Have the pea plants in your garden turned white?
If you look at the photo below, you will see that new (uninfected) growth is bright green, as it should be. Everything else on the plant looks bleached. That bleaching is symptomatic of a fungal disease known as Fusarium wilt.
Like Verticillium wilt, Fusarium wilt is a common vascular disease in which a fungus, Fusarium oxysporum, clogs vascular vessels. It’s pretty much the coronary artery disease of the plant world. In addition to bleaching, common symptoms of Fusarium wilt include chlorosis, stunting, damping off, brown veins, necrosis, and premature leaf drop.
This soil pathogen occurs worldwide. Rain, water splash, tools, infected seeds, and transplants can all carry the disease. Fusarium wilt enters a healthy plant when germinating spores (mycelia) stab at the plant’s root tips and any damaged root tissue. That’s where some amazing thing starts to happen!
The Fusarium oxysporum fungus has no known sexual stage. Instead, it produces three different asexual spores: microconidia, macroconidia, and chlamydospores. The germinating spores (mycelia) inject themselves into a plant’s root system. From there, the mycelia move through the cells of the root cortex and into the xylem (a plant vein). Then, it starts producing microconidia (asexual spores). The microconidia join the sap stream for a free ride to the rest of the plant. Eventually, there are so many microconidia that a vein is blocked. That’s when they germinate.
The vein blockage stops the plant from absorbing and moving nutrients, so the stomas close, the leaves wilt, everything looks bleached, and it dies. As the plant dies, the fungus spreads throughout the plant and sporulates. [Cool word, right? It means “to produce spores”]
Plants affected by Fusarium wilt
Fusarium wilt attacks many garden plants and can specialize according to the victim. Fusarium wilt can attack peas, beans, tomatoes, tobacco, sweet potatoes, cucumber, other cucurbits, and even banana plants! When Fusarium attacks cabbages and other cruciferous vegetables, yellowing and browning leaves are the most common symptom. This particular form is called Fusarium yellows.
Fusarium wilt controls
Plants infected with Fusarium wilt must be removed and thrown in the trash. Planting resistant varieties in the garden can help prevent Fusarium wilt. Crop rotation is not an effective control method because the chlamydospores can hang out in the soil indefinitely. Some fungicides can be marginally effective.
Since Fusarium oxysporum prefers heavy, moist soil, aeration and increasing soil organic matter can improve soil structure and oxygen levels, reducing the welcome mat effect for many types of fungus. Ensuring proper drainage is the best way to avoid this garden menace.
You can grow a surprising amount of food in your own yard. Ask me how!
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