All Things Gardening forum: Xylella fastidiosa

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Name: Rj
Just S of the twin cities of M (Zone 4b)
Garden Ideas: Level 1 Plant Identifier Million Pollinator Garden Challenge
Dec 3, 2017 9:11 PM CST
Plant disease explained: The dangers of Xylella fastidiosa

Dried branch of olive tree partly infected by the bacteria Xylella fastidiosa near Lecce, Italy. CREDIT: TIZIANA FABI /AFP

Dr Rebekah Robinson, rhs plant pathologist
23 FEBRUARY 2016 • 3:58PM
Recent outbreaks of a serious plant disease in Europe have put the UK on a state of high alert. The bacterium, Xylella fastidiosa, causes severe damage to plants in North, Central and South America and is classed as one of the most harmful plant pathogenic bacteria in the world. Plants at risk include grape, peach, citrus, olive, oak, sycamore and many other common trees and ornamental plants (such as euphorbia, hebe, lavender, rosemary).

The bacterium lives in the water-conducting vessels (xylem) of plants and spreads between plants via xylem-feeding insects such as leafhoppers and spittlebugs.

Although insects can transport the bacterium, the most likely route of entry of Xylella into the UK is through the importation of infected plant material.

This means that home gardeners are unlikely to be the first to spot the disease should it arrive in the UK. Growers and retailers importing plants will provide the front line of defence.

Xylella was first found in Europe in October 2013, causing disease of olive trees in the Lecce province of Italy. A separate outbreak was discovered in Corsica and mainland France in July 2015 on ornamental plants (Polygala myrtifolia).

Action was taken to control these outbreaks through destruction of susceptible plants within a 100m radius, control of insects that spread the disease, and a 10km restriction on movement of susceptible plants. Within Europe all imports of susceptible plants must now be accompanied by documentation confirming their origin from a disease-free site.

Infection by Xylella can result in symptoms of leaf scorch, stunted growth, reduction in fruit quality and size, and dieback. Similar symptoms can be caused by other diseases and environmental conditions such as frost damage. Therefore symptoms alone cannot confirm the disease and laboratory tests based on DNA sequences or antibody detection are required.

In Europe, 359 plant species have been identified as susceptible to Xylella. However, many infected plant species show no symptoms. These symptomless plants are difficult to detect and provide a reservoir for re-infection of other plants. This ability to infect a wide range of plants and the ability to 'hide' in symptomless plants makes Xylella difficult to control.

The potential impact of a Xylella outbreak in the UK is difficult to predict due to the existence of multiple subspecies of the bacterium, the unknown effect of UK weather and the occurrence of susceptible plants and insects that spread the disease. Should an outbreak occur in the UK, the outcome could be devastating for the horticultural industry and the landscape.

Suspected outbreaks of Xylella fastidiosa must be reported to the relevant Plant Health Service authority; in England and Wales contact the local APHA Plant Health and Seeds Inspector; in Scotland contact the Scottish Government's Horticulture and Marketing Unit.

Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed.

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