Olive Trees

Olive Trees

The cultivation of the olive tree dates back to ancient times. The Minoan colonists from Asia Minor (modern-day Turkey) were among the first to domesticate the wild olive tree, introducing it to the island of Crete and other Mediterranean islands around 2400 BCE.

Since then, the olive tree has become an important crop in many parts of the world, particularly in regions with a Mediterranean climate. These trees can grow to impressive heights and widths, with some reaching up to 30 feet tall and sporting trunks up to 6 inches wide.

While olive trees are drought tolerant once established, they require regular irrigation when young or planted in hot climates such as those found in Phoenix and Los Angeles. Although olive trees can be grown as far north as Canada, they need protection from cold weather, especially during the winter months.

There are many different types of olive trees, each with their own unique qualities. Some varieties are more resistant to drought or disease, while others produce more oil or have a longer lifespan. However, regardless of the type, olive trees can live for hundreds of years, although they only produce olives for around 50 years. Despite this, a mature tree can produce thousands of pounds of olives each year.

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Pests of Olive Trees in California

Olive Fruit Fly

The Olive Fly (Bactrocera oleae) is the most destructive pest of olive trees in California. They feed on the fruit, causing it to rot and drop prematurely. The larvae tunnel into the fruit, further exacerbating the damage. Early identification is crucial for effective control. Use traps or baits to monitor the fly population and apply appropriate treatments, such as insecticides, at the right time to prevent infestations.

Black Scale

Black Scale (Saissetia oleae) is a sap-sucking insect that can cause significant damage. The insect feeds on the leaves and fruit, leading to a reduction in yield and quality. Use horticultural oil or insecticides to control the population. Pruning the tree to remove infested branches can also help reduce the population.

Olive Psyllid

The Olive Psyllid (Euphyllura olivina) is a sap-sucking insect that feeds on leaves and shoots, leading to a reduction in yield and quality. Use insecticides to control the population. Pruning the tree to remove infested branches can also help reduce the population.

California Red Scale

The California Red Scale (Aonidiella aurantii) feeds on the leaves and fruit, leading to a reduction in yield and quality. Use horticultural oil or insecticides to control the population. Pruning the tree to remove infested branches can also help reduce the population.

Diseases of Olive Trees in California

Olive Peacock Spot

Olive peacock spot, caused by the fungus Cycloconium oleaginum, is a common tree disease. The disease affects the leaves, causing circular, dark spots with a light-colored center. In severe cases, the leaves can yellow and drop prematurely, leading to reduced photosynthesis. The disease can be prevented by practicing good sanitation and removing infected leaves and branches. Fungicides can also be used to manage the disease.


Anthracnose, caused by the fungus Colletotrichum spp., is another common disease of olive trees in California. The disease affects the fruit, causing sunken lesions that can lead to fruit rot. In severe cases, the fruit can drop prematurely. The disease can be prevented by pruning trees to improve air circulation, removing infected fruit, and using fungicides.

Verticillium Wilt

Verticillium wilt, caused by the fungus Verticillium dahliae, is a serious disease. The disease affects the roots, causing them to turn brown and rot. Symptoms can also appear on the leaves, including yellowing, wilting, and stunted growth. The disease can be prevented by using certified disease-free planting material, practicing good sanitation, and avoiding planting olive trees in soil previously used to grow crops susceptible to Verticillium wilt.

Olive Knot

Olive knot, caused by the bacterium Pseudomonas savastanoi, is a bacterial disease. The disease affects the branches, causing them to form galls or knots. In severe cases, the disease can girdle the branches, resulting in reduced yield and even death. The disease can be prevented by pruning infected branches and using bactericides.

Olive Quick Decline Syndrome (OQDS)

Olive quick decline syndrome (OQDS) is a new disease of trees in the Bay Area, first detected in 2017. The disease is caused by the bacterium Xylella fastidiosa and affects the tree’s vascular system, leading to rapid decline and death. Symptoms include leaf scorch, wilting, and necrosis of the branches. OQDS is currently spreading in Italy, Spain, and France, and poses a significant threat to the olive industry in California. The disease can be prevented by using disease-free planting material and practicing good sanitation.

Olive trees are one of the oldest cultivated plants in the world.

Olive trees have been cultivated since biblical times and are believed to be among the first domesticated fruit trees. Olive oil has been an important part of Mediterranean diets for thousands of years with the olive first cultivated in Crete, where it still grows wild today. The earliest evidence of domesticated olives comes from sites in southern Turkey that date back at least 7,000 years ago; however, there are also reports that cultivation began even earlier in present-day Palestine.

Learn more about trees in the Bay Area

Is an olive a fruit?​

Yes, an olive is a fruit. More specifically, it is a drupe, which is a type of fruit that has a fleshy outer layer and a hard inner layer that contains the seed.
Olive Fruit

How to distinguish an olive tree from other trees?

Olive trees are distinguished by their leaves which are often shiny and smooth, with no hairs or prickles.

The olive tree grows in pairs at the base of its branches. These pairs of leaves grow opposite each other on the stem and have short stalks called petioles that attach them to their branches. The shape of an olive leaf is elliptical or lanceolate in outline, meaning it has a long point at one end like an arrowhead. This shape helps maximize surface area for photosynthesis while minimizing surface area for evaporation during dry weather.

Take Care of Your Trees

Proper tree care is essential to maintaining healthy growth and longevity. To take care of your trees, you should water them deeply and regularly, especially during hot and dry months. Avoid overwatering, as this can cause root rot and other problems. A layer of mulch around the base of the trees can help conserve moisture and regulate soil temperature. To prevent rot, make sure not to pile mulch too high against the trunk.

Pruning trees regularly helps maintain shape and structure, removes dead or diseased wood, and promotes healthy growth. Pruning should be done during the dormant season, typically late winter or early spring. In the spring or early summer, fertilize your trees to provide them with the necessary nutrients for growth. Monitoring for signs of pests and disease and taking action immediately when necessary is also important for protecting your trees. Seasonal care such as removing fallen leaves in autumn, providing extra protection during winter, and monitoring for pests and disease all year round, is crucial for the health of your trees. With time and attention, proper tree care can result in healthy and long-lasting trees.

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