Managing Common Foliar Diseases in Mulberry Cultivation

Mulberry leaves are the sole natural food source for silkworms (Bombyx mori), which means the health of the leaf canopy directly determines the success of silk production. Unlike most crops where a disease might damage fruit or yield indirectly, in sericulture the leaf is the product. When fungal pathogens attack the foliage, they reduce both the quantity of harvestable leaves and their nutritional quality – and diseased leaves fed to silkworms can severely impact cocoon production. Research on mulberry diseases identifies foliar diseases as one of the biggest challenges facing sericulture farmers globally, with losses ranging from minor yield reductions to complete defoliation in severe outbreaks. Understanding these diseases, their specific symptoms, and the conditions that favor them is the first step toward effective management.

Why foliar diseases are so damaging in mulberry 🔗

In most crops, foliage diseases are a secondary concern – the harvest target (grain, fruit, tuber) may still be viable even when leaves are damaged. In mulberry cultivation, this logic is reversed. The leaf is the harvest. Any disease that compromises leaf surface area, texture, or nutritional composition directly cuts into income. Studies from Karnataka, India – one of the most significant mulberry-producing regions – recorded leaf spot disease incidence rates as high as 84% in farmer fields and germplasm plots, with substantial defoliation and loss of leaf quality reported. Beyond yield loss, diseased leaves alter the moisture, protein, and sugar content of foliage, making them unsuitable or even harmful for silkworm feeding, ultimately affecting cocoon quality and silk output.

Major foliar diseases of mulberry 🔗

Four fungal diseases are the most commonly reported and economically significant foliar threats in mulberry cultivation: leaf spot, powdery mildew, leaf rust, and leaf blight. Each has a distinct causal organism, characteristic symptoms, and a preferred set of environmental conditions.

Leaf spot – Cercospora moricola 🔗

Cercospora moricola is the primary cause of leaf spot disease in mulberry and is considered among the most widespread foliar pathogens affecting mulberry cultivation, particularly in South and East India. Disease records from India show that leaf spot typically causes 10-12% leaf yield loss under normal conditions, rising to 20-35% in severe or prolonged outbreaks.

The disease begins as minor circular light brown spots on either side of the leaf blade. These spots gradually enlarge and turn dark brown. As lesions develop, they form brown patches with pale centers and yellowish margins. When multiple spots merge, the necrotic tissues at the center dry out and fall away, creating characteristic “shot holes” in the leaf. Heavily infected leaves yellow prematurely and drop, a process that not only reduces harvestable leaf area but also stresses the plant. The fungus spreads primarily through rain-splash dispersal of conidia onto the lower leaf surface – the only surface in mulberry where stomata are present – and thrives at temperatures of 24-26°C with relative humidity of 70-80%. The peak disease period in India typically runs from July through December.

Powdery mildew – Phyllactinia corylea 🔗

Phyllactinia corylea (also classified as P. guttata) is the causal agent of powdery mildew in mulberry, and it is recognized as a major foliar disease worldwide wherever mulberry is cultivated for silkworm rearing. Unlike most fungal pathogens that demand constant moisture, powdery mildew can establish even in relatively dry spells, though it accelerates rapidly under humid conditions. The disease peaks in autumn and spring across most growing regions, with outbreaks extending into the monsoon in hilly areas.

The most distinctive symptom is the appearance of white, powdery patches – made up of fungal mycelium and conidia – on the lower surface of leaves. The corresponding portions on the upper surface develop yellow (chlorotic) lesions. As the infection advances, the white powdery coating turns brownish-black, leaves become coarse and yellow, and their nutritive value declines significantly. Research evaluating mulberry germplasm confirms that foliage losses from powdery mildew can reach up to 20% while also degrading cocoon production due to reduced leaf quality. The pathogen spreads through airborne conidia and favors temperatures between 24-28°C with relative humidity of 75-80%.

Leaf rust – Cerotelium fici 🔗

Leaf rust, caused by Cerotelium fici, is described by researchers at India’s Central Sericultural Research and Training Institute as one of the greatest epidemiological constraints in Indian mulberry cultivation, affecting nearly all commonly grown cultivars. The pathogen has also been reported in Brazil, where it was confirmed on Morus nigra, highlighting its global reach as a sericulture threat.

Leaf rust presents as small, pinhead-sized brown pustules on the lower (abaxial) surface of mature leaves. These pustules contain urediniospores that are released and carried by wind to initiate new infections on nearby plants. On the upper leaf surface, corresponding reddish-brown or yellow spots appear directly above the pustules. Studies confirm that initial symptoms typically appear as small pustules on the underside of fully expanded leaves, with chlorotic and necrotic lesions developing on the upper surface as the infection progresses. In severe cases, leaves turn completely yellowish, leaf margins dry out, and premature defoliation occurs. Disease development is strongly influenced by temperature, humidity, and crop age, with the rainy season presenting the highest risk.

Leaf blight – Alternaria alternata and Fusarium pallidoroseum 🔗

Leaf blight in mulberry is caused by two distinct fungal species – Alternaria alternata and Fusarium pallidoroseum – which can act independently or together to produce severe foliar damage. Alternaria alternata is a broad host pathogen known to infect over 380 plant types and is particularly aggressive under warm, humid conditions. The initial symptoms in mulberry appear as irregular brown to black patches, typically starting at leaf margins or tips and spreading inward. The spots often develop dark concentric rings, and as they merge, affected areas can take on a scorched or blighted appearance. Entire leaves may become unusable for silkworm feeding in severe outbreaks.

Fusarium pallidoroseum contributes to a similar pattern of tissue decay, often producing water-soaked lesions initially that later turn brown and dry. Leaf blight is particularly severe during periods of prolonged rainfall or overhead irrigation, which facilitate spore dispersal from leaf to leaf. High humidity, mild to warm temperatures, and stressed or nutrient-deficient plants all increase disease susceptibility.

Environmental conditions that favor outbreak 🔗

All four foliar diseases share some common environmental triggers. High relative humidity – generally above 75% – combined with moderate temperatures (typically 24-28°C) creates ideal conditions for fungal sporulation and infection. Dense plantings that restrict airflow keep leaf surfaces moist for longer, extending the infection window after each rainfall or irrigation event. Overhead irrigation mimics rain splash and actively helps spread conidia across the canopy. Additionally, plants already stressed by nutrient deficiencies, drought, or pest damage have weaker natural defenses and become easier targets for fungal invasion. Monitoring weather patterns and crop condition is therefore an important part of anticipating and preventing disease outbreaks.

Management strategies 🔗

Effective control of mulberry foliar diseases depends on combining cultural, chemical, and biological approaches rather than relying on any single method. This integrated strategy is especially important in sericulture because any chemical applied to mulberry leaves must be safe for silkworms – a constraint that limits the range of usable fungicides and makes cultural practices all the more critical.

Cultural practices 🔗

Proper plant spacing is one of the most impactful preventive measures. Recommendations for mulberry plantations include following wider spacing (90 cm × 90 cm) or paired row systems such as (90 + 150) × 60 cm to ensure adequate air circulation. Good airflow reduces the duration of leaf surface wetness after rain, limiting the window for spore germination. Regular pruning removes diseased and overcrowded growth, while prompt collection and disposal of fallen leaves – by burning or deep burial – eliminates the primary inoculum source that allows pathogens to persist from one season to the next. The Royal Horticultural Society similarly recommends thorough removal and disposal of prematurely fallen leaves to help prevent disease recurrence. Avoiding overhead irrigation and instead using drip or furrow methods significantly reduces leaf wetness and spore splash.

Fungicide application 🔗

When disease pressure is high, targeted fungicide applications are necessary, but the choice of product must account for silkworm safety. Research from India recommends Hexaconazole 5% SC as the preferred fungicide for leaf spot management, as it achieves complete suppression of pathogen mycelial growth, is cost-effective, and is widely available – importantly, it is also considered safer for silkworms compared to alternatives. Propiconazole 25% EC and Tebuconazole 250 EC have also shown strong efficacy in laboratory evaluations. For powdery mildew, spraying 0.2% Karathane (Dinocap 30% EC) or Bavistin (carbendazim) on the lower leaf surface is recommended, with a mandatory safe period of 5 days before leaf harvest for silkworm feeding. Sulfex (sulphur 80WP) at 0.2% is another option with a longer safe period of 15 days. All fungicide applications should strictly respect the prescribed safe periods to avoid silkworm toxicity.

Biological control 🔗

Biocontrol agents offer a valuable complement to chemical management, particularly given the silkworm-safety constraints in sericulture. Laboratory and field studies on powdery mildew management found that culture filtrates of Trichoderma viride and Trichoderma harzianum at 50% concentration inhibited conidial germination by over 70% and provided disease control comparable to carbendazim. These biocontrol agents work by producing antifungal compounds that suppress pathogen development and can be integrated into spray programs alongside or in place of synthetic fungicides, especially near harvest periods when silkworm safety is paramount.

Resistant varieties and monitoring 🔗

Growing disease-resistant mulberry varieties is the most sustainable long-term approach. Screening of 147 mulberry germplasm sources from 18 countries identified roughly 6.8% with useful resistance to powdery mildew, highlighting that resistant options exist but are not yet widely adopted. Species such as Morus laevigata and Morus serrata have shown resistance to Phyllactinia corylea infection. Regular field scouting – particularly during the high-risk rainy season months – allows farmers to detect early symptoms, time fungicide applications accurately, and avoid the spread that occurs when infections go unnoticed.

Safe period and silkworm considerations 🔗

A point that cannot be overstated in mulberry disease management is the concept of the “safe period” – the minimum number of days that must pass after a fungicide application before leaves can be fed to silkworms without risk of toxicity. Different fungicides carry different safe periods: Karathane and Bavistin require 5 days, while sulphur-based Sulfex requires 15 days. Failing to observe these periods can result in silkworm mortality, negating the entire benefit of disease control. Farmers should maintain spray records and plan leaf harvests accordingly, always prioritizing silkworm health alongside plant health.

What do you think? Given that mulberry leaves must be safe for silkworm feeding, how do you think farmers should balance the urgency of controlling a disease outbreak with the need to observe safe periods before leaf harvest? And with resistant varieties covering only a small fraction of available germplasm, what role should breeding programs play in making foliar disease management more practical for smallholder sericulture farmers?

References

1. https://www.researchgate.net/publication/383308800_Diseases_of_Mulberry_and_Their_Management
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC10665727/
3. http://mulinfo.csrtimys.res.in/index.php/en/foliar-fungal-diseases/cercospora-leaf-spot
4. https://www.forestpests.eu/pest/cercospora-moricola
5. https://scialert.net/fulltext/?doi=ppj.2005.103.106
6. https://link.springer.com/article/10.1007/s10327-010-0221-x?error=cookies_not_supported&code=9d9e4d14-dedd-4e7d-968f-eaf3a7ca6c25
7. https://www.tandfonline.com/doi/abs/10.1080/03235400500181097
8. https://apsjournals.apsnet.org/doi/10.1094/PDIS-11-22-2656-PDN
9. https://extension.illinois.edu/plant-problems/early-blight-or-alternaria-leaf-spot
10. https://www.slideshare.net/slideshow/diseases-of-mulberry/157800990
11. https://www.rhs.org.uk/disease/mulberry-leaf-spot
12. https://www.proquest.com/scholarly-journals/management-powdery-mildew-phyllactinia-corylea/docview/749226773/se-2