Field research was conducted to characterize hemp dogbane crown root carbohydrates, to quantify crown root lipids, and to determine seasonal fluctuation of each. The effect of day length on the release of hemp dogbane crown bud dormancy was studied in growth chambers. Total nonstructural carbohydrate (TNC) levels fluctuated with seasonal lows occurring during bud to mid-flowering and seasonal highs in fall predormancy periods. Starch was the primary storage carbohydrate, comprising up to 39.6% of crown root dry weight at the highest seasonal level. Ethanol soluble reducing sugar levels were negatively correlated with seasonal starch levels, and appeared to be maltose and glucose accumulated before conversion to sucrose for translocation. Most lipids were in ethanol soluble fractions and were inversely correlated with seasonal TNC patterns. The maximum level of total lipids in crown roots was 6%. Lipids appeared to be by-products of metabolism in nonarticulated lacticifers and not a significant carbon energy source. An 18-h day length resulted in a 10-fold increase in intact, 2-yr-old crown root dormancy release compared with 10- or 14-h day lengths in growth chamber studies. Seasonal carbohydrate fluctuations in hemp dogbane suggest the most effective control with mowing or tillage would occur when applied at mid- to full flower before root carbohydrates begin to recover. The most effective translocation of phloem mobile herbicides to crown roots would occur after mid- to late flower through leaf senescence when carbohydrates are being stored in the roots.

Absorption and translocation of 14C-glyphosate [N-(phosphonomethyl)glycine] by moisture-stressed common milkweed (Asclepias syriaca L. ♯ ASCSY) was studied in greenhouse and growth chamber experiments. Water-stressed [13% (w/w) soil moisture] common milkweed plants treated with glyphosate at 1.1 kg ae/ha produced shoot regrowth equal to untreated plants, whereas shoot regrowth of nonstressed [25% (w/w) soil moisture] glyphosate-treated plants was only 6% of untreated plants. All shoot regrowth originated from buds on the proximal half of roots. Common milkweed plants, maintained at 25% soil moisture, absorbed 44% of the 14C-glyphosate applied and translocated 20% from the treated leaf, whereas plants at 13% soil moisture absorbed 29% and translocated 7%. Wiping the leaf with tissue paper wetted with distilled water or chloroform prior to 14C-glyphosate application increased absorption from 35 (unwiped leaves) to 62 and 77%, respectively, for plants at 25% soil moisture, and increased absorption from 14 to 42 and 46%, respectively, for plants at 13% soil moisture. Wiping failed to increase translocation out of the treated leaf for plants at either soil moisture regime. Latex samples taken from the abaxial leaf surface opposite 14C-glyphosate-treated leaves and from petioles of treated leaves did not contain 14C, indicating that glyphosate did not enter laticifers. Proximal root buds accumulated less 14C-radioactivity than distal root buds and had lower respiratory rates, suggesting that proximal root buds are more dormant than distal root buds and thus accumulate less glyphosate.