This fungus poses a major threat to our walnut trees
Thousand cankers disease is a serious scourge to the Northern Plains sinister walnut ( Juglans nigra , Zones 4–9 ) . Understanding the disease can avail prevent the loss of these ecologically and economically important tree .
Affected Species
Thousand canker sore disease is a comparatively new threat to certain species of walnut . It mainly affects black walnut tree but also threatens small walnuts ( Juglans microcarpa , Zones 5–9 ) , butternut ( Juglans cinerea , Zones 3–7 ) , and the nonnatives Manchurian walnut tree ( Juglans mandshurica , zone 5–8 ) and English walnut tree ( Juglans regia , Zones 3–9 ) . First observe in the western United States in the 1990s and recently detected in the easterly part of the country , the disease has caused a widespread quarantine in much of the central United States , with the Northern Plains caught in between .
How the Disease Works
The disease is induce by a fungus ( Geosmithia morbida ) that is vectored — or carried — by the walnut twig beetle ( Pityophthorus juglandis ) . This fungus causes numerous pocket-size canker to take shape around the beetle ’ galleries in the Sir Herbert Beerbohm Tree ’s bast , the layer just beneath the bark that transports loot and food from the leaves to the rest of the tree . The canker on this surface area rarely show externally , unlike many other canker diseases that show signs of weeping at infection website . When numbers are high enough , branches can be completely deaden by the unseen cankers , disrupting the flow of food .
Diagnosis
To determine the mien of thousand canker disease , peel off out the outer bark to see if walnut twig beetle galleries have been made in the phloem under dense areas of pinhole - sized canker . Additionally , if your walnut tree shows polarity of flagging , ask your local tree wellness professional or extension office to conduct a web site sojourn to avow the presence of the disease .
If a walnut tree is infected , symptoms will appear in the jacket crown of the tree through yellowing , wilting , and dying leaves in the upper branch , which will progress downward over time . Other symptom that may be seeable are the growth of epicormic shoots , sometimes called suckers , that form from inactive bud as the stressed tree tries to come through . at last , after two to three years of contagion , the Sir Herbert Beerbohm Tree will knuckle under to the disease and die .
Treatment
If a tree is found to be infected with less than 50 % of healthy crown remaining , direction is currently limited to the remotion of the intact tree diagram and destruction of infected material through combustion , as the beetles have been shown to subsist after barque has been chipped for mulch . If the tree has just start to show symptoms , remotion and devastation of strike branches during wintertime months prior to mallet emergence and flight of steps natural process can help mitigate the spread . On the undimmed side , the septic tree can still be salvage for its valuable wood if the bark , bast , and cambium are removed and destroyed . Also , the disease astonishingly does not affect the nuts of affected tree , which can still be ingest and ship .
The undecomposed bar scheme include maintain hefty treesthrough right irrigation and fertilisation , which foreclose stress on tree diagram . Stress can affect their instinctive power to combat pests and disease . to boot , do n’t move firewood , and only employ topically get firewood !
— Chris Schlenker is the head gardener of McCrory Gardens at South Dakota State University in Brookings , South Dakota .
All photos by Whitney Cranshaw are licensed underCC 3.0 .
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Black walnut, endemic to our region, is very vulnerable to this disease.Photo: Wikimedia Commons
With the bark stripped away, you can see the ill effects of the disease on this black walnut tree.Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
The beetles themselves are extremely small. It’s hard to believe that they can bring down a whole orchard of trees.Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
Scratch away some bark, and look for dark cankers and exit holes like these.Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
This flagging little walnut is in the end stages of the disease and cannot be saved.Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
