Pests and diseases 63
Pests and Diseases
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sually few major pest and disease problems will be encountered in
perennial gardens if time has been put into the proper selection of
insect- and disease-resistant species, as well as into locating plants in
the proper sites for optimal growth. There should be no reason to grow
plants that require serious chemical controls given that so many
outstanding perennials are free of pests or are unlikely to be seriously
damaged. Battling pests with the use of controls that aren’t truly
necessary is a waste of time and contributes to the destruction of our
environment. We need to be tolerant of a few holes or spots on leaves,
or even in some years the destruction of the whole plant. Remember, herbaceous
perennials will often send up new foliage later in the season even if totally defoliated
early on or if pruned down as a result of serious damage. They will at least be back
the following year to give it another try. Give a plant a couple of seasons—it may be
affected with ailments some years, while in others it sails through cleanly, usually
depending on weather conditions. If all our efforts at proper plant selection, sound
cultural practices, patience, and the use of environmentally sound control methods
have failed, then I think it’s time to ask the afflicted plant to leave the garden!PEST AND DISEASE PREVENTION
A stress-free plant is less susceptible to disease and insects than one growing in a
stressful environment. Proper soil and water management are crucial to reducing
stress on perennials. Keeping the garden free of debris is also helpful. Some
gardeners believe that yellow foliage attracts insects and so believe that dead-
leafing is vital to avoid welcoming trouble (although I have not found this to be the
case). Many insects and diseases overwinter on decaying foliage of certain
perennials, so infected foliage should be removed from the garden in the
autumn—do not compost these materials if your pile does not reach temperatures
high enough to ensure that the pests are killed. Avoiding overhead irrigation can
help reduce the chance of disease and its spread. The spacing of perennials in the
garden can affect certain species’ susceptibility to pests. Having a diverse number
of species in the garden is important because many pests and diseases are
species-specific, and so your whole garden or a big part of it won’t be wiped out if
you include species that are not prone to the pest in question.Perennials that are sharp or
spiny, such as this globe thistle
(Echinops ritro), are naturally
deer resistant.