Postfire Defoliation Response of Agropyron spicatum and Sitanion hystrix

Prescribed fire is an important management tool to increase herbaceous productivity and maintain seral communities of Intermountain sagebrush grasslands. Currently, pastures treated with prescribed fire are rested from livestock grazing before burning to allow fine fuel accumulation, and rested a full year following burning to restore bunchgrass vigor. This study examined the post-fire defoliation response of Agropyron spicatum and Sitanion hystrix to three different defoliation treatments: an early season defoliation during the boot phenological stage, late season defoliation after seedset, and non-defoliation. Plant response to these defoliation timings was compared to determine the amount of non-use required to restore vigor to these species following fire. Mortality was low for late and non-defoliated plants of both species. Results indicate no differences between late season and non-defoliated plants for biomass production, basal area, or culm number for Agropyron. No differences in Sitanion culm number resulted between the late and non defoliated treatments. Sitanion biomass production differed between late and non-defoliated treatments at Emmett, but not at Craters of the Moon. Basal area and culm number of late and non-defoliated plants of both species increased as compared to the first post-burn season.

Etiolated Growth of Range Grasses for an Indication of Tolerance to Atrazine

Our purpose was to investigate the influence of growth reserves of perennial range grasses on their tolerance to applications of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Competing annual grasses were removed with atrazine treatment at 1.1 kg/ha. The carbohydrate reserves of the perennial grasses were reduced by mowing the previous season. Crested wheatgrass [Agropyron desertorum(Fisch. ex Link) Schult.] plants with reduced carbohydrate reserves, as indicated by reduced etiolated growth, were less tolerant to atrazine than their nonmowed counterparts. Without reduced carbohydrate reserves, squirreltail [Sitanion hystrix(Nutt.) J. G. Smith] was much more susceptible to atrazine than crested wheatgrass. Thus, the weed control treatment did not necessarily increase the density of desirable perennial grasses.

Septoria passerinii. [Descriptions of Fungi and Bacteria].

A description is provided for Septoria passerinii. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Hordeum brachyantherum, Hordeum distichon, Hordeum jubatum, Hordeum secalinum, Hordeum vulgare, Hystrix patula, Lolium multiflorum, L. perenne, L. temulentum, Poa pratensis and Sitanion hystrix. DISEASE: Speckled leaf blotch of barley. Forming linear lesions with indefinite margins on leaves with very small, dark brown pycnidia embedded in tissues developing on straw-coloured blotches and causing defoliation, low yields and formation of light kernels. GEOGRAPHICAL DISTRIBUTION: Africa (Ethiopia, Libya); Australasia & Oceania (Australia); Europe (Bulgaria, Cyprus, Denmark, Germany, Italy, Netherlands, Rumania, Spain, U.K.); North America (Canada, U.S.A.). TRANSMISSION: The pathogen overwinters as mycelium or as pycnidia in crop residues, producing macrospores and microspores the following summer. High humidity (>93% R.H.) is required for the release of spores which are formed abundantly on infected material after rain. Spores may be spread by insects or splashing raindrops (44, 1528; 46, 106; 40: 530). Dissemination of the pathogen on barley straw residues has also been attributed to the use of combine harvester-threshers in Western Canada (35: 418) and to high winds in Minnesota, U.S.A. (40: 530).