Anthracnose caused by Colletotrichum acutatum

Colletotrichum acutatum is a fungal pathogen associated with anthracnose, fruit rots, blossom blight, and occasionally crown, stem, or leaf lesions on a wide range of crops. In the United States, important examples include strawberry, pepper, peach, almond, blueberry, apple, pear, and citrus. Disease is favored by warm, wet conditions and spreads mainly in infected planting material and splashing water.

Colletotrichum acutatum is an important anthracnose-associated fungus affecting fruit, flowers, crowns, stems, leaves, and occasionally roots. In U.S. horticulture it is particularly significant on strawberry, but documented disease associations also include peach, almond, pepper, blueberry, apple, pear, and citrus.

Symptoms vary with the host and with the particular lineage. On strawberry, fruit anthracnose produces firm, sunken, tan-to-brown lesions that may develop salmon-colored spore masses. Flowers, petioles, runners, and crowns can also be infected. On citrus, related lineages cause postbloom fruit drop or Key lime anthracnose. Accurate identification may require laboratory culture, microscopy, PCR, or DNA sequencing because several Colletotrichum species produce similar symptoms.

• Strawberry: circular, sunken brown lesions on green or ripe fruit; rapid soft rot; salmon to orange spore masses; dark lesions on petioles and runners; wilt or collapse when crowns are infected.
• Peach, almond, apple, and pear: sunken fruit spots that enlarge into rot, sometimes with concentric rings or orange-pink sporulation; blossoms or young fruit may also be affected.
• Pepper: sunken, expanding lesions on green or mature fruit, often with abundant spore production and rapid crop-to-crop spread.
• Citrus: blossom necrosis, premature fruitlet drop, persistent calyces, or distorted lesions on Key lime fruit, leaves, and twigs.
• Blueberry: fruit rot and, depending on the isolate and host, infection of leaves or other tissues.

The pathogen is commonly introduced on infected or symptomless planting material. It survives in infected plants, crop residue, mummified fruit, and sometimes symptomless tissues. Spores are produced in sticky masses on diseased tissue and are moved mainly by splashing rain, overhead irrigation, wet tools, workers, animals, and contact between crowded plants. Long-distance airborne spread is not considered the primary pathway.

Warm, wet weather is especially important. In strawberry, flowers and ripening fruit are highly susceptible, while wounds, insect injury, sunscald, hail, and prolonged surface wetness increase infection risk. Different populations and lineages may vary in host range, aggressiveness, fungicide sensitivity, and preferred infection site.

The fungus persists between crops in infected crowns, leaves, runners, stems, fruit, and plant debris. Under warm, wet conditions it produces conidia in acervuli or similar fruiting structures, often embedded in a sticky spore mass. Water releases and disperses the spores to nearby flowers or plant surfaces.

After landing on a susceptible, wet surface, spores germinate and form appressoria that help the fungus penetrate the plant. Lesions may remain small before expanding rapidly as fruit mature or weather stays wet. New lesions generate additional spores, creating repeated secondary infection cycles during the season. Some infected planting material may remain symptomless while carrying the pathogen.

Remove and discard diseased fruit and severely infected plants as soon as practical. In strawberries, remove affected fruit without allowing it to contact neighboring plants, and manage infected crowns or runners aggressively because they can maintain the disease. In orchards, prune infected tissue during dry weather and destroy prunings rather than leaving them beneath the canopy.

Improve airflow, reduce irrigation wetting, and correct drainage or excessive canopy density. If disease is confirmed early in a valuable crop, consult the relevant state extension service or crop adviser for a crop-specific fungicide program. Product performance can be affected by pathogen lineage and resistance, so applications should be based on diagnosis, local recommendations, resistance-management principles, and the current legal label.

• Use certified clean transplants, resistant or less-susceptible cultivars where available, and strict nursery sanitation.
• Use drip irrigation, mulch, wider spacing, canopy ventilation, and prompt removal of diseased tissue to reduce surface wetness and inoculum.
• Remove mummified fruit and plant debris that can support sporulation.
• Biological or organically approved products may provide suppression in some crops, but efficacy is variable and must be verified for the specific host, disease, and production system.
• Do not assume that a product labeled for one anthracnose disease or crop is effective or legal for another.

• Start with certified, disease-free planting material and inspect transplants before planting.
• Use raised beds, plastic mulch, good drainage, adequate spacing, and drip or furrow irrigation rather than overhead watering where practical.
• Keep fruit, flowers, and lower foliage as dry as feasible; irrigate early enough for foliage to dry quickly.
• Harvest strawberries, peaches, peppers, and other susceptible fruit frequently and remove diseased or overripe fruit promptly.
• Remove mummified fruit, infected runners, severely diseased plants, and crop debris from the production area; do not compost diseased tissue unless the composting process is reliably hot and complete.
• Disinfect pruning tools and avoid working among wet plants.
• Use crop rotation and avoid planting susceptible crops immediately beside heavily diseased plantings when feasible.
• In orchards, prune for airflow and remove dead or infected twigs and fruiting wood according to crop-specific extension guidance.

• Colletotrichum acutatum is now understood as part of a species complex rather than a single uniform biological population.
• Strawberry anthracnose may be caused by several related Colletotrichum species, and the organism named in older references may not correspond exactly to the species recognized by current DNA-based taxonomy.
• On citrus, postbloom fruit drop is associated with flower infection and premature fruitlet abscission, whereas Key lime anthracnose primarily affects fruit, leaves, and twigs.
• Some isolates can infect more than one crop, but host specificity varies; a confirmed pathogen identification should not be generalized to every plant showing similar lesions.
• Sticky spore masses and water splash are epidemiologically important, which is why sanitation and moisture management are central to control.