Organic Methods for Controlling Fungal Diseases in Peaches, Plums, Cherries and Other Stone Fruits

By Guest Author John Hammond

What are stone fruits?

Stone fruits are those that have a large pit inside of the fruit – referred to as a “stone”. Some refer to the stone as the seed, but it isn’t – the seed is actually inside the stone. Examples of stone fruits include apricots, cherries, plums, coconuts, peaches, dates, mangoes, and olives.

What organic methods can be used to prevent fungal diseases in stone fruits?

As a fruit tree grower, I understand the importance of preventing fungal diseases in stone fruits. These diseases can wreak havoc on fruit trees, compromising their health and productivity. Thankfully, several organic methods can be employed to combat fungal diseases and ensure the well-being of a stone fruit orchard.

Cultural practices

One of the fundamental organic approaches to disease prevention is using proper cultural practices. Good orchard hygiene goes a long way in preventing the spread of fungal pathogens. Regularly removing fallen leaves, picking out and picking up diseased or dropped fruit, pruning dead or diseased branches, avoiding overhead watering, and ensuring adequate air circulation within the tree can minimize the conditions that favor fungal growth.

Pruning and sanitation

As a seasoned fruit tree grower, I have witnessed firsthand the transformative effects of pruning and sanitation on the health and productivity of stone fruit orchards.

Pruning is a critical cultural practice. By removing dead, damaged, or diseased branches, we can eliminate potential entry points for fungal pathogens. Proper pruning techniques also promote better air circulation within the canopy, allowing the foliage to dry quickly after rain or irrigation. This reduces the amount of time moisture lingers on the leaves, creating an environment less conducive to fungal growth.

Sanitation practices go hand in hand with pruning to control fungal diseases. Proper sanitation is the removal and disposal of fallen leaves, fruit mummies, and other plant debris from the orchard floor. These materials serve as potential sources of fungal spores, which can infect healthy fruit trees.

Regularly cleaning and disinfecting pruning tools also helps to reduce fungal diseases. Tools can harbor fungal spores and other pathogens, and if not properly sanitized, they can inadvertently spread diseases from branch to branch and tree to tree. A simple practice of wiping tools with a disinfectant solution or dipping them in a bleach solution between cuts helps prevent the transmission of fungal pathogens.

Timing is crucial when implementing pruning and sanitation practices. Pruning during the dormant season is ideal, as the absence of foliage allows for better visibility and access to dead, damaged or diseased branches. Destroy pruned materials promptly (do not compost) to prevent the accumulation of infectious spores. Sanitation should be practiced throughout the year, with particular attention paid to fallen leaves and diseased fruit.

Irrigation

Implementing a well-thought-out irrigation system is crucial for organic disease management. Overhead watering, such as sprinklers, can promote the spread of fungal spores by creating moist conditions on the leaves and fruit surfaces. Instead, opt for drip irrigation or soaker hoses that deliver water directly to the soil, minimizing wet leaves. This practice helps reduce the likelihood of fungal infections and supports healthier tree growth.

Spacing your trees

Proper spacing between stone fruit trees is another cultural practice that helps with disease prevention. Sufficient spacing allows for adequate air circulation, which helps to dry foliage and minimize the chance of fungal spores finding favorable conditions to grow and multiply. It is important to consider the mature size of the trees when planting, allowing ample room for the canopy to develop without crowding neighboring trees.

Mulching

Mulching is a valuable cultural practice that can provide numerous benefits, including disease control. Organic mulch materials, such as wood chips or straw, create a barrier between the soil and the fruit, reducing the likelihood of soil-borne fungal pathogens splashing onto the fruit during rain or irrigation. Mulch also helps regulate soil moisture, preventing excessive wetness that can contribute to fungal disease development.

Proper nutrition

Promoting tree vigor through proper nutrition and soil health is crucial. Organic fertilizers, rich in essential nutrients, can strengthen the tree’s natural defense mechanisms, making it more resilient to fungal infections. Conducting soil tests to assess nutrient levels and pH can guide the application of organic amendments to optimize soil conditions for healthy tree growth.

Monitor the tree or orchard

Regularly monitoring and scouting the orchard (or the area around your tree) are essential cultural practices for disease control. By inspecting the trees for early signs of fungal infections, such as leaf spots or fruit rot, immediate action can be taken to reduce the spread of the disease. Prompt removal and disposal of infected plant parts, coupled with appropriate organic treatments if necessary, can prevent the disease from spreading further and affecting the entire orchard.

Organic fungicides

Organic fungicides derived from natural sources can also be effective in managing fungal diseases. One of the most commonly used organic fungicides in stone fruit orchards is copper-based sprays. Copper has long been recognized for its fungicidal properties and is widely used in organic farming. They are particularly effective against diseases like peach leaf curl, bacterial spot, and brown rot. It is important, however, to use copper fungicides judiciously, as excessive applications can lead to copper accumulation in the soil, which may have adverse effects on soil health, soil pH, and beneficial microorganisms.

Organic growers also use biological fungicides derived from naturally occurring microorganisms:

Bacillus subtilis

When applied to stone fruit trees, Bacillus subtilis creates a protective barrier on the plant surface, preventing fungal pathogens from establishing. It is effective against diseases like brown rot and canker. Moreover, Bacillus subtilis is non-toxic to humans, animals, and beneficial insects, making it an excellent choice.

Trichoderma harzianum

Another promising biological fungicide is Trichoderma harzianum, a naturally occurring fungus. Trichoderma harzianum colonizes the rhizosphere and root system, inhibiting the growth of pathogenic fungi. It is particularly effective against soil-borne pathogens like Armillaria root rot and Rhizoctonia root rot.

Essential oils

In recent years, essential oils derived from plants have gained attention as potential organic fungicides. For example, extracts from neem oil, derived from the seeds of the neem tree, have been shown to exhibit antifungal properties. Neem oil disrupts fungal cell membranes, inhibiting their growth and reproduction. It is effective against diseases such as powdery mildew and brown rot. Neem oil is biodegradable, non-toxic to humans and animals, and poses minimal risk to beneficial insects.

Multiple ingredient organic fungicides

Apart from these specific fungicides, there are also organic fungicide formulations that combine multiple active ingredients. These formulations often contain a combination of natural compounds and plant extracts that work synergistically to control fungal diseases. They provide a broader spectrum of disease control and offer improved efficacy against challenging pathogens.

Soil Amendments

When it comes to organic fruit tree cultivation, the health and vitality of the soil cannot be underestimated. As a seasoned fruit tree grower, I have come to appreciate the crucial role that soil amendments play in preventing fungal diseases in stone fruits.

Soil amendments can help with disease prevention. Organic matter, such as compost or well-rotted manure, improves soil structure and enhances its ability to retain moisture while promoting beneficial microbial activity. Healthy soil conditions help to fortify the tree’s natural defenses, reducing its susceptibility to infections.

The presence of organic matter in the soil also encourages the growth of beneficial microorganisms. These microscopic allies play a vital role in maintaining soil health and balance. Certain beneficial bacteria and fungi can suppress fungal pathogens by either outcompeting them for resources or directly inhibiting their growth. By nurturing a diverse and thriving microbial community through the addition of soil amendments, we create an ecosystem that naturally combats fungal diseases.

Organic matter also helps to regulate soil moisture levels. It acts as a sponge, absorbing excess water during periods of heavy rain and slowly releasing it during dry spells. Maintaining proper soil moisture is vital in preventing fungal diseases, as many fungi thrive in damp conditions.

Soil amendments contribute to the overall long-term health and sustainability of the soil. By adding organic matter regularly, we improve soil structure and fertility, which in turn promotes a balanced ecosystem. A healthy soil ecosystem encourages the growth of beneficial organisms that naturally suppress fungal diseases. It also supports the growth of beneficial plants, such as cover crops or companion plants, which can contribute to disease prevention.

Biological controls

Beneficial organisms such as predatory mites or beneficial fungi can be used to combat specific fungal pathogens. These natural allies prey on the harmful fungi or compete for resources, effectively suppressing the target fungi populations and preventing disease development.

Predatory mites

One notable example of a biological control method is the use of predatory mites. These tiny arachnids are natural enemies of various pest species, including some fungal pathogens. Predatory mites actively seek out and feed on the harmful fungi, reducing their populations.

Beneficial fungi

Another biological control is beneficial fungi. Some species of fungi, known as mycoparasites, possess the remarkable ability to attack and destroy fungal pathogens. These mycoparasitic fungi invade the harmful fungi, competing for resources and ultimately leading to their demise.

Trichoderma species are widely recognized for their antagonistic properties against fungal pathogens. These beneficial fungi colonize the root zone, establishing a protective barrier that prevents the colonization of harmful fungi. Through their competitive interactions and production of antifungal compounds, Trichoderma species effectively suppress fungal diseases in stone fruits.

Beneficial bacteria

Some strains of bacteria have been found to produce compounds that inhibit the growth of fungal pathogens. These bacteria can be applied to the tree as a spray or incorporated into the soil, providing long-term protection against fungal diseases.

Biological control methods are not a one-size-fits-all solution. They require careful consideration and understanding of the target pathogens, as well as the beneficial organisms being introduced. Select the appropriate species or strains of beneficial organisms that are effective against the specific fungal diseases affecting your stone fruits. Proper application techniques and timing should be followed to maximize success.

Unlike synthetic chemical treatments, biological controls do not leave harmful residues or negatively impact the environment. They work in harmony with nature, promoting a balanced ecosystem within the orchard. However, their effectiveness can vary depending on the specific disease, environmental conditions, and cultural practices. Biological controls should be combined with other organic strategies, such as cultural practices and disease-resistant varieties, to achieve comprehensive disease management.

Plant disease-resistant varieties

As an experienced fruit tree grower with a passion for organic cultivation, I am thrilled to share my insights on effective disease-resistant stone fruit varieties that can be grown organically. Selecting the right cultivars minimizes the risk of disease outbreaks and ensures the health and productivity of your trees. These are a few noteworthy stone fruit varieties that have shown excellent disease resistance in organic growing conditions:

1. Reliance Peach (Prunus persica): Reliance Peach is a remarkable variety known for its exceptional resistance to peach leaf curl. This cultivar thrives in organic orchards and produces flavorful, juicy peaches.
2. Saturn Peach (Prunus persica): The Saturn Peach, also known as the Donut Peach, is an outstanding variety with good resistance to bacterial spot, a prevalent disease in stone fruits. This unique peach variety produces flat, disc-shaped fruits with a sweet, juicy flavor.
3. Elberta Peach (Prunus persica): Elberta Peach is a classic variety renowned for its excellent disease resistance and versatility. It is resistant to multiple fungal diseases, including peach leaf curl and brown rot. Elberta peaches are large, juicy, and aromatic.
4. Redhaven Peach (Prunus persica): Redhaven Peach is a widely grown variety known for its vigorous growth and remarkable resistance to brown rot. With its firm, flavorful fruits and strong disease resistance, Redhaven is an ideal choice for organic growers.
5. Flavor Grenade Pluot (Prunus domestica x Prunus salicina): A cross between plum and apricot, Flavor Grenade Pluot stands out not only for its exceptional flavor but also for its resistance to bacterial canker. This variety produces elongated, green-skinned fruits with a flavor reminiscent of tropical fruits.

Intercropping and companion planting

As a dedicated fruit tree grower, I am always on the lookout for innovative organic strategies to control fungal diseases in stone fruits. One approach that has caught my attention is intercropping or companion planting, which involves growing different plant species together to enhance the overall health and resilience of the orchard ecosystem. For example, interplanting stone fruits with aromatic herbs like basil or marigold can repel some fungal pathogens.

Intercropping and companion planting offer a range of benefits that can contribute to the control of fungal diseases in stone fruits. One advantage lies in the manipulation of the microenvironment. By carefully selecting companion plants, we can create an ecosystem that is less favorable to fungal pathogens. Certain companion plants possess natural defense mechanisms that repel or suppress the growth of fungi, helping to reduce disease pressure on stone fruit trees. Companion plants like garlic, onion, or chives contain natural compounds that have antifungal properties, which can inhibit the growth and spread of fungal pathogens when grown alongside stone fruit trees.

In addition to altering the microenvironment, intercropping and companion planting can also enhance biodiversity within the orchard. A diverse ecosystem promotes a healthy balance of beneficial insects, such as ladybugs or lacewings, which are natural predators of fungal pests. These helpful insects contribute to the biological control of diseases by consuming the pests that transmit fungal pathogens, effectively reducing their population and limiting disease spread.

While intercropping and companion planting hold promise as organic strategies to control fungal diseases in stone fruits, it is important to note that they should not be seen as standalone solutions. These techniques work best when integrated with other cultural practices and disease management strategies. Regular monitoring for disease symptoms, maintaining proper orchard hygiene, and implementing organic fungicides when necessary are all important components of an effective disease control program.

Author’s Bio: John Hammond is a seasoned backyard fruit tree grower with a degree in horticulture. Hailing from the Midwest, John’s love for gardening and cultivating fruit trees began at a young age. He is an expert in his field and his advice is highly sought-after by fellow gardeners and fruit tree enthusiasts. John continues to push the boundaries of fruit tree cultivation and has recently started experimenting with new grafting techniques.