Common Diseases of Cashew Trees and How to Manage Them

Cashew trees are remarkably resilient crops, but like any cultivated plant, they are not entirely free from disease. Compared to the pest pressures they face, cashew trees deal with relatively fewer fungal diseases – but the ones that do strike can cause serious damage if left unmanaged. Two diseases in particular deserve close attention from growers: die-back (Pink Disease), which threatens mature branches during the rainy season, and damping-off, which targets seedlings right at the nursery stage. Understanding how these diseases develop, what to look for, and how to respond is key to protecting your cashew crop.

Die-back or pink disease: the rainy season threat 🔗

Die-back, commonly known as Pink Disease, is one of the most frequently occurring diseases in cashew, typically intensifying during the south-west monsoon period. It is caused by the fungal pathogen Corticium salmonicolor (also referred to scientifically as Erythricium salmonicolor), which targets the woody tissue of branches.

The name “die-back” describes exactly what happens: the fungus penetrates the bark and kills the shoot from the tip downwards. The name “Pink Disease” comes from the distinctive coloration of the fungal growth itself – the mycelium starts as a silvery-white silky thread visible on branches after heavy rains, and gradually shifts to a general pink color at later stages.

Symptoms to watch for 🔗

The first visible sign is a whitish or pinkish growth on the bark of affected branches. As the fungus moves deeper into the tissue, the bark eventually splits and peels away. Leaves on affected branches turn yellow and drop, leaving that section of the tree looking barren and bare. Infection begins at the growing tips and works its way down the main stem, so early detection at the branch tips is critical. In some trees only a single branch is affected, while in severe cases multiple branches can be lost.

According to Plantwise Knowledge Bank, growers should consider taking action when two to three trees per acre begin showing symptoms, because waiting until basal leaves and multiple twigs are attacked means the disease has already progressed significantly.

Why the rainy season is the danger zone 🔗

High humidity and persistent moisture on bark surfaces are the conditions that allow Corticium salmonicolor to thrive and spread. Trees are most susceptible in areas with high rainfall, which is why the disease peaks during the monsoon months and tapers off as conditions dry out. The fungus produces asexual spores that are individually colorless but appear pink in large masses – these spores germinate readily in water and become the infective agents that penetrate the bark, leading to further spread through rain splash or contaminated tools.

Managing die-back and pink disease 🔗

Effective management of this disease requires acting early and combining physical removal with fungicide protection. The Tamil Nadu Agricultural University (TNAU) Agritech Portal recommends a clear, step-by-step approach:

• Prune infected branches well below the site of infection, ensuring healthy tissue remains. Destroy the pruned material – do not compost it, as the spores remain viable even after removal.
• Seal cut surfaces immediately with Bordeaux paste to prevent the fungus from entering through fresh wounds.
• Spray with 1% Bordeaux mixture if the disease is severe or widespread. Two sprays are recommended – one in May-June before the monsoon intensifies, and a second in October as the monsoon recedes.
• Collect and remove all dried and affected branches from around the tree to reduce the available inoculum in the environment.

On the cultural side, spacing trees at least 10 meters apart improves air circulation through the canopy and reduces the humid microclimate the fungus needs to spread. Avoid pruning during wet conditions, as this increases the risk of spreading spores to healthy tissue.

Research published in Crop Protection found that applying 1% Bordeaux mixture in the pre-monsoon period provided the best control of pink disease, with additional post-monsoon sprays further reducing disease incidence.

Damping-off: the nursery stage disease 🔗

While die-back threatens established trees, damping-off is a disease that strikes cashew at its most vulnerable point – as a young seedling in the nursery. The disease occurs in nurseries where drainage conditions are poor, and its consequences can be rapid: seedlings can collapse and die within days of infection.

The primary pathogens responsible for damping-off in cashew nurseries are Phytophthora palmivora and Cylindrocladium scoparium, though several other fungi including Fusarium spp., Pythium spp., and Sclerotium rolfsii have also been found associated with the disease in cashew. These pathogens are soil-borne and thrive in warm, waterlogged conditions – precisely the environment that poorly managed nursery beds tend to create.

How the disease develops 🔗

Damping-off presents in two distinct phases depending on when infection occurs. In pre-emergence damping-off, seeds rot underground before they can break through the soil surface, resulting in poor or patchy germination. In post-emergence damping-off, the seedlings emerge normally but then collapse at the soil line – the classic sign of this disease. The pathogens attack the roots or the collar region of seedlings, or both simultaneously.

When infected by Phytophthora palmivora specifically, seedlings become pale, develop water-soaked lesions at the collar region that turn dark and girdle the stem, and eventually droop and die. In severe cases, water-soaked lesions also appear on the leaves, enlarging and merging until they cover entire leaf surfaces. Environmental conditions such as high humidity at temperatures of 26°C-28°C further encourage pathogen activity, making the rainy season a particularly high-risk period in nurseries.

Why poor drainage is the root cause 🔗

The link between waterlogged conditions and damping-off is well established. Because most damping-off pathogens are soil-borne or water-borne rather than airborne, good phytosanitary practices and drainage management are the primary tools for keeping the disease in check. Overcrowded seedling beds, excessive irrigation, and the use of poorly draining soil mixes all compound the problem by maintaining the persistently wet conditions these fungi need to multiply and spread.

Managing damping-off in cashew nurseries 🔗

The management strategy for damping-off centers on improving the physical growing environment and applying protective fungicide treatments when necessary.

Improving nursery conditions 🔗

The first and most important step is drainage. Adequate drainage must be provided in both nursery beds and polythene bags used for raising seedlings. Containers should have sufficient drainage holes, and beds should be raised or sloped to prevent standing water. Watering practices also matter – watering early in the day allows excess moisture to dry off before cooler, more humid nighttime conditions set in.

Soil sterilization before planting is another effective preventive step. Nursery managers can reduce damping-off by promoting fast germination and good seedling growth through controlling soil drainage, organic matter content, and the timing of irrigation. The University of Massachusetts Extension also recommends using a soil-less or sterilized growing medium and keeping equipment and containers clean to avoid reintroducing pathogens.

Fungicide treatment 🔗

When damping-off is detected or conditions are high-risk, chemical intervention is necessary. Drenching nursery beds or polythene bags with 0.1% Agallol or 1% Bordeaux mixture is the standard recommended treatment. Bordeaux mixture – a combination of copper sulfate and lime – acts as a broad-spectrum fungicide effective against Phytophthora and related pathogens. For nurseries where Cylindrocladium scoparium is a concern, drench applications of thiophanate-methyl have been found effective against this particular pathogen.

The bigger picture: prevention over cure 🔗

Both die-back and damping-off share a common thread – they are diseases that gain a foothold when growing conditions favor the pathogen over the plant. For die-back, that means the warm, wet bark surfaces of the rainy season. For damping-off, it means the persistently waterlogged nursery bed. In both cases, proactive cultural management – proper spacing, good drainage, timely pruning, and pre-monsoon spraying – dramatically reduces disease pressure before it becomes a crisis.

Cashew may be a relatively low-maintenance crop in terms of disease, but these two conditions demonstrate that even resilient trees need attentive management at key growth stages and during high-risk seasons. Staying observant and acting early makes all the difference between a healthy plantation and one struggling to recover.

What do you think? If damping-off and die-back are both fungal diseases favored by wet conditions, could the same pre-monsoon fungicide schedule used for mature trees also serve as a preventive measure in nurseries? And in regions with extended rainy seasons, how practical is it for smallholder cashew farmers to implement the twice-yearly Bordeaux mixture spraying regimen recommended by agronomists?

References

1. https://agritech.tnau.ac.in/crop_protection/crop_prot_crop%20diseases_plantation_cashew.html
2. https://agriverge.in/die-back-in-cashew-symptoms-management/
3. https://www.plantwise.org/KnowledgeBank/pmdg/20207800213
4. https://en.wikipedia.org/wiki/Erythricium_salmonicolor
5. https://www.sciencedirect.com/science/article/abs/pii/0261219494901090
6. https://en.pagacas.com/diseases-of-cashew-nut-plants-inflorescence-blight-anthracnose-damping-off-die-back-pink-disease-leaf-spot-disease-sooty-mould-blo97
7. https://link.springer.com/article/10.1007/s13593-017-0417-y
8. https://pnwhandbooks.org/plantdisease/pathogen-articles/common/fungi/damping-tree-nurseries
9. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/damping-off-of-bedding-plants-vegetables