Scab situation in 1993 [in apple orchards, in Belgium]
1994
Creemers, P. | Vandenwijngaert, S. (Koninklijk Opzoekingsstation van Gorsem, Sint-Truiden (Belgium))
In 1993 there was a strong ascospore pressure in a large number of the [Belgian] apple orchards. Due to the relatively dry climate conditions, this did not lead to disastrous scab infestations in spring. In some regions however, a so called 'light infection' in the beginning of May caused serious scab lesions on the third and the fourth leaf of the long shoots. Explanations were sought in the extreme climate conditions before and after this infestation period, which had a negative influence on the effect of preventively as well as curatively applied fungicides. Research is being done to obtain a better quantification of the degree of infection by taking into account also biological parameters (ascospore pressure and infectable leaf area) apart from the climatic parameters. This will offer the possibility to determine the treatment data even better in function of the infection pressure during the growing period. When using DMI-fungicides, it is important to incorporate anti-resistance strategies in the treatment scheme. The emphasis is always put on reducing the number of treatments to a maximum of six and on adding each time a contact fungicide. In order to slow down the progressive evolution of resistance it is also necessary not to use a lower dose of the DMI-fungicide and to take into account the climatic conditions to guarantee optimum uptake of the DMI-fungicide. Treatments at temperatures above 10 degrees Celsius and a high relative humidity are favorable for the uptake. For treatments on dry crop and at low relative humidity it is indicated to increase the water volume per ha.
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