Seasonal nonstructural carbohydrates in the crowns and rhizomes of in situ populations of Japanese knotweed (Fallopia japonica) and the hybrid Bohemian knotweed (F. x bohemica)

Authors: BECKER, ROGER - University Of Minnesota; MENTZ, RYAN - University Of Minnesota; SMITH, ALLEN - University Of Minnesota; ANNOR, GEORGE - University Of Minnesota; SINGH, NAVJOT - University Of Minnesota; SARANGI, DEBALIN - University Of Minnesota; ANDERSON, NEIL - University Of Minnesota; Heuschele, Deborah; KATOVICH, JEANIE - University Of Minnesota; CLARK, MATHEW - University Of Minnesota

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2025
Publication Date: 4/25/2025
Citation: Becker, R.L., Mentz, R.S., Smith, A.G., Annor, G.G., Singh, N., Sarangi, D., Anderson, N.O., Heuschele, D.J., Katovich, J., Clark, M.D. 2025. Seasonal nonstructural carbohydrates in the crowns and rhizomes of in situ populations of Japanese knotweed (Fallopia japonica) and the hybrid Bohemian knotweed (F. x bohemica). Weed Science. 73. Article e73. https://doi.org/10.1017/wsc.2025.11.
DOI: https://doi.org/10.1017/wsc.2025.11

Interpretive Summary: Knotweeds are invasive perennial weeds that form large expanding rhizomes and root networks that can damage building foundations and break up rock formations. These weeds are difficult to control due to the lack of basic growth information. To better understand when control methods should be applied, starch and sugar use and storage of these compounds in roots and crowns was monitored throughout two growing seasons. The two species of invasive knotweeds tested displayed low storage reserves in June and July, corresponding with most of the growth and reproduction of the plants, with starch accumulation for over winter survival beginning in August. These results suggest that managers should remove above ground biomass immediately before flowering to reduce starch accumulation in the roots and decrease winter survival. Also, treating the plants with a systemic herbicide in August would ensure that the chemical is transported to the below ground tissues to kill root and rhizomes. The results will assist invasive plant managers to better time applications of herbicides for effective weed control.

Technical Abstract: Herbaceous perennials must annually rebuild the above ground photosynthetic architecture from carbohydrates stored in crowns, rhizomes, and roots. Knowledge of carbohydrate utilization and storage can inform management decisions and improve control outcomes for invasive perennials. We monitored the non-structural carbohydrates in a population of the hybrid Fallopia xbohemica [Chrtek and Chrtkova´] (Bohemian knotweed) in 2020 and 2021, and in F. japonica [Houttuyn] Ronse Decraene) (Japanese knotweed) in 2021. Carbohydrate storage in knotweed crowns followed seasonal patterns typical of perennial herbaceous dicots corresponding to key phenological events. Starch was consistently the highest nonstructural carbohydrate present. Sucrose levels did not show a consistent inverse relationship with starch levels, which would reflect starch metabolism to sucrose for transport to metabolic sinks as the season progresses. Lateral distribution of starch in rhizomes, and more broadly non-structural carbohydrates sampled prior to dormancy break showed a trend of higher levels in rhizomes compared to crowns. Total nonstructural carbohydrate levels in crowns reached seasonal lows in June and July (13.9 to 18.9 %), corresponding to depletion to support the observed maximum shoot elongation and vegetative canopy development by the end of July, just prior to entering the reproductive phase in August. Maximum starch accumulation in crowns followed complete senescence of above ground tissues by mid- to late-October. We theorize that removal of above ground shoot biomass in late-July, prior to flowering in mid-August with a follow up removal of vegetation in early September prior to senescence would optimize the most effective use of time and labor in depleting carbohydrate reserves over time. Additionally, foliar applied systemic herbicide translocation to below ground tissue should be maximized with applications in late-August through early fall, to prior to fall senescence, which is typically late-September in Minnesota.