At Agro Vivero del Mediterráneo, we have spent years dedicating ourselves body and soul to the fascinating world of the pistachio tree. Our experience in the field has taught us that the success of an orchard does not only lie in the choice of a quality pistachio plant, but also in a deep understanding of the challenges that may arise. One of the most recurrent problems that most worries farmers is, without a doubt, the appearance of “gum” on the trunk and branches of the trees. This phenomenon, technically known as gummosis, is a warning sign that we must never ignore. warning

Throughout this article, we are going to share with you our vision and accumulated knowledge about gummosis. We will break down exactly what it is, how to identify it in time, what its most common causes are, and, most importantly, what strategies and treatments we have proven to be most effective in combating and preventing it. Our goal is to provide you with a complete and practical guide so that you can protect your orchards and ensure the health and productivity of your pistachio trees, thus guaranteeing the profitability of the orchard.

What exactly is gummosis in the pistachio tree? 🤔

Gummosis is not a disease in itself, but a symptom, a tree’s response to a stressful situation. It manifests as an exudation of modified sap, an amber and sticky substance, similar to resin, that flows through wounds, cracks, or damaged areas of the bark on the trunk and branches. This “gum” is, in essence, a defense mechanism of the pistachio tree. By secreting it, the tree tries to seal the wounds to prevent the entry of pathogens (fungi, bacteria) and isolate the affected areas.

However, although it is a natural reaction, its presence is a clear indication that something is wrong. Persistent or widespread gummosis weakens the tree, as it loses sap and valuable energy resources. If the underlying cause is not addressed, the problem can worsen, affecting the general vigor of the pistachio tree, reducing its productive capacity and, in the most severe cases, even causing the death of the specimen. That is why, at Agro Vivero del Mediterráneo, we always insist on the importance of constant observation of the orchard. Early diagnosis is the key to successful management.

Identification: How to recognize gummosis in our trees? 🕵️‍♂️

Detecting gummosis in its early stages is essential. Fortunately, the signs are quite evident if we know what to look for. We recommend conducting periodic visual inspections of the trunks and main branches, especially after periods of heavy rain, pruning, or adverse weather events.

The main symptoms we should pay attention to are:

• Gummy exudations: This is the most characteristic sign. Look for spots or trails of a gelatinous, sticky, amber or brownish substance emanating from the bark. At first, it may be a small “tear,” but over time it can form large masses or crusts that harden and darken upon contact with the air.

• Moisture and darkening of the bark: Before the gum is visible, an area of the bark with a moist or darker than normal appearance can often be observed. Pressing lightly on that area may cause it to exude liquid or gum.

• Cracks and cankers: Gummosis is usually associated with wounds or lesions on the bark. Pay attention to the presence of vertical cracks, sunken or necrotic areas (dead tissue) in the wood, known as cankers. Gum often emanates from the edges of these lesions.

• Discoloration of the cambium: If we carefully remove a piece of the affected bark (a practice that must be done with extreme care so as not to further damage the tree), we will observe that the inner tissue, the cambium, presents an abnormal coloration, generally brown or blackish, instead of its healthy green or whitish color.

• General weakening of the tree: In advanced cases, gummosis can be accompanied by other symptoms of decline: yellowing and premature leaf drop (chlorosis and defoliation), less shoot development, reduction in nut size, and a general decrease in the vigor of the pistachio tree.

The location of the gummosis also gives us important clues. If it appears at the base of the trunk, near the soil line, it is very likely that we are facing a Phytophthora problem. If it is located mid-way up the trunk or on the main branches, it may be related to other fungi such as Botryosphaeria or to mechanical damage.

The causes behind the gum: A multifactorial problem

As we have mentioned, gummosis is a symptom of stress. Understanding what is causing that stress is the first step to being able to apply the correct treatment. The causes can be very varied and often act in combination. From our experience, we group them into two broad categories: abiotic causes (non-infectious) and biotic causes (infectious).

Abiotic causes (environmental and management factors)

They are the most common and often the gateway for infectious problems. Inadequate orchard management can generate the stress that triggers gummosis.

• Root asphyxia: This is undoubtedly one of the main causes we observe in the field. Excess water in the soil, whether due to inadequate irrigation (too frequent or abundant), poor land drainage, or prolonged rainy periods, causes a lack of oxygen in the roots. The roots, unable to breathe, weaken, die, and become vulnerable to attack by soil pathogens, mainly fungi of the genus Phytophthora. Water stress is transferred to the rest of the tree, manifesting itself in the form of gummosis at the base of the trunk.

• Mechanical wounds: Any physical damage to the bark is a potential entry route for pathogens and a point of gum exudation. These wounds can be caused by agricultural machinery (tractors, brush cutters), pruning tools, rodents, hail damage, or even by the rubbing of trunk protectors if they are not well placed. It is crucial to take exquisite care during agricultural tasks to avoid hitting the trees.

• Grafting problems: Poor compatibility between the rootstock and the variety, or a deficient grafting technique that results in an imperfect union, can generate tension at the graft point. This area becomes a weak point prone to developing gummosis and the entry of diseases. Therefore, it is vital to start with a pistachio plant of the highest quality, with a well-healed and lignified graft.

• Frost damage or sunburn: Late spring frosts can damage young tissues and cause cracks in the bark. Similarly, excessive insolation in very hot summers, especially in young trees with unprotected trunks, can cause sunburn (necrosis) on the southwest face of the trunk, which can subsequently exude gum.

• Nutritional deficiencies: Although less frequent as a direct cause, a severe nutritional imbalance, especially the lack of certain microelements such as copper, can weaken the tree’s defenses and make it more susceptible to the factors that cause gummosis.

• Unsuitable soils: Planting pistachios in heavy, clayey, and poorly drained soils is buying all the lottery tickets to have root asphyxia problems and, consequently, gummosis. The pistachio tree requires loose, deep, and well-aerated soils.

Biotic causes (infectious agents)

These pathogens usually act as opportunists, taking advantage of stress conditions or wounds caused by abiotic factors to infect the tree.

• Phytophthora (Phytophthora spp.): It is “public enemy number one” when we talk about gummosis on the crown of the pistachio tree. This oomycete (a pseudo-fungus) lives in the soil and proliferates in high humidity conditions. It infects the roots and the base of the trunk, causing crown and root rot. Gummosis that appears right at ground level or slightly above is a classic symptom of this disease. The affected tree shows progressive decline, yellowish leaves, and can even die if action is not taken quickly.

• Botryosphaeria (Botryosphaeria dothidea): This fungus is another of the main culprits of gummosis in pistachio trees, especially on the trunk and main branches. It causes the appearance of cankers (sunken and dark lesions) from which abundant gum emanates. It usually penetrates through pruning wounds, frost cracks, or sunburns. It is a disease that can be very destructive, drying out entire branches and even the whole tree.

• Other fungal diseases: Fungi such as Cytospora or Phomopsis can also cause cankers and gummosis, although they are usually secondary pathogens that attack trees already severely weakened by other causes.

• Bacteria (Pseudomonas syringae): Although it is better known for affecting other fruit trees, under certain conditions, this bacterium can cause lesions on the bark of the pistachio tree, with gummy exudations that are more watery in appearance and often foul-smelling.

Management strategies and effective treatments 🛡️

The management of gummosis must be comprehensive. There is no single magic solution; success lies in combining preventive measures with specific curative treatments for the underlying cause. At Agro Vivero del Mediterráneo, we have developed an action protocol based on our direct experience, ranging from land preparation to the treatment of already affected trees.

Preventive measures: The best defense is a good offense

Prevention is, without a doubt, the most powerful and profitable tool we have at our disposal. A healthy and vigorous tree, grown in the right conditions, has a much greater capacity to defend itself against pathogens and resist environmental stress.

1. Land selection and preparation: Before planting, it is essential to carry out a soil analysis. We must avoid plots with poor drainage or that easily become waterlogged. If the soil is heavy, it is advisable to make amendments to improve its structure, build ridges or raised beds to plant the trees, and ensure that the root collar remains above the general ground level.

2. Irrigation management: This is a critical point. We must adjust irrigation to the real needs of the tree and to the soil and climate conditions. Drip irrigation is the most efficient system, as it allows us to precisely control the amount of water provided. It is essential to avoid waterlogging and wetting the trunk. The drippers must be separated from the trunk, about 30-50 cm away, so that the wet bulb develops at a safe distance from the crown. We recommend the use of moisture sensors to optimize irrigation management.

3. Plant quality: Starting with healthy and certified plant material is the first step towards success. In our nurseries, we pay special attention to using resistant rootstocks, such as UCB-1, known for its vigor and greater tolerance to adverse soil conditions. In addition, we ensure that the graft point is high (at least 25-30 cm from the root collar) and perfectly healed. A quality pistachio plant is the best investment.

4. Proper pruning practices: Performing correct pruning is vital. Drastic cuts must be avoided and always made cleanly, with sharp and disinfected tools (with diluted bleach or alcohol) between trees so as not to transmit diseases. It is important to seal large cuts (more than 2-3 cm in diameter) with a healing paste containing a fungicide to protect the wound.

5. Trunk protection: In young trees, it is essential to protect the trunk from both mechanical damage and sunburn. The use of micro-perforated protectors is a good option, but they must be checked periodically to ensure they do not rub against the trunk and that they allow ventilation. It is also highly recommended to paint the trunks with a mixture of lime or kaolin and a copper fungicide to reflect sunlight and create a protective barrier.

6. Balanced nutrition: A proper fertilization program, based on soil and foliar analyses, ensures that the tree has all the nutrients it needs to grow strong and healthy. Copper, in particular, plays an important role in the plant’s defense system and in the lignification of tissues.

Curative treatments: How to act when the problem has already appeared

If, despite all preventive measures, we detect a tree with gummosis, we must act quickly and decisively. The treatment will depend on the identified cause.

1. Canker surgery or wound cleaning: This is the first step and is crucial for most cases of gummosis located on the trunk or branches (caused by Botryosphaeria, wounds, etc.).

   • Scraping: With a sharp and disinfected knife or pocketknife, we must scrape and remove all the affected bark, which has a dark color and is impregnated with gum. You have to keep scraping until you reach healthy, green tissue. It is important to be meticulous and not leave any necrotic tissue behind.

   • Cleaning and disinfection: Once the damaged part is removed, the wound must be thoroughly disinfected. We can use a 2-3% copper sulfate solution or commercial bleach diluted to 10%. It is applied with a brush, making sure to cover the entire exposed surface well.

   • Sealing: After disinfection, and once the wound is dry, it is essential to apply a healing and protective paste or mastic. There are specific commercial products that, in addition to creating a physical barrier, usually incorporate fungicides that prevent reinfection. This layer will protect the living tissue while the tree generates the healing callus.

2. Specific treatments for Phytophthora (Phytophthora): If the gummosis is located on the crown of the tree and we suspect a Phytophthora attack, wound surgery is the first step, but it must be complemented with specific chemical treatments.

   • Uncover the crown: The first thing is to remove the soil around the base of the trunk to leave the crown and main roots exposed. This helps the area dry and aerate, creating a less favorable environment for the fungus.

   • Surgical cleaning: Perform the cleaning of the affected area as described in the previous point, removing all necrotic tissue.

   • Fungicide application: There are very effective systemic fungicides against Phytophthora. The most widely used are those based on Fosetyl-Aluminum or Metalaxyl-M (Mefenoxam). These products can be applied in several ways:

     • Brushing on the wound: After cleaning, a fungicidal paste can be applied directly to the wound.

     • Foliar application: Fosetyl-Al based products are absorbed by the leaves and translocated throughout the plant, both upwards (acropetal action) and downwards (basipetal action), reaching the roots. This allows the tree to be protected internally.

     • Application via irrigation: Metalaxyl-M based products are applied in the irrigation water, being absorbed directly by the roots and protecting them from the soil.

   It is important to alternate active ingredients to avoid the appearance of resistance and always follow the manufacturer’s instructions for dosage and safety periods.

3. Treatments for Botryosphaeria (Botryosphaeria): In addition to canker surgery, which is essential, it is recommended to carry out preventive fungicidal treatments at times of greatest risk (after pruning, after a hailstorm, etc.).

   • Winter treatments: The application of cupric fungicides (copper oxychloride, copper hydroxide, or cuprous oxide) during winter dormancy, after leaf fall, helps reduce the amount of fungal inoculum present in the orchard.

   • Treatments during vegetative growth: During spring, applications with specific fungicides can be made if disease pressure is high. Products based on tebuconazole, pyraclostrobin, or boscalid have proven to be effective.

The importance of professional advice

As you have seen, the management of gummosis in the pistachio tree is complex and requires deep technical knowledge. Every orchard is a world of its own, with its own soil, climate, and management characteristics. Correctly identifying the cause of the problem is essential to avoid wasting time and money on ineffective treatments.

At Agro Vivero del Mediterráneo, we are not only dedicated to producing plants of the highest quality. We offer a comprehensive technical advisory service to accompany farmers in all phases of their project. Our services range from the preliminary study of the farm to the preparation of personalized fertilization and phytosanitary treatment plans. We firmly believe that our clients’ success is our own success.

If you are thinking of starting a pistachio orchard or if you already have one and are dealing with problems like gummosis, do not hesitate to contact us. Our team of experts will be happy to study your case and offer you the most appropriate solutions. You can even request a personalized quote through our reservation form.

The key to keeping gummosis at bay and ensuring the longevity and productivity of your pistachio trees lies in a proactive and well-founded approach. Prevention, through good agricultural practices, is the cornerstone. This includes exquisite irrigation management, balanced nutrition, the choice of top-quality plant material, and maximum precaution to avoid wounds. When the problem appears, a quick and precise identification of the cause will allow us to apply the correct curative treatment, which often combines cleaning surgery with the application of specific phytosanitary products. Remember that a healthy pistachio tree is a productive pistachio tree, and your attention and care are the best guarantee to ensure the profitability of your investment for many, many years. We are here to help you achieve it. 🌳💚