Tamara Benjamin

The Effect of Biochar on Native and Invasive Prairie Plant Species

Abstract Biochar, a carbon-rich product formed by the incomplete combustion of biomass, has been shown to improve soil quality and increase crop growth but has not been evaluated in prairie ecosystems. We assessed the response of a native perennial grass, big bluestem, and an invasive herbaceous perennial, sericea, to biochar amendments in two greenhouse experiments in 2010 and 2011. In the first experiment, big bluestem and sericea were grown in monoculture; the main treatments were soil type (silt, sand), percent biochar (0%, 1%, 2%, and 4%) and nitrogen (0 and 10 g N m−2). Big bluestem growth was increased by the addition of biochar, particularly in the sand soil. In contrast, sericea growth was either not affected or decreased when biochar was added to the soil, particularly at the higher biochar rates. Adding N to the soil appeared to increase sericea growth in the presence of biochar and the silt soil, which suggests that biochar may have reduced N availability. A replacement series was used in the second experiment to evaluate the effect of biochar on competition between the two species. Main treatments were biochar rates (0% and 2%), nitrogen rates (0 and 10 g N m−2) and the following big bluestem to sericea ratios: 6 ∶ 0, 4 ∶ 2, 3 ∶ 3, 2 ∶ 4, and 0 ∶ 6. After 180 d, big bluestem height and biomass were significantly greater in biochar-amended soils than in unamended soils. However, sericea height and biomass were unaffected by biochar amendments and the addition of biochar did not alter competitive outcomes. Competition between big bluestem and sericea was asymmetrical; sericea reduced the growth of big bluestem but big bluestem had relatively little effect on the growth of sericea. Our research suggests that biochar has the potential to increase the growth of big bluestem and may be a useful tool for prairie restoration. Nomenclature: Big bluestem, Andropogon gerardii Vitman, sericea, Lespedeza cuneata (Dumont) G. Don. Management Implications: Sericea is an important weed in prairie and grassland systems in North America. The use of biochar as a soil amendment has the potential to improve the growth of big bluestem and may limit sericea growth in some soils. However, our research suggests that sericea is much more competitive than big bluestem and that biochar amendments alone may not be sufficient to alter competitive outcomes between these two species.

Effects of Production Practices on the Abundance of Quarantine Pests in Dracaena marginata in Costa Rican Production Fields

Abstract To mitigate risks of invasive pests, international nursery exporters may soon be expected to participate in clean stock programs that reduce the probability of shipping crops that contain pests of quarantine significance. We worked with Costa Rican producers of Dracaena marginata Lam. (Ruscaceae) to identify critical pests, as well as the field conditions and production practices that could be explored for lowering pest abundance in a clean stock program. We sampled the abundance of leafhopper and katydid eggs, armored scales, and snails on leaves using a 10- by 10-m grid in a total of 34 production plots located in two distinct growing regions during the rainy and dry seasons of 2006. Growers were surveyed to determine the production practices in each field. Populations of leafhoppers and snails increased during the rainy season, whereas armored scale populations reached higher densities in the dry season. Fertilizer applications were associated with a greater abundance of leafhoppers, the keystone pests in the system. In contrast, abundances of armored scales and katydids were somewhat lower in fertilized fields. Insecticide applications targeting leafhoppers succeeded in reducing their populations, but secondary outbreaks of armored scales and katydids were observed. Increased frequency of herbicide application was associated with lower populations of leafhoppers with no significant effects on the other herbivores. Although effects of specific production practices in a given plot are confounded, the effects of fertilizer, insecticide, and herbicide use on leafhoppers are consistent with those predicted by literature on this pest. For this reason, the 10- by 10-m sampling grid is sensitive enough for use in controlled studies that evaluate effects of specific practices on pest abundance. As such, it is likely to be a useful tool for developing a clean stock program for D. marginata in Costa Rica.

Factors Influencing the Abundance of Pests in Production Fields and Rates of Interception of Dracaena marginata Imported from Costa Rica

ABSTRACT Importation of live nursery plants, like Dracaena marginata Lamoureux (Ruscaceae), can provide a significant pathway for the entry of foliar pests from overseas into the United States. We studied the abundance of foliar pests of quarantine importance found on Costa Rican-grown D. marginata. These include five genera of leafhoppers (Heteroptera: Cicadellidae, Oncometopia, Caldweliola, Diestostema, Gypona, and Empoasca), Florida red scale (Heteroptera: Disapididae, Chrysomphalus aoinidum (L.) ), katydids (Orthoptera: Tettigoniidae), and a snail (Succinea costarricana von Martens (Gastropoda, Stylommatophora, Succineidae) ). In our first study, we examined the rationale behind size restrictions on Dracaena cuttings imported into the United States from Costa Rica. When comparing plant size, no differences were found in the abundance of quarantined pests on small (15–46 cm), medium (46–81 cm), and large (81–152 cm) propagules. In a second study, we estimated monthly abundances of pests in production plots for 1 yr to determine their relationship to rates of interception at U.S. ports. In any given month, <6% of the marketable shoots standing in the field were infested with at least one quarantine pest. There was no relationship between the average monthly frequencies of pest detection in the field and in U.S. inspection ports. Pest detections increased during the 1 mo when average monthly shipments were abnormally high. Our data suggest that off-shore postprocessing efforts to remove pest-infested material from the market stream need to be adjusted to accommodate sharp increases in the volume of shipped plants.

Effects of Weed Cover Composition on Insect Pest and Natural Enemy Abundance in a Field of Dracaena marginata (Asparagales: Asparagaceae) in Costa Rica

ABSTRACT Weeds and their influence on pest and natural enemy populations were studied on a commercial ornamental farm during 2009 in the Atlantic Zone of Costa Rica. A baseline survey of the entire production plot was conducted in February, along a 5 by 5 m grid to characterize and map initial weed communities of plants, cicadellids, katydids, and armored scales. In total, 50 plant species from 21 families were found. Seven weed treatments were established to determine how weed manipulations would affect communities of our targeted pests and natural enemies. These treatments were selected based on reported effects of specific weed cover on herbivorous insects and natural enemies, or by their use by growers as a cover crop. Treatments ranged from weed-free to being completely covered with endemic species of weeds. Although some weed treatments changed pest abundances, responses differed among arthropod pests, with the strongest effects observed for Caldwelliola and Empoasca leafhoppers. Removal of all weeds increased the abundance of Empoasca, whereas leaving mostly cyperacaeous weeds increased the abundance of Caldwelliola. Weed manipulations had no effect on the abundance of katydid and scale populations. No weed treatment reduced the abundance of all three of the target pests. Differential responses of the two leafhopper species to the same weed treatments support hypotheses, suggesting that noncrop plants can alter the abundance of pests through their effects on arthropod host finding and acceptance, as well as their impacts on natural enemies.