Control of yellow Himalayan raspberry (Rubus ellipticus Sm.) with cut stump herbicide treatments in Hawaii Volcanoes National Park

Abstract

Yellow Himalayan raspberry (Rubus ellipticus Sm.), introduced to Hawai'i Island approximately 30 years ago, has become a serious pest in the 'Ola'a Tract of Hawaii Volcanoes National Park. This shade-tolerant raspberry forms dense thickets, which replace native understory vegetation. Four herbicides were effective cut-stump treatments for yellow raspberry: imazapyr (Arsenal, 50% in water), triclopyr triethyl mine salt (Garlon 3 4 50% in water), triclopyr butoxyethyl ester (Garlon 4, 50% in diesel oil), and metsulfuron methyl (Escort, 28 gm/liter water). Ninety-five to one hundred percent of raspberry plants treated with these chemicals died within 24 months. With each of the four treatments, 10-15% of raspberry plants resprouted from the roots, but at least half of the resprouts later died. Two other herbicides tested were much less effective at killing raspberry. Picloram potassium salt (Tordon 22K, 20% in water) killed only 65% of treated plants, and a commercial mix of 2,4D and triclopyr (Crossbow, 50% in diesel oil) caused the death of 75% of treated raspberry. Fifteen common native plant species and 10 others of sporadic occurrence were monitored for a year in plots surrounding treated raspberry plants. No statistically significant changes in number were observed for any native species in any herbicide treatment. In general, the number of individuals taller than 0.1 m counted in herbicide plots increased over the year for six common native fern species, one sedge, and one herb. Results were more variable for seven native woody species common in study plots, with increases in numbers in some treatments and small decreases in others. Both picloram and imazapyr plots displayed losses in a larger variety of native woody species than were observed in the other treatments. Saplings of one native tree, olomea (Perrottetia sandwicensis) appeared to be particularly sensitive to both picloram and imazapyr applied to nearby raspberry stumps.