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Weed & Pest

Invasive control involves cooperation from all concerned parties

Written by Saige

“Managing pests and invasive species is everyone’s business,” said Maui County, Hawaii Soil and Water Conservation Service District Director Mae Nakahota. 

Nakahota and other conservation professionals across the West presented for the Western Governors’ Association webinar series on invasive species management. Each speaker presented on different issues affecting their area, as well as the importance of cooperation amongst parties.

Cover crops 

“As conservationists, we have often pushed cover crops without really paying attention to some of the negative impacts they can have,” said Nakahota. “These cover crops created the perfect home for semi slugs.” 

Nakahota explained the semi slug is very small and has a structure on its back that resembles a backpack. The slugs can carry a number of diseases including rat lungworm disease. 

“Rat lungworm disease originates from rats and is passed to amphibians such as frogs and slugs and then onto humans,” said Nakahota. “Recently, 60 people became ill after consuming a beverage left outside that had a slug crawl into it.”

“The islands have been highlighted as a source of the worms,” Nakahota said. “Cover crops need to be sprayed as an absolute no- amphibian zone.”

Purpose gone wrong

We also have to remember not all invasives start as an accident. Some species are brought in for a specific purpose and get out of control. 

“After massive pasture die-off, we brought in glycerin to help, and it got completely out of control,” said Nakahota. “What appears to be okay today may not always be okay tomorrow or in the distant future.” 

“The axis deer was brought to the islands as a gift to the King of Hawaii and has wreaked havoc ever since,” explained Nakahota. “The deer were in very limited numbers at first but became very popular among hunters, and their numbers have exploded.” 

She noted the deer compete with native species and livestock and have caused massive damage to watersheds. 

“The deer not only physically damaged the watersheds and caused erosion, they also spread disease by defecating in the water,” said Nakahota.

“We have to have boots on the ground and be proactive when it comes to any non-native species that we introduce purposely or is brought in accidentally,” said Nakahota.  

Collaboration is key 

In Oregon, the Clackamas River Invasive Species Partnership (CRISP) is using their numerous partnerships with local organizations to fight the ever-growing issue of garlic mustard, said Lindsey Karr, program coordinator.

“CRISP meets twice per year to discuss concerns regarding invasive species within the area,” said Karr. “Through this collaboration, we are able to discuss successes and failures with control and set priorities for controlling garlic mustard.”

Aside from trading ideas and information, the group is also able to secure more funds to aid in the control of invasive species, according to Karr. 

She explained the group took the watershed approach and divided the area into smaller zones and set habitat priorities. 

“We want to focus on areas that have good habitat and human recreation interest,” she noted. “Human activity can be a major source of spreading for species such as garlic mustard.”

“The trickiest part of this area is there are a lot of island,” said Karr. “Ownership is difficult to determine, and management history has been problematic.” 

She explained through their partnership they collaborated with local partners to figure out ownership of islands and who and how they had been treated. Local partners in the area donated use of a boat, enabling CRISP to treat invasive on the islands.

Analysis and treatment

“When we looked at garlic mustard, we found that 23 percent of the infestations outside our area were within the floodplain, and 87 percent were within the area were in the floodplain,” Karr pointed out. 

“What this shows is the advanced survivability of the seeds,” she said. “They do really well with disturbances and can spread around in a river setting.” 

Karr explained this analysis allowed for their team to create an educated plan to go about controlling the plant. 

“We spray in the spring in the fall,” she explained. “In the spring, we do two sprays and try to catch the plants before they seed.” 

She continued, “The plant flowers in its first year and in the second year is a rosette. We also utilize pulling, which allows for greater flexibility with the weather and to catch any plants that missed the initial spray.” 

She noted they would also spray in the fall because it is useful for carpets of seedlings or those mixed in with native annual seeds. 

“By treating in the fall, we allow native annuals to go to seed so they can regenerate it makes spring treatments lighter, as well,” according to Karr.

Callie Hanson is the assistant editor of the Wyoming Livestock Roundup. Send comments on this article to This email address is being protected from spambots. You need JavaScript enabled to view it..