Fusicoccin

Fusicoccin, or constriction canker, is a fungal disease of almonds and peaches.


You may find this word easier to say than to read at first. It is pronounced FUSE-ih-koksin. Once you say it aloud a few times, it doesn’t feel nearly as intimidating. [Unfortunately, I couldn’t find a few image, but I have a request in the works.]


When I first found this word, the disease was not present in California. Now it is. These things keep moving forward which is why we need to keep learning.


Fusicoccin is a disease that forces plants to open their stoma. Stomata are tiny breathing holes found most often on the underside of leaves, but also on stems and other tissues. Plants use stomata to create bubbles of high humidity which then evaporate, pulling moisture up a plant’s vascular system. This is how plants pull water from the ground and it’s pretty amazing when it works the way it should. When stomata stay open, plants start drying out.


Disease progression

This disease is caused by the Fusicoccum amygdali fungi, which is found throughout the United States, Argentina, China, Spain, Italy, and Hungary.  These fungi produce chemicals that acidify plant cell walls, causing stoma to open permanently. They enter plants through leaf scars and stipules in the fall and bud scars, blossoms, and fruit scars in spring. Basically, any place there is a fresh opening.


Fusicoccin symptoms

The first sign of fusicoccin is wilted leaves and shoots, followed by long, brown cankers on infected buds and nodes. These symptoms are usually seen in early summer and become worse as the disease progresses. You may see constructed areas at the base of infected shoots. Gum may be seen oozing from infected areas, but don’t use that as a diagnostic tool since gumming is a common response to several diseases and disorders. Fruit on infected stems tends to shrivel up and fall to the ground, further spreading the disease.


Managing fusicoccin

Research has shown that certain fungicides can control this disease. But many of these products can cause birth defects, cancer, and infertility. Not exactly what you want around your tomatoes and basil!


Another option is to fight fire with fire. Or, in this case, fight fungi with fungi. Trichoderma harzianum and Trichoderma viride are antagonistic fungi that work as biofungicides, parasitizing fusicoccin pathogens. Of course, they will also damage your homegrown mushrooms. As gardeners, we must choose our battles. You can buy these biofungicides online or from your local garden center.


In the case of fusicoccin, prevention involves keeping trees healthy in the first place, applying biofungicides according to package directions, and buying resistant varieties whenever possible. If fusicoccin appears on your peach or almond trees, remove infected branches by cutting several inches below the affected area and throwing those twigs in the garbage.