Dogbane

Abstract: 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.

Abstract: Stagonospora apocyni causes a leaf spot disease on hemp dogbane (Apocynum cannabinum L.). The fungus produced phytotoxins citrinin, mellein, tyrosol and α–acetylorcinol in liquid culture. All toxins caused necrosis when placed on leaves of hemp dogbane, and eight other weed species. All four toxins were non–specific phytotoxins. Citrinin showed antimicrobial properties against some bacteria and fungi. Zusammenfassung Stagonospora apocyni verursacht eine Blattfleckenkrankheit bei hemp dogbane (Apocynum cannabinum L.). In Flussigkultur produzierte der Pilz die Phytotoxine Gitrinin, Mellein, Tyrosol und α-Acetylorcmol. AUe Toxine verursachten Blattnekrosen bei A. cannabinum und acht weiteren Unkrautspezies. AUe vier Toxine sind unspezifische Phytotoxine. Gitrinin zeigte zusatzlich antimikrobielle Eigenschaften gegenuber einigen Bakterien- und Pilzarten.

Abstract: Hemp dogbane is sensitive to fluroxypyr and tolerant to clopyralid. Absorption, translocation, and metabolism of clopyralid and fluroxypyr were studied in hemp dogbane to determine if differences in these processes could be responsible for differential sensitivity. In addition, the effect of growth stage on herbicide absorption and translocation was evaluated. The 14C-herbicides were applied to the adaxial side of a single leaf located near the midpoint of hydroponically cultured plants. Uptake of fluroxypyr was more rapid than clopyralid. At 72 h after treatment (HAT), fluroxypyr and clopyralid absorption was 62 and 38%, respectively. Clopyralid was much more mobile than fluroxypyr, with 75% of the absorbed 14C from 14C-clopyralid recovered outside the treated leaf compared to only 45% for fluroxypyr 72 HAT. Relative to fluroxypyr, a higher percentage of 14C-clopyralid recovered outside the treated leaf translocated acropetally, especially when plants were treated during the vegetative stage. Treatment during the early reproductive stage increased basipetal and reduced acropetal translocation relative to the vegetative stage. Neither herbicide was metabolized rapidly. Approxi- mately 60 and 90% of the recovered 14C was attributable to unaltered fluroxypyr and clopyralid, respectively, 72 HAT. Some differences in absorption, translocation, and metabolism between clopyralid and fluroxypyr exist, but they cannot fully account for differential sensitivity of hemp dogbane to these two herbicides. Differences in activity at the target site may be responsible for differential activity of these herbicides on hemp dogbane. Nomenclature: Clopyralid, 3,6-dichloro-2-pyridinecarbox- ylic acid; fluroxypyr, ((4-amino-3,5-dichloro-6(fluoro-2- pyridinyl)oxy)acetic acid; hemp dogbane, Apocynum can- nabinum L. #3 APCCA. Additional index words: Uptake, translocation, metabolism, selectivity, APCCA.