Colletotrichum acutatum
(black spot of strawberry)

Some country records may refer instead to the Glomerella cingulata-Colletotrichum fragariae aggregate.

A record of C. acutatum in Chile (EPPO, 2009; CABI/EPPO, 2010) published in previous versions of the Compendium has been removed as the pathogen in the original source (Peredo et al., 1979) is now confirmed as a separate species, Colletotrichum pseudoacutatum (Damm et al., 2012). C. acutatum is a quarantine pest for Chile (Servicio Agrícola y Ganadero, 2013).

C. acutatum has not been considered to be a quarantine pest by EPPO or any other regional plant protection organization. A certain ambiguity remains on its geographical distribution and impact on the strawberry crop, due to confusion with other Colletotrichum spp. In several countries of mainland Europe, the names C. fragariae or C. gloeosporioides have been used for all fungi causing anthracnose on strawberry. C. acutatum was only described on strawberry in the 1960s (Simmonds, 1966) and it is not clear whether its subsequent appearance as a strawberry pathogen in the literature is due to geographical spread of a pathogen which previously had a restricted distribution, to the rise in importance of a pathogen which was previously insignificant, or simply to the clarification of a taxonomic situation which was previously confused. As C. acutatum attacks several other crops without being a serious cause of concern, and indeed many other plant species, it does not appear logical to attempt to control it by international phytosanitary measures. In addition, identification in imported consignments presents difficulties because of the confusion with related species. Pathogen-free certification of strawberry planting material seems the best approach.

Phytosanitary Measures

The inclusion of C. acutatum (and other Colletotrichum spp.) among the species covered by a strawberry certification scheme would ensure that healthy planting material is traded nationally and internationally. A suitable scheme has been recommended by EPPO (OEPP/EPPO, 1994).

The species has a very wide host range, but is economically most important on strawberries.

C. acutatum can apparently affect almost any flowering plant, especially in warm temperate or tropical regions, although its host range needs further clarification. It has rarely been noted on other than agricultural or forestry land.
 

The conidia germinate to form appressoria on plant surfaces, from which penetration hyphae develop into plant cells. Infection may occur through almost any plant surface, but for the particularly susceptible herbaceous species such as strawberry and anemone, the crown with its relatively humid microclimate is often favoured. In suitable conditions, the fungus can grow rapidly inside the plant and cause severe symptoms very quickly, but in other circumstances the fungus may be quiescent inside host tissues for a period, in some cases only becoming apparent after harvest. Once the fungus has developed sufficiently inside the plant, dark fruit-bodies are produced, causing typical anthracnose symptoms. Conidia are formed liberally, and are normally dispersed by watersplash (Yang et al., 1992). They may lie dormant in the soil for some time, often overwintering in this fashion. Survival is longest under relatively cool, dry conditions (Eastburn and Gubler, 1992). The fungus can also remain dangerous for long periods in dead plant material on the surface or buried in the soil.

Although the disease in strawberry crops tends to be more virulent in warm climates, where damage can be devastating, it frequently has its origins in cooler conditions where propagating material is grown (Opgenorth et al., 1989; Wilson et al., 1990; Sutton, 1992). The disease may possibly occur in all countries where strawberries are cultivated. However, it is reported to be absent from the premises of most major strawberry propagators in the UK, and it may be possible to exclude the fungus from these sites despite its presence elsewhere in the areas concerned. There is little information on the biology of C. acutatum other than for strawberry crops.

In some crops, notably mango (Liu et al., 1986) and tamarillo (Yearsley et al., 1988), C. acutatum causes postharvest diseases of fruits.

No rapid methods exist, although early results from a detection system using monoclonal antibodies are promising. Current tests involve either inoculation of apples with strawberry petioles or paraquat treatment of petioles to stimulate sporulation of the pathogen (Cook, 1993). These tests are time-consuming and labour-intensive.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

The only serious research on control has been in connection with strawberry crops. Some success was reported in New Zealand by spraying with dichlofluanid and a captan-benomyl mixture (Cheah and Soteros, 1984), with various chemicals in Australia (Washington et al., 1992), and in South Africa with captan (van Zyl, 1985). Recently in the USA, studies showed that no acceptable fungicide is effective (Milholland, 1989). Fungicide-resistant strains of related species have been reported in the USA and Japan (Chikuo and Kobayashi, 1991; McInnes et al., 1992). There have been considerable efforts in the USA to develop resistant strawberry cultivars, but limited success has been achieved due to the presence of varied races within the species (Delp and Milholland, 1981; Smith, 1985; Smith and Black, 1990; McInnes et al., 1992). Gupton and Smith (1991) have suggested some potentially useful directions for further research.

In the UK, the disease is rare owing to strict quarantine controls and a policy of destroying affected crops and fumigating soil. McInnes et al. (1992) found that nursery material derived from tissue culture which was free from the related species C. fragariae and planted in isolated fields remained healthy, suggesting that careful selection of disease-free stock and soil sterilization in affected beds might be at least as effective as attempting chemical control.

In celery crops, Wright and Heaton (1991) found both a variation in cultivar susceptibility and amenability to chemical control of the disease. For anemone, disease incidence decreased with storage of corms (Doornik and Booden, 1990), and treatment by soaking with hot water proved effective (Doornik, 1990). Yearsley et al. (1988) found that dipping of tamarillos in imazalil and prochloraz reduced the incidence of postharvest disease caused by C. acutatum. However, dipping strawberry plants in hot water or fungicides did not eliminate the disease.

For pine, regular applications of prochloraz have been found to be effective, as has dichlofluanid (Vanner, 1990).