The monilia (or moniliasis) is a highly problematic fungal disease that puts our crops at risk. It primarily affects stone fruits, namely cherry, peach, apricot, and plum. The fungus attacks both parts of the plants and fruits during their maturation phase, striking under specific environmental conditions. In this article, we explore intervention methodologies to prevent moniliasis.
Specifically, we’ll examine appropriate techniques and permitted products in organic agriculture.
Monilia or Moniliasis
Moniliasis of stone fruits is a disease caused by various fungi that, under favorable conditions, can cause severe damage to certain plants. Different fungal species causing this cryptogamic disease belong to the genus Monilia and Monilinia. These pathogens have distinct characteristics when observed under a microscope. However, concerning symptoms on crops, these agents are indistinguishable. Monilinia laxa is the typical species affecting crops like peach, cherry, apricot, and plum. Being active at low temperatures (5-10 °C), it can cause extensive infections at different times during the season. It affects both vegetative organs (flowers, shoots) and maturing fruits. Other species prevalent in our country are Monilia fructigena and M. Fructicola. These become active at higher temperatures, mostly affecting fruits during maturation. M. Fructigena also attacks Pomaceae. M. Fructicola, on the other hand, is a species that has spread more recently but is concerning due to its rapid development and higher sporulation potential.
The Biological Cycle of Monilia
The biological cycle of these pathogens is similar for all monilia species. Overwintering occurs as mycelium on affected fallen fruits, as well as on mummified fruits that remain on the plant. The mycelium also survives on cankers caused by copper. Severe attacks occur during flowering and on fruits nearing harvest. The most significant risks come with humidity, fog, and prolonged rains. Under these conditions, fungal mycelia release spores dispersed by water, wind, and insects, causing primary infections. The pathogen penetrates the tree through natural openings or microlesions. Monilinia laxa can affect vegetative organs (flowers and small fruits). The other species find optimal conditions to damage fruits at temperatures between 15 and 30 °C and near-saturation humidity levels. In ideal conditions, the fungus’s cycle completes in about a week, generating new spores initiating secondary infection cycles. However, if environmental conditions are not favorable, monilia infections can remain latent on fruits, only manifesting as visible rot after harvesting. In years with hot and dry springs and summers, the disease incidence is limited.
Damage Caused by Monilia to Crops
Monilia causes severe damage to crops. Typical symptoms include:
- Leaves with dark brown and/or reddish spots;
- Suddenly withered young shoots or those turning soft and discolored, resembling scalding in boiling water;
- Biological material oozing from branches with a gummy appearance;
- Fruits with yellow spots and mold, which can also be found in the pulp. The fruits may either fall immediately or remain attached but appear unsightly and mummified.
Most Susceptible Varieties
Among stone fruits, certain varieties are more susceptible to monilia; let’s summarize which ones.
- Apricot: The most susceptible varieties are Aurora, Palummella, and Antonio Errani.
- Cherry: Varieties prone to splitting, such as Celeste and New Star, and those with clustered fruiting, like Lapins and Sweet Heart, are more sensitive to cherry monilia.
- Peach: For peach trees, which we’ve already studied concerning their main parasites and peach bubble, late-harvested peaches and nectarines are highly susceptible.
- Plum: Chinese or Japanese plum varieties are more susceptible to monilia during harvest, while European varieties are vulnerable during flowering.
Prevention with Agronomic Techniques
To prevent monilia outbreaks, proper agronomic practices are necessary. During winter pruning, it’s crucial to remove and discard mummified fruits remaining on the plant. Eliminating branches affected by cankers is also necessary. When possible, the removed material should be burned. Through pruning operations, ensure the canopy has proper airflow. Another agronomic choice is a wide planting distance, allowing air passage between plants. Effective weed management is vital. Maintaining acceptable ground cover levels is necessary. Mismanagement in this aspect fosters favorable humidity conditions for the fungus. Other measures to prevent monilia include:
- Controlling plant vigor with low nitrogen fertilization
- Preventing water stagnation with proper drainage systems
- Managing irrigation correctly to avoid excessive fruit ripening (and rapid ripening), which can lead to splitting.
Treatments for Monilia with Approved Organic Agriculture Products
Let’s explore interventions using products permitted in organic agriculture (here’s the European regulation on organic production). For organic treatments, calcium polysulfide, sulfur, and sulfur proteins are used. Used correctly, these products can significantly limit fungal attacks. Interventions should be done pre and post-flowering, following recommended dosages. During flowering, sulfur can be used at lower dosages (a good product can be found here), perhaps mixed with propolis or sodium silicate. For peaches, intervention pre-harvest can use sodium silicate or sulfur proteins. In such cases, intervention should be 8-10 days before harvesting and repeated if necessary after 3 days. It’s important to note that in years with strong disease pressure, these remedies may not suffice.