Biology and Management of Bushkiller (Cayratia japonica)

Abstract

Bushkiller [Cayratia japonica (Thunb.) Gagnep] is a nonnative invasive perennial vine in the Vitaceae family that was identified in North Carolina in 2005. Concern of potential economic and environmental consequences of this introduction prompted research to be conducted at North Carolina State University evaluating bushkiller biology and management. A risk assessment was prepared following the USDA†APHIS template entitled “Weed†Initiated Pest Risk Assessment Guidelines for Qualitative Assessments†, v. 5.3. Phenotypic plasticity, rapid growth rate, persistence of underground rhizomes, lack of natural control agents, stress tolerance, increasing costs of control, impacts on ecosystem function and structure, and societal impacts are some of the characteristics that yielded a medium†high risk potential for bushkiller, emphasizing it should be listed at the Federal level, the state level (NC), or both. Selected herbicides were evaluated to develop bushkiller control recommendations. In greenhouse study 1 at 4 WAT, triclopyr (2.24 or 4.5 kg ae/ha), triclopyr plus 2,4†D (1.12 and 1.12 kg ae/ha), triclopyr plus 2,4†D plus aminopyralid (1.12, 1.12, and 0.12 kg ae/ha), and triclopyr plus glyphosate (1.12 and 1.12 kg ae/ha) controlled bushkiller 100%. In greenhouse study 2 at 4 WAT, 2,4†D (1.12 kg ae/ha), DPX†KJM44 (0.35 kg ae/ha), DPX†KJM44 plus 2,4†D (0.35 and 1.12 kg ae/ha), sulfometuron plus DPX†KJM44 (0.33 and 0.35 kg ae/ha), and sulfometuron plus imazapyr (0.33 and 1.68 kg ae/ha) controlled bushkiller at least 98%. In field study 1, glyphosate (4.4% v/v), triclopyr (2.2% v/v), triclopyr plus 2,4†D (2.2 and 1.75% v/v), and triclopyr plus aminopyralid (2.2 and 0.18% v/v) controlled bushkiller 88 to 93% at 1 MAT. However by 10 MAT, no control from these treatments was observed. In field study 2, bushkiller was controlled 88 to 99% at 10 MAT by DPX†KJM44 (0.5% v/v), imazapyr (2.5% v/v), sulfometuron (1.5 g/L), and sulfometuron plus metsulfuron (1.5 and 0.3 g/L). Results from the herbicide studies indicated triclopyr controlled bushkiller in the greenhouse, but not in the field, where DPX†KJM44, imazapyr, and sulfometuron plus metsulfuron showed the greatest control. Research trials were conducted to evaluate bushkiller under inter†and intraspecific competition. In the interspecific competition study, bushkiller [Cayratia japonica (Thunb. ex Murray)], trumpetcreeper [Campsis radicans (L.) Seem.], and wild grape (Vitis spp.) were grown alone, two species per pot, or three species per pot. Bushkiller had the greatest final height and biomass of the three species when each was grown alone. When all three species were grown together, bushkiller grew over twice the height of trumpetcreeper, over 3 times the height of wild grape, and over 4 times the biomass of either species. When height was plotted over time, competition did not affect bushkiller or wild grape growth rate, but trumpetcreeper growth was reduced when grown with bushkiller. This indicates bushkiller will grow faster than trumpetcreeper and wild grape and may alter ecosystem structure and function with time. In the intraspecific competition study, bushkiller was grown in cultures of 1, 2, and 3 plants per pot. Final height of bushkiller was not affected by intraspecific competition; however bushkiller dry weight decreased with increasing competition. Bushkiller is likely to thrive in monoculture, however biomass per plant may be lowered as number of plants per population increases.