Colletotrichum orbiculare (Berk. & Mont.) Arx 1957

California Plant Pest Rating for
Colletotrichum orbiculare (Berk. & Mont.) Arx 1957
Pest Rating: B

Initiating Event:

None. A permanent rating for Colletotrichum orbiculare is proposed herein.

History & Status:

Background: Colletotrichum orbiculare is a fungal pathogen causing anthracnose disease of cucurbit plants particularly watermelon, cantaloupe, and cucumber. The species is often known by its synonymized scientific name, Colletotrichum lagenarium and belongs to the taxonomic family Glomerellaceae, within the phylum Ascomycota. C. orbiculare is the asexual (anamorph) stage of the pathogen. The sexual stage (telemorph) with the name Glomerella lagenarium has been reported but is rarely found in nature. Two distinct populations of the pathogen are known: one from watermelon (race 1) and the other from cucumber and melon (race 1 and 3) (Sitterly & Keinath, 1996).

Hosts: The pathogen commonly attacks members of the family Cucurbitaceae, especially melon and watermelon. Hosts include Althaea officinalis (marsh-mallow), Artocarpus heterophyllus (jackfruit), Benincasa hispida (wax gourd), Citrullus lanatus (watermelon), Cucumis melo (melon), Cucumis sativus (cucumber), Cucurbita maxima (giant pumpkin), C. moschata (pumpkin), C. pepo (ornamental gourd), Momordica charantia (bitter gourd) and Trichosanthes cucumerina var. anguinea (snake gourd) (CABI, 2014).

Symptoms: Host plants infected with Colletotrichum orbiculare exhibit symptoms of anthracnose and fruit rot. In California, except for seedless watermelon, anthracnose is unusual on cucurbit crops and can cause leaf, fruit, and/or stem lesions. On cucurbits, leaf spots are usually large (>10 mm diameter) and tan to pale brown with distinct margins. However on watermelon, these foliage lesions are dark brown to black. Brown or black lesions appear on fruit. These lesions grow to 20-30 mm diameter, become sunken, wrinkled and dark, with concentric rings of sub-surface, tiny, black, saucer-shaped asexual structures that containing spores or conidia (acervuli). In wet weather, pink or orange spores ooze from these asexual structures (CABI, 2014; UCIPM, 2008). Fruit is susceptible to infection approximately at the time of ripening and severely infected fruits are often tasteless or bitter and usually invaded by soft rotting bacteria and fungi (Agrios, 2005).

Damage Potential: Anthracnose disease caused by Colletotrichum orbiculare has recently been considered to be particularly important wherever cucurbits are cultivated under highly controlled conditions. High infections may cause formation of numerous leaf lesions and vine defoliation resulting in poor quality fruit and yield loss (Egel, 2014). Watermelon artificially inoculated with C. orbiculare (as C. lagenarium) caused up to 63% losses in yield (CABI, 2014).

Disease Cycle: The species has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on cucurbit plant residue in soil, on infected volunteer plants, and on or in cucurbit seed. During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers. Conidia are transmitted to host plants. Humid, wet, rainy weather is necessary for infection to occur. Condia germinate and grow optimally at 22-27°C and 100% relative humidity for 24 hours. These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem in transplants grown under controlled environments of greenhouses. Condia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue up to 72 hours after deposition. Symptoms are produced about 96 hours after infection. The sexual stage (telemorph) is rarely found in nature (Sitterly & Keinath, 1996).

Transmission: Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution: Colletotrichum orbiculare is widely distributed throughout the world and has been reported from several countries in Asia, Africa, North America, South America, Central America and Caribbean, Europe and Oceania. In the USA it has been found in Alabama, California, Colorado, Connecticut, Florida, Hawaii, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Minnesota, Mississippi, Nebraska, North Carolina, North Dakota, Oklahoma, Pennsylvania, South Carolina and Texas (CABI, 2014; Farr et al., 1989).

Official Control: Currently Israel, Chile and Jordan include Colletotrichum orbiculare on their Harmful Organism List.

California Distribution: in California, Colletotrichum orbiculare has been detected in a greenhouse in Tehama County (Koike et al., 1991).

Historically, it has also been detected in southern coastal region counties which include: San Benito, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, Orange and San Diego Counties (K. F. Baker Herbarium, CDFA in The California Plant Disease Host Index by A. M. French, 1989).

Details of the south coastal region detections are not available. Given the absence of reports on the field detection of the pathogen in California, it is likely that the south coastal region detections were mainly limited to greenhouses. On the other hand, those south coastal counties would share a similar climate including higher incidence of rainfall and wind driven rain necessary for infection and establishment of the disease.

California Interceptions: The pathogen has not been intercepted in quarantine shipments of plants.

The risk Colletotrichum orbiculare would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

Low (1) Not likely to establish in California; or likely to establish in very limited areas.
Medium (2) may be able to establish in a larger but limited part of California.
High (3) likely to establish a widespread distribution in California.

Risk is Low (1) – Colletotrichum orbiculare requires humid, wet, rainy weather for conidia to infect host plants. This is a main reason why the pathogen has not been able to fully establish and spread under dry field conditions in California. It has, however, been detected in controlled greenhouse environments.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

Low (1) has a very limited host range.
Medium (2) has a moderate host range.
High (3) has a wide host range.

Risk is Moderate (2) – Although the host range for Colletotrichum orbiculare is mainly limited to members of the family Cucurbitaceae, plants, the cultivation of cucurbits, mainly melon and watermelon, is in significant acreage and of major importance in California.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

Low (1) does not have high reproductive or dispersal potential.
Medium (2) has either high reproductive or dispersal potential.
High (3) has both high reproduction and dispersal potential.

Risk is High (3) – The pathogen has high reproductive potential and conidia are produced successively. They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A.   The pest could lower crop yield.
B.   The pest could lower crop value (includes increasing crop production costs).
C.   The pest could trigger the loss of markets (includes quarantines).
D.   The pest could negatively change normal cultural practices.
E.   The pest can vector, or is vectored, by another pestiferous organism.
F.   The organism is injurious or poisonous to agriculturally important animals.
G.   The organism can interfere with the delivery or supply of water for agricultural uses.

Low (1) causes 0 or 1 of these impacts.
Medium (2) causes 2 of these impacts.
High (3) causes 3 or more of these impacts.

Risk is High (3) – Under suitable climates, the pathogen could lower crop yield, value and trigger the loss of markets.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A.   The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B.   The pest could directly affect threatened or endangered species.
C.   The pest could impact threatened or endangered species by disrupting critical habitats.
D.   The pest could trigger additional official or private treatment programs.
E.   The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

Low (1) causes none of the above to occur.
Medium (2) causes one of the above to occur.
High (3) causes two or more of the above to occur.

Risk is Medium (2) – The pathogen could significantly impact cultural practices, home gardening or ornamental plantings.

Consequences of Introduction to California for Colletotrichum orbiculare:

Add up the total score and include it here. (Score)

–  Low = 5-8 points
–  Medium = 9-12 points
–  High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Colletotrichum orbiculare to California = (11).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–  Not established (0) Pest never detected in California, or known only from incursions.
–  Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–  Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
–  High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Medium (-1). Colletotrichum orbiculare has been reported from counties in the California’s south coastal region however, details of those detections are not available. Given the absence of reports on the field detection of the pathogen in California, it is likely that the south coastal region detections were mainly limited to greenhouses. Nevertheless, those south coastal counties would share a similar climate including higher incidence of rainfall and wind driven rain necessary for infection and establishment of the disease.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10.


As discussed above, there is little to no verifiable evidence of the occurrence of Colletotrichum orbiculare in field environments within California. Such information may strengthen or lower the proposed rating for this pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose of cucurbits pathogen, Colletotrichum orbiculare is B.


Agrios, G. N. 2005. Plant Pathology (Fifth Edition). Elsevier Academic Press, USA. 922 p.

CABI. 2014. Colletotrichum orbiculare datasheet report. Crop Protection Compendium.

Egel, D. S. 2014. Vegetable diseases: Anthracnose of cucumber, muskmelon, and watermelon. Purdue Extension BP-180-W, Purdue University.

Farr, D. F, G. F. Bills, G. P. Chamuris and A. Y. Rossman. 1989. Fungi on Plants and Plant Products in the United States. St. Paul, Minnesota, USA: APS Press, 1252 pp.

Kitterly, W. R., and A. P. Keinath. 1996. Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’. Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Koike S. T., T. E. Tidwell, D. G. Fogle and C. L. Patterson. 1991. Anthracnose of greenhouse-grown watermelon transplants caused by Colletotrichum orbiculare in California. Plant Disease, 75(6):644.

UCIPM. 2008. Cucurbits anthracnose pathogen: Colletotrichum lagenarium. UCIPM Online, Statewide Integrated Pest Management Program, University of California Agriculture & Natural Resources.

Responsible Party:

Dr. John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110,[@]

Pest Rating: B

Posted by ls