Greenhouse experiments were conducted to assess the storage of nonstructural carbohydrates in the stems and roots of honey mesquite and their mobilization and utilization following defoliation by hand or clopyralid. All leaves were removed by hand from one group of plants while leaving stems intact. Another group received a foliar spray of clopyralid at a sublethal acid equivalent rate of 0.07 kg ha−1. Samplings at treatment on day 0 and at 14, 28, 42, and 58 d after treatment measured leaf area; dry weight of leaves, stems, and roots; and grams and percent total nonstructural carbohydrates in stems and roots. Controls accumulated dry weight and grams total nonstructural carbohydrates in stems and roots, while maintaining a constant percent total nonstructural carbohydrates throughout the experiment. Percent and grams total nonstructural carbohydrates in stems and roots of hand defoliated plants decreased by about one-half from day 0 to 14 as new leaf growth occurred, but increased and returned to pretreatment levels on day 28. A similiar, though slower, pattern of decline and recovery of total nonstructural carbohydrates in stems and roots occurred in response to defoliation by clopyralid. These results showed that the nonstructural carbohydrates in stems and roots of honey mesquite were important sources of carbohydrates to support new leaf regrowth following defoliation by hand or herbicide.

Rhizobacteria have been shown to be phytotoxic to leafy spurge in laboratory assays. This field study investigated the influence of two strains of Pseudomonas fluorescens [Trevisan, (Migula)], deleterious rhizobacteria (DRB), on root weight, root bud number, and root carbohydrate content of leafy spurge at three sites located in northeast and north-central South Dakota. Soils were inoculated with 2 g of starch-based granules containing no bacteria or starch granules containing 108colony-forming units (cfu)/g of either bacterial strain LS102 (Montana origin) or LS174 (South Dakota origin). Bacterial strains were detected on root samples from treated areas. Root weight and root carbohydrate content were reduced about 20% compared to roots from control plots.

All land uses in eastern and southeastern Nebraska were infested to some extent with hemp dogbane (Apocynum cannabinum L.). The highest infestations were observed in oats (Avena sativa L.) and soybeans [Glycine max (L.) Merr.] and the lowest infestations were in alfalfa (Medicago sativa L.), pastures, and winter wheat (Triticum aestivum L.). Yield reductions from hemp dogbane infestations ranged from 0 to 10% in corn (Zea mays L.), 28 to 41% in soybeans, and 37 to 45% in sorghum [Sorghum bicolor (L.) Moench]. Emergence of hemp dogbane from crown roots occurred when the soil temperature was 17 to 19 C, during April in 1977 and 1978. Plants attained the bud stage within 4 to 7 weeks after emergence. Early flower, full bloom, and pod initiation occurred subsequently at about 1 week intervals. Seeds produced were first viable 10 weeks after full bloom. Root activity or regenerative capacity as measured by length and number of new shoots and roots produced at monthly intervals in the germinator showed a cyclic pattern. The highest activity occurred in the spring and late fall and lowest activity in summer and early fall. Protein levels in the roots ranged from 7 to 9% in the fall and spring to 4 to 5% during the summer. Percentage total nonstructural carbohydrates (TNC) ranged from 20 to 31% in lateral roots and 32 to 53% in crown roots, but there was not a consistent cyclic pattern of percentage TNC during the growing season.

Horsenettle was described quantitatively in two grazed bermudagrass pastures for two years. Six times from April through October, plants were counted, phenologically documented, and tops were harvested for estimation of above-ground phytomass. Roots were sampled for carbohydrate, N fraction, and macronutrient analyses. Top growth, flowering, fruiting, and chemical composition were similar between sites within years, but differed between years. Starch and total non-structural carbohydrates in roots increased following reproductive periods both years. Root concentrations of protein and non-protein N increased and concentrations of P decreased in August and September in one year only. Analysis of the relationship between seasonal trends in carbohydrate fluctuation and pasture management practices suggests that systemic herbicide application in mid-summer may lead to more effective control than application in spring.

Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] root samples were collected at monthly intervals over a 2-yr period from two locations to determine seasonal fluctuations in the presence and growth potential of root buds. Root bud growth was highest during late fall and winter months following death of the aerial shoots. Root fragments incubated at a constant 15 C for 2 weeks in continuous light consistently had more buds than nonincubated roots, which indicated active bud differentiation during the incubation period. Incubated roots produced 3 to 9 cm of new shoot length/cm root length. There were no obvious seasonal patterns in the presence of root buds or their ability to elongate at different times of the year. Carbohydrate reserves were stored preferentially in roots rather than in developing root buds or the bases of shoots. These reserves ranged from as low as 3% of root fresh weight during spring months to as high as 26% in late fall months, although the levels did not increase consistently during summer months over the locations and years of this study.