The disease is mostly caused by Fusarium oxysporum. This fungal agent spreads through asexually produced sores, microconidia, macroconidia, and chlamydospores. This soil pathogen is a saprophyte feeding on dead and decaying organic matter. The fungi enters the root system of the plants and blocks the conducting vessels. This makes the leaves yellow and wilt.
A fusarium spore can survive in soil matter for many years and spreads easily through water, latching on to insects, and even plant equipment. The fungus is more viable in hot weather and becomes destructive when the temperatures of the soil and air reach anywhere between 32°-35° C; below 24° C, the symptoms aren't as aggressive.
As the infection takes a hold of the plant, it causes stunted growth and ultimately death. The pathogen doesn't hesitate to attack flowers like, lilies, carnations, coriander, zinnias, sunflowers, petunias, and foxgloves, to name a few.
When they appear on flowering plants, they form pinkish or white spores called conidia on the surface of the stems that are infected or dead. You'll notice the presence of these spores on soil close to the plant's perimeter, or in clusters on the bulbs.
How Fusarium Wilt Affects Plants
There are different host plants that are affected by this disease. These plants suffer from wilting, necrosis, chlorosis, premature leaf dropping, stunting, damping-off, etc. There are over 100 formae speciales of Fusarium oxysporum.
Most of these are specific pathogens to certain host plants. When the pathogen takes over the vascular system―the storehouse of food and water tissues―they multiple while being transported to different parts of the plant through the plant's sap.
Besides the given vegetable and fruit plants, this pathogen is also known to affect other spice- and produce-supplying shrubs, crops, and trees like, Brussels sprouts, catnip, pepper, radish, asparagus, cucumber, cumin, lettuce, kale, strawberries, sesame, turnip, and flax, to name few.
A strong fungicide will have to be used for severe cases (some infestation problems cannot be solved by using a fungicide, because it may not be available), where you'll have to first disinfect the area surrounding the infected plant(s) before fumigating the area.
Fumigate the soil with either chloropicrin (or PS) or methyl bromide, where brands like Vapam HL can be made use of. You can opt for Fusarium-resistant plants that can withstand a pathogen attack, and be sure to burn and trash dead plants far from the plantation site, backyard, or kitchen garden.
It is important to treat fungal growth when immediately noticed, and to follow the instructions of how to use a fungicide as mentioned on the product. Also, get rid of rotting or decaying parts of a plant that reveal signs of an infestation, before it gets out of control.