Downy mildew of broccoli, cauliflower and cabbage is caused by the fungus Peronospora parasitica. Cool moist environmental conditions favor the development of downy mildew on these crops. Several potential new fungicides were evaluated for control of this disease on broccoli in 1999. The final severity of downy mildew in this trial was moderately high. Significant reduction in disease severity compared to nontreated plants was achieved by application of standard compounds such as Aliette, Ridomil Gold+maneb, maneb and Trilogy as well as nonregistered chemistries including Acrobat, Actigard, Curzate, Flint, Quadris, Serenade, Sovran, BAS 500, DPX-KP481 and RH-7281. The future registration and subsequent availability of one or more of these new chemistries for broccoli and related crops could enhance the overall level of disease control as well as help minimize the risk of development of resistance to fungicides used to manage downy mildew.

In Arizona, Sclerotinia leaf drop of lettuce is caused by two different species of fungi, Sclerotinia minor and S. sclerotiorum. Relatively cool and moist environmental conditions favor this disease. Some new fungicides in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing season of 1998-99. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. The final severity of leaf drop in these trials was moderately high. Significant reduction in the final count of dead lettuce plants compared to nontreated plots was usually achieved by application of the standard compounds Ronilan and Rovral as well as an appropriate rate of the experimental compounds Elevate, Medallion or Serenade. Medallion and Elevate provided equivalent disease control to that of the current standard materials with 0.178 and 0.5 lb active ingredient (a.i.) per acre, respectively, compared to the current 1.0 lb a.i. per acre required with the standard compounds. Continued demonstration of efficacy by Serenade may provide the opportunity to utilize a biological control product to reduce the incidence of Sclerotinia leaf drop of lettuce.

No description available.

No description available.

One of the major aims of the research presented in this thesis was to assist managers of native vegetation communities in southeastern Australia in understanding the dynamics of P. cinnamomi with an important ecological species, Xanthorrhoea australis. It trialed the use of phosphite in large-scale field applications to establish the usefulness of this management option for the first time on Victorian flora. This thesis describes the process of disease development within mature X. Australia plants. For the first time it was shown that within X. australis plants, secondary disease symptoms are related to the percentage of stem that has been infested by the disease. It was evident that after initial invasion the pathogen moves via root xylem and throughout the plant within vascular to the stem, especially within the desmium. The research shows that the pathogen could not be isolated consistently even though it was considered to be responsible for disease symptoms. Trials of a control fungicide (Foli-R-fos 200) shows that protection occurs in many susceptible plants when 2 and 6g a.i./L phosphite is applied. Phytotoxicity occurred in native plants at Anglesea and within controlled environment trials when using ≥ 6g a.i./L. It will be shown that 2g a.i./L phosphite controls disease in sprayed plots within heathlands at Anglesea and a recently burnt coastal woodland community at Wilson’s Promontory. The proportion of healthy X. australis plants treated with phosphite was significantly higher than the proportion in control plots without phosphite. The research shows that phosphite was recovered from leaves of three species treated with Foli-R-fos 200 in the field. For the first time it has been shown that seed germination was reduced in two species when high concentrations of phosphite were applied. The first documentation of the effect that phosphite has on soil properties showed that nitrogen and oxidised organic carbon were the only parameters to alter significantly. This thesis provides answers to some important questions, answers that can now be used by managers in formulating better policies and actions at an operational level. There has been a dire need in Victoria to address many issues regarding P. cinnamomi and this thesis provides relevant and informative approaches to disease control, and a better understanding of the disease progress.

Thesis (PhD)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Barry J. Jacobsen. Includes bibliographical references.

No description available.

Forecasts for the first fungicide application to manage cercospora blight of carrot (Daucus carota L. subsp. sativus (Hoffim) Arcang) caused by Cercospora carotae (Passerini) Solheim were evaluated during the summers of 1991 and 1992. In the forecast based on infection, the blight severity values (BSV) were calculated for each day using duration of leaf wetness, relative humidity and temperature. The first fungicide was applied when the cumulative blight severity value reached 14 (CBSV 14) and 18 (CBSV 18). The forecasts were compared with the 50% disease incidence threshold method where the first fungicide was applied when the middle leaf of 50% of plants was diseased, and the conventional method where the first fungicide application was made when the plant height reached 15 cm. For the threshold of CBSV 14 and CBSV 18, no loss was observed in yield and fewer fungicides were applied as compared to conventional and 50% disease incidence threshold methods. Three years of weather data from experimental plots and 155 commercial field data were used to study the behaviour of CBSV at 50% disease incidence threshold. Only in 3% of the fields, the disease incidence of 50% was observed before the CBSV reached 11. The increase from CBSV 11 to 20 was rapid. Depending on environmental conditions the first fungicide at a CBSV range of 11 to 20 is proposed rather than a critical threshold since no loss in yield was observed at 18 in the experimental plots. No fungicide is applied until the CBSV reaches 11 and the application must not be delayed after CBSV reaches 20.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 176-187).

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 91-107).