What are the Brown Spots on Feijoa or Pineapple Guava Leaves?

The feijoa (Acca sellowiana), commonly known as pineapple guava, is an evergreen fruiting shrub or small tree from the Myrtaceae family, that is native to South America. It is widely grown in the subtropics and in warm temperate areas.

This remarkably hardy plant is quite resistant to pests and diseases, heat-tolerant and moderately salt-tolerant, making it suitable for coastal conditions, and for use as a wind break or privacy screen. It can be hedged to shape, and also grown in containers.

Feijoas prefer moist, well-drained soils, rich in organic matter, with a slightly acidic pH of 6.2, but will tolerate less than ideal soils, ranging from sand to heavy clay.  They grow best in full sun (6 or more hours of direct sunlight a day), flowering and fruiting most heavily, but will tolerate partial shade (2 to less than 6 hours of direct sunlight) with reduced flowering and fruiting.   

The leaves of feijoas have a green upper surface and a silvery coloured underside. They are shaped either ovate (egg-shaped, widest below the middle) or elliptical (like an ellipse, widest at the centre), and are usually around 5-7cm (2-3”) long and 2.5cm (1”) wide.

Leaf Spot Fungal Diseases of Feijoas

Leaf spotting on feijoa leaves can be caused by various fungal pathogens, such as Sphaceloma sp., Cercospora sp., Pseudocercospora feijoae, Cylindrocladium scoparium, and Phyllosticta sp.

Typically, with the leaf spot diseases of feijoas, the leaf spots first appear on older leaves starting as brown spots which enlarge to form larger patches of necrotic (dead leaf tissue) areas, which may be followed by leaf abscission (leaf drop). The symptoms of nutrient deficiency do not look like this, or follow this pattern of progression.

The way in which leaf spot diseases weaken plants is by damaging the leaf, causing a reduction in photosynthesis. Most leaf spot diseases only affect a small area of the total leaf surface, and therefore are a minor stress factor to plant health, and won’t cause any seriously harm.

Action is required when leaf spot diseases cause moderate to total leaf loss for a period of two to four years in a row. Of the fungal diseases mentioned, the leaf-spotting fungus Sphaceloma sp. occasionally requires treatment when infection results in leaf drop.

How to Manage Leaf Spot Diseases

Leaf spot diseases can affect a wide range of plants, shrubs and trees. Many of the leaf spot diseases have similar biology, and are therefore treated in a similar way.

Even though leaf spot diseases generally won’t cause seriously harm, there are many cultural controls we can use to manage the diseases, and reduce their impact in the following years.

• Prevent disease spread by raking up and destroying fallen infected leaves, that will re-infect plants in the next growing season.
• Create conditions less favourable to disease proliferation by pruning trees or shrubs to improve air circulation and light penetration into the canopy, as fungal diseases generally prefer damp, shady conditions. Also ensure that plants aren’t overcrowded, that there is enough space between them or nearby wall or fences.
• Avoid creating wet conditions that promote disease, don’t splash water on leaves when watering, especially if watering during the late evening, as leaves will stay wet overnight. Water trees at their base when hand watering, or use drip irrigation or a soaker hose. Don’t use sprinklers, jets sprays or misting jets.
• Reduce plant stress, as stressed plants are more susceptible to diseases and less capable of protecting themselves. Prevent drought-stress by watering consistently during the growing season, especially during, hot, dry weather, and use a layer of mulch 5-10cm (2-4”) thick, over the soil, to reduce evaporative water loss.
• Protect plants with fungicides, apply before symptoms appear on the leaves, spray thoroughly to ensure complete coverage of every part of the plant. Fungicides can also be used to prevent the spread of the disease once it has appeared.

Suitable fungicides for leaf spot diseases include copper-based fungicides and potassium bicarbonate fungicides.

More articles on Garden Pests, Diseases and Problems

References

• North Carolina Extension, Extension Gardener Plant Toolbox – Acca sellowiana
• University of Minnesota Extension – Leaf spot diseases of trees and shrubs, by Michelle Grabowski, Extension educator, Reviewed in 2018
• El-Gholl, N. E., Alfieri, S. A., Schubert, T. S., & Schoulties, C. L. (1988). Pseudocercospora feijoae sp. nov. Causing a Leaf Spot Disease on Feijoa sellowiana in Florida. Mycologia, 80(6), 769–775. https://doi.org/10.2307/3807553
• Morton, J. 1987. Feijoa. p. 367–370. In: Fruits of warm climates. Julia F. Morton, Miami, FL.
• Buitrago, Sebastian & Leandro, Manuel & Fischer, Gerhard. (2021). Symptoms and growth components of feijoa (Acca sellowiana [O. Berg] Burret) plants in response to the missing elements N, P, and K. Revista Colombiana de Ciencias Hortícolas. 15. e13159. 10.17584/rcch.2021v15i3.13159.