P. Vilardell

Evaluation of BSPcast Disease Warning System in Reduced Fungicide Use Programs for Management of Brown Spot of Pear

A forecasting model (BSPcast) developed for prediction of brown spot (Stemphylium vesicarium) of pear was evaluated as an advisory system for reduced fungicide use in disease management programs. Eleven trials were performed during 1995, 1996, and 1997 in five orchards in two different climatic areas in Catalunya (Spain) and Emilia-Romagna (Italy). Values of 3-day cumulative daily infection risk (CR) provided by the model were used to determine risk periods during the growing season of pear and were taken as thresholds to schedule fungicide sprays. The fungicide application programs tested using the model consisted of guided schedules with CR action thresholds of 0.4, 0.5, or 0.6, and fixed sprays following a standard commercial schedule. In nine out of 10 trials, no significant differences were observed in disease incidence on fruit at harvest between the fixed-spray commercial schedule and guided sprays using thresholds of 0.4 or 0.5. The average savings in number of fungicide sprays applied using BSPcast compared with the fixed-spray schedule were 20 to 70% when using fungicides with a 15-day protection period (kresoxim-methyl or procymidone) and ranged from 20 to 50% when using a fungicide with a 7-day protection period (thiram).

Evaluation of FAST as a forecasting system for scheduling fungicide sprays for control of Stemphylium vesicarium on pear.

The influences of temperature on mycelial growth and of temperature and relative humidity on germination of conidiospores were studied in six strains of Stemphylium vesicarium isolated from lesions on pear fruit (Pyrus communis) grown in areas of Catalunya, Spain. Optimal temperatures were 15-25 C for mycelial growth and 20-30 C for germination of conidia. Conidia germinated only when relative humidity ranged from 98 to 100% and free moisture encompassed the conidia. Comparison of these data with weather parameters during epidemics indicated that under climatic conditions in Spain, the principal limiting factor for epidemic development is duration of wetness (.)

Susceptibility of selected European pear cultivars to infection by Stemphylium vesicarium and influence of leaf and fruit age.

Nonwounded fruit of 16 European pear cultivars (Pyrus communis) and potted Conference pear plant were inoculated with conidia of Stemphylium vesicarium. Cultivars Passe Crassane, Alexandrine, Conference, Doyenne du Comice, Duc de Bordeaux, Abate Fetel, and General Leclerc were highly susceptible. Cultivars Williams, Blanquilla, Beurre Hardy, Louis Bonne, Grand Champion, and Highland were slightly or not susceptible. The susceptibility of fruit decreased logarithmically from fruit set to harvest in very susceptible cultivars. Younger leaves developed 1.8-3 times more disease than older leave

Effect of bactericides, phosphonates and nutrient amendments on blast of dormant flower buds of pear: a field evaluation for disease control

Blast of dormant flower buds (BDFB) of pear is a disease of economic importance in the major pear production areas of Europe. To obtain information concerning control measures and disease origin, chemical control trials were performed which included bactericides (kasugamycin and copper), phosphonates (fosetyl–Al and ethephon), and nutrient amendments (boron, calcium, and microelements). Although Cu levels in bactericidal treatments and microelements in nutrient amendments increased significantly in trees, there was no significant effect on disease control. However, incidence of disease was reduced significantly with phosphonate derivative compounds, and effects were observed only the year after the treatment was performed. Additional field trials were done to determine optimum dose and application timing, and a schedule consisting of three spray applications of fosetyl–Al (240 g a.i. hl-1) during May and June was the most effective treatment. This schedule was evaluated in 31 field trials performed in commercial orchard plots from 1989 through 1998. In the year after the treatment, average disease incidence decreased in 30 of 31 trials. The decrease of disease incidence was significant in 71% of the trials (average decrease of 46%). Neither the presence nor the population levels of P. syringae were consistently related to disease levels nor to the fosetyl–Al treatment effects on blast incidence of dormant flower buds.

Control of brown spot of pear by reducing the overwintering inoculum through sanitation

Stemphylium vesicarium, the causal agent of brown spot of pear, overwinters in the leaf residues of pear and herbaceous plants of the orchard floor. Pseudothecia of the teleomorph, Pleospora allii, are formed on these residues where they produce ascospores. New methods were tested aimed at reducing this overwintering inoculum and increasing the efficacy of control of brown spot of pear. Sanitation methods were evaluated in nine trials in Girona (Spain) and Ferrara (Italy) over a 4-year period. The sanitation methods were leaf litter removal in December to February, and application of biological control agents (commercial formulates of Trichoderma spp.) to the orchard ground cover from February to May. Fungicides were also applied to the trees during the pear-growing season, scheduled according to the BSPcast model. The different methods were tested as stand-alone applications or in combination. All methods consistently reduced the disease incidence at harvest on fruit with an efficacy between 30 to 60% for leaf litter removal and more than 60% for the combination of leaf litter removal and biological control. Efficacy of sanitation alone (leaf litter removal and biological control) in reducing the brown spot level on fruit was similar in most of the trials to the efficacy obtained when fungicides were applied alone. However, integration of sanitation methods and fungicides did not improve the efficacy of disease control over the level provided by fungicides alone.