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WALNUT DISEASES

   
Walnut

 

Bacterial diseases

1-Walnut Blight:

The causal organism Xonthomonas campestris Or Pseudomonas Juglandis

Also known as ' bacterial blight', and formally as 'Xanthomonas campestris pv. juglandis' or 'Pseudomonas juglandis'.

Symptoms:

Causes small black spots on leaflets, leading to large withered areas. Can also cause die back of shoots and damage to the fruits, notably blotches and holes. A large part of the crop is likely to be lost in a serious attack, especially when the male catkins are affected.

This is very much a disease of new growth and nuts, and infection occurs only in wet weather. The most damaging circumstances are wet, cool periods around flowering time.

The bacteria will survive over winter in apparently healthy dormant buds, leading to new infection of young growth-varieties which leaf early are most at risk.

Control:

Infected parts should be cut out a good way back from visible damage and burnt. Defenses against blight include keeping soil PH above 6, avoiding wetting the foliage with spray irrigation, guarding against excessive nitrogen feeding and pruning enough to give an open structure for aeration.

Crown gall:


The causal organism Agrobacterium tumefaciens

Which mainly enters through wounds, swellings appear on the roots and lower trunk. These are not usually damaging

Fungal Diseases:

1-walnut leaf blotch:

The causal organism  Gnomonia leptostyla

Symptoms:

A widespread fungus causing brown blotches on young fruits and leaves, when severe will cause the nuts to abscise (fall prematurely) after turning black and considerable leaf fall.

Another disease which favors wet weather for infection, it usually appears in late May and early June and will over winter on leaf litter.

Control:

-Fallen leaves should be cleared and burnt or properly composted

Use COCOX 250G/100L.W

2- Root Rot:

The causal organisms  Armillaria mellea

Symptoms:

This is a disease affecting many species of trees, and causes defoliation, dieback and death. It can enter at wounds and roots, and can spread through the ground to neighboring plants. It rots roots, collar and butt and is most dangerous to already weaken.

Control:

The only defense is to remove diseased trees and their roots, and any nearby stumps. Some of American walnut species (J. hindsii, J. nigra and hybrids) are resistant to honey fungus sousing them as rootstock is one option- however this increases the chance of attack by Black line.(virus disease) 

3- Botrytis rot

The causal organism Botrytis cinerea

The disease is likely to affect plants in very wit or humid conditions. The fungus can affect harvest nuts if they are not dried correctly

Control: 

Use BELLIS 50G/100L.W.

Virus Disease:

Black line:

This disease, caused by a strain of the Cherry leaf Roll virus (CLRV-W), affects only non-regain rootstocks.

Symptoms include a dark line between the stock and grafted tissue ('scion'), poor growth, yellow drooping leaves and early leaf fall. As the disease progresses the tree suffers dieback and eventually death.

The virus is transmitted through the use of infected tissue fir grafts, by pollen and seed-so it can and will spread rapidly. The spread through individual trees is slow so serious symptoms may not appear for several years after infection.

Insect of walnut

Leaf gall mite


The walnut leaf gall mite (Aceria erinoea, previously known as Eriophyes erineus) causes unsightly damage to the leaves, causing a raised hollow bump about half an inch long and with the appearance of a caterpillar's body. The mites are tiny-less than 0.1mm-and lurk over winter in unopened buds, doing their damage before the leaf is properly developed. Unless the infestation is huge it will not cause the tree much strain, and is in any case very difficult to get rid of entirely.

Control:

Use one of the following pesticides:

NOMOLT 50cm/100L.W

CHALLENGER 40cm/100L.W

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Phone:202-35391811/2/3 202-35391515 Fax: 202-35391814