Faculty of Environmental Sciences, Department of Forest Science, Institute of Silviculture and Forest Protection in poplar short rotation coppices (SRC) Economic importance and possible preventive measures on ecological base Richard Georgi & Michael Müller - Professorship in Forest Protection - 1. Economic importance

untreated: damage on apical leafs

treated: no damage on leafs Example 1

The Great Red Poplar Leaf Beetle () is the main pest species in poplar SRC in Germany. To quantify the influence of the feeding to the increment of the poplar, a field trial with 120 untreated and 120 through plant protection products threated plants was performed. The results (figure right) show, that the weekly increment differs most at the same time the extend of feeding (dimensionless value representing all damaging stages of the red poplar leaf beetle) was in the maximum. At the end of the year, untreated poplars were on average 15 % smaller than threated poplars. Example 2

The gregarious poplar sawfly (Nemtus papillosus) is another common pest species in poplar SRC, but mass outbreaks are rare. But in the case of a mass outbreak damages are considerably greater than feeding by C. populi (Example 1). The extent of damage depends on the time the sawfly occur in the year - the sooner the more heavy damage are to be feared. The figures on the right show the height and the number of harvestable cuttings per stump, were an mass outbreak occurred in May (1th Generation) or in July (2nd Generation) in comparison to unaffected growth.

2. Possible preventive measures on ecological base (on the example of the red poplar leaf beetle)

2.1. Mixture of varieties 2.2. Importance and promotion of natural enemies

nigritarsis

mite Linobia coccinellae

The figure above shows the preference of the C. populi for six different poplar varieties. For the ex- spider predatory bug Picromerus bidens tachina wasp Schizonotus sieboldi periment newly emerged leafs were used except for Max 1 old. The results show a significant pre- promotion through ference of this pest species for the variety Max 1. Due to the fact that this variety is the most used one in SRC in Germany at present, the Red Poplar ongoing research Leaf Beetle will find optimal conditions for develop- ment. The use of a mixture of varieties would be a flowering plant strips good strategy to minimize the risk of damage. Flowering plant strips are important food sources for many natural enemies. Therefore further research will focus on the effect of different floral resources on longevity and fecundity 2.3. Use of selective pesticides of important natural enemies. Under special conditions a mass outbreak can oc- alternative prey/hosts cur in spite of all preventive measures and the use of chemical control becomes inevitable. The best permanent habitat/shelters Most natural enemies can solution would be to use selective insecticides, The presence of permanent ha- also develop on alternative because they spare otherwise beneficial organis- bitats/shelters is essential for prey/hosts. Therefore further ms (see natural enemies on the right). But by now survival. Especially shelters for research will focus on pos- there are no selective insecticides available for the overwintering will be focused in sible alternative pray/hosts, Red Poplar Leaf Beetle. current research activities. to maximize the population density of the antagonists.

Contact Richard Georgi [email protected], +49 35203/38 31623 Prof. Dr. Michael Müller [email protected] Internet www.agrofornet.de Poster Download