Previously we shared some information about sweet potatoes and why we love them. We also shared some helpful information from our consultants on successful cultivation of sweet potatoes.This week our in house entomologist Kudzi weighs in on some potential pests and insects that could attack your crops and what you can do about it.
According to Kudzi there are over 10 species of insects that could potentially attack sweet potato plant and roots. These insects can damage your plants in many ways. It could be argued that some insects may have a symbiotic and beneficial relationship with sweet potatoes, however a sudden population over growth could be potentially very damaging for your crops. In some instances this damage could occur while the crops are still in the field and could even occur while they are in storage, resulting in serious economic losses.
Below we look at three main insects that could potentially damage your sweet potato crop.
Sweet Potato weevil
Sweet potato weevils probably pose the greatest threat to your crop. They can either be black or brown. Some have described them as looking like large ants. This insects has been known to attack any and all parts of the plant. They can feed directly on the outside silky protective layer of the vines and the leaves ( epidermis) it also attacks the external surface of root bulb. A good tell-tale sign is punctures found on the storage roots . The females can also tunnel through the stems or roots and lay their eggs inside. The developing larvae also tunnel into the roots and stems while feeding. An interesting fact about the adult weevil is that it will play dead when expectantly disturbed.
The most highly recommended method of keeping weevil infestation at bay is the use of cultural control practices. Some of these methods include but not limited to : Crop rotation for 2-3 seasons where possible. Also consider the use of clean (uninfested) planting materials, especially vine tips. Weevils tend to lay eggs in the older woodier parts of the vine. Use of barrier crop such as maize especially planted in advance so that the vegetation is high and helps to restrict weevil migration.Flooding the field for 48 hours after harvest to drown weevils has proved helpful. Hilling up of soil around the base of plants to limit or fill in soil cracks. This practice can also result in increased crop yields. Lastly ash can be sprinkled onto the sweet potato plants and surrounding soil to help kill crawling insects.
Natural Biological Controls include:Ants, spiders, carabids, and earwigs. These insects are natural predators that can feed on weevils and keep their population at bay. There are times when Chemical Controls could be very useful. Dipping planting material in an insecticide solution (such as carbofuran or diazinon) for 30 minutes prior to planting can control sweet potato weevils for the first few months of the growing season
Whiteflies (bemisia) are known pests that not only attack sweet potatoes but many other agricultural crops as well like tobacco and tomatoes for instance. They can cause serious physical damage to the crop itself but they are also potential virus carriers. In sweet potatoes they are known to suck on the sweet potato plant and thereby removing sap and nutrients. The species, Bemisia tabaci, is particularly damaging pest of sweet potato crops. When they feed, they produce honeydew; sooty and black mold grows on the honeydew-covered leaves, reducing photosynthesis and quality grade thereby reducing yields.
Several Cultural controls can be used. One important control method is removing infected plants and destroying them during the growing season. After harvest, crop residue should be removed so that there are no plant materials for whiteflies to feed on during the crop-free periods. Also any plant that could potentially be an alternative host should also be removed. Biological Control: Many species of insects, mites, and spiders feed on immature and adult whiteflies. Lacewing larvae and lady beetles also prey on whiteflies.
Chemical Control : Farmers are advised to treat white fly populations before they reach outbreak levels. The immature whiteflies can be sprayed with a mixture of insecticidal soap or insecticidal oil in water and special attention should be directed toward the lower surface of the leaves where they tend to infest. Use this method sparingly as repeated applications of the same product may build high resistance levels in whiteflies. To delay and manage resistance, do not treat successive generations of whiteflies with same product. It is recommended that you rotate insecticides often.
SWEET POTATO APHIDS
Another pest insect that could damage your crops are sweet potato aphids. The adults and young ones of these soft-bodied, pear-shaped insects are usually pale to dark green but sometimes yellow.
Their method of attach is similar to that of whiteflies. They also pierce the leaves to extract sap and nutrients while feeding and could potentially transmit viruses as well. . The honeydew secreted by the aphids also promotes the development of black sooty mold on the leaves. Aphids tend to spread rapidly from field to field, transmitting a number of viral diseases. Melon aphid is a primary vector of sweet potato. These aphids are known to transmit feathery mottle virus which is a common virus in sweet potatoes.
Cultural Controls: The best mode of control for aphids is the removal of infested crops as soon as they are identified. It is also important not to rotate sweet potatoes with a crop that could be an alternative host for aphids. Sometimes blasting them off with a stiff spray of water from a hose pipe can help.Biological Controls :Natural predators such as ladybird, beetles and lacewings tend to naturally control the aphids. They both love to feed on aphids.
Chemical control: If the problem persists and just won’t go away, the first choice would be insecticidal soaps and oils that work on direct contact with the pest, and they should be and sprayed on all the leaf surfaces above and below. These will however also kill the beneficial insects so be sure to use sparingly.
For more on the pointers listed above or for more information on how to obtain potato splits or roots, a drip kit irrigation system or any other helpful resources please get in touch with us. Also please contact us if you are interested in starting your very own sweet potatoes project. We have consultants available for a one on one session on how you can get your very own project off the ground. We are happy to assist any individual, whether they are an urban or rural small-holder farmer or commercial farmer. We will also work with groups or organizations interested in getting a jumpstart on their very own project. Please contact us today for an appointment and details on how to get started on a new and exciting farming venture with us.
Collins, W. W. (1995). Sweet potato. Purdue University Center for New Crops and Plant Products. Available at: http://www.hort.purdue.edu/newcrop/cr…. [Accessed 16 April 15]. Free to access.
Webb, S. E (2015). Insect Management for Sweet Potatoes. University of Florida IFAS extension. Available at :http//edis.ifas.ufl.edu/ig159/ig159. [Accessed January 20 17]Free to access
PadillaCRT 2017. Intergrated Pest Management. North Carolina Sweet Potato Commission Available at:http://www.ncsweetpotatoes.com/sweet-potato-industry/growing-sweet-potatoes-in-north-carolina/integrated-pest-management. [Accessed January 21,2017]Free to access