Inactivation of fenitrothion on stored maize at different moisture contents

Biological activity of fenitrothion on stored maize at various moisture contents and at different times after application was measured by biological assay using adults of Tribolium castaneum (Herbst). Inactivation of actual residues over time was then determined after making the necessary allowance for chemical breakdown. At a given moisture content, the inactivation process was substantially completed during the first 6 weeks after application and loss of effectiveness from 6 weeks onwards resulted mainly from chemical breakdown. At a given time after application, residues were less active at higher moisture content (m.c). Differences in activity between moisture contents were apparent within a few hours of application and continued to increase for up to 3 days, with relatively little change thereafter during storage of 24 weeks. Thus after 24 weeks, residues on maize of 18% m.c. had an activity about 20% that of similarly-aged residues at 10% m.c. and 4% that of freshly-applied residues at 10% m.c. These results were in general accord with changes in the proportion of the residue which was collected from the kernels by a surface wash with methanol, this readily-extractable residue presumably representing the insecticide that may be picked up by insects.     

On the origin of bacterial resistance to penicillin: comparison of a beta-lactamase and a penicillin target

Structural data are now available for comparing a penicillin target enzyme, the D-alanyl-D-alanine-peptidase from Streptomyces R61, with a penicillin-hydrolyzing enzyme, the beta-lactamase from Bacillus licheniformis 749/C. Although the two enzymes have distinct catalytic properties and lack relatedness in their overall amino acid sequences except near the active-site serine, the significant similarity found by x-ray crystallography in the spatial arrangement of the elements of secondary structure provides strong support for earlier hypotheses that beta-lactamases arose from penicillin-sensitive D-alanyl-D-alanine-peptidases involved in bacterial wall peptidoglycan metabolism.     

The influence of forage quality and concentrate level on dry matter intake and milk production of British Friesian heifers

Thirty-six British Friesian heifers were divided into two groups during weeks 3-26 of lactation and received ad libitum either good (G) or average (A) quality grass silage. The in vitro digestible organic matter in the DM was 680 and 600 g kg^-1 for silages G and A, respectively. In addition, the heifers in each group were offered concentrate at either a low (4.3 kg DM d^-1), medium (64 kg DM d^-1) or high (8.4 kg DM d^-1) level. The concentrate contained 180 g (kg DM)^-1 of crude protein and had a calculated metabolizable energy concentration of 12.9 MJ (kg DM)^-1. Increasing concentrate level significantly increased milk yield (P < 0.01), milk protein concentration (P < 0.05), and yield of both milk protein depressed milk fat concentration (P < 0.001) and silage intake (P < 0.001). Although the overall effect of silage quality on milk yield was not significant, the milk yields for silage G at each concentrate level were higher, significantly so for low level, than the corresponding values for silage A. An improvement in silage quality did not affect milk fat concentration but significantly increased the concentration of milk protein (P < 005) and yields of both milk fat (P < 005) and protein (P < 0001). The response of silage DM intake to improved silage quality was 0 06 kg DM per 10 g rise in vitro DOMD value. Each additional kg concentrate DM depressed intake of silages G and A by 0-63 and 0-27 kg DM, respectively. Substitution rate was also significantly related to stage of lactation. With both silages, the digestibility coefficients determined in vivo for acid detergent fibre (ADF) decreased significantly (P < 0.001) when concentrate level was increased from low to high. Differences for DM, OM and total N digestibility coefficients between treatments were not established as significant at the 5% level. Estimates of mean efficiency of utilization of ME for lactation, made on a weekly basis, were 049 and 052 for the heifers given silages G and A. respectively, and 048, 052 and 052 for those given the low, medium and high levels of concentrate. Energy balances were calculated on a mean weekly basis.     

Factors Affecting Latent Infection of Prune Fruit by Monilinia fructicola

ABSTRACT Experiments were conducted in three prune orchards in California. In each orchard, inoculations with Monilinia fructicola, the causal agent of brown rot of stone fruits, were performed on branches of trees at bloom and fruit developmental stages. Five inoculum concentrations were used in each inoculation. Six and four wetness durations were created for each inoculum concentration at bloom and fruit developmental stages, respectively. Fruit were harvested 3 weeks before commercial harvest. The overnight freezing incubation technique was used to promote sporulation and to determine incidence of latent infection (ILI) of fruit brown rot. No differences in ILI among locations were found. A seasonal pattern of bloom and fruit susceptibility to latent infection was determined. Susceptibility to latent infection at bloom stage was at a moderate level and increased to reach the highest level at pit hardening stage. Subsequently, fruit susceptibility to latent infection decreased, reaching the lowest level in early June at embryo growth stage. Thereafter, the susceptibility increased again with fruit development and maturity until harvest. Linear relationships between ILI and inoculum concentration were obtained for most combinations of growth stage and wetness duration. Incidence of latent infection increased linearly with increased wetness duration at bloom stage and increased exponentially with increased wetness duration at early and late fruit developmental stages. The optimum temperatures for latent infection at pit hardening stage ranged from 14 to 18 degrees C, but the effect of temperature on latent infection was reduced at resistant stages. The temperature range favorable to latent infection varied for different wetness durations.     

Media evaluated for extended sweetpotato transplant production in heated beds 1

‘Georgia Jet’ sweetpotato [Ipomoea batatas (L.) Lam] transplants were produced in heated beds to compare aged pine sawdust or builders’ sand (traditional media) to fresh pine bark and aged pine bark, or fresh pine sawdust (alternative media), with regard to transplant production and quality over an extended harvest period. At the first harvest, highest transplant numbers (mean 1400 transplants/m²) were obtained with fresh pine sawdust or fresh pine bark. Media effects on transplant numbers at the first harvest agree with the results of an earlier experiment. The greater productivity of fresh pine bark compared to aged pine media and builders’ sand at the early‐harvest (two harvests) in the previous experiment was not confirmed in this experiment. Extended‐harvest (four harvests) transplant production was greater with fresh pine sawdust (2030 transplants/m²) than with aged pine sawdust (1380 transplants/m2), but was not greater than the number of transplants produced with the other media. Transplant production averaged over the five media, decreased from 1060 and 360 transplants/m² at the first and second harvests, respectively, to 130 transplants/m² at each of the last two harvests. Differences in mean transplant weights due to media were found only at the third harvest. At the first harvest, greater mean lengths of transplants grown with the fresh pine media (mean 25.7 cm) than with the aged pine media (mean 21.4 cm). Shortest transplants were produced with builders’ sand at the first harvest (17.8 cm) and throughout the extended season (17.5 cm). Similar effects of media on mean transplant length were observed at the early‐ and extended‐harvest periods. Media had no effect on the percentage of intact roots at the end of the 15‐week season (mean 71%).     

An Economic Evaluation of Alternative Stand Treatments in Relation to the Development of Understorey Vegetation and Subsequent Regeneration Costs

A study on the development of understorey vegetation and itseconomic implications in managed stands of Sitka spruce in GwydyrForest, North Wales, is described. The relationships betweenstand age, relative light intensity, thinning regime, and Yieldor Quality Class are used to predict the possible developmentof understorey vegetation. This prediction mechanism is thenused, together with economic analysis techniques, to determinewhether the money economically available for weeding is adequatefor this purpose. Four combinations of current and future thinningregimes and five Yield Classes are considered. It is shown thatin the higher Yield Classes light thinning is advisable butheavier thinning appears more profitable in the lower YieldClasses. It is emphasized that these conclusions are applicableonly where the assumptions used are valid but that the techniqueis of universal application.