Improving pest and disease resistance is one of our breeding objectives. Consequently, we follow a no-spray approach where ever possible, relying on natural predators for pest control.
Thrips (possibly Western Flower Thrip) are by far our greatest problem, as they damage the terminal bud and youngest expanding leaves on the main leader (image opposite). Around half of our first year seedlings were affected during 2014. The severe stunting of extension growth is often accompanied by profuse and undesirable lateral shoot production (image below), presumably triggered by the damage to the terminal bud and breaking of apical dominance. In some case repeated, corrective, summer pruning is required to re-establish a single leader. We are not sure how this affects the rate at which seedlings progress through the juvenile phase, but the evidence so far suggests significant retardation.
It is clear that first and second year seedlings are damaged more severely by thrips compared with older seedlings, possibly due to the greater height of the terminal buds on the latter. Early season growth is least affected, with most of the damage occurring between June and August, after which extension growth generally recovers. Encouragingly, numbers of both larval and adult Pirate bugs (i.e. Anthocoris nemoralis), natural predators of thrips, have increased.
Caterpillars and aphids have, so far, caused only minor damage, affecting a few seedlings early in the growing season.
Canker, Scab, Rust and Powdery Mildew are our commonest diseases. Canker causes the death of between 10-20 seedlings per year. Mildew causes serious systemic damage to a similar number of seedlings (image opposite), and low to moderate damage to a larger number. However, it is rarely fatal and we score its severity, which varies on a given seedling from year to year.