THE APPLICABILITY OF BILLING'S SYSTEM FOR SPRAY-WARNINGS AGAINST FIREBLIGHT
Infection occurred on fewer days than expected using Billing's criteria for infection. This would have led to the application of too many sprays, should they have been carried out shortly before completion of calculated incubation-periods.
In 13 out of the 20 times that fresh ooze or other symptoms were observed, the correlation with the calculated day of appearance can be considered to be sufficient to justify a spray-warning shortly before completion of calculated incubation-periods. In the other cases a spray based on such a warning would have been carried out too late or too early, taking into account the limited effective period of such a spray.
Further investigations should provide solutions for both problems before Billing's system can be used as basis for a warning service for fruitgrowers. The influence of sprays shortly before completion of an incubation-period on following infections should also be investigated.