Inflorescence blight
Inflorescence blight symptoms are characterized by water-soaked areas appearing on primary or secondary branches resulting in drying up the flower stems. From these small wounds, the sap exudes and turns pinkish-brown within 1 day, enlarges and coalesces in 2-3 days.
These lesions join to form larger lesions resulting in drying out infected inflorescences. This disease will get any worse as it is cloudy. Many studies conducted at Ullal Cashew Research Station (India) show that this disease is caused by the fungus Gloeosporium mangiferae, Phomopsis anacardii, and the tea mosquito Helopeltis antonii Sign.
Management
- Sprays of fungicides (Cuman 0.1% or Blitox 0.25%) and insecticides (Dimecron 0.03%) together (Anon, 1960 and Anon, 1965, 1966).
However, in some recent studies, Nambia et al. (1973) have shown that tea mosquito’s bites first cause lesions, and then above harmful fungi considered as saprophytic agents penetrate through these lesions, which leads to inflorescence blight. From this important discovery, it is possible to prevent this disease right from the process of preventing tea mosquitoes.
Fig.1 - Inflorescence blight in cashew flowers
Anthracnose disease
This was one of the most spread diseases with a high incidence of cashew nut plants. This disease has been detected in the states of Kerala, Karnataka, Tamil Nadu, Andhra Pradesh and Goa (India), causing serious losses to the cashew industry. In Tamil Nadu, it is called "Soorai" (Singh et al., 1967, Anon, 1967). In Brazil, Anthracnose disease also causes major economic losses to crops (Agnoloni and Giuliani, 1977). In Vietnam, the disease has also affected the cashew plots, with a damage rate of over 50% (Le Nam Hung, 1984).
The pathogen of Anthracnose disease is Colletotrichum gloeosporioides (Singh et al., 1967). Symptoms had variable incidence depending on the localities. The earliest appearance of anthracnose is water-soaked, reddish-brown, and exudative lesions. These lesions soon enlarge and shed diseased branches and buds. Diseased young leaves appear to be dry and fall off. Stalks of infected inflorescences turn black, then the flowers die off and fall off. Cashew apple (nut & fruit) is infected by fungi that penetrate through the stigma. These fungi grow along with the growth of the cashew apples from the onset of fruit set to harvest. If they survive to harvest, infected fruits will appear black necrosises on the seed coat and the fruit becomes shriveled.
Anthracnose develops in hot and humid conditions, especially in heavy rainfall, coincident with the flowering season of cashew nut plants. Wind is also a factor that helps this disease spread widely. The general opinion is that Anthracnose disease also originates from mosquito bugs that attack cashew plants first and then harmful fungi that invade and cause disease.
Fig.2 - Anthracnose in young cashew apple
Management
- All diseased parts should be removed at the onset of the rainy season to limit the spread of the disease.
- For newly planted cashew orchards, seeds should be thoroughly disinfected if grown from seeds or using seedlings from disease-resistant varieties. Every care should be taken to prevent introduction of disease in these orchards.
- Sprays of preventive drugs including copper-containing products (Bordeaux 1% or Cupravit 0.3 - 0.5%) and non-copper products (Dithiocarbamate or Captan 0.5%) should be done. (when using commercial products containing 50% active ingredients).
- Spraying at the time of foliage and repeat spraying three or more times at 15-20 days interval if serious disease is found.
- In Brazil, the effective inhibition of the growth of Colletotrichum gloeosporioides was tested with a preparation from Bacillus sutilis Cohn. (Batos C.N., De Figueiredo J.M., 1967).
Root Rot (Damping off)
This disease is very common to young cashew trees in nurseries with poor soil drainage. Several fungi can cause the decay of seeds or seedlings, including species of Fusarium spp, Pythium sp, Phytophthora palmivora, Cylindrocladium scoparium and Sclerotium rolfsii (Anon, 1960; Kumararaj and Bhide, 1962; Susamma Philip, 1973; Agnoloni and Giuliani, 1977).
These fungi attack the rhizosphere or the rhizosphere or both at the same time in the seedlings with a band of blackened tissue around the stem. As the disease progresses, the seedlings may curl down and the root parts of the plant may also become infected. The leaves show bulging, transparent blisters that grow up to a certain point and then join together. Environmental conditions such as high humidity levels (26°C-28°C) will also encourage its growth and the disease will be more severe in the rainy season.
Management
Other steps for preventing damping-off include the followings:
- Mainly applying several agronomic measures including good drainage of seedlings or potting bags and moderate shade adjustment for seedlings.
- Bordeaux mixture 1% or Ceresan - Wetable powder mixture 0.1% should be sprayed for nursery beds or potting bags.
- In the case of serious root rot of seedlings due to the attack of Pythium ultimum and other fungi, it should be prevented by drying and mixing Dexon into the soil at a dose of 113.6 kg/ha (Olunlogo, 1976).
Die-back or pink-disease
This disease is caused by Corticium salmonicolor (= Pellicularia salmonicolor) and is common during the rainy season (Anon, 1960, Rao, 1969, Estibeiro, 1970). It is characterized by the appearance of white or pinkish bumps on the bark on diseased branches. These fungi penetrate deeper tissues and cause the shoots to die from top downwards, which is why this disease is -called die back. Filamentous membranes of fungi appear on the branches as the end of the rainy season approaches. This mycelium is silvery-white at first, and then it gradually becomes pink. Asexual spores are transparent on their own but put in large masses are pink and proliferate readily in water and form infected branches. Then the shell cracked and peeled off. The leaves on these branches turn yellow and fall, making part of the tree barren and unable to grow.
Management
- Prune and remove infected branches below the infected areas, protect the cuttings by applying Bordeaux paste.
- Spray prevention with 1% Bordeaux twice, the first time in May - June before the start of the rainy season and the second time in October.
Leaf spot disease
Fig.3 - Cashew leaves with leaf spot disease
The disease is caused by the fungus Cercospora anacardii Muller & Chrupp, found in all cashew orchards in India, East Africa, Brazil (Golato C., 1970; Julio Da Ponte J.,1971). There are dark spots 1-4 mm in diameter on the leaves. These spots correspond to the fungal spores located on the underside of the leaves.
Management
- Sprays of Zineb 0.2% at the first signs of disease and then spray every 20 days (Golato C, 1970).
In addition to Cercospora anacardii, there are some other fungi such as Pestolotia microspora, P. dichaeta (gray leaf spot), Phyllosticta sp. (red leaf spot), Colletotrichum gloeosporioides (brown leaf spot), and Colletotrichum gloeosporioides (brown leaf spot), Phomatospora anacardicola (rust-colored leaves), and the algae Cephaleuros mycoides (red-rust leaves), etc. (Batista, 1957; Anon, 1960; Guba, 1961; Early and Punithalingam, 1972).
Management
- Sprays of Bordeaux 1% or copper oxide 0.3% or Benlate 0.3% (Anon, 1960; Matta and Lellis, 1973).
Sooty mould
The symptom is blackish brown velvety thin membranous Capnodium sp covering on both sides of the leaf, interfering with the normal photosynthetic activity of the plant, causing poor growth (Anon, 1960; Arailde and Mattos, 1971).
Management
- Spraying of starch 2% should be done, which will prevent both insects from working together and make the soot molds dry off from the leaves and fall to pieces.
REFERENCE
Thanh P. D. Cashew nuts - Production and Processing. (2003)
-1.jpg)
