Stem end rot

Dothiorella dominicana, Phomopsis spp., Botryodiplodia theobromae Lasiodiplodia theobromae

Several fungi are responsible for causing stem end rot (SER), which mostly affects woody horticultural crops in Australia. SER causes a soft watery rot to develop in the stem end as fruit ripens after harvest. Crop losses can be significant, as SER can cause what was once thought to be a high-quality crop to be downgraded or ruined. SER has a wide host range, including citrus and is most damaging to mangos and avocados. It also occurs in native bushland.

Description

Symptoms of SER start in the stem end of fruit, characterised by dark brown – black rot which produces a dark brown ring which progresses down the fruit. SER and anthracnose are often hard to distinguish between. The main difference is dark streaking in the water conducting tissues produced by SER, which is absent in anthracnose. Post-harvest, SER is favoured by warmer temperatures of greater than 25 °C during ripening.

Fungi responsible for causing SER are present internally in the trees vascular system. SER infection occurs by an endophytic pathway, where the fungus is already present in the fruit prior to harvest entering the fruit via the fruit stem Once infected and during the post-harvest ripening, the fungus becomes necrotic and spreads into the vascular bundles, resulting in SER. Mangos which are placed on the ground for desapping can also become infected from inoculum present in the bark, litter and soil.

Control

A holistic approach, including cultural and chemical practices should be implemented to control SER. Eliminating the primary source of inoculum, by removing dead material from within the canopy and orchard floor is recommended. Additionally, keeping an open canopy allows air to move through more easily, enabling foliage and fruit to dry quickly after rain, making it less conducive for fungal growth. Maintaining water supply during fruit development is imperative, as water stress during this phase can increase the risk of infection.

The health and nutrient status of trees is important in the management of SER. Research from New Zealand in avocados has shown higher calcium levels reduced the occurrence of SER. This research also demonstrated the use of thicker mulches and less rain prior to harvest reduced the incidence of SER. Where possible, avoid picking fruit when wet as this can increase the risk of damage and subsequent infection. Avoid harvesting immature fruit and once picked, place fruit in cool, well ventilated containers. It is suggested fruit picked from orchards with a history of SER should not be kept for long term storage. To avoid the spread of SER post-harvest, maintaining good hygiene is important, therefore packing equipment should be cleaned daily.

Chemical and biological fungicides applied pre and post-harvest, play an important role in the control of SER. To assess the severity of SER, randomly harvest 100 mature fruit and store them untreated at 25 °C until ripe. A threshold of less than one tenth and no more than one third should develop SER once ripe. If the upper limit is reached, a post-harvest fungicide may be required.

Luna® Sensation is a chemical fungicide used in-crop to control SER. Studies have shown it can contribute to a superior shelf life of fruit after harvest. Luna Sensation is registered for use in mangos and avocados to control SER. Serenade® Opti is a biological fungicide, which is best applied prior to disease symptoms developing. It is registered for the suppression of SER in avocados and mangos.

Related Pests

Anthracnose

Colletotrichum gleosporioides (Avocado), Colletotrichum gleosporiodes and Colletotrichum acutatum (Mango), Colletotrichum orbiculare (Rockmelon, watermelon, honeydew and cucumber), Colletotrichum musae (Banana), Colletotrichum lindemuthianum (Bean), Colletotrichum lupini (Lupin), Sphaceloma rosarum (Rose), Microdochium panattonianum (Lettuce), Elsinoe ampelina (Grape)

Anthracnose is one of the most prevalent and serious fungal diseases of many horticultural crops in Australia. It is also a problem in broadacre cropping programs, affecting pulse crops including lupins and lentils, although it hasn’t yet been discovered in lentil crops in Australia. Anthracnose is also known as pepper spot disease on avocado twigs, de-greening burn in citrus, blossom blight in mango, and black spot in grapes. Yield losses from anthracnose are generally associated with prolonged periods of wet weather.

Refer to the links below for more detailed information on anthracnose in other crops.

References

McCauley, D. (2020), ‘Growing Avocados – Fungal diseases of fruit’, Department of Primary Industries and Regional Development, Growing Avocados-Fungal diseases of fruit | Agriculture and Food

Queensland Government (2018), ‘Stem end rot’, Department of Agriculture and Fisheries , Stem end rot | Department of Agriculture and Fisheries, Queensland (daf.qld.gov.au)

Queensland Government (2014), ‘Management of post-harvest mango diseases’, Department of Agriculture and Fisheries, Management of post-harvest mango diseases | Department of Agriculture and Fisheries, Queensland (daf.qld.gov.au)