Phytophthora Gum Disease: Symptoms, Prevention, and Treatment

Phytophthora gummosis is a serious fungal disease affecting citrus trees worldwide. Caused by fungi of the genus Phytophthora , including P. citrophthora and P. parasitica , this disease can lead to a significant reduction in fruit production, a decline in tree vigor, and in severe cases, tree death. At Agrumiverse , we help citrus growers prevent and combat this disease by providing quality citrus plants and expert citrus growing advice .

Symptoms of Phytophthora Gum Disease

Symptoms of gummosis can vary depending on the species of Phytophthora and the part of the tree infected. The most common symptoms include:

• Gum exudation: A slimy gum discharge on the trunk and main branches, often the first visible symptom. The gum turns reddish-brown as it oxidizes.
• Bark necrosis: The bark around infected areas becomes dark, cracked, and may peel off in scales.
• Yellowing leaves: Leaves on infected branches may turn yellow, wilt, and then drop prematurely.
• Branch drying: Infected branches gradually dry out and die.
• Fruit Rot: Brown spots appear on fruit, often accompanied by areas of rot.
• Root Destruction: If the roots are infected, the tree may wilt without visible gum exudation.

Citrus species affected by Phytophthora gummosis

All citrus fruits can be affected by Phytophthora gummosis, but some species are more susceptible than others:

Very sensitive:

• Lemon
• Lime tree
• Grapefruits (especially the Star Ruby variety)

Sensitive:

• Orange tree
• Mandarin
• Clementine

Moderately sensitive:

• Kumquat
• Calamondin
• Limequat

Variable sensitivity:

• Satsuma mandarin (depending on the variety)
• Buddha's Hand (little information available)

Factors favoring Phytophthora gummosis

Several factors can promote the development of Phytophthora gummosis:

• Excess moisture in the soil: Poorly drained soils or excessive watering create ideal conditions for the proliferation of the fungus.
• High temperatures: Temperatures between 28 and 32°C are optimal for disease development.
• Bark Wounds: Wounds, whether caused by pruning tools, insects, or weather, are entry points for the fungus.

Prevention of Phytophthora Gum Disease

At Agrumiverse , we advocate rigorous preventative measures to combat this disease. Here are some recommendations:

• Choosing a resistant rootstock: Bitter orange ( Citrus aurantium ) is often used because it has some resistance to gummosis. Other resistant rootstocks can be considered depending on the species and soil conditions.
• Ensure good drainage: Plant citrus trees on mounds to improve drainage and prevent water from accumulating around the roots.
• Manage irrigation: Avoid overwatering and ensure the soil can dry between waterings.
• Prune properly: Regularly remove diseased or damaged branches, and apply a healing sealant to pruning wounds.
• Avoid injury: Protect your trees from mechanical injury and insect or rodent attacks.

Treatment of Phytophthora gummosis

If your orchard is infected, it is crucial to act quickly to limit the spread of the disease. Here are the recommended treatment options:

• Curative treatment of lesions: Scrape off the infected parts of the bark until healthy tissue is reached, then apply a suitable fungicide to the wounds.
• Preventive foliar sprays: Sprays of fosetyl-Al (Aliette), a systemic fungicide, can be applied twice a year to protect trees from infection.

Integrated approach to the management of gummosis

An integrated approach , combining preventative measures and curative treatments, is generally the most effective method for controlling Phytophthora gummosis. It is important to consult a crop protection specialist for recommendations tailored to your specific situation. At Agrumiverse , we can advise you on best practices for protecting your crops.

FAQ

What are the first symptoms of Phytophthora gummosis?

Early symptoms include exudation of slimy gum on the trunk and main branches, bark necrosis, and yellowing of leaves.

Which citrus species are most susceptible to Phytophthora gummosis?

The most susceptible species include lemon, lime and grapefruit, especially the Star Ruby variety.

How to prevent Phytophthora gummosis?

Prevention involves choosing resistant rootstocks, improving soil drainage, rigorous irrigation management, and avoiding tree injuries.

What are the factors that promote Phytophthora gummosis?

Contributing factors include excess moisture in the soil, high temperatures, and injuries to the bark.

What is the recommended treatment for Phytophthora gummosis?

Treatment includes cleaning infected lesions and applying fungicides such as fosetyl-Al (Aliette).

Why is it important to adopt an integrated approach to Phytophthora gummosis?

An integrated approach combining prevention and treatment helps limit the spread of the disease and protect long-term tree health.