How does Phytophthora affect citrus trees?
According to the University of California Agriculture and Natural Resources, Phytophthora affects the whole tree or plant, and depending on severity, may actually completely destroy it. Here are the signs to watch out for:
Leaf – yellowing foliage and small shoots dying. If citrus weevils are also present on your tree, your leaves may also have notching from adults feeding on them.
Fruit – may be smaller in size and yield.
Trunk and branches – dark water soaked areas will highlight where the infection is active. Lesions will occur on the bark of the tree, as well as at the bud union. Lesions will exude sap or lots of gum, with a brown necrotic patch underneath. Lesions may spread around the circumference of the trunk slowly girdling the tree.
Phytophthora will result in overall poor tree health, a thinner canopy and failure to make new growth. When roots are directly affected, the surface of the root will become soft and appear water-soaked and discoloured. Finally, for citrus trees specifically, if you have citrus root weevil present on your tree as well, these symptoms will progress quicker and your tree will become damaged much faster.
Treatment of Phytophthora
Unfortunately, Phytophthora is not a very treatable problem. If you do notice the symptoms above in your citrus tree early, there are a couple of ways you can reduce the damage. Examining the soil line for root rot or any water-logging should be the first step. If the soil is very moist, replace it and let the crown tissue of your tree dry out.
If any gummosis has begun to occur on the branches or trunk, the best thing to do is carefully cut away the infected areas to reduce spreading.
Prevention of citrus root rot and gummosis
The best way to prevent this fungal disease from harming your citrus trees and other plants is simply by being clean, tidy and keeping a close eye on your garden. Having good water management is the top priority for reducing the threat of Phytophthora. Here are a couple of tips for water management and general garden maintenance that can help your garden thrive without any Phytophthora problems:
- Avoid prolonged soil saturation. This includes standing water around tree bases and over-irrigating your garden. Having a mist irrigation system or irrigation that only sprays the soil may be the most helpful.
- Provide good soil drainage for vegetable, fruit and other orchard plants. When there is extensive wet weather or moist conditions, you do not want the roots or crown of a plant to remain wet for more than 4 hours. It generally take 4-8 hours for Phytophthora to infect a plant.
- Avoid installing irrigated turf around the base of trees.
- Remove all weeds from susceptible plants.
- Having raised garden beds for vegetable plants may be helpful, as they provide great soil drainage.
- Finally, group plants based on their watering needs in your garden. This is to avoid waterlogging soil and over-watering plants that do not need it.
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