite control methods. 

Using integrated weed management is the most effective way to manage tamarisk. Tamarisk will reproduce by root shoots or seeds. Burning the trees encourages more shoots, and cutting them down alone is not effective as the tree will regrow.  

Hoyer recommends the cut-stump method which works by applying a mixture of 25% Triclopyr and 75% bark oil to the tree stump after cutting it down. This is best done in the fall as the tree moves nutrients to the roots for winter. 

Hoyer also uses Imazapyr as a foliar treatment. This has to be sprayed on the tree while it is actively growing to work. It is important to follow up after spraying because some may have survived and the seedbed is left behind. 

Following herbicide labels to apply the right rate at the right time is important and can help save money. Other herbicide tips include not spraying in the wind or when it is very hot to reduce killing non-target areas and trying to revegetate bare spots quickly to avoid invasive species moving in. 

Tamarisk infestations can be dense and full of stickers, and some people are finding success in using drones to spray.  

“Getting after them while they are smaller, I recommend the foliar,” Hoyer said, “but when you start getting to these bigger trees, I recommend the cut-stump method.”  

There is not much predation or animal use for tamarisk in the Montana region. There is a species of defoliator moth that will eat the leaves and flowers of tamarisk which hinders seed production. This was an effective biocontrol, but it is not allowed any more because the Southwest Flycatcher, a federally endangered bird, uses the tamarisk tree for habitat. 

Eastern redcedar is not a resprouting tree, meaning if it is cut below the lowest branch or burnt, it will not grow back.  

Mechanical means are effective for light encroachment of smaller trees. Prescribed fire also works well at this level and is preferred by some. 

Beyond that level, prescribed fire is highly effective if allowed in the area. Once the trees get larger, they have less vegetation growing around them making it difficult to fuel the fire, so a combination of mechanical means and fire is needed. 

“We call it ‘cutting and stuffing’ where you cut the dead trees and shove them up in the live stands and that acts as fuel so a crown fire can be carried across the thick and heavily infested areas,” Kelly said. 

Before doing a prescribed fire, it is recommended to work with a prescribed burn association or someone with extensive experience. Planning and preparation before a prescribed fire is important. 

If a medium to heavy encroachment of trees has been mechanically removed, it is important to follow up with a prescribed fire otherwise the seeds will start sprouting and a thicker stand will develop.  

As alternatives for light encroachments, herbicides can be used on trees less than one foot tall, and goats will provide bio-control for smaller trees. 

In a bulletin, Stevan Knezevic, University of Nebraska-Lincoln professor of integrated weed management said, “most eastern redcedar trees less than 24 inches tall can be killed by goats in a paddock grazing system within the first year.” 

Regardless of the management method or tree being worked with, it is important to work with clean equipment and outerwear such as shoes to avoid spreading invasive species between sites. 

Overall, it is going to take a collective effort to stop the spread of invasive woody species to protect rangeland productivity. 

“Not one person can do it,” Hoyer said. “It is going to take a whole team.”