Avocado Pests and Diseases: Symptoms, Control and Prevention

Last updated on October 23rd, 2023 at 08:19 pm

In this article we are going to give you all the guidelines on how to identify the main pests and diseases that avocado can suffer. We will also tell you what damage they can cause to the tree and the measures we can take to control and prevent them.

Avocado trees, like any plant, can be susceptible to various pests and diseases. Identifying the symptoms, controlling, and preventing these issues is crucial for maintaining healthy avocado trees. Here are some common avocado pests and diseases, along with strategies for control and prevention:

Pests:

1. Avocado Lace Bug (Pseudacysta perseae):
   • Symptoms: Yellow stippling or speckling on the leaves, which may lead to leaf drop.
   • Control and Prevention: Apply insecticidal soap, neem oil, or horticultural oil to deter lace bugs. Regularly monitor for infestations and remove affected leaves.
2. Avocado Thrips (Scirtothrips perseae):
   • Symptoms: Deformed and twisted leaves, silvery streaks on leaves, and scarring on fruit.
   • Control and Prevention: Use beneficial insects like thrips-eating predators. Apply neem oil or insecticidal soap for control. Remove and destroy damaged leaves and fruit.
3. Redbay Ambrosia Beetle (Xyleborus glabratus):
   • Symptoms: Sawdust-like frass at entry holes, wilted foliage, and dieback.
   • Control and Prevention: Remove and destroy affected trees to prevent the spread of this destructive pest. Implement preventive measures like traps and insecticides.

Diseases:

1. Avocado Black Streak (Persea declinata):
   • Symptoms: Black streaking on the fruit, reducing market value.
   • Control and Prevention: Maintain good sanitation practices, control insect vectors, and select resistant avocado varieties.
2. Avocado Root Rot (Phytophthora cinnamomi):
   • Symptoms: Wilting, yellowing leaves, dieback, and eventually tree death.
   • Control and Prevention: Improve soil drainage, avoid overwatering, and use disease-resistant rootstocks. Fungicides may also be used for control.
3. Anthracnose (Colletotrichum gloeosporioides):
   • Symptoms: Dark, sunken lesions on fruit, leaves, and stems.
   • Control and Prevention: Prune to improve air circulation, remove affected plant parts, and apply copper-based fungicides during the growing season.
4. Phytophthora Blight (Phytophthora spp.):
   • Symptoms: Root rot, dieback, and canopy decline.
   • Control and Prevention: Improve soil drainage, avoid excessive irrigation, and use resistant rootstocks. Fungicides may be applied in severe cases.
5. Scab (Sphaceloma perseae):
   • Symptoms: Raised scab-like lesions on fruit and leaves.
   • Control and Prevention: Prune for better air circulation, remove affected plant parts, and apply copper-based fungicides.

To prevent pest and disease issues in avocado trees, practice good orchard management, maintain proper nutrition, irrigate appropriately, and monitor for early signs of trouble. Regular inspection, prompt action, and careful selection of disease-resistant avocado varieties are key components of successful pest and disease control. Consulting with local agricultural extension services can provide valuable guidance on specific issues in your region.

Avocado pests

1.1. Crystalline avocado mite

Oligonychus perseae, commonly known as the crystalline avocado mite, is the most important pest of this crop in Spain. It is a mite of the same family as the red spider mite, the tetranychids, and is present in all areas of the territory. This mite is yellowish in color and colonizes the underside of the leaf, protected by a dense web, where it feeds while producing necrotic spots. Its period of activity can vary between May and September depending on the area where we are.

What damage is caused by the avocado crystalline mite?

The main damage of this mite is concentrated on the underside of the leaves, first producing spots on the central nerve, which will spread throughout the leaf after some time. Initially, these spots will appear green and then darken as the leaf necroses. This necrosis will eventually lead to leaf drop and possible fruit burns, although this mite does not cause direct damage to the fruit.

Avocado mite control and prevention measures

As prevention measures, the most advisable is the implementation of cover crops and/or plant reservoirs, such as grasses, which serve as refuge and provide food for the natural enemies of this mite.

As biological control measures, natural enemies can be released. In this case, as it is a tetranychid mite, the most outstanding natural enemies are phytoseiid mites, such as Neoseiulus californicus, Euseius stipulatus and Euseius scutalis.

For more information on beneficial insects and how to attract them to your orchard you can consult this article: How to attract beneficial insects: The 10 best tricks.

If you intend to apply any chemical control measure, it is important to check that the product is compatible with the survival of the natural enemies mentioned above.

1.2. Avocado brown spider mite

The brown avocado spider (Olygonichus punicae), like the crystalline mite, also belongs to the tetranychid family, although its importance is not as noticeable. This spider has its origin in Central America and acquires its brown color when it reaches adulthood, being its period of greatest incidence during autumn.

What is the damage caused by the avocado brown spider mite?

The main damage, unlike the crystalline mite, will occur on the upper side of the leaf, since this is the part where colonization begins, normally from the midrib to cover the entire leaf. Initially we will appreciate a discoloration of the main nerve in brown tones that will extend to the rest of the leaf.

Avocado brown spider mite control and prevention measures

The attacks of this mite are not usually very strong, so it is generally not necessary to take any measures; the natural enemies themselves are capable of controlling the mite.

However, it is important to emphasize the care of auxiliary vegetation that acts as a reservoir of natural enemies, such as phytoseiid mites, so any measure that favors their survival will be beneficial for pest control.

1.3. Pyriform mealybug

The pyriform mealybug or Protopulvinaria pyriformis is a type of mealybug from America that affects many tropical fruit trees, such as avocado. In the juvenile stages, mealybugs are very mobile and light-colored. As they grow, they increase in size and darken to a brownish color, with a puffy appearance, because the adult females carry the eggs under their bodies.

What damage is caused by the pyriform mealybug?

This mealybug is located on the nerves of the leaf, normally on the underside, where it will feed on the sap and cause direct damage to the tree. However, this direct damage is not as important as indirect damage: the mealybug, as it feeds, secretes a honeydew that, on the one hand, attracts ants and, on the other, favors the appearance of black leaf spot. The appearance of this disease is the most important indirect damage caused by the pyriform mealybug.
Control measures and prevention of the pyriform mealybug

• Encourage the survival of natural enemies by means of auxiliary vegetation, as in the previous cases.
• Carry out a balanced nitrogen fertilization.
• Carry out pruning to allow proper aeration.
• In case the mealybug population increases too much, parasitoids of the genus Metaphycus and predators such as Cryptolaemus montrouzieri and Chrysoperla carnea can be released.
• Control ant populations

1.4. Avocado mealybug or coconut mealybug

The avocado mealybug is a hemiptera called Nipaecoccus nipae, which affects numerous species of tropical trees and is widely distributed throughout the world. It can develop throughout the year, so it can appear at any time.

What is the damage caused by the prickly mealybug?

The females feed on the sap while secreting honeydew, normally located on the nerves on the underside of avocado leaves. However, as in the case of the pyriform mealybug, the direct damage caused by this hemiptera is not as serious as the indirect or secondary damage, since it can lead to the appearance of fungi such as Cladosporium or Negrilla, which can cause serious damage. In addition, the secretion of molasses can induce the appearance of ants that will use it as food and protect the mealybugs from their natural enemies.

Control and prevention measures for prickly mealybugs

Control and prevention measures will be similar to those for the pyriform mealybug:

• Favor the survival of natural enemies by means of auxiliary vegetation, as in the previous cases.
• Carry out a balanced nitrogen fertilization.
• Carry out pruning to allow proper aeration.
• In case the mealybug population increases too much, parasitoids of the genus Metaphycus and predators such as Cryptolaemus montrouzieri and Chrysoperla carnea can be released.
• Control ant populations

1.5. Avocado galling

Avocado gall is a pest caused by the hemiptera Trioza anceps which, as its name suggests, causes the appearance of galls on the leaves of the tree. In Spain there is no record of this pest, but in countries such as Mexico and Guatemala it is frequent.

What damage is caused by avocado galling?

Females lay eggs on avocado leaves and, after hatching, the young feed on the sap, producing galls or bumps on the leaves. In addition, the nymphs will remain lodged in the leaves until they complete their life cycle, using them as protection against predators. At the beginning they will be green and, with time, they will increase in size and darken.

Control and prevention measures for avocado blight

The main measure to follow when we have evidence of this pest in our orchard will be to eliminate and burn the affected leaves.

As in the pests described above, it will always be positive to favor the presence of natural enemies by means of auxiliary vegetation.

Lastly, we could release calcidoid or aphelinid hymenopteran parasitoids.

1.6. Thrips

In Spain, the species Heliothrips haemorrhoidalis stands out in avocado, although there are many other species such as Scirtothrips perseae, Liothrips perseae or Frankiniella occidentalis.

What damage do thrips cause on avocado?

Thrips feed on both leaves and fruit, producing grayish or brownish spots. They can also inhibit flower fertilization and, therefore, reduce fruit formation.

Thrips control and prevention measures

Thinning pruning to allow light to enter the less illuminated areas of the tree, as these are usually the preferred places for thrips.

In Spain, it is not usually necessary to intervene, since the native fauna exerts sufficient control. However, natural enemies such as phytoseiid mites (Amblyseius swirskii), anthocorid bugs (Orius laevigatus) and mirids and thrips (Aeolothrips and Franklinothrips) can be released.

Avocado diseases

Diseases are plant health problems caused mainly by fungi, but also by bacteria and viruses.

2.1. Phytophthora

Phytophthora cinnamomi is a fungus that produces the disease known as tristeza or root rot and affects numerous species. This fungus lives in the soil and damages plant roots, feeding on them and, in many cases, causing the death of the plant.

What damage does Phytophthora cause on avocado?

The tree will begin to take on a general wilting appearance. Leaves will appear smaller than normal and yellowish in color. If the disease continues to progress, the tree will dry out more and more and may even die.

Phytophthora control and prevention measures

Once a soil is contaminated with this fungus, its elimination is almost impossible, so most measures are focused on prevention:

• Avoid waterlogging and excessive moisture.
• Adding mulching or organic matter to the topsoil to improve root development.
• Carrying out solarization practices
• Pruning the affected trees, disinfecting the tools used afterwards.
• Improve drainage
• In soils with high clay content, ridges can be made to avoid waterlogging.

2.2. Rosellina

Rosellina necatrix is a fungus that produces the so-called white root rot, a disease that also causes damage to the root system of plants and affects numerous species.

What damage does Rosellina produce in avocado trees?

On the one hand, this fungus will cause damage to the roots in the form of white spots with a cottony appearance. The wood will darken and take on a necrotic appearance.

On the other hand, the leaves of the tree become yellower as they wilt, but will remain attached to the tree.
Rosellina control and prevention measures

• If in our orchard we have previously had a tree that is also prone to suffer from this disease and we want to plant the avocado in the same place, we must wait some time to plant it, because it is very likely that there are still remains of the fungus. It will also be necessary to remove from the soil any plant debris from the previous plant.
• As we already mentioned in the article How to grow avocado (avocado or avocado): Complete Guide, if our orchard has a tendency to waterlogging, it will be more likely to develop this type of disease.
• Using Rosellina tolerant rootstocks
• Use soil solarization techniques, as in the case of Phytophthora.

2.3. Negrilla

Negrilla, also known as fumagina, is a disease caused by fungi of the Capnodium genus, which normally appear due to honeydew secreted by pests such as mealybugs.

What damage does Negrilla cause in avocado?

Negrilla can appear on leaves, branches and fruits, showing a black powder that falls off if we scrape it.

Control measures and prevention of black scab

The main control measure is aimed at controlling the pests that cause it, which, in the case of avocado, would be the prickly mealybug and the pyriform mealybug, described in point 1.3. and 1.4. of this post.

Once the disease has been contracted, all infected branches or parts should be removed.

2.4. Anthracnose

Anthracnose is a disease caused by the fungus Colletotrichum gloeosporioides, present mainly in tropical areas where high temperatures and humidity favor its development.

What damage does anthracnose cause in avocado?

Symptoms are mainly observed on the leaves, with young trees being especially vulnerable. Leaves show reddish or orange spots with necrosis. It can also cause flower drop and hinder fruit formation.

Anthracnose control and prevention measures

The main measures are focused on prevention, pruning to improve aeration in the canopy of the trees with subsequent sealing of wounds and elimination of plant debris, where the fungus could still proliferate.

Verticillosis

Verticillium verticillosis is a disease caused by fungi of the genus Verticillium that live in the soil and whose appearance is favored by excess humidity and waterlogging.

What damage does Verticillium Verticillium cause on avocado trees?

The fungus enters the tree almost exclusively through the roots, although, to a lesser extent, it could also enter through the area, for example, through a wound in the branches. This will slow down the development of the tree and reduce its size.

In addition, we will observe how the leaves of the infected branches will show a yellowing from the tip towards the part closest to the junction with the branch and, over time, they will dry out.

If the disease continues to progress, when a cut is made on one of the main branches, we will observe something similar to what is shown in the following image:

Control measures and prevention of verticillium verticillosis

There is no 100% effective treatment that eliminates this disease once it is present on the tree. Therefore, most measures are focused on prevention:

• Avoid waterlogging and improve drainage.
• Maintain balanced nutrition, especially avoiding phosphorus and potassium deficiencies.
• Soil solarization

2.6. Botryosphaeria

Botryosphaeria is a disease caused by fungi of the Botryosphaeriaceae family, which spreads through the air and affects numerous plants, affecting leaves and branches.
What damage does Botryosphaeria cause on avocado trees?

Leaves will show necrosis at the apex, which will progress to the entire leaf, until it dries out completely. If the disease continues to progress, cankers and whitish spots will appear on the outside of the trunk.

Botryosphaeria control and prevention measures

As in previous cases, most measures are aimed at prevention, since once the disease appears, treatments will not completely eliminate it.

A good way to control this disease is by selective pruning, eliminating the residues as soon as possible to prevent the fungus from being transmitted again through the spores.
Another practice is to avoid high relative humidity, for example by weeding and controlled drip irrigation to avoid waterlogging.
Use irrigation water with low salt content.
Use of contact fungicides or healing products to treat pruning wounds.
Copper oxychloride applications