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Date Palm Diseases

DISEASES OF DATE PALM

Prof. Ahmed A.M. Dawabah

I- FUNGAL DISEASES

1. Bayoud (Fusariose)

2. Fusarium Wilt

3. Black Scorch

4. Diplodia Rot

5. Graphiola Leaf Spot

 

1- BAYOUD (Fusariose)

The disease was first reported from Morocco in 1870, and derived its name from the Arabic word "Abiadh" which means white. So, "Bayoud" in Arabic means whitish referring to the whitening of the diseased palm fronds.

Causal agent: The fungus Fusarium oxysporum f. sp. albidinis

Morphological Symptoms
External symptoms start to appear on one or two leaves of the middle crown. Leaves takes the grey then white color from bottom to top in a very distinguished pattern. Spines on one side of the frond begin to whitened from bottom to top, then whitening turn to the spines of the other side starting from top to bottom. Brown stains also appear on the dorsal side of the rachis starting from base to the tip of the fronds. After several weeks fronds hang down along the trunk, and whitening extends in the same way to the adjacent leaves. Affected palms die when the terminal bud is affected.

Control
A) Chemical measures
Soil treatment of this type of disease is useless. But, in the case of the discovery of primary sources of infection in a healthy area, affected palms should be uprooted and incinerated on the spot. The soil is then treated with a fumigant, and the area closed off with replanting prohibited until further notice.
B) Cultural measures
Factors that favour high yield in date are, also, favour the development of the fungus. So, cultural measures are not advised. However, since the contamination occurs mainly by root contact, disease-free palms can be isolated by digging a trench of 2 m deep around them. Water should be provided by a trough bridging the rest of the grove to this isolated plot. Under these conditions these palms can be protected for more than 10 years.
Prophylactic measures
The essential task is to prevent the movement of contaminated plant materials (offshoots, palm fragments, manure, infested soil, and all artifacts that made from these materials) from infected palm groves to healthy ones. Also, contaminated vegetative materials should not be moved from one country to another, or from one region to another.
Resistant cultivars
Many resistant cultivars have already been obtained in Morocco.

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2- Fusarium wilt

The disease was first reported from Qassim region, Saudi Arabia in 1990, and differed from bayoud disease and also from false bayoud disease which have been reported from Al-Hassa, Saudi Arabia in 1991.

Causal agent: The fungus Fusarium oxysporum

Morphological Symptoms
The fungus attack old palms as well as offshoots and young palms. Spines on one side of the frond begin to whitened from bottom to top, then whitening turn to the spines of the other side starting from top to bottom, with a brown discoloration along the midrib of the leaves. Symptoms extend from the outer leaves to the young ones, then to the apical meristeme, leading to the death of the palm tree. A discoloration of the parenchymal and vascular tissues occurs in the transverse section of affected leaves. The discoloration of the vascular tissues also occurs in the transverse section of the affected palms.

Control
1- Sterilization of the pruning tools.
2- Systemic fungicides could be useful in case of early infections.
3- Planting the offshoots produced only from the healthy palms.

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3- Black scorch disease

The disease has different names according to the type of infection and the developed morphological symptoms. These names include: Theilavopsis bud rot, Bending head, Crazy disease (Medjnoon), Inflorescence blight, Terminal bud rot, Trunk rot, Leaf black scorch, Stem bending, Dry basal rot, Heart rot.

Causal agent : The fungus Thielaviopsis paradoxa (perfect stage: Ceratocystis paradoxa).

Morphological Symptoms
Symptoms on palm of all ages are usually expressed in four distinct forms: black scorch on the leaves, inflorescence blight, heart or trunk rot and bud rot. In all cases, infections are characterized by partial to complete necrosis of the tissues. Typical lesions are dark brown to black in color, hard, carbonaceous, and - as a mass - give the petioles, fruit strands and fruit stalks a scorched, charcoal-like appearance.

Control
1- Good sanitation.
2- The affected fronds, leaf bases and inflorescences should collected and immediately burned.
3- The pruning cuts and surrounding tissues should be protected by spraying with any copper-based fungicides.
4- Severely affected palms should be removed and burnt.

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4- Diplodia Rot disease

Causal agent: The fungus Diplodia phoenicum.

Morphological Symptoms
Symptoms are severe on offshoots which can be die, either while they are still attached to the mother palm or after they have been detached and planted out. The fungus may infect the outside leaves, and kill the younger leaves and the terminal buds. Yellowish-brown streaks extend along the leaf base. On the leaves of older palms, the ventral mid-portion of the stalks is commonly affected, showing yellowish brown streaks, 15- >100 cm length, extending along the leaf base and rachis. The upper part of the leaves may still green and unaffected.

Control
1-disinfecting all tools and cut surfaces.
2- Dipping or spraying the offshoots with any disinfectant solution.

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5- Graphiola leaf spot

Causal agent: The fungus Graphiola phoenicis.

Morphological Symptoms
The disease develops sub-epidermal small spots on both sides of the pinnae leaves. The numerous fruiting structures emerge as small-yellow/brown to black sori. These sori are abundant on three year-old leaves, conspicuous on two year-old leaves, but absent or infrequent on one year-old leaves. This is because of the 10 - 11 month incubation cycle for this pathogen.

Control
1- Leaf pruning, coupled with the treatment with any wide spectrum fungicide.
2- Use of tolerance or resistant cultivars.

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