Reported as major problem in many countries in South East Asia, Caribbean (Jamaica) and Africa (Kenya). Bud rot, caused by the fungal agent Phytophthora palmivora, is one of the major diseases of palms. Bud rot occurs on coconut and other palms (e.g., betel nut, oil palm), but Phytophthora palmivora infects many other crops (e.g., cocoa and papaya), as well as weeds, in Pacific island countries.

The infection affects coconut of all stages: nursery to the end of the production cycle. Young palms are more susceptible to infection more so during monsoon seasons.

The disease is reported to be economically important in Indonesia, the Philippines, India, the Pacific Islands and Jamaica. It often causes severe economic impact to the growers due to loss of entire trees.

• Common symptoms include bud rot and premature nut fall.
• Internally, the tissues beneath the bud are discoloured pink to purple with a dark brown border.
• Infected nuts show brown to black necrotic areas with a yellow border developing on the surface; internally, they have a mottled appearance.
• In adult palms, the first visible symptom is the colour change of the spear, which becomes pale and breaks at the base and hangs down. The rotting slowly progresses downwards, finally affecting the meristem and killing the palms. This is accompanied by drooping of successive leaves. Even then, nuts that are retained on the palm may grow to maturity.
• Young nuts are highly susceptible and fail to mature, they then fall off the tree; older infected nuts ripen normally.
• In seedlings, the earlier symptom is the yellowing of one or two younger leaves. Basal tissues of the leaf rots quickly and can be easily pulled out from the crown.

For early diagnosis look for a wilt of the spear leaf, which bends over slightly. Look at the bases of the petioles of the young leaves to see large yellow to brown rots (pestnet, 2022) Direct isolation from infected plant tissues is the most practical and effective diagnostic method. P. palmivora can be detected through laboratory culture (CABI CPC, 2021) Sporangia may occur on fruits, pods and leaves, and can be mounted on directly on slides and viewed under a light microscope. This enables confirmation to the genus level. A culture is required for identification to species level. Alternatively, molecular characterization using PCR assay can be conducted (need related details on coconut).

Category - Fungi

Genus - Phytophthora

Species - palmivora

Common Name - Coconut Budrot

Scientific Name - Phytophthora palmivora

Tropic and subtropical regions of the USA; Latin America; Southeast Asia; Africa; Europe; Oceania; India

Cultural

• Adopt proper spacing and avoid overcrowding in bud rot prone gardens (pestnet, 2022). Plant palms at least 10 m apart; wide spacing allows air movement through the plantation, and reduces the times that leaves are wet and spores can infect
• Removal of infected debris and the removal and destruction of infected coconut trees helps to reduce spread (CABI CPC, 2021)
• In nurseries, potting material to be steamed to kill Phytophthora inoculum
• In areas where Phytophthora has not been recorded, exclusion is essential - exclude animals by fencing, limit movement of vehicles and people through the field, clean soil from vehicles, boots and tools before they are brought into the field

Phytosanitary

Planting materials imported from high risk areas should be sent for quarantine and molecular diagnosis before arrival into respective countries. P. palmivora is a soil-borne pathogen. Importation of potting material/soil from high risk countries requires monitoring.

Resistant Varieties

The tolerance to bud rot varies between varieties. Malayan yellow and red dwarf varieties are susceptible to bud rot caused by Phytophthora palmivora, but hybrids with dwarf and tall parents are less so. The Polynesian Tall and Rennell Tall have good tolerance.

Chemical

• Remove all the affected tissue of the crown region and drenching the crown with Copper oxychloride 0.25%. Apply Bordeaux paste and protect it from rain till normal shoot emerges. (Dissolve 100 gm of copper sulphate and 100 gm of quick lime each in 500ml. water separately and mix to form 1 litre of Bordeaux paste).
• Spray 0.25% Copper oxychloride or 1 % Bordeaux mixture on the crown of the neighbouring palms as a prophylactic measure before the onset of monsoon. Palms that are sensitive (Dwarf palms) to copper containing fungicides can be protected by mancozeb. Small, perforated sachets containing 2 g of mancozeb may be tied to the top of leaf axil. When it rains, a small quantity of the fungicide is released from the sachets to the leaf base, thus protecting the palm

Leaves, Nut