Mango powdery mildew is a widespread fungal disease impacting mango crops globally. This disease can affect various parts of the mango plant, leading to economic concerns for growers by reducing yields and fruit quality. It is a recurring problem in susceptible mango cultivars, often appearing seasonally. Understanding this disease is important for those involved in mango cultivation, as it influences productivity and profitability.
Recognizing Mango Powdery Mildew
Identifying mango powdery mildew involves observing white, powdery patches on various parts of the plant. On the leaves, these patches appear, causing young leaves to curl and become distorted. Severely infected leaves may develop grayish, necrotic lesions or large, irregularly shaped spots, leading to premature defoliation. On some cultivars, the whitish fungal residue may be more noticeable on the lower leaf surface, particularly along the midrib.
The disease’s presence on flowers and inflorescences appears as a whitish growth that can cover the flower stalks and young fruits. Infected flowers may fail to open, turn brown, and dry. This infection can lead to a blight-like appearance and prevent successful fruit set.
Young fruits exhibit white powdery spots that can develop into purplish-brown blotches as the fruit matures. These infected areas may crack and form corky tissue, and heavily infected fruits can become yellow, misshapen, and drop prematurely. The entire fruit may become covered by the mildew.
Understanding Its Development
Mango powdery mildew is caused by the fungal pathogen Oidium mangiferae, found globally. This fungus is an ectoparasite, growing on plant tissue surfaces and absorbing nutrients through haustoria. The fungus produces numerous spores, called conidia.
The development and spread of Oidium mangiferae are influenced by specific environmental conditions. Moderate temperatures, ranging from 10 to 31°C, combined with high relative humidity (60-90%), favor the spread of the disease. Optimal conditions for infection occur around 23°C with high relative humidity followed by an abrupt reduction in humidity. Cool, dry conditions can also favor disease development.
The fungal spores are primarily disseminated by wind. Rain splash can also contribute to localized spread. The pathogen survives between seasons as mycelium in dormant buds or on old infected leaves. Young, tender tissues on leaves, flowers, and fruits are most susceptible to infection, and builds up rapidly during seasonal flushes of new growth.
Effects on Mango Plants and Fruit
Powdery mildew impacts mango plants by interfering with fruit development and overall tree health. Infection of inflorescences can lead to widespread flower blight and failure of flowers to open. This severe blossom infection can result in substantial flower drop and poor fruit set, leading to yield reductions, sometimes ranging from 70-90% on individual plants.
The disease affects the quality and marketability of developing fruit. Young fruits covered in the white powdery growth may become stunted, misshapen, or turn yellow. As infected fruits mature, the affected epidermis can crack and form corky, russeted tissue, rendering them unappealing for sale. This damage reduces the overall value of the harvest, causing financial losses for growers.
Beyond direct fruit loss, repeated or severe infections can weaken the entire mango tree. Defoliation of young leaves and the general stress from the disease can reduce the tree’s vigor. A weakened tree may be more susceptible to other pests and diseases, potentially affecting its long-term productivity and future yields.
Strategies for Management
Controlling mango powdery mildew involves a combination of practices aimed at preventing infection and treating existing outbreaks. Cultural practices play a significant role in reducing disease incidence. Proper tree spacing and selective pruning of overcrowded branches after harvest improve air circulation and light penetration within the canopy, which helps to reduce humidity levels that favor fungal growth. Removing and destroying infected plant parts, such as fallen leaves and panicles, helps reduce the amount of fungal inoculum in the orchard. Avoiding excessive nitrogen fertilizer application can also limit the production of succulent new tissues, which are highly susceptible to infection.
Selecting mango varieties with known resistance to powdery mildew offers a long-term control measure. While no completely resistant cultivars have been identified, some varieties show greater tolerance to the disease, such as Kent, Sensation, Tommy Atkins, and Van Dyke. Growers should consult local agricultural recommendations to determine which varieties perform best in their specific climate.
Fungicide application is often a necessary component of management, especially for susceptible varieties or during periods of high disease pressure. Common fungicides include sulfur-based products, which can be applied as dusts or sprays, and various synthetic options like carbendazim, tridemorph, or copper-based fungicides. Applications should begin preventively, often as flower buds are opening or at very early flowering stages, with follow-up sprays every 7-14 days until fruit set. Adhering strictly to label instructions for application rates and safety precautions is important.
An integrated pest management (IPM) approach combines these strategies for comprehensive disease control. This involves monitoring trees regularly for early signs of infection, making informed decisions about fungicide applications based on weather conditions and disease predictions, and incorporating biological control agents like Bacillus subtilis or Ampelomyces quisqualis where appropriate. Combining different methods helps to reduce reliance on chemical treatments and promotes sustainable orchard health.