By: Mary Ellen Ellis
The fungus that causes sweet potato stem rot, Fusarium solani, causes both field and storage rot. The rot can affect leaves, stems, and potatoes, creating large and deep lesions that ruin the tubers. You can prevent and control this infection with some simple measures.
The signs of a Fusarium infection, also known as root rot or stem rot, may be seen in the plants in your garden or later in the potatoes that you store. Rotting sweet potato plants will show early signs on the tips of young leaves, which turn yellow. Older leaves will then begin to drop prematurely. This can result in a plant with a bare center. The stems will also begin to rot, right at the soil line. The stem may appear blue.
Signs of the disease in the sweet potatoes themselves are brown spots that extend well into the potato. If you cut into the tuber, you’ll see how deeply the rot extends and you may also see white mold forming in cavities within the areas of rot.
There are several ways to prevent, minimize, and control this fungal disease in sweet potatoes to reduce crop losses:
It is important to watch for signs of this infection because, if left unchecked, it will ruin many of your sweet potatoes, rendering them inedible.
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The most serious diseases can be avoided by home gardeners by following sound, sanitary garden practices:
* Use the best-quality seed or slips possible. Look for "certified" slips and seed potatoes.
* If possible, find plants of disease-resistant varieties.
* If you store your own seed stock, keep it away from your kitchen potatoes to prevent any diseases that strike them from reaching the seed potatoes.
* Consider treating seed stock with a seed protectant or fungicide before bedding them.
* Use clean soil in hot beds and cold frames if you can. Change the soil each season, replacing the old soil with soil from a section of garden that hasn't grown sweet potatoes for several years.
* Rotate the crop. Wait three years before planting sweet potatoes back in the same place.
* Till or spade in all crop residues after the harvest to remove breeding grounds for diseases and pests.
* Never use "volunteer" slips that sprout from roots left in the ground after the season.
Fusarium (also known as stem rot, yellow blight or blue stem)
Fusarium is one disease common to many gardens. It's caused by a fungus that can live for several years in the soil on decaying vegetation and can pass from diseased seed stock to the plants. The youngest leaves on the plant lose their vibrant color and turn yellow between the veins. The vines wilt, and the stems darken inside. There is no known control. Pull out infected plants to prevent spreading.
Soft rot (rhizopus rot)
Soft Rot attacks sweet potatoes after harvest. The decay begins in wounds or bruises that haven't healed. It shows first as a white, whiskery mold and quickly claims the whole potato. To avoid this disease, cure your sweet potatoes carefully and don't bump or injure them while harvesting.
Nematodes can be a problem in southern gardens. There are several species of these microscopic aquatic worms. They can stunt plant growth, kill root systems and cut down on your yield. It's very hard to deal with a bad nematode infestation. Specific rotations of cover crops and vegetable crops, as well as soil solarization (using 4-mil-thick clear plastic) are viable control measures. If you're experiencing nematode-caused problems, ask your local cooperative extension agent for advice about handling the situation.
Several kinds of insects and soil grubs can damage the sweet potato crop, but home gardeners don't usually have any serious problems. In the North, for example, flea beetles may bother the plants just after you set them out, but that's usually not a big problem.
In the South, the sweet potato weevil and the sweet potato beetle are two common pests. The larvae of the weevils, also known as root borers, eat down through the plant from the stems, tunneling into the roots. They occasionally emerge from sweet potatoes in storage. Damaged potatoes taste bitter. Throw them away.
Weevils don't hibernate. To keep them in check, you have to remove their food supply by tilling in or disposing of crop residues after the harvest.
The larvae of the sweet potato beetle feed on the leaves of the plant. Sometimes they eat entire leaves, causing the plants to wilt and die.
Some other pests may damage vines and leaves, but sweet potato plants grow so fast that for many home gardeners the bugs can't keep up with the leaves.