Pruning plays a fundamental role in blueberry production from a plant health perspective, as it directly contributes to maintaining healthier, more productive orchards with lower disease pressure.
According to Andrés France, Ph.D. in Plant Pathology from Cornell University, one of the main reasons pruning requires special attention is that every cut represents a potential entry point for wood-infecting fungi.
“It is important to protect pruning wounds because they serve as entry points for wood fungi. Once these pathogens enter the stem, they advance toward the crown, colonize the plant, and can ultimately cause its death. Since they develop inside the stems, they are very difficult to control because they are not exposed like many other pathogens. That is why prevention is far more important than control,” says Dr. France.
The specialist adds that symptoms often do not become visible until several years after the initial infection.”If preventive measures are not taken, dead branches may begin to appear one or two seasons later, eventually leading to plant collapse.”
Simón Muñoz, International Blueberry Production Consultant at CASM Blueberries, emphasizes that pruning also plays a key role in reducing foliar diseases and fruit rots by improving plant architecture.
“Pruning has an enormous impact on fruit quality. By improving sunlight exposure and promoting better air circulation within the canopy, it reduces the pressure from fungi and diseases. Fruit hidden beneath several layers of leaves is much less likely to remain healthy than fruit that is well exposed to sunlight,” he explains.
Muñoz notes that shaded environments with poor ventilation create favorable conditions for foliar and fruit pathogens.
“Fungi generally thrive under low-light, poorly ventilated conditions. That is why canopy management and plant architecture through pruning are essential for reducing the pressure of Botrytis and other diseases.”
Chile and Peru: two production systems, different challenges
Strategies for protecting pruning wounds vary according to the production conditions of each country.
In Chile, pruning is generally carried out during winter, when plants are dormant. In Peru, however, pruning is commonly performed during the summer while plants are actively growing, and in some cases even during harvest.
“In Peru, everything happens much faster. If a microorganism infects a pruning wound, it can spread so rapidly that there is no time to react. That is why prevention is absolutely essential,” says Dr. France.
The specialist stresses that the same principle applies in every production region: every pruning wound should be protected immediately.
“It doesn’t matter where the orchard is located. Every time we make a pruning cut, we must protect it. Even in Chile, where winter temperatures provide slightly more flexibility, the recommendation remains to apply protection immediately after pruning.”
The plant pathologist warns that although lower temperatures slow pathogen development, a brief period of warm weather is enough for microorganisms to colonize exposed tissues.
“Once a pathogen enters through a pruning wound and progresses into the plant, it often escapes control measures that might be applied several days later.”
The importance of same-day action
In regions where pruning is performed during the summer, such as Peru, Mexico, Ecuador, Colombia, and even parts of northern Chile, immediate protection of pruning wounds is no longer simply a recommendation—it is a necessity.
“Under these conditions, protective applications must be made on the very same day as pruning. Not the following day, and certainly not several days later. From a microbiological standpoint, the first organism to arrive is the one that dominates,” states Dr. France.
One of the greatest risks under these conditions is Lasiodiplodia theobromae, a fungus that releases large quantities of spores during warm periods. “This pathogen perfectly coincides with the summer pruning season, when inoculum pressure is high and temperatures strongly favor its development.”
Another challenge is the phenomenon known as sap bleeding from pruning wounds. After a large portion of the canopy is removed, the plant continues transporting sap, which exudes through the freshly made cuts.
“When pruning wounds bleed sap, some protective products may be washed away, reducing their effectiveness. In addition, the sap itself is rich in nutrients, creating favorable conditions for pathogen infection,” explains the expert.
To address this issue, Dr. France recommends several management strategies. One option is to leave a vigorous central branch without heading it back, allowing sap to flow through that branch instead of bleeding from the pruning wounds.
Another alternative is to perform what is known as a “dirty pruning,” temporarily leaving leaves and shoots on the remaining branches, usually about 30 to 40 centimeters long. “These leaves help draw the sap upward and reduce sap bleeding from the pruning wounds.”
A third strategy is the use of biological protectants based on Trichoderma, which are capable of developing on the sap exuded after pruning. “Trichoderma can establish itself directly on the sap, so instead of being washed away, it proliferates. It can also be complemented with chitosan applications, which serve as a nutrient source because Trichoderma is chitinolytic—it feeds on chitin—while also promoting wound healing.”
A tool for orchard sanitation
Beyond preventing new infections, pruning also removes diseased plant material that can serve as a source of inoculum for future seasons.
In Chile, for example, Dr. France highlights its importance for controlling dieback associated with Phomopsis vaccinii. “This fungus colonizes twigs from their tips and progresses toward the base. Pruning allows infected tissues to be removed before the disease reaches structural branches or the crown.”
Pruning also facilitates the removal of old or weakened wood that is susceptible to colonization by bacteria such as Pseudomonas syringae and other opportunistic pathogens.
In Peru, where complete cane renewal is often practiced, the sanitary benefits are mainly associated with reducing foliar diseases. “Pathogens such as powdery mildew, rust, and Botrytis can survive on leaves, flowers, or shoots. Pruning helps remove this infected material and reduces inoculum pressure for the following season.”
Dr. France concludes that pruning strategies must always be adapted to the phytosanitary conditions of each orchard. “If disease or pest pressure is high, as much infected tissue as possible should be removed. Pruning not only shapes the plant’s architecture—it is also one of the most important plant health tools for maintaining orchard health.”
