Controlling Anthracnose: Colletotrichum and other fungal diseases in Tasmania

Anthracnose is a group of fungal diseases that affects plants typically in warm or humid areas. Even so, Anthracnose can infect plants in temperate climates like Tasmania given the right conditions.

If you live in Tasmania, you might be most familiar with Anthracnose with regards to blueberries. Between 2007 and 2010 Tasmania maintained an interim ban on the importation of blueberry plants and fruit after Quarantine Tasmania intercepted a consignment of fruit from New South Wales infected with blueberry anthracnose. However, the interim import ban has since been lifted after the Department of Natural Resources and Environment Tasmania (DPIPWE) deemed Tasmanian conditions unfavourable to the spread of the fungi.

Beyond Tasmania, anthracnose is most prevalent in Queensland and targets many fruit crops such as avocado, mango, rockmelon and bananas. It can also be found on species of shade trees and a huge number of other crops throughout Australia.

One of the more widespread anthracnose species is Colletotrichum lupini, which has prompted government responses in West Australia, South Australia and New South Wales. It infects all lupin plants, with albus, yellow and blue lupin considered the most susceptible. As these are the largest pulse crop in Australia, there are state bodies working to control anthracnose outbreaks.

Colletotrichum

One of the pathogens responsible for anthracnose, Colletotrichum, is a fungi found throughout the world. There are over 200 species of Colletotrichum and they have a huge impact on many food production crops, causing fruit rot or damage to growing plant tissues. Often a species of Colletotrichum fungi will have a specific range of closely related host species.

It is most active in tropical and subtropical climates, requiring wet or humid weather with temperatures between 10-25 degrees Celsius, it generally infects plants in late winter or early spring. It spreads via spores, carried by wind, water or on seeds.

It works by penetrating plant cells and secreting enzymes that break down cell walls and cause lesions throughout the plant, leading to twisted stems and dying leaves around the lesions. Colletotrichum is considered one of the most important plant pathogens because of its prevalence and impact on nearly every production crop.

Figure 1. Anthracnose Colletotrichum gleosporioides on an avocado

Anthracnose in trees

Tree species that are susceptible to anthracnose infection are Fraxinus, Acer, Platanus, Quercus, Betula and Liquidamber, and in large trees there are a few different species of fungi that cause anthracnose symptoms, specific to each tree species.

Although there are different pathogens the symptoms are similar, as are the cycles of infection and presentation. Often the effects of anthracnose in large trees will only be aesthetic, causing disfigured branchlets or leaf spots, and often a tree can withstand many years of infection without any lasting impact. Anthracnose can be easily confused with other tree stressors, such as heat, drought, or frost, as it can cause premature browning or shrivelling of leaves.

In all tree species anthracnose follows the same seasonal cycle as it does for fruit and production crops, fungi will develop in dropped leaf material during the winter, or spores will be present on the plant while it is dormant, then as the temperatures warm and rainfall increases throughout spring infections begin to develop.

Symptoms are present from late spring into summer, and the most common are; brown papery lesions and distorted leaves, twig or shoot cankers and lesions resulting in twisted branchlets. Severe infections can cause a tree to drop all its leaves by early summer, but will generally refoliate by midsummer with healthy leaves.

Controlling Anthracnose

Whether anthracnose is actively controlled depends on if it is on crop plants or large trees, the methods used are the same. In large trees anthracnose is often tolerated, as it does not have a significant impact on the overall health of the tree, often mature foliage is resistant to infection and maintaining a healthy environment for the tree can minimise chances for infection.

Removal of fallen leaves and pruning infected twigs from the canopy also reduces the likelihood that reinfection will occur, ensuring that any material is destroyed. Similarly, there are some species that are more resistant than others in each genus, which is something to consider if you are planting.

For fruit and crop plants, removal of infected material also applies, and some states have r control anthracnose, and is used to protect harvests in a production scenario, when applying fungicides to fruit or crop plants it is important to ensure complete coverage of the plant, including all leaves, buds and stems.

For large trees fungicide is often not necessary, unless a tree has suffered heavy infections multiple years in a row or if it has been recently transplanted. The timing of application is important, and must be done before any visible symptoms occur. If a large tree is to be treated by fungicide, high pressure applicators and correct handling is required.

In any case, the DPIPWE encourages anyone seeing signs of the disease to report the case by calling 1300 368 550.

How can we help?

Tasmanian Tree Care and it’s highly trained arborists can identify potentially harmful fungi in your garden or property. If you’re unsure about the health of your natural assets, please contact us to organise an assessment.

Content collected by Jack Colbeck

Robert Scott is a loyal and cautious trainee arborist. He is also our hardworking grounds person, managing all the work and machinery. Rob is an expert rock climber and a rapidly improving tree climber, receiving tuition from our more experienced team members when he gets the opportunity to climb.

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