Plant DiseaseOct. 2006

PD-33

Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperationwith the U.S. Department of Agriculture. Andrew G. Hashimoto, Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mänoa, Honolulu, Hawai‘i 96822.An equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, age, religion, color, national origin, ancestry, disability,marital status, arrest and court record, sexual orientation, or status as a covered veteran. CTAHR publications can be found on the Web site <http://www.ctahr.hawaii.edu/freepubs>.

Identification Guidefor Diseases of Tea (Camellia sinensis)

The purpose of this guide on diseases associated withtea (Camellia sinensis) is to assist with problem

identification and raise awareness of serious plant dis-ease pathogens not yet present in Hawai‘i. Blister blight,horse-hair blight, and twig dieback/stem canker are verydestructive diseases found in major tea-producing re-gions, but they are not known to occur in Hawai‘i. It isimportant to prevent such diseases from entering thestate, because they are very difficult to eradicate or evento manage once established.

You should be aware that there is a risk of introduc-ing new diseases into the state through infected plantseven when they do not have obvious disease symptoms.

Early detection is often critical to success in eradi-cating new diseases. Familiarize yourself with the symp-toms of serious tea diseases. Proper identification is es-sential for making sound pest management decisions. Ifyou suspect problems but are unfamiliar with the dis-ease symptoms, we recommend that you submit samplesto CTAHR’s Agricultural Diagnostic Service Center foridentification. Samples for ADSC may be taken to thenearest Cooperative Extension Service office. For moreinformation on collecting samples, see “Collecting plantdisease and insect pest samples for problem diagnosis”CTAHR publication SCM-14, <http://www.ctahr.hawaii.edu/oc/freepubs/pdf/SCM-14.pdf>.

Lisa Keith1, Wen-Hsiung Ko2, and Dwight M. Sato2

1United States Department of Agriculture, Agricultural Research Service, Pacific Basin Agricultural Research Center2CTAHR Department of Plant and Environmental Protection Sciences

Algal leaf spot

Pathogen: Cephaleuros virescens

SymptomsLeaves develop lesions that are roughly circular, raised,and purple to reddish-brown.

Alternate hostsAlgal leaf spot has a wide host range among tropical trees.

Life cycleThe alga produces microscopic, rust-colored, spore-likebodies on the surface of the leaf spots, giving them areddish tinge. The “spores” are dispersed by wind or rain.The alga may spread from leaves to branches and fruit.

Poor soil drainage, imbalanced nutrition, and exposureto relatively high temperature and humidity predisposetea plants to infection by algal leaf spot, so it is importantto strengthen the plant through proper cultivation and fer-tilization. Most algal spots develop on the upper leaf sur-face. Older infections become greenish-gray and look like

lichen. Cephaleuros usually does not harm the plant.

Control measuresAvoid plant stress. Avoid poorly drained sites. Promotegood air circulation in the plant canopy to reduce hu-midity and duration of leaf wetness.

UH–CTAHR Identification Guide for Diseases of Tea PD-33 — Oct. 2006

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Brown blight, grey blight

Pathogens: Colletotrichum sp., Pestalotiopsis sp.

These fungi are considered weak pathogens and usuallyonly affect plants that have been weakened by impropercare or adverse environmental conditions. The diseaseis favored by poor air circulation, high temperature, andhigh humidity or prolonged periods of leaf wetness.When young twigs of susceptible cultivars are cut andused to root new plants, latent mycelium in the leaf tis-sue may start to invade nearby cells to form brown spots,and this may lead to death of leaves and twigs.

SymptomsSmall, oval, pale yellow-green spots first appear onyoung leaves. Often the spots are surrounded by a nar-row, yellow zone. As the spots grow and turn brown orgray, concentric rings with scattered, tiny black dots be-come visible and eventually the dried tissue falls, lead-ing to defoliation. Leaves of any age can be affected.

Alternate hostsNone are known.

Life cycleThe tiny, black spots on the lesions contain the fungalspores. Rain splash transports the spores from one plantor site of infection to another. If the spores land on aleaf, they germinate to start a new leaf spot or a latentinfection.

grey blight and brown blight occurring in the same leaf

brown blight

Control measuresAvoid plant stress. Grow tea bushes with adequate spac-ing to permit air to circulate and reduce humidity andthe duration of leaf wetness.

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UH–CTAHR Identification Guide for Diseases of Tea PD-33 — Oct. 2006

Horse hair blight

Pathogen: Marasmius crinisequi

SymptomsBlack fungal threads resembling horse hair are attachedto upper branches and twigs by small brown discs. Thefungus penetrates and infects the twigs from the discsand produces volatile substances that cause rapid leafdrop.

Alternate hostsNutmeg, rubber, coconut, cacao.

Blister blight

Pathogen: Exobasidium vexans

Blister blight is the most serious disease affecting shootsof tea and is capable of causing enormous crop loss. Thedisease is endemic to most tea-growing areas of Asia butis not known to occur in Africa or the Americas. Cloudy,wet weather favors infection. Shan or Indian varieties oftea are somewhat resistant to this disease.

SymptomsSmall, pinhole-size spots are initially seen on youngleaves less than a month old. As the leaves develop, thespots become transparent, larger, and light brown. Afterabout 7 days, the lower leaf surface develops blister-likesymptoms, with dark green, water-soaked zones sur-rounding the blisters. Following release of the fungalspores, the blister becomes white and velvety. Subse-quently the blister turns brown, and young infected stemsbecome bent and distorted and may break off or die.

Alternate hostsNone; the only known host is Camellia sinensis.

Life cycleThe disease cycle repeats continuously during favorable(wet) conditions, and the spores are readily dispersedby wind. Spores that land on a leaf with adequate mois-ture will germinate and infect it, producing visible symp-toms within 10 days. The fungus can directly penetratethe leaf tissue. The basidiospores have a low survivalrate under conditions of drought or bright sunlight. Thelife cycle of the fungus is 3–4 weeks.

Life cycleThis pathogen is spread from infected twigs to healthytwigs by extending its hair-like threads.

UH–CTAHR Identification Guide for Diseases of Tea PD-33 — Oct. 2006

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Common name: Twig die back, stem cankerTwig dieback, stem canker

Pathogen: Macrophoma theicola

This disease is capable of reducing yields and can killentire plants. Rainy weather favors its spread, and dryconditions promote its development.

SymptomsThe first symptoms include browning and drooping ofaffected leaves. As the disease spreads into the shoots,they become dry and die. The entire branch can die fromthe tip downward. Dying branches often have cankers—shallow, slowly spreading lesions surrounded by a thickarea of bark.

Alternate hostsNone are known.

Life cycleThe fungus produces spores on small, pear-shaped pyc-nidia on dead branches. Spores are spread when splashedby rain and can survive for several weeks on prunedbranches left in the field. The fungus usually requireswounded plant tissue to gain entry and initiate infection.

AcknowledgmentsThe authors thank Scot Nelson for review and comments.Publication support was received from the USDA-ARSValue Added Product Program and the Western Centerfor Risk Management Education.