No description available.

The effect of interrupted leaf wetness (IWP) and %RH on infection by Cercospora carotae (Pass.) Solh. was studied by inoculating carrot leaves (Daucus carota var sativa DC. L.) and subjecting the plants to different IWP treatment, continuous leaf wetness (CWP) and to different combinations of %RH and temperature with and without an initial wet period of 6 hr. IWP significantly reduced infection as compared to CWP. Infection was optimal under leaf wetness and decreased with decrease in percent RH. The effect of temperature and duration of moist period on sporulation of C. carotae was studied on carrot plants under leaf wetness, 96%RH, and 96%RH with an initial 12 hr of leaf wetness. For all types of moisture conditions, sporulation increased with the increase in temperature up to the optimum (28$ sp circ$C) and then declined. Logistic and polynomial models were used to describe the effect of temperature and time on sporulation under these moisture conditions. The incubation period of Cercospora carotae was studied in the field. First lesions were observed 6 to 8 days after inoculation and new lesions appeared until the 10th to 14th day. The beginning, mean, and end of incubation period was modelled as a function of mean daily temperature and mean daily RH $ ge$ 90%. A model describing lesion appearance as a function of time was developed using a logistic function (R$ sp2$ = 0.84). A prediction model containing series of equations that described mathematically the interaction among predicted inoculum, infection and sporulation equivalents for the environment was developed and validated. In general, the model predicted adequately Cercospora blight progress. A weather-based forecasting system was developed to time the first fungicide spray to manage Cercospora blight of carrot based on the accumulation of critical number of disease severity units.

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No description available.

No description available.

No description available.

An Enzyme-Linked Immunosorbent Assay (ELISA) was developed which detected slug antigens in postmortem gut analysis of carabid beetles. The ELISA was used to identify beetles which fed on slugs in three fields of oilseed rape and winter wheat in the Tyne valley, Northumberland. Generalist species such as Harpalus rufipes, Pterostichus melanarius, Pterostichus nladidus, Anlara silnilata and Nebria brevicollis fed on slugs in the field. Molluscan specialists such as Carabus violaceus and Cychrus caraboides also fed on slugs in the field. Laboratory studies indicated that many large and medium sized carabids were able to predate small slugs. Some beetle species did not eat slugs but exposure to the beetles increased slug mortality. Therefore, postmortem investigations may underestimate the impact that carabids exert on slugs as they do not measure the number of slugs killed. Slug mucus affected the locomotory activity of generalist and specialist beetle species. Beetles foraged longer, covered greater distances, made more turns, walked slower and spent more time stationary on soil covered in slug mucus compared to control areas. Abax parallelepipedus, P.melanarius, Pterostichus niger and H.rufipes all reduced slug damage to a chinese cabbage crop in a miniplot experiment compared with unprotected plots. However, these differences were not significant. A.parallelepipedus was most effective at reducing slug damage to the chinese cabbage but was rare in arable land. H.rufipes was least effective at reducing slug damage but was abundant in arable land in both years of the study. A high proportion of H.rufipes beetles fed on slugs in the field. None of these four species occurred at densities in the field which reduced slug damage in the miniplot experiment.

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No description available.

Graduation date: 1971