BY DR. ANDRÉS FRACE, PHYTOPATHOLOGIST, INTERNATIONAL ADVISOR
As a country increases its blueberry production, a rise in rejections due to fruit rots is also observed—a problem that does not distinguish between large or small orchards. Today, the country that has most accelerated its production is Peru, and with this growth, the volume of fruit arriving at destination with some degree of deterioration has also increased. Global postharvest loss averages range between 10% and 12% of the fruit, with postharvest fungi—commonly referred to as rots—being the main cause of these losses.
This average has remained stable for many years, although the absolute volumes of rejected fruit vary depending on each country’s export levels and the distance to destination markets. As supply increases, pressure on logistics, packing facilities, and the cold chain also rises, and it is often at these points where problems that began silently in the field become evident.
Two critical stages: field and postharvest
From a phytopathological perspective, it is essential to distinguish between fruit that becomes infected in the orchard and fruit that is contaminated during postharvest. In the first case, we are dealing with latent infections: the pathogen enters during flowering or in the early stages of fruit development and remains inactive until storage conditions favor its growth. In the second scenario, the fruit may leave the field healthy but become contaminated at collection points, during precooling, along sorting lines, in storage rooms, or even during transport to the final consumer.
This distinction is not minor. In many cases, the orchard is blamed as the main source of rejections, when in fact the downstream chain may have multiple points of cross-contamination. Cold storage facilities at destination, for example, receive fruit from different countries and species, and strict segregation is not always maintained. The presence of spores in closed, humid environments is enough to trigger new infections, especially if the fruit has micro-injuries or if condensation occurs.
To determine the true origin of a rot, the use of retention samples at origin is a key tool. Opening these samples in parallel with the fruit’s arrival at destination allows for an assessment of whether the problem developed in the orchard or during transit. However, this information is often handled privately, making broader, more transparent sector-wide analysis more difficult.
Botrytis cinerea: biology and persistence
The main pathogen involved in blueberry fruit rots is Botrytis cinerea. Its importance lies not only in its high prevalence in orchards and packing facilities, but also in its ability to grow at temperatures close to 0 °C. While other postharvest fungi drastically reduce their activity under cold conditions, Botrytis can continue developing slowly during storage and transport, which explains why fruit may arrive with visible symptoms after several weeks in transit.
From a biological standpoint, Botrytis produces abundant spores that are easily dispersed through the air. It colonizes flowers, fruits, senescent tissues, floral debris attached to the fruit, and microscopic wounds. Infection can establish during flowering and remain latent until the fruit reaches a more susceptible physiological stage, as occurs during postharvest.
High relative humidity is a key factor. Levels above 95% favor spore germination, especially when free water is present due to condensation. Rainfall is not always necessary; persistent dew, fog, or microclimates created by high planting density are sufficient. In protected structures such as tunnels or macrotunnels, inadequate ventilation can turn the environment into ideal conditions for the development and proliferation of the pathogen.
Microclimate, density, and orchard architecture
Orchard architecture—that is, the spatial arrangement of plants—directly influences the epidemiology of fruit rots. High planting densities, excessive foliage, and inadequate pruning reduce air circulation and prolong periods of leaf wetness. This increases inoculum pressure and makes it more difficult for fungicides to reach all susceptible plant organs.
A well-balanced plant, with good ventilation and adequate exposure to solar radiation, tends to show lower disease incidence. However, there is an ongoing trade-off between maximizing yield per hectare and maintaining optimal sanitary conditions. Higher density means greater production potential, but also a higher risk of creating microenvironments favorable to fungal development.
Cultural management, therefore, is just as important as chemical control. The removal of floral debris, fallen fruit, and diseased plant material significantly reduces inoculum load and the potential for rot development. Likewise, sanitation in packing facilities—processing lines, cold storage units, evaporators, trays, bins, and floors—is an essential component of integrated disease management.
Postharvest: time, temperature, and ethylene
Once harvested, the fruit begins a natural process of senescence. In this state, tissues become more susceptible to pathogen attack. The natural production of ethylene—although lower than in other species—contributes to accelerating physiological processes that facilitate fungal development.
The time between harvest and precooling is critical. Every hour at ambient temperature increases the respiration rate and the likelihood that latent infections will become active. While rapid and uniform cooling is one of the most effective measures to delay the progression of rots, reaching a low temperature is not enough—it is essential to keep it stable.
Breaks in the cold chain lead to condensation on the fruit surface. In turn, this free water enables the germination of spores that would otherwise remain inactive under dry conditions. For this reason, thermal stability during maritime or air transport is a determining factor in ensuring that fruit arrives at destination in sound condition. A technically adequate cold system, if poorly managed, can become a facilitator of disease.
Interaction with insect damage
n this context, damage caused by insects becomes highly relevant. Scirtothrips dorsalis, present in countries such as Peru and Mexico, feeds on young tissues, causing abrasions and micro-wounds on shoots and developing fruit. While thrips are not pathogens, these injuries can become entry points for opportunistic fungi.
In warm climates, with high nitrogen fertilization and vigorous vegetative growth, populations of this thrips can multiply rapidly. The result is an increase in susceptible tissue and superficial damage that, under high humidity, facilitates secondary infections by Botrytis cinerea or other fungi such as Colletotrichum, the causal agent of anthracnose.
Integrated pest management—including biological control, constant monitoring, and cultural strategies—not only protects orchard yield but also indirectly helps reduce the incidence of final fruit rots. Plant health should be understood as an interconnected system.
Distance to markets and sanitary requirements
International logistics add another layer of complexity. Countries such as Chile face long transit times to distant markets, which requires extremely high standards in both field and postharvest management. Peru, despite having certain logistical advantages to some destinations, is not exempt from risk—especially as volumes grow rapidly and infrastructure must adapt.
In all cases, the key is understanding that fruit rots are not an isolated event, but the result of multiple cumulative factors. From flowering to the retail shelf, every agronomic and logistical decision influences the final sanitary outcome. The challenge is not simply to apply more fungicides, but to integrate cultural practices, pest control, strict hygiene, and rigorous cold chain management.
When analyzing rejections at destination, it is essential to look at the entire system. Only by understanding the interaction between field, postharvest, transport, and market can the impact of fruit rots be sustainably reduced and competitiveness maintained in a context of growing global supply.
Fungicide resistance and sustainability of control
A key aspect in managing fruit rots is the resistance of Botrytis cinerea to fungicides. This pathogen has a high adaptive capacity and, due to its genetic variability and rapid reproductive cycles, can develop resistance when the same modes of action are used repeatedly. In intensive production systems—where applications are frequent during flowering and preharvest—the selection pressure is particularly high.
To prevent this, a strategic use of fungicides is essential. This includes rotating active ingredients with different modes of action, targeting applications at critical phenological stages, and continuously monitoring their effectiveness in the orchard. The goal is not to increase the number of applications, but to apply them at the right time, ensuring proper coverage and considering environmental conditions. In orchards with dense canopies, for example, product penetration may be limited, leaving unprotected areas where the fungus can establish and proliferate.
Market requirements regarding maximum residue limits demand a careful balance between sanitary efficacy and regulatory compliance. This reinforces the need to integrate cultural practices that reduce inoculum pressure and, in turn, decrease reliance on chemical control alone.
Latent infections and their expression at destination
One of the most complex phenomena in blueberries is latent infection. During flowering, spores of Botrytis cinerea can colonize floral debris and young tissues without causing visible symptoms. The fruit continues its development appearing healthy, with the pathogen present but inactive. Once the fruit is harvested and enters a process of ripening and senescence, the fungus reactivates its growth.
This behavior explains why, in some cases, field assessments show low incidence, while significant rots appear at destination. Stress associated with harvesting, handling, cooling, and transport can act as a trigger. Therefore, sanitary management must begin at flowering—not at preharvest.
Timely removal of senescent flowers attached to the fruit, humidity control during critical periods, and strategic fungicide protection at full bloom are measures that help reduce the likelihood of latent infections that manifest weeks later.
Physiological quality and susceptibility
Not all fruit has the same level of susceptibility. Factors such as nutrition, water balance, and crop load directly influence the physiological quality of the fruit. Plants with excessive nitrogen, for example, may produce softer tissues that are more prone to infection. Prolonged water stress followed by heavy irrigation can lead to microcracks that are not always visible, but that facilitate pathogen entry.
Fruit firmness and soluble solids content are variables that affect natural resistance to infection. In some cases, an agronomic strategy focused solely on maximizing fruit size and yield can compromise attributes that support postharvest life.
In this sense, balanced nutritional management and crop load regulation are indirect yet fundamental tools in the prevention of fruit rots.
True integration of the plant health system
When fruit rots are analyzed from an integrated perspective, it becomes clear that there is no single solution. The problem is systemic. It begins at flowering, is influenced by orchard architecture and microclimate, continues through harvest and handling, and culminates in the stability of the cold chain and storage conditions at destination.
The interaction with pests such as Scirtothrips dorsalis reinforces this systemic view. The damage it causes may seem secondary from an immediate production standpoint, but by creating microscopic wounds and altering tissue physiology, it indirectly increases sanitary risk. Therefore, timely and integrated pest management is part of the preventive framework, just as much as disease control.
In highly competitive international scenarios—where margins are tightening and markets are increasingly demanding—reducing losses by just a few percentage points can make a significant difference in the final profitability of an orchard. However, that reduction is not achieved through a single measure, but through technical consistency at every stage of the process.
Experience shows that the most successful programs are those that combine constant monitoring, decisions based on real climatic conditions, strict sanitation in packing facilities, proper training of harvest personnel, and a stable and verifiable cold chain. The rot observed at destination is ultimately the visible manifestation of a series of accumulated decisions throughout the entire production system.
The starting point for reducing rejections and maintaining export-quality fruit in a global market that does not tolerate repeated sanitary failures lies in understanding this entire chain, rather than seeking isolated points of blame.
