The Hop-growing Year: Plant Protection*
As much as necessary, as little as possible.
The hops can be attacked by various pests and diseases (refer to Friends and Enemies). Their occurrence depends greatly on the interaction between the weather conditions, the pests' way of living and the resistance of the plants.
Before they can be used by the hop-growers the chemicals used to control these pests and diseases are subject to stringent tests for effectiveness, environmental behaviour and non-toxicity for the crop. Special sprayers (power sprayers) have been developed to distribute the plant protectives, which evenly spray the insecticides over the entire height of the hops. On 1st July 1998 the current plant protection law came into effect. Consequently the EU directive on the marketing of plant protectives (91/414/EWG) was transposed into national legislation.
The hop wilt disease has occurred in Germany since 1952. It is mainly caused by a fungus and there are no means of controlling it with chemicals, the virus diseases cannot be chemically controlled either. Diseased hills have to be grubbed and healthy new rhizomes must be used when replanting.
Depending on the location and weather conditions pests such as weevils, hop aphids and the red spider mite attack the parts of the plant above the ground such as leaves and cones and cause considerable damage if they are not controlled early enough. In recent years the powdery mildew has increasingly become a problem.
The hop peronospora (downy mildew) has occurred regularly since 1924. Above all in damp-warm summers the crippled shoots, caused by this disease can be seen, which are called "spikes". It is particularly threatening when the flower is attacked and dies off and the crop can be diminished to a total loss.
Peronospora warning service
At the beginning of the 1980s a forecasting model was developed In HŸll for the most important hop disease the downy mildew (pseudo peronospora humuli). With the aid of this forecast it is possible to give the hop-grower the exact date for the required spraying. Consequently the 15 sprayings previously made could be reduced to on an average 6 to 7 applications annually.
Another reduction in the chemicals used is attained by growing the newly bred Hüll varieties. Experimental plots confirm that even with three sprayings the Hüll-bred varieties were free from peronospora at the time of harvesting.
* © Extract from the LfL- Bavarian State Research Centre for Agriculture