Your trusted source for independent, high-quality, science-based advice
© 2025 Berryworld, All Rights Reserved
The anthracnose fungus (Colletoctricum acutatum) can infect almost any part of the strawberry plant, and the characteristic fruit infections are often seen without obvious plant infections. When crowns are infected, whole plants can wilt. Stolons can be girdled by black lesions, and flowers can be infected and killed, while leaf spotting is rare.
Anthracnose is a soil-borne pathogen and spores can survive almost a year without host plants. The fungus infects strawberry plants through roots and flower/fruit through soil splash.
Anthracnose really thrives in warm, wet weather. Its optimum temperature is 26-27°C, and infection risk reduces significantly under 18°C. Contrast this to botrytis, which can operate even in our 4°C chiller, and whose optimum is around 20°C.
As spring warms up, we’re naturally getting more frequent temperature periods where anthracnose can thrive.
We can see this increased risk in the Anthracnose model that Tau Research is running at a strawberry block in Auckland, in a project supported by the Horticentre Charitable Trust, Berryworld, and Danube Orchard.
The risk is represented by the turquoise line below, and when the line wanders up over 0.15 (purple line), we’re in the “medium risk” zone.
The first time we see a risk period is 18 August, briefly, when there is rain and the temperature reaches 18°C. Since the start of September there have been more frequent times when infection is likely. The biggest infection risk so far this year was 7th October, when rainy weather coincided with 18-20°C temperatures. That was two weeks ago, and growers should be on the look out for anthracnose infections.
It’s common for fruit lesions to be the first thing noticeable in the field, which is unfortunate. Last year when I was checking our Auckland variety trial in mid-December, the fruit lesions were quite apparent. They seemed to affect the best fruit!
Notice the very distinct edges of the anthracnose infection on the red fruit
If it’s warm and humid in the field, you can see the fungus making orange or salmon-coloured spores in the dark lesions. If you’re seeing dark spots on fruit but no spores, put them in a closed container with a moist paper towel on the kitchen bench for a day or two, and the spores will grow.
You can see the orange Anthracnose spores forming in “pustules” with a 10x field lens.
Phomopsis and Gnomonia are two other fungi that can cause similar fruit lesions and make spores in similar “mini pustule” structures. But when on fruit, these two fungi typically start infection from the calynx-end, have less distinct lesions (margins aren’t as defined), and their spores are a bland off-white or brownish colour. Anthracnose spores are characteristically orange or pink, growing from very dark brownish-black lesions.
Gnomonia fungus infecting strawberry fruit
In soil production systems, mulch early to prevent soil splash to plants. Transplants can have latent anthracnose infections that aren’t immediately apparent, so many nursery producers treat for anthracnose preventatively during the plant production cycle.
Pre-flower there are effective systemic fungicides that can be used. Azoxystrobin or ‘Amistar,’ is a good group 11 option, preflower. Once flowering has started, we’re left with a moderately-effective broad spectrum protectant like Captan. Switch has moderate efficacy as well.