Cotton Root Rot On Citrus Trees: Treating Citrus With Cotton Root Rot Disease

Cotton Root Rot On Citrus Trees: Treating Citrus With Cotton Root Rot Disease

By: Bonnie L. Grant, Certified Urban Agriculturist

Citrus trees provide us with the fruits for our favorite juices. These warm region trees have a host of potential disease issues with cotton root rot one of the more serious. Cotton root rot on citrus is one of the more devastating. It is caused by Phymatotrichum omnivorum, a fungus which attacks over 200 types of plants. A more in-depth look at citrus cotton root rot info can help prevent and combat this serious disease.

What is Citrus Phymatotrichum?

Fungal diseases in fruit trees are very common. The Phymatotrichum omnivorum fungus attacks many plants but really causes issues on citrus trees. What is citrus Phymatotrichum rot? It is a disease also known as Texas or Ozonium root rot, which can kill citrus and other plants.

Diagnosing cotton root rot on citrus can be difficult because initial symptoms seem to mimic many common plant ailments. The first signs of an infected citrus with cotton root rot appear as stunting and wilting. Over time, the number of wilted leaves increases, becoming yellow or bronze instead of healthy green.

The fungus progresses rapidly with the top foliage showing signs first and the lower within 72 hours. Leaves die by the third day and remain attached by their petioles. Around the base of the plant, cottony growth can be observed. By this time, the roots will have become fully infected. Plants will easily pull out of the ground and decayed root bark can be observed.

Control of Citrus Cotton Root Rot

Citrus with cotton root rot often occurs in Texas, western Arizona and the southern border of New Mexico and Oklahoma, into Baja California and northern Mexico. Symptoms usually show up from June to September as soil temperatures achieve 82 degrees Fahrenheit (28 C.).

The cottony growth on soil at the roots shows up after irrigation or summer rain. Citrus cotton root rot info explains the fungus is most prevalent on calcareous clay soil with a pH of 7.0 to 8.5. The fungus lives deeply in soil and can survive for several years. Circular areas of dead plants appear, which increase 5 to 30 feet (1.52-9.14 m.) per year.

There is no way to test soil for this particular fungus. In areas that have experienced the disease, it is important not to plant any citrus. Most citrus that is on sour orange rootstock seem to be resistant to the disease. Amending soil with sand and organic materials can loosen soil and make roots less likely to become infected.

Nitrogen applied as ammonia has been shown to fumigate soil and reduce root rot. In some cases, infected trees have been rejuvenated by pruning the plant back and building a soil barrier around the edge of the root zone. Then 1 pound of ammonium sulfate for each 100 square feet (30 m.) is worked into the barrier with the interior of the barrier filled with water. The treatment must be done again in 5 to 10 days.

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