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Watermark Disease

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Watermark Disease

What is it and how does it affect the global supply of willow?

Since the beginning of the twentieth century the cricket bat willow, Salix aalba var.caerulea, has been subject to a serious infections disease, Watermark Disease. Watermark Disease results in the crown of the tree dying back, but rarely brings the death of an entire tree. This infection is known as watermark disease because the wood of the trees suffering from it suffer from a dark watery stain. This is of great economic importance, because any marked willow will not be accepted by willow merchants, or makers of bats.

Trees of any age are liable to infection, but those under five years of age seldom show any signs of attack. The disease is easy to recognise by the stain in the wood, but the external symptoms are sometimes confused with those of the honey fungus, Armillaria mellea, which slowly kills the tree without staining the wood, and with die back due to various causes such as drought or bad drainage.

Trees infected by the disease present with certain visible symptoms. The first signs that a tree has the disease is in about the third for fourth week in April or early in May: the first leaves, which by then have appeared, lose their grey colour, wither and turn reddish. With the first onset of really hot weather thereafter (late may and early June) the later leaves, now fully expanded, rapidly wither on actively infected branches,
and turn red. The red leaf symptom may appear at any time through the summer and early autumn. The whole crown is never affected in this way and sometimes in the early stages the number of withered and reddened leaves are so small as to escape notice.

The internal symptoms show that the wood of all dying shoots and branches is watermarked, and the stain may be present in many of the larger limbs, and also in the trunks and roots. In some trees only the shoots with withered leaves are watermarked, an indication that the trees have been recently infected. In other cases the watermark may extend throughout the tree, and showing up in cross sections of the stem, root and nearly every branch as a wide continuous ring of discoloured wood.

The fact that the watermark is often so extensive in trees showing few external signs of injury means that even slightly diseased willows are unsaleable for cricket bats. The risk of stained wood is too great.

The disease is caused by an organism called Erwinia salicis which grows, multiplies and spreads rapidly both upwards and downwards in the wood vessels, which transport the water from the roots. In the process of growth the bacteria secrete substances that ooze through the walls of the vessels and create the watermark stain. When the bacteria reach the newly formed wood of any shoot, death of these tissues quickly ensues and is manifested by the withering of the leaves.

Observations show that the disease seems to appear first on the trees in valley bottoms, especially those that are narrow and wooded, it then travels upwards to trees planted along feeder tributaries and ditches.

It is impossible to guard against the possibilities mentioned previously, beyond obtaining sets (young trees for planting) form a disease free district. The only means of controlling the disease is to destroy infected
trees as soon as the disease is identified. Diseased trees should be felled at once and the main stem and branches removed and burnt. Though unsuitable for making cricket bats, watermarked timber can be used for other products such as chip baskets, match spills, toys and brush heads, also for wood pulping. The price obtained for wood pulping is of course much lower than that for clean timber suitable for bats.

Willow suffering from watermark disease produce poor quality willow, and older trees with the narrow grained willow are harder to find, hence the trend is going back to the traditional ½ inch spacing for the grain on the face of the bat.

The willow is not only stained but is weaker. The disease affects the tree but researchers are unclear as to whether the buried trunk section of the tree is infected so a recommendation of a strong dose of creosote to the
stump should kill any residue left behind. It is thought that an area formerly affected should be clear enough for replanting in about twelve months from treating the stump. If a seed bed is found to be affected the
plants have to be destroyed and the bed cannot be used for three years by order of several counties in the UK. Strict orders are being carried out by county councils and they may serve orders on owners, requiring infected trees to be destroyed.

Watermark affects the Global supply of willow by drastically decreasing the amount of trees available for processing into clefts suitable for batmaking. Much damage has been done in the principal growing districts, especially in Essex and Hertfordshire.

With controls in place the spread of watermark disease is being reduced thus increasing the willow supply again, however many batmakers have been guilty of not treating stumps and burning branches when the disease has been spotted thus all these measures put in place take time.

As far as implications to cricketers, there is no major shortage of cricket bat willow, and provided the authorities remain vigilant watermark disease will not cause major problems for cricketers or cricket bat makers.

With diseases such as this the quality of the willow is affected and older trees with the narrow grained willow are harder to find hence the trend is going back to the traditional ½ inch spacing for the grain on the face of
the bat.

Thanks to J.S.Wright & Sons Ltd for information on Watermark disease.
www.cricketbatwillow.com 

Next months topic - What is a cricket bats Coefficient of restitution?

James Laver
Senior Bat Maker - Laver & Wood
james@laverwood.co.nz
www.laverwood.co.nz

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