Though sweet potatoes are vulnerable to several diseases and a number of pest predators, keeping them safe and healthy is easy.
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Types of Sweet Potato Wilt
There are a couple of diseases that can affect the health of sweet potato plants. Sweet potatoes can be infected by several types of wilts. Wilts make the plant look droopy, like it hasn't been watered. The leaves can suddenly shrivel up and fall off. Some wilts are highly contagious.
You can tell a plant has bacterial wilt by looking at the stem. It causes it to soften and become slimy and smelly. The bacteria can live in the soil where it can affect plants season after season. Since this bacteria can survive in the ground for up to 5 years, some farmers have to leave infected gardens empty for a long time. Bacterial wilt can also be spread by cucumber beetles. That's why it's important to remove any sick plant immediately. Put it in the trash, not the compost, that way you'll get rid of it for good.
Fusarium and Verticillium wilts attack many types of plants, including sweet potatoes. The first signs are yellowing leaves at the bottom of the plant. As the disease gets worse it works its way up the plant until all of the leaves turn yellow and they fall off. The stems turn brown and often split, weakening or eventually killing the plant. One way to protect against these wilts is to solarize the soil by covering it with black plastic to make the ground hot. Another way is to continue turning the soil over, letting the soil dry and heat up before turning it again.
Sweet Potato Weevil
One pest that can cause serious damage to your crop is the sweet potato weevil. It's found from North Carolina to Texas to New Jersey. These bugs have a long snout and are shaped a little like an ant. They have blue wings, a red throat and red legs. The adults live on the stems and leaves, but the real damage is clear when the sweet potatoes are harvested. The larvae of the sweet potato weevil eat the growing sweet potatoes, leaving them gnarled and bitter. If you suspect you might have weevils, dig up the most infested plant to check the young potatoes. If it's infected, throw it away; if not, very carefully replant it in the ground.
Beetles cause lots of problems for gardeners. They attack just about any and everything. There are 2 beetles that damage sweet potatoes: the yellow and black striped Cucumber beetles and pin-head sized Flea Beetles. Cucumber beetles eat young foliage, they lay their larvae in the ground where they can eat the plant roots and they spread a certain type of bacterial wilt. Flea Beetles make so many holes on plant leaves that it looks like you're growing lace rather than vegetables. Using row covers on young plants can protect them, but as soon as blooms emerge the row covers have to come off so that the flowers get pollinated.
Aphids attack vegetable plants and landscape plants. They cluster on small buds or in tight spaces between leaves. What makes them so different is that they give birth to live young, not larvae like lots of other pests. This means they can multiply quickly. These small insects suck the sap out of the host plant, leaving it deformed and stunted. Once colonies get large enough, winged aphids appear. These fly off to infest and colonize other plants, not just your vegetables. Lady bugs are great at getting rid of aphids and they're available for sale in garden centers and through mail-order catalogs.
Check Crop Often
Both diseases and pests live in the soil around a particular vegetable. Crop rotation can control and sometimes wipe out health problems. To stay on top of the health of your sweet potatoes, check them often for signs of stress. Do this by looking at the upper and lower surfaces of the leaves. Notice any drooping or discolored leaves and any pests that have made your garden their home. Sweet potatoes are often targeted by a variety of beetles. Remove any beetles from the plants as you check on your plants. By removing damaged foliage and beetles it keeps diseases and pests from multiplying.
Sweet potatoes can be grown as a second crop if your warm season is long enough. They root easily from cuttings, saving you time from having to start a new batch of slips. To take a cutting, use a clean knife to cut about 4 inches off the tip of a healthy sweet potato vine. Pull off any lower leaves, leaving only one or two at the top. Immediately dip the cut end into rooting hormone. The hormone comes as a white powder and you can buy it at any home and garden center for $5-$15, depending on the size of the jar. One jar is enough to do lots of cuttings.
Plant your cuttings in peat pots or a seed tray until roots begin to develop. This usually takes a few weeks. Water your new cuttings lightly and cover them with plastic wrap to hold the moisture in. Open the plastic once every few days to give the plants air and more water if necessary. Once the cuttings are large enough, about 5 inches tall with lots of new roots, you can move your new plants to the garden.
Sweet potatoes are ready to harvest when they're large enough to use, about 4 months after they're planted. You can check on the size of your potatoes by gently pulling the soil away from the roots with your hands. Don't pick them until they're large enough to eat.
Sweet potatoes can be stored in a cool dark place for months; you have to make sure they're clean and dry before you put them away. The best way to do this is to cure them. Lay the potatoes in the sun for a full day. Then move them to a shady well-ventilated place like a covered patio for about a week. This dries them out just enough to get rid of any pests or humidity on the skins.