Carbohydrate trends in broom snakeweed (Xanthocephalum sarothrae)

Broom snakeweed (Xanthocephalum sarothrae) is a suffretescent shrub widely distributed in the southwestern United States and northern Mexico. This weed is a serious problem in range management since it is toxic and it is a strong competitor with the desirable grasses in the plant community. Therefore, its control is amply justified.

Translocation of foliar applied growth regulating herbicides is associated with total nonstructural carbohydrate (TNC) translocation in the plant. Foliar herbicides have to be applied at a time when carbohydrates are translocated throughout the plant to be effective. Therefore, knowledge of TNC trends is fundamental to application of foliar applied herbicides.

The study was conducted at two locations in Lea County, New Mexico, on broom snakeweed: (a) to estimate trend of TNC concentration through the year; (b) to correlate TNC to phenological stages; and (c) to evaluate the influence of environmental parameters that affect TNC. Environmental parameters measured included soil water content and soil temperature.

Three plant parts: small stems, large stems and roots were analyzed for TNC by the method of acid extraction with .2N HCl and determined by spectrophotometry.

The general trend had two peaks and two depressions at Location 2, but a less defined peak in midsummer at Location 1. No particular tissue was more important for storing carbohydrates than others. Snakeweed accumulated TNC during periods when elaboration of carbohydrates exceeded the demand for respiration and growth. Reserves were used for regrowth and for flowering. Soil temperature (30-cm depth) was the environmental parameter most closely associated with TNC.