Walnut trees are a source of fruit and wood.
Walnut trees (Juglans regia) are valued both for their nuts and wood, and are a native of Northern Persia. The trees are among the small order of shrubs and trees called Juglandeae and are the largest tree in the group. Walnut trees can reach a height of 60 to 70 feet and younger trees are susceptible to frost injury. The trees remain productive for a great age and grow well in nearly all well-drained soils. Grafted walnut trees are relatively less liable to suffer from diseases and pests. However, any tree in poor health and which lacks adequate nutrition can be infected by disease or pests.
Walnut Blight
Walnut blight is also referred to as bacterial blight or Pseudomonas juglandis and is caused by the pathogen Xanthomonas campestris pv. Juglandis. Walnut blight is more common on new growth and nuts and appears only during wet weather, especially when the climate is cool and wet at flowering time. The bacteria overwinter in the healthy buds and start to infect new growth at springtime. Walnut blight appears as small, black spots on new leaves, which enlarge to create larger, withered areas. As the disease spreads it causes dieback of new shoots and starts to damage the fruit by creating holes and blotches. The disease can potentially lead to the loss of large crops, especially when it affects the male catkins. Control methods include pruning visibly damaged growth and using Bordeaux mixture sprays.
Walnut Leaf Blotch
Walnut leaf blotch is also known as walnut anthracnose, gnomonia leptostyla or marssonina juglandis. It is a fast-spreading fungal disease that leads to blotches on young foliage and fruit. In severe cases there is defoliation and the nuts start to turn black and fall prematurely. Walnut leaf blotch also occurs most frequently during wet weather. However, it is also not uncommon in late May and early June. The fungus overwinters on the fallen leaves; hence it is important to keep trees clear of leaves that should either be properly composted or burnt. In serious infections, Bordeaux mixture can prove helpful.
Honey Fungus
Honey fungus is also referred to as shoestring fungus, mushroom root rot and oak root fungus. The fungus afflicts many tree types including walnut and leads to defoliation, dieback and death. The fungus enters the tree through tree wounds and roots and spreads through the soil. The fungus rots the roots, butt and collar of trees and proves fatal to already weak and stressed trees. The fungus can be controlled by removing diseased trees and their roots so that the fungus does not spread to other vegetation. The species J. hindsii and J. nigra and their hybrids are well resistant to honey fungus.
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