Trees, like all plants, have their predators. By and large nature finds an equilibrium between predator and prey, when predator species do well and multiply they decimate their prey, meaning they haven’t enough to sustain their numbers and their population declines. When prey species over expand predators flourish and cut back their numbers. The same is true in the botanical world.
The trouble is that the equilibrium is established on a biosphere scale. To prevent local elimination of species, or, in our case, the loss of individual trees its worth limiting pests such as aphids if they are too widespread or the trees are particularly vulnerable. Until they are well established over a number of years, newly planted trees are more vulnerable so may need protecting.
In Spring 2021 we found that aphids were becoming a problem on some newly planted cherry trees, which we set about controlling biologically by introducing parasitic wasps.
This is how we noticed the problem:
…and this is how we are tackling it: