Lack of vigor or sudden death by the phytophthora root and crown rot is nearly always caused by too much water.
The name is from the Greek phytón (plant) and phthorá (destruction), so the name Phytophthora means the plant-destroyer. There are different types of Phytophthora that attack different host plants.
What is Phytophthora root and crown rot?
Phytophthora [fie-TOF-ther-uh ] is a family of water molds, called oomycetes. Oomycetes fall somewhere between fungi and algae in the web of life. There are many different types of Phytophthora molds. They generally attack stems and roots. Stem damage normally occurs at or just above the crown, where the stem meets the roots, at the soil line, though it can also occur elsewhere on a plant. These molds cause many different plant diseases, including sudden oak death, potato blight, damping-off disease, and crown rot. Phytophthora root and crown rot, in particular, can kill a tree or shrub if the soil remains wet for too long, or when planted too deeply. [Moist soil around the trunk is never a good idea.]
Nearly all fruit and nut trees, including cherries and kiwifruit, are susceptible to Phytophthora root and crown rot. But so are alfalfa, and members of the nightshade and cabbage families. This means tomatoes, eggplant, and potatoes are vulnerable, as are kale, cauliflower, Brussels sprouts, broccoli, kohlrabi, horseradish, cabbage, collards, turnips, rutabagas, radishes, bok choy, and mustard. And all because of too much water.
Symptoms of Phytophthora root and crown rot
Plants affected by Phytophthora root and crown rot look drought stressed. This is particularly unfortunate because the natural response is to provide more water - the last thing you want to do when Phytophthora is present. Symptoms normally start in just one branch or area of the tree or shrub before spreading to the rest of the plant. Leaves may turn purple or reddish. Sudden wilting and plant death may occur when the basal stem or crown are attacked, or the mold may attack the root system, causing plants to linger poorly for years before dying.
Symptoms can vary greatly, depending on the type and age of plant, the plant’s genetic resistance to infection and overall health, as well as soil temperatures and moisture levels, but you will probably see darkened areas of the bark around the crown and upper roots of infected plants. You may also see dark sap or gum oozing from damaged areas. Using a sharp knife, you can cut away an area of bark. Infected trees will show reddish brown streaks or patches. Water-soaked areas on roots may also be visible. If you also see white threads between the bark and the inner layer, or around the roots, the infection is from Armillaria root rot, rather than Phytophthora.
Preventing Phytophthora root and crown rot infestation
Proper water management is the best way to prevent and control Phytophthora root and crown rot. Never allow standing water to remain around tree and shrub trunks. Also, don’t let sprinklers hit tree trunks. These other tips can help you manage Phytophthora in your garden or landscape:
You may be able to maintain an infected plant, with proper irrigation and good cultural practices, but it will never be the same. Phytophthora can stay in the soil for many years, so prevention is far easier than control.
NOTE: One new-to-us variety, Phytophthora tentaculata, is on the Dept. of Agriculture’s watch list. If it appears in your garden or landscape, please contact your local Cooperative Extension Office right away. They may have helpful advice that will protect your plants, and they need to know how far this disease is spreading.
You can grow a surprising amount of food in your own yard. Ask me how!