TDA136 Yellow Peril – Brown Trees?
Tree Damage Alert No 136
10th May 2010
Yellow Peril – Brown Trees?
“Yellow peril ..... its a dandelion invasion” was a heading in a tabloid newspaper on Thursday 22nd April 2010. The article reported “….an invasion of Dandelions defacing lawns and roadside verges.” Many people will have appreciated the bright splash of colour on the otherwise developing green; naturalists may welcome the swathes of yellow flowers for the pollen and nectar they provide for the early insects.
Aficionados of high quality lawns are likely to be less tolerant of such defacing growths. Many gardeners and other land managers will have concern about the estimated “... 20,000 wind dispersed seeds” each plant can produce and the implications they have for weeding during the coming summer months.
What will be the likely response? The sales and use of selective herbicides and ‘weed and feed’ products may be expected to rise. The use of such chemicals will generally be trouble-free although the deeper tap roots of Dandelions may show some resistance. Trees and shrubs surrounded by ground that is to be treated, particularly those with roots near the soil surface, may, however, be damaged by the chemicals.
The manufacturer’s label rarely mentions that a chemical designed for lawn care is usually designed to be highly selective in that it will kill broadleaved weed plants and have no effect on the grasses. So what you may say. The problem is that to these chemicals a tree or shrub is a broadleaved plant and therefore fair game! Some chemicals are readily absorbed through thin fleshy bark of the sort found on large structural roots.
Each year AAIS and Forest Research receive enquiries about damage to trees and shrubs which traced back from symptoms, circumstantial evidence and in extremis chemical analysis, to probable weed-killer damage – sometimes selective and sometimes non-specific chemicals.
Owners of properties are often understandably loathe to admit that they use chemicals. Persistent directed questioning will generally lead to admission of a specific product which can be very helpful in determining a cause of damage.
If herbicides, particularly selective formulations, are to be used on lawns avoid treatment under the canopy of trees and shrubs. Also, in areas where there are tree and shrub roots close to the lawn surface avoid use of proprietary specialist herbicides that are selective to favour grass growth. Damage may be particularly noticeable where the chemical might become concentrated, for example where ground slopes towards trees and shrubs and near paths.
If you are investigating trees or shrubs growing in or close to high quality grass sward and that have suddenly become sickly, don’t forget to ask if anything has been used on the grass.
Derek Patch
Arboricultural Advisory and Information Service, Farnham.
AAIS l Alice Holt Lodge l Wrecclesham l Farnham l Surrey l GU10 4LH
Call the Tree Helpline on: 09065 161147
Calls cost £1.50 per minute