Substituting vetch and chicory for rye in a cover crop mixture enhanced nutrient release

Increasing the functional diversity of cover crop polycultures has potential to modify nutrient cycling. Aboveground tissue from rye (Secale cereale), vetch (Vicia villosa subsp. dasycarpa), and chicory (Cichorium intybus) was arranged in litterbags, and rates of nutrient supply were measured. A control, monocultures of each species, a biculture of rye:vetch, and a polyculture of rye:vetch:chicory were compared. Increasing functional diversity through reducing the quantity of rye tissue by 30% to include 10% chicory and 20% vetch increased the total amount of nitrogen released by 257%.

Aminocyclopyrachlor Absorption, Translocation and Metabolism in Field Bindweed (Convolvulus arvensis)

Field bindweed is extremely susceptible to aminocyclopyrachlor compared to other weed species. Laboratory studies were conducted to determine if absorption, translocation, and metabolism of aminocyclopyrachlor in field bindweed differs from other, less susceptible species. Field bindweed plants were treated with 3.3 kBq14C-aminocyclopyrachlor by spotting a single leaf mid-way up the stem with 10 µl of herbicide solution. Plants were then harvested at set intervals over 192 h after treatment (HAT). Aminocyclopyrachlor absorption reached a maximum of 48.3% of the applied radioactivity by 48 HAT. A translocation pattern of herbicide movement from the treated leaf into other plant tissues emerged, revealing a nearly equal aminocyclopyrachlor distribution between the treated leaf, aboveground tissue, and belowground tissue of 13, 14, and 14% of the applied radioactivity by 192 HAT. Over the time-course, no soluble aminocyclopyrachlor metabolites were observed, but there was an increase in radioactivity recovered bound in the nonsoluble fraction. These results suggest that aminocyclopyrachlor has greater translocation to belowground plant tissue in field bindweed compared with results from other studies with other herbicides and other weed species, which could explain the increased level of control observed in the field. The lack of soluble metabolites also suggests that very little metabolism occurred over the 192 h time course.

Evaluation of Verticillium Wilt Resistance in Mentha arvensis and M. longifolia Genotypes

Verticillium wilt, caused by Verticillium dahliae, is a major constraint to mint (Mentha spp.) production in the United States, and the use of resistant cultivars is an important component of Verticillium wilt management. Two Mentha arvensis and four M. longifolia genotypes were evaluated for resistance to Verticillium wilt in the greenhouse using V. dahliae isolates obtained from different hosts and belonging to different vegetative compatibility groups. Isolates of V. dahliae obtained from peppermint (M. × piperita) caused significantly higher disease severity, plant mortality, and yield reduction than isolates obtained from other hosts. Disease severity, plant mortality, and pathogen incidence in aboveground stems were higher and yields lower in peppermint, the susceptible standard, compared with the resistant standard, native spearmint (M. spicata). Root-dip inoculations of M. arvensis and M. longifolia with isolates of V. dahliae obtained from peppermint produced severe symptoms; however, both species displayed the ability to recover from infection and produce asymptomatic growth from rhizomes. Both M. arvensis cultivars exhibited lower mean disease severity ratings following cutback and regrowth and were not significantly different than native spearmint. The restriction of pathogen movement in aboveground tissue and ability to recover from infection may be important components of V. dahliae resistance in perennial mint cropping systems.

Aminopyralid and Clopyralid Absorption and Translocation in Canada Thistle (Cirsium arvense)

Aminopyralid is a new auxinic herbicide that provides Canada thistle control at lower use rates than clopyralid. Studies were conducted to determine if differences in absorption, translocation, or metabolism account for aminopyralid's greater biological activity. Radiolabeled aminopyralid and clopyralid were applied to individual leaves of rosette-stage Canada thistle plants. Nonionic surfactant was used for the absorption studies because it provided higher aminopyralid absorption than methylated seed oil or crop oil concentrate. Clopyralid was absorbed very rapidly, reaching 72% 24 h after treatment (HAT) and remaining near or above 80% during a 192-h time course. During the same time period, aminopyralid absorption increased from 34 to 60%. Clopyralid translocation out of the treated leaf was significantly higher than aminopyralid, 39% compared with 17%, respectively, 192 HAT. More of applied clopyralid translocated to aboveground tissue 192 HAT (27%) than to roots (12%), whereas aminopyralid translocation was similar in aboveground tissue (10%) and roots (7%) 192 HAT. Neither aminopyralid nor clopyralid was metabolized 192 HAT. Although aminopyralid is effective at lower use rates than clopyralid, clopyralid absorption and translocation were higher in Canada thistle. These results suggest that aminopyralid's chemical structure may provide for greater biological activity at the target site than clopyralid.

Growth and reproduction of invasive Vincetoxicum rossicum and V. nigrum under artificial defoliation and different light environments

The exotic vines Vincetoxicum rossicum (Kleopow) Barbar. and Vincetoxicum nigrum (L.) Moench have become increasingly invasive in low- and high-light habitats in North America, and a biological control program is being developed. These plants experience little damage in North America, so it is unclear how they might respond to introduced herbivores. I conducted an artificial defoliation study on seedlings and mature plants of V. rossicum and V. nigrum grown under different light environments. Under high light, V. nigrum produced more seed and allocated more resources to aboveground tissue (root:shoot ratios < 1), whereas V. rossicum allocated more resources to roots with root:shoot ratios of 1.9 for mature plants and > 3 for seedlings. These differences disappeared with shading. Increasing frequencies of 100% defoliation caused greater reductions in biomass and seed production for both species and plant stages. Shading further reduced biomass and no seed was produced. Defoliation of shaded, but not unshaded, plants caused high mortality. Additional cutting of stem tips increased branching only. Defoliation may be effective against Vincetoxicum plants growing in low-light environments such as forest understories, but appears to be of more limited value in high-light environments unless repeated defoliation occurs.

Nutrient Content of the Aboveground Tissue of 12-week-old Loblolly Pine Intraprovenance and Interprovenance Crosses

Nutrient content (P, K, Ca, Mg) of the aboveground tissue of a series of full-sib loblolly crosses was found to vary by genotype. Variability among and within seed sources is indicated for the ability to absorb Ca and Mg. Absorption of P and K was not found to be dependent on seed source, but the full-sib crosses differ. Good linear relationships were found between plant dry weight and weight of element but not between plant dry weight and percentage of element. Certain highly efficient crosses can be expected to be good producers of dry matter on sites low in available nutrients.