Page 30 - ALG Issue 3 2019
P. 30

pest & disease
RHS pest and disease ranking reveals impact of joint hottest summer.
Above average temperatures in 2018 exacerbated some plant health issues, according to the 23rd annual pest
and disease ranking from the Royal Horticultural Society (RHS).
The charity’s analysis of thousands of gardener enquiries revealed that the warm weather played into the hands
of several existing problems and lent itself to some new ones. Box tree caterpillar topped the pest ranking for the third time as it spread to Wales and Northern Ireland. Honey fungus also remained the most prominent garden disease – as it has done since the ranking’s inception in 1995. More than a quarter (26%) of all disease reports and enquiries related to honey fungus last year as trees suffering from drought stress were more likely to display symptoms.
However, the southern green shield bug was catapulted into the top ten
for the first time as it benefitted from the warm weather in early summer, becoming the sixth most popular pest enquiry in 2018. A sap feeder with some preference for vegetables, especially beans, it became established in Britain in the early 2000s and is thought to have been introduced from mainland
on the plot
Europe. The immature stages, called nymphs, are distinctively black with white or pink markings and the adult is similar
to the harmless native green shield bug but does not feature a brown marking at its rear.
Likewise, pear rust
was of increasing
concern to
gardeners. The
fungus, which causes orange spots to appear on pear leaves and canker-like swellings on branches of Juniper, has become very common over the past 16 years due in part to warmer, drier summers.
However, this same weather also helped to keep some problems at bay such as box blight and leaf spot and canker of Prunus. Both diseases are favoured by warm, wet weather during the growing season, meaning the drier weather minimised its spread last year.
The RHS is conducting research into several of the most prevalent pests and diseases including the range of slug and snail species in the UK, controls
  TOP PESTS 2018
1 Box tree caterpillar
2 Slugs and snails
3 Viburnum beetle
4 Vine weevil
5 Woolly aphid
6 Southern green shield bug
7 Fuchsia gall mite
8= Capsid bug 8= Cushion scale 10 Ants
TOP DISEASES 2018
Honey fungus
Phytophthora root rots
Pear rust
Volutella blight of box Verticillium wilt
Blossom wilt of fruit trees
Box blight
Kerria twig and leaf blight
Leaf spot and canker of Prunus Powdery mildew of Prunus
  The Southern Green Shield Bug is slightly larger than the native bug, at around 12mm long (1⁄2 inch) and is uniformly green, without a dark area at the rear end. The immature bugs are green or black, and have white, yellow or pinkish circular markings on the upper surface.
       Our pest and disease ranking may be evidence of how climate change is impacting on what we find in our gardens
for box tree caterpillar and box blight and improved strategies for managing honey fungus. Findings and advice will be available at the end of 2019.
Matthew Cromey, Principal Scientist at the RHS, said: “Our pest and disease ranking may be evidence of how climate change is impacting on what we find in our gardens. With the UK predicted to see wetter winters, warmer summers and more extreme weather events, root diseases of trees and shrubs could become even more problematic and the array of pests is likely to change. As the UK faces new plant health problems it’s imperative that the country has the skills needed to predict, exclude and manage the worst”.
‘Pentatomidae - Nezara viridula f. torquata’ by Hectonichus is licensed under CC SA-3.0.
 The native Common Shield Bug is broad, flat and green, with a strongly contrasting blackish brown darker area at the rear end. The nymphs have a rounded shape and are pale green with some black markings.
Common Shield Bug, image credit: jubsen@morguefile.com
    30 Allotment and Leisure Gardener























































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