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Common Nut Tree Diseases – What Diseases Affect Nut Trees

Common Nut Tree Diseases – What Diseases Affect Nut Trees


By: Kristi Waterworth

Your friends are busy boasting about their homegrown strawberries and melons, but you have much bigger plans. You want to grow nut trees. It’s a big commitment, but it can yield a big reward if you have the space and time to dedicate to nut growing. One of the many things you’ll want to learn more about is diseases that affect nut trees. Treating a sick nut tree early is important to preserving all your hard work and protecting your harvest! Read on for information on what diseases affect nut trees.

Common Nut Tree Diseases

Although we don’t have enough space to cover all possible nut tree diseases and nut tree disease symptoms, we’ve picked out some common nut tree diseases to highlight to get you started on your nut tree care adventure. As your trees grow and mature, keep your eyes open for these common problems:

Anthracnose. Wet weather in late spring and early summer make anthracnose better able to survive on nut trees. When the fungus infects leaves, it can cause them to drop prematurely, resulting in tree defoliation, or pinkish lesions may form on the nuts themselves. You can choose to replace your trees with anthracnose resistant varieties or you can try to save the trees you have with sprays of fungicides like mancozeb or benomyl.

Sanitation is really important for preventing reinfection, as is establishing a preventative spray program. Spray with a fungicide when the leaves just start to unfold, then four more times at two week intervals.

Leaf spots. Various leaf spot diseases occur in nut trees, resulting in decreased ability to photosynthesize and increased stress. Leaf spots might be yellow, brown or black, the size of the head of a pin or of a coin, but in nut trees they can all significantly influence your yield.

When you notice leaf spots, start a spray program using copper fungicide (unless fruit are still very young, in which case a phytotoxic reaction is possible). Ideally, you’ll begin spraying when the leaves unfold and spray monthly until mid-summer.

Oak root fungus. When small gold-colored mushrooms appear at the base of your nut tree, it’s not a good sign. Your tree may be suffering from oak root fungus, also known as honey mushroom rot. Unfortunately, once you see the mushrooms, it’s years too late to prevent the infection or reverse it. Infected trees will show an overall decline, may experience dieback and if you peel the bark back, you’ll find the signature white mycelial fans that are the hallmark of the disease.

There’s no cure and no long-term treatment. The best you can do is remove the tree and try to prevent the fungus from spreading. Make sure all the parts of the tree have been cleaned up, including chunks of root that might be buried.

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Walnut Diseases

Plant diseases may be caused by fungal, bacterial, or viral pathogens. They are transmitted from plant to plant by wind, water, soil, or insect vectors, often entering into the plant by way of natural openings or wounds. One of the most prevalent soil borne diseases affecting walnut production in California is crown gall, caused by the bacteria Agrobacterium tumefaciens. Crown gall manifests itself as large irregular growths at the base of the tree and reduces the flow of water and nutrients to the tree. All rootstocks are susceptible, but Paradox seedling is more susceptible than Northern California black walnut (UC IPM website, 2012). Other important soil borne fungal diseases causing crown and root rot are Phytophthora and Armillaria mellea (oak root fungus).

Walnut blight (Xanthomonas juglandis) is the most common nut and foliage disease. It is most common in wet and humid spring conditions. Cultivars with early leaf dates tend to be more susceptible to walnut blight, although fungicide treatments are effective in managing the diseases in most years. Other diseases that may affect the trunk, scaffolds and branches include deep bark canker (Brennaria rubrifaciens), shallow bark canker (Brennaria nigrifluens), and branch wilt (Hendersonula Toruloidea) (Teviotdale and Schroth 1998).

The most important viral disease of walnut is blackline, caused by the cherry leafroll virus. Blackline disease is prevalent in California coastal regions and San Francisco bay area counties. The virus is transmitted through pollen. Viral infections are asymptomatic in the English walnut scion but the rootstock has a hypersensitive reaction killing the infected cells and girdling the tree at the graft union. This disease can be avoided by growing trees on their own roots.

Photo Gallery

These photos of some of the major pests are accessed from the UC ANR Repository, are available courtesy of University of California research and extension personnel and programs, including the UC Statewide IPM Program. Photo information, including the photographer, is displayed when the larger image is viewed.


Main diseases

Apple mosaic virus

The most frequent form of attack manifests on the leaves, through the appearance of some irregular yellow spots. Usually, the attack can be observed on one side of the leaves. If the temperatures are between 18 and 20 degrees Celsius the spots turn brown. This can lead to a production decrease and weakening of the attacked trees. The virus is transmitted through grafting, pollen, infected seeds, and in the nursery by touching of the roots.

Prevention and control measures:

  • Using healthy graft
  • Taking out the attacked trees from the orchard
  • Planting resistant species.

Bacteriosis

Bacterial blight produced by Xanthomonas campestris pv. Corylina

It is very dangerous in the hazelnut plantations. The bacteriosis attacks the buds, sprouts and leaves. The buds turn brown and don’t develop, the sprouts will become dry, and at the surface of the branches, ulceration that can lead to its break will appear . The bacteriosis is transmitted through the bacterial exudate that is transported by the water drops, wind or through the maintenance procedures. Black spots appear on the leaves , placed on the spaces between the nerves. The spots become united and destroy the entire leaf.

Prevention and control measures:

  • Gathering and destroying the leaves and fruits fallen on the soil.
  • Treatments with Champ 77 WG, Melody Compact 49 WG, Funguran OH 50 WP, Copernico Hi-Bio, Bouillie Bordelaise WDG.

Anthracnose produced by Sphaceloma coryli

This fungus attacks the leaves, fruits and flowers of the shrub. Necrotic, black spots appear on the leaves. If the attack is severe the nerves of the leaves become black. Small wounds appear on the leaves, that determine its deforming and abortion. Necrotic, brown-black spots appear on the fruits. After the attack, the fruits fall prematurely.

Prevention and control measures:

  • Burning or burying the leaves from the orchard
  • Chemical treatments with Topsin 500 SC, Score 250 EC, Bravo 500 SC, Topas 100 EC, Curzate Manox.

Anthracnose produced by Gloeosporium coryli

This disease attacks the flower buds and the vegetative ones. Brown spots appear on the buds, that will cover the whole surface of the buds. After the attack the buds are destroyed, and the production will be decreased.

Prevention and control measures:

  • Burning or burying the leaves from the orchard
  • Chemical treatments with Topsin 500 SC, Score 250 EC, Bravo 500 SC, Topas 100 EC, Curzate Manox.

Brown rot produced by the fungus Monilinia laxa

This disease attacks all the aerial organs of the shrubs, producing significant losses during the cold and rainy years. The attacked leaves hang without falling, the flowers turn brown and become dry, and the branches bend as a hook. The young fruits wrinkle, turn brown and massively fall. The fungus spends the winter on the attacked fruits and in the bark of the attacked branches.

Prevention and control measures:

  • Cutting and burning the affected branches
  • Cutting the affected branches up to the healthy area, applying treatments with Bouillie Bordelaise 4-5% and covering the wounds with healing mastic resin
  • Chemical treatments in the vegetative rest with products based on copper (ex: Bouillie Bordelaise) and preventive treatments applied in vegetation with Switch, Score, Topsin.

Powdery mildew produced by the fungus Phyllactinia corylea

The attack appears on the leaves of the young sprouts through the appearance of some white spots. They extend and cover the whole leaf. The disease evolves, and the mycelium becomes grey and dusty. The attacked tissue wrinkles and dries. The fungus attacks the young fruits too. They are covered with a white micelian felt. The fruits crack and rot.

Prevention and control measures:

  • Using of resistant species
  • Burning the attacked sprouts and fruits
  • Treatments in vegetation with Systhane Plus 24 E, Thiovit Jet 80 WG, Kumulus DF, Topas 100 EC, Karathane M 35 CE.

Grey mold produced by Botrytis Cinerea

The fungus appears in high humidity and low light conditions and can have a high impact on the production, even after the harvesting. The symptoms of this fungus can be observed on the aerial organs of the shrub. The attacked area turns brown and becomes covered with a grey fluff that represents the fungus’ fruition. The fungus lives on the vegetable debris from the surface of the soil, and the spores are transported on the healthy plants by the wind and the water drops.

Prevention and control measures:

  • Gathering and destroying the vegetable debris after harvesting
  • Treatments with Bravo 500 SC, Ortiva 250 SC, Rovral 500 SC, Teldor 500 SC, Switch 62.5 WG.


Rosette

Rosette is caused by a zinc deficiency. In infected trees, you’ll first notice yellowing leaves in the tops of the trees. Later, leaves become small and entire branches may die back or become defoliated. To treat this condition, spray the leaves with a solution of 1 tablespoon zinc sulfate per gallon of water. You can also add zinc to the soil for a longer lasting solution. Make applications based on soil test results or at a rate of ½ pound per inch of trunk diameter. Spread the zinc evenly on the soil from the trunk to the drip line.


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