No abstract

Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) is a common fungal disease of creeping bentgrass (Agrostis palustris Hudson). Field experiments were conducted to quantify the effects of leaf surface moisture displacement, N fertilization, and collecting or leaving clippings on severity of dollar spot. Tests were conducted on A. palustris cv. Penncross maintained at 0.6 cm (putting green height) and on turf containing A. palustris cv. Penncross and annual bluegrass (Poa annua L.) maintained at 1.1 cm (fairway height). Six mowing treatments, four of which displaced morning leaf surface moisture and three of which collected clippings, were imposed on turf fertilized with 0, 36.6, and 73.2 kg N ha−1 in 1992 and 1993. Significant reductions of dollar spot after morning mowing or poling treatments, or both, were recorded on turf at both heights of cut and in both years. Maximum reductions of disease due to mowing treatments across all N levels were 81% on fairway turf in 1992 and 53% on putting green turf in 1992. Collecting or leaving clippings did not consistently affect the severity of dollar spot. The effects of N fertilization were significant at various levels in both tests and in both years. Maximum disease reductions comparing 0 and 73.2 kg N ha−1 were 57% on putting green turf in 1992 and 44% on fairway turf in 1993. There were no consistent interactions in the severity of dollar spot among mowing treatments and N levels.

Invertases of the placento-chalazal and pedicel tissues are much more active than invertase from the pericarp of Zea mays L. kernels 12 to 40 days after pollination. Sucrose 9 and 10 Am at 4-day intervals from 12 to 40 days after controlled self-pollination. Husks were removed, and the cobs, with kernels attached, were frozen on Dry Ice and then lyophilized to a constant dry weight. Prior to freezing, the pericarp at the distal end of each kernel was slashed through to the endosperm to accelerate dehydration and to prevent kernel collapse. Fifty kernels were removed from each ear, and the placento-chalazal and pedicel tissues were excised, re-dried (by lyophilization), and weighed. As a measure of invertase activity in maternal tissue not involved in sugar transport, pericarp tissues from the upper half of 25 freeze-dried kernels were excised and treated as above.Samples of the placento-chalazal tissue and subsamples of a similar dry weight of pedicel and pericarp tissues (70 mg) were homogenized with a Duall' tissue grinder (Kontes Glass Co., Vineland, N. J.) in 10 mm tris-maleate buffer, pH 7.0. The suspended material was precipitated by centrifugation at 30,900g for 20 min. The precipitates were washed twice with the tris-maleate buffer and the successive extractants combined. To remove the soluble sugars, the crude extracts were dialyzed overnight against 10 mM tris-maleate buffer. pH 7.0. The dialyzed extract was adjusted to 50 ml with 10 mM trismaleate buffer and used as the source of soluble enzymes. All of the above operations were done at 4 C. This extraction procedure was a modification of that employed by Tsai et al. (13) in their study of the enzymes of carbohydrate metabolism of '

Alfalfa (Medicago sativa L.), a forage crop unique in that it has high potential in terms of both yield and quality, has considerable capacity for animal production when grazed under management that is based on its growth and development. Two grazing experiments, using balanced change‐over designs, were set up to measure the ingestive behavior of beef heifers (Bos taurus) during the first, second, and third hours of grazing sessions on alfalfa pastures established on Maury silt loam (fine, mixed, mesic Typic Paleudalfs). In Exp. I where the herbage mass, in terms of dry matter (DM), was 3.06 Mg ha−1 and the herbage DM allowance was 6.1 kg h−1 per heifer, animals ingested DM at 2.96, 1.88, and 1.56 kg h−1 during their first, second, and third hours of grazing, respectively. The mean rates of biting were 26, 21, and 19 bites min−1 for the same periods. Herbage DM intake per bite declined linearly from 1.96 to 1.54 to 1.36 g for each hour increment in grazing time. Forage utilization was 51, 32, and 27% for the same increments. In Exp. II where the herbage mass (DM) was 1.74 Mg ha−1 and the allowance was 3.4 kg h−1, heifers ingested 2.35, 1.47, and 1.20 kg h−1 during their first, second, and third hours of grazing, respectively. The mean rates of biting were 34, 22, and 18 bites min−1 during the same periods within the grazing session. Herbage DM intake per bite averaged 1.17 g and did not vary within the grazing session. Forage utilization was 75, 47, and 37% during the three consecutive hours within the grazing session. Maximum rates of herbage intake were characterized by larger bites and relatively slow rates of biting. Rates of herbage intake were considerably higher during the first hour of grazing than during the second and third hours. In a 3‐h grazing session, animals consumed 47, 29, and 24% of their intake during the first, second, and third hours, respectively.

Larvae of arthropod ectoparasites of livestock, such as the horn fly, Haematobia irritans (L.), may be exposed to acyl-loline alkaloids in dung of ruminant livestock ingesting herbage of the tall fescue (Festuca arundinacea Schreb.)-endophyte association [Neotyphodium coenophialum (Morgan-Jones & W. Gams) Glenn, Bacon & Hanlin comb. nov.]. Biological activity of alkaloid-supplemented bovine dung was assayed by growth, development, and survival of 1st instars of horn fly. An extract from tall fescue seed, containing N-formyl loline (NFL), N-acetyl loline (NAL), and loline (59:21:20 by mass, respectively) caused 100% mortality of horn fly larvae when dung was supplemented at > or = 100 micrograms/g. Probit analysis of data corrected for natural mortality indicated a LD50 of 30 micrograms/g (95% fidicial limits: 20-49 micrograms/g). When horn fly larvae were introduced to dung supplemented with up to 50 microM of acyl-loline derivatives, mortality of larvae varied significantly between alkaloids (P < 0.0001). Probit analysis indicated that NFL [LD50: 34 microM (95% fidicial limits: 3-53 microM)] was more toxic than NAL [LD50: 46 microM (0-83 microM)], and that loline hydrochloride was not toxic.