Effect of split applications of fenpropimorph-containing fungicides on sensitivity of Erysiphe graminis f.sp. tritici

A field trial was conducted in the south of the Netherlands over a period of 3 years (1992–94) in order to test the effect of fenpropimorph-containing fungicides on the sensitivity of Erysiphe graminis f.sp. tritici to fenpropimorph. In general, use of split applications resulted in a better protection against wheat powdery mildew than use of normal applications. This is ascribed to a better timing of the split applications. The sensitivity to fenpropimorph of the mildew population in plots treated with normal applications of both fungicides did not change during the growing seasons of the years investigated. In contrast, the sensitivity of the mildew population from plots treated with split applications of Corbel became significantly lower. A significantly lower sensitivity was also found in the mildew population from plots treated with split applications of Tilt Top in 1993 and 1994. These results indicate that split applications can increase the rate at which E. graminis f.sp. tritici can become less sensitive to fenpropimorph. Because maintenance of sensitivity of the pathogen population is valued highly, the split application strategy of fenpropimorph-containing fungicides is not recommended for wheat powdery mildew control.     

Validation of thresholds for serological tests that detect Clavibacter michiganensis subsp. sepedonicus in potato tuber tissue

To evaluate positive/negative thresholds for serological tests, composite samples consisting of 200 potato-tuber cores were extracted and tested for the presence of Clavibacter michiganensis subsp. sepedonicus by ELISA and immunofluorescence using specific monoclonal antibodies. Transformed ELISA absorbance values for ring rot-infected tuber tissue diluted in 10-fold increments in known negative composite sample extracts were fitted to a'broken stick'nonlinear regression model. Of the 103 dilution series that were tested, 91% fitted the model with R ² > 0.98. The model consisted of a response and non-response domain. The absorbance values in the non-response domain, which served as estimates of background readings, ranged from 0.006 to 0.049. The values did not differ significantly among brands of ELISA plates used for between laboratories, and thus provided a reference point for setting a positive/negative threshold for the ELISA test. In the immunofluorescence test, 94% of composite samples from 1003 commercial seed lots had <1 immunofluorescing unit (IFU) per microscope field; only 1% of samples had >2 IFU per field. A positive/ negative threshold at 5IFU per field was considered to be appropriate for avoiding false positive readings.     

Risk of abortion associated with Neospora caninum during different lactations and evidence of congenital transmission in dairy cows

OBJECTIVE: To examine the relationship between exposure to Neospora caninum and abortion in dairy cows during their first, second, third, and fourth or later lactations and to establish the main mode of transmission in female calves from birth until their first pregnancy was terminated by abortion or parturition. DESIGN: Prospective observational study. ANIMALS: 460 Holstein cows and 79 female calves. PROCEDURE: Cows were classified as seropositive or seronegative to N caninum within 7 days after calving; incidence of abortion was compared between groups during different lactations. Blood samples were collected from female calves before ingestion of colostrum and every 6 months until their first pregnancy was terminated by abortion or parturition; number of seropositive calves was compared between seropositive and seronegative dams. RESULTS: During the first pregnancy of their second lactation, risk of abortion for seropositive cows was 2.8 times that of seronegative cows. Among 10 calves born to seropositive cows, 4 were classified as seropositive at birth and thereafter. Among 69 calves born to seronegative cows, all were classified as seronegative at birth; 67 calves remained seronegative thereafter. CONCLUSIONS AND CLINICAL RELEVANCE: Exposure to N caninum alone was not significantly associated with abortion in cows during the first, third, and fourth or later lactations. Seropositive cows that have aborted previously may have subsequent abortions attributable to N caninum. Congenital infection was the main mode of N caninum transmission in a cohort of female calves.     

Haemoproteus lophortyx infection in bobwhite quail

This report chronicles recurring outbreaks of Haemoproteus lophortyx infection in captive bobwhite quail. Clinically, the signs of infection included reluctance to move, ruffled appearance, prostration, and death. These signs were associated with parasitemia, anemia, and the presence of large megaloschizonts in skeletal muscles, particularly those of the thighs and back. The average cumulative mortality for flocks experiencing outbreaks was over 20%. In a typical outbreak, mortality rose when the birds were 5-6 wk of age, peaked in 8-to-10-wk-old quail, and declined rapidly when the quail were 9-11 wk old. Outbreaks occurred exclusively between the months of May and October, and warm weather was determined to be a risk factor for H. lophortyx mortality. This protozoan most likely overwinters in native California quail in the area and is transmitted to quail on the ranch by an insect vector that emerges in warm weather. Infection of the large population of na?ve bobwhite quail on the ranch leads to amplification of H. lophortyx, resulting in epidemics in successive flocks.     

Intertarsal and tarsometatarsal arthrodesis using 2.0/2.7-mm or 2.7/3.5-mm hybrid dynamic compression plates

Proximal intertarsal or tarsometatarsal arthrodesis was performed in four dogs using either 2.0/2.7-mm or 2.7/3.5-mm hybrid dynamic compression plates. Mean radiographic follow-up time was 30.5 weeks (range, 15 to 60 weeks). Mean owner follow-up time was 40.5 weeks (range, 27 to 60 weeks). All cases went on to form stable, healed arthrodeses. Owners reported no noticeable lameness problems long term. Complications occurred in one case and included pressure sores and fracture of the calcaneus. Implant failure did not occur in any case.     

Predicted impact of transgenic, herbicidetolerant corn on drinking water quality in vulnerable watersheds of the mid-western USA

In the intensely farmed corn-growing regions of the mid-western USA, surface waters have often been contaminated by herbicides, principally as a result of rainfall runoff occurring shortly after application of these to corn and other crops. In some vulnerable watersheds, water quality criteria for chronic human exposure through drinking water are occasionally exceeded. We selected three settings representative of vulnerable corn-region watersheds, and used the PRZM-EXAMS model with the Index Reservoir scenario to predict corn herbicide concentrations in the reservoirs as a function of herbicide properties and use pattern, site characteristics and weather in the watersheds. We compared herbicide application scenarios, including broadcast surface pre-plant atrazine and alachlor applications with a glyphosate pre-plant application, scenarios in which losses of herbicides were mitigated by incorporation or banding, and scenarios in which only glyphosate or glufosinate post-emergent herbicides were used with corn genetically modified to be resistant to them. In the absence of drift, in almost all years a single runoff event dominates the input into the reservoir. As a result, annual average pesticide concentrations are highly correlated with annual maximum daily values. The modeled concentrations were generally higher than those derived from monitoring data, even for no-drift model scenarios. Because of their lower post-emergent application rates and greater soil sorptivity, glyphosate and glufosinate loads in runoff were generally one-fifth to one-tenth those of atrazine and alachlor. These model results indicate that the replacement of pre-emergent corn herbicides with the post-emergent herbicides allowed by genetic modification of crops would dramatically reduce herbicide concentrations in vulnerable watersheds. Given the significantly lower chronic mammalian toxicity of these compounds, and their vulnerability to breakdown in the drinking water treatment process, risks to human populations through drinking water would also be reduced.     

Efficacy of metaphylactic florfenicol therapy during natural outbreaks of bovine respiratory disease

The efficacy of an injectable formulation of florfenicol (300 mg/mL) as metaphylactic control of naturally occurring bovine respiratory disease (BRD) was evaluated in two double‐blind randomly controlled field studies on two Dutch veal calf herds (A and B). Cattle aged not older than 3 months and in the direct presence of calves with clinical respiratory disease were randomly allocated to treatment with 40 mg/kg florfenicol subcutaneously (s.c.) a positive control treatment (12.5 mg/kg tilmicosin p.o. twice daily for five consecutive days in herd A, and 12.5 mg/kg doxycycline p.o. twice daily for five consecutive days in herd B), or a negative control (one placebo saline s.c. administration on D0). The predominant respiratory pathogens present in pretreatment respiratory samples from affected animals were Mycoplasma bovis and Pasteurella multocida in outbreaks A and B, respectively. Metaphylactic administration of florfenicol resulted in a statistically significant weight gain, decreased rectal temperature for five consecutive days after treatment and decreased metaphylactic failure percentages compared with both positive and negative control groups. In summary, these studies demonstrated that a single s.c. injection of florfenicol is effective and practical for control of the bacterial component of BRD in veal calves.     

Susceptibility to tuberculosis: composition of tuberculous granulomas in Thorbecke and outbred New Zealand White rabbits

We sought to characterize the lung cellular immune responses to inhaled Mycobacterium tuberculosis (Mtb) of the susceptible inbred Thorbecke rabbit (the genomically sequenced strain, now unavailable) and compare it to outbred, Mtb-resistant, New Zealand White rabbits. Using Mtb CDC1551, we confirmed that the inbred rabbits allowed establishment of infection with this low virulence strain, compared to poor establishment in outbred rabbits. With a more virulent strain, Mtb Erdman, that establishes infection well in both rabbit strains, we analyzed granulomas from rabbit lungs 5 weeks after aerosol infection. The lung granulomas of inbred rabbits had significantly higher frequencies of cells expressing MHC Class II and CD11b, and lower frequencies of CD8+ T cells than the outbred controls. Macrophage-sized cells expressing MHC Class II in inbred rabbit granulomas showed significantly decreased intensity of expression, suggesting impaired maturation. Although the inbred dermal tuberculin reactions were decreased, the in vitro IFN-gamma mRNA responses of hilar node lymphocytes to tuberculin were higher than those of outbred rabbits. Further delineation of the outbred rabbit's resistant immune response to Mtb infection is warranted.