Grower’s Thoughts: Minimize the Risk of Anthracnose Fruit Rot

Anthracnose fruit rot (AFR) is the most significant disease that directly affects the fruit of blueberries in Florida. In years past, AFR, also known as ripe rot, has been of minor concern for Florida growers; however, within the last three to five years, reports of substantial losses are on the rise. In this article, we will try to understand the disease cycle, factors that can promote disease, and management tools to reduce disease risk in your field. AFR is a real heartbreaker that can not only reduce the amount of harvestable fruit just as the year’s investment starts to pay out but then come back with the sucker punch of reducing the quality and quantity of the harvested berries due to fruit spoilage, lower pack-outs, and shorter shelf life. 

Like many of our disease concerns on blueberry, AFR is caused by a common fungal pathogen, Colletotrichum gloeosporioides.  It is easily identifiable on the berries it destroys because of the bright orange slime produced on the sunken surface of the soft rotting blue fruit. That orange slime contains tens of thousands of tiny spores that can spread the disease through water splash or on contaminated surfaces the fruit may come into contact with. Infection can occur as early as bloom but then usually lays in wait without producing any visible symptom (latent infection) until fruit ripening, when the fungus begins breaking down the fruit from the inside. Orange slimy spores produced on damaged or soft harvested fruit can then infect other blue fruit during the post-harvest sort and pack, sparking off a potential chain reaction of secondary spoilage. The process is impacted by the environment in the field, the method of harvest, and post-harvest storage conditions. Changes to both the horticultural practices of our industry and within the pathogen population have contributed to the recent uptick of AFR damage and losses.  

Where does it come from each season? The pathogen is very common on dead and damaged twigs, leaves, and other plant parts where it can survive by breaking down the dead tissues (as a saprophyte) during winter. The fungus is not very active when temperatures are low and conditions are dry. It overwinters on bud scales and infected twigs, and in evergreen systems, it can carry over to the new season in leaf spots within the canopies of infected plants. When temperatures are mild to warm (between 68° and 77°F), and rain events or overhead irrigation keep foliage wet for extended periods (typically eight hours or more), spores are produced on these infected plant parts, becoming a source of infection for flowers and fruit. How much sporulation, and how favorable those conditions are following spore production, determine the number of successful infections and the incidence and severity of the ensuing disease. Each warm-wet period from bloom through harvest represents another opportunity for the pathogen to infect fruit, and for us to try to prevent it from being successful. It can be hard to understand management efforts during this time, although we can’t see the disease doing anything yet, pay dividends at and after harvest when our management options are more limited and less effective (an ounce of prevention is worth a pound of [berries] cure).  

So how do we know when the infections are occurring? —keep reading, there’s a tool for that.  

There are three primary angles of attack when dealing with AFR:  

1) Reduce the amount of fungus present to potentially infect; 

2) Modify the environment to reduce the likelihood of fungus that is present being able to successfully infect plants and cause symptoms; 

3) Protect the plants when the environment is favorable and the fungus is present.  

Efforts to reduce the pathogen can only go so far, but general sanitation efforts are one important step. Sanitation can mean bush maintenance to remove from the field twiggy dieback and dead plants prior to bloom, managing late-season anthracnose leaf spot disease (particularly in evergreen production), and taking steps to disinfect/sanitize harvesting equipment like totes or contact surfaces of mechanical harvesters, as well as sorting and packing lines.

Modifying the environment in the field can be challenging since it largely depends on the weather. However, we can take steps towards moderately reducing leaf wetness duration through avoiding overhead irrigation when at all possible and by pruning the plant canopy to allow better airflow. These steps can help to minimize AFR and other diseases’ development as well. Specific to AFR, we can reduce the exposure of fruit to potential infection by taking steps to get ripe fruit out of the field and into cold storage as gently and quickly as possible by avoiding delays in harvesting and through the utilization of hand-harvest (when conditions and labor availability allow). Mechanical harvesters have come a long way and have huge labor-saving benefits, but they are less discerning of rotting fruit, and bruised or damaged fruit are more susceptible to AFR.  Regardless of the harvest method, it is much easier to control the environment once the fruit is in the cooler compared with the unpredictable conditions of leaving it in the field any longer than we have to.

Finally, we have tools available to help us protect fruit from infection when all else fails and our susceptible blooms and berries come into contact with the pathogen that has evaded our efforts and during a period when the conditions favor infection. Application of suggested fungicides during bloom and fruit development can help reduce the risk of AFR. These include the products suggested in Table 1, Anthracnose Fruit Rot Options. Many growers apply fungicides preventatively using a calendar-based method, typically at seven- to 10-day intervals. An alternative is to use risk signals from the Blueberry Advisory System ( to time fungicide applications (Figure 1), possibly reducing the number of applications while maintaining a similar level of control. Users of this tool will receive a text and/or email notification when there is a moderate or high level of risk for the development of AFR. Growers may also choose to put out a less costly fungicide like Captan when the risk is only moderate, and save more expensive (and effective) products for use during periods of high levels of risk for their area.

In summary, AFR continues to be a disease of increasing importance. Shifts to a higher proportion of evergreen production and machine harvesting, climate trends toward warmer, wetter conditions during bloom through harvest, and the loss of efficacy of the QoI group of fungicides (Pristine, Abound) due to fungicide resistance all seem to suggest this will be an ongoing issue for the industry moving forward. By implementing suggested cultural and chemical controls during bloom and fruit development, growers can help reduce the risk of AFR infection and development.

credits: PHIL HARMON, Professor, UF Plant Pathology Department,

& DOUG PHILLIPS, Blueberry Extension Coordinator, UF Horticultural Sciences Department

Figure 1. Anthracnose fruit rot risk chart.


Table 1. Anthracnose Fruit Rot Management Options


Management options

Amount of formulation per acre

Effectiveness (least = + to most = +++++)

Restricted entry interval (REI)

Postharvest interval (PHI)



Cyprodinil + fludioxonil (Switch® 62.5WG)

11–14 oz.


12 h

0 days

Applications can be made at 7- to 10-day intervals when conditions warrant. Do not apply more than 56 oz. of product per acre per year. Make no more than two sequential applications before using another fungicide with a different mode of action.


Pyraclostrobin + boscalid           (Pristine®)

18.5–23 oz.


12 h

0 days

Resistance to this fungicide in the ripe rot pathogen is common in central Florida. Use a captan product in a tank mix where resistance is known. Do not mix Pristine® with anything other than captan.


Ziram                     (Ziram 76DF)

3 lb.


48 h

~30 days

Do not apply later than 3 weeks after full bloom.


Captan                (Captan 50 WP)

5 lb.


48 h

0 days

Do not apply more than 70 lb. per acre per crop year.


Captan                (Captan 4L®)

2 qt.


48 h

0 days

Do not apply more than 35 qt. per crop year.


Fluazinam        (Omega® 500F)

1.25 pt.


12 h

30 days

Do not use more than 7.5 pints per acre per season. Do not tank mix with an adjuvant.


Metconazole   (Quash®)

2.5 oz.


12 h

7 days

Do not make more than three applications per acre per crop year.

Alternate with a fungicide with another mode of action.


Prothioconazole (Proline® 480 SC)

5.7 fl oz.


12 h

7 days

Make up to 2 applications per year on a 7–10 day schedule. A tank mix with Captan is recommended for resistance management and to provide Botrytis suppression.


Fluopyram + Pyrimethanil          (Luna Tranquility®)

13.6–27 fl. oz.


12 h

0 days

Do not apply more than 54.7 fl. oz. per acre per year. Rotate to a different fungicide group after no more than 2 applications. Reapplication interval is 7 to 14 days. Only Luna Tranquility is labeled by supplemental label for blueberry in Florida.

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