Compendium of Sweetpotato Diseases, Pests, and Disorders, Second Edition

Second Edition

Compendium of Sweetpotato Diseases, Pests, and Disorders, Second Edition

Sweetpotato Diseases, Pests, and Disorders

Clark, Ferrin, Smith, and Holmes, editors

Compendium of

APS PRESS

Introduction

Importance and Utilization of Sweetpotato The sweetpotato is an important crop in many areas of the world. Approximately 75% of the world’s sweetpotatoes are grown in China, where the crop ranks second to rice in terms of production. Sweetpotato is grown on all continents except Antarctica, and it ranks seventh among all crops worldwide in total food production. These facts underscore the crop’s suitability for a wide range of climates and altitudes.

The sweetpotato plant is versatile and can be adapted to high-­ and low-­input agricultural systems. For example, it is grown commercially as a row crop in production systems that are characterized by a high degree of mechanization and technological inputs, such as those found in the United States, Japan, and Australia. The crop also thrives in production systems that are labor intensive and characterized by a lack of technological inputs, such as the use of herbicides and fertilizers. In addition, sweetpotato genotypes can be selected to fit the needs of particular uses and consumer groups. The crop’s ability to thrive in low-­input environments renders it a viable option for production and consumption in regions where food insecurity is a persistent problem.

How sweetpotato is used depends largely on where it is grown. In general, staple-­type cultivars have white-­to cream-­ colored flesh and higher content of dry matter, starch, and protein than dessert-­type cultivars. Dessert types generally have orange flesh and higher content of ß-­carotene and simple sugar than staple types. High dry matter and high starch content are important for industrial uses and animal feed; high protein content is also needed for animal feed. The Highlanders in Papua New Guinea rely on sweetpotato as a staple food, using it to meet 60–­90% of their energy requirement and as a major source of protein. In China, sweetpotato is utilized for human consumption, as animal feed and secondary products, and for industrial purposes. In the United States, sweetpotato is produced for consumption as a supplemental vegetable and is traditionally associated with holiday meals in many regions.

Sweetpotato is a high-­energy food. Its storage roots have a total carbohydrate content of 25–­30%, of which 98% is considered easily digestible. Sweetpotato provides an estimated 113 cal/100 g, whereas potato provides 75 cal/100 g. Despite the caloric difference between the two, potato may elevate blood sugar content more than sweetpotato; thus, sweetpotato is often preferred for persons with diabetes. Sweetpotato is an excellent source of provitamin A carotenoids. An average serving of a dessert-­type cultivar provides 5,345 international units (IU) of vitamin A per l00 g, or 121% of the recommended dietary allowance. However, different types and cultivars vary in

carotene content over the range of 0–­8,000 IU/100 g. Sweetpotato also is a source of vitamin C (20–­30 mg/100 g), potassium (200–­300 mg/100 g), iron (0.8 mg/100 g), and calcium (11 mg/100 g). The amino acid content is relatively well balanced, with a higher percentage of lysine than rice or wheat but a somewhat limited content of leucine. However, like most other starchy root and tuber crops, sweetpotato has relatively low protein content, ranging from 2.5 to 7.5% of dry weight, depending on the genotype. Eating a combination of legumes and sweetpotato could combat protein-­calorie malnutrition in some areas of the world. Current studies of the role of vitamin A and fiber on long-­range human health may further enhance the nutritional “fingerprint” of sweetpotato.

Historically, sweetpotato used as animal feed has been a by-­ product of crops grown for human consumption. In the United States, only sweetpotatoes culled from grading lines or left in the field after harvest have been fed to animals. However, in Asia, the use of sweetpotato as animal feed is increasing.

Unfortunately, the roots contain sufficient amounts of trypsin inhibitor to require heat inactivation of the inhibitor before feeding sweetpotato to animals in large quantities. Technologies are currently being developed to produce dried sweetpotato products suitable for both storage and subsequent use as animal feed.

Sweetpotato has the potential for industrial uses, and available germplasm includes genotypes with greater yield and dry matter, which will be required for these uses. Although initial efforts to use sweetpotato as a source of starch in the United States were not economical, the plant is used for industrial production of starch in Japan. It is also a potential raw material for ethyl alcohol production: 100 kg of fresh sweetpotato can yield 14.5 L of ethanol, compared to 11.4 L from potato; 11.9 L from sugar beet; 17.6 L from wheat, barley, and oats; and 44.9 L from maize. However, since sweetpotato generally brings a relatively high price when marketed for human consumption, growing the crop exclusively for ethanol production is not economically feasible at present.

Selected References Bouwkamp, J. C., ed. 1985. Sweet Potato Products: A Natural Resource for the Tropics. CRC Press, Boca Raton, FL. Edmond, J. B., and Ammerman, G. R. 1971. Sweet Potatoes: Production, Processing, Marketing. Avi, Westport, CT. Villareal, R. L., and Griggs, T. D., eds. 1982. Sweet Potato, Proceedings of the First International Symposium. Publ. 82-­172, Asian Vegetable Research and Development Center, Tainan, Taiwan.

Woolfe, J. A. 1992. Sweet Potato: An Untapped Food Resource. Cambridge University Press, Cambridge, England.

(Prepared by A. Villordon) 1

What’s in a Name?

There is a long list of names commonly used for the sweetpotato in various regions of the world, but interestingly, people in widely separated geographic groups use variations of only three names: batatas, kamote, and kumara. Use of these common names has created confusion as to the identity of the crop produced from the Ipomoea batatas plant, especially in the United States. Unfortunately, this confusion has sometimes led to uncertainty over how to handle and market the crop.

In the United States, sweetpotato production before the 1930s involved predominantly cultivars with white-­or light-­ colored flesh and high dry matter. As moister, orange-­flesh cultivars were developed and adopted by the U.S. industry, it became common practice to refer to sweetpotatoes as “yams.”

This name was derived from a Fulani word from West Africa, ñam or nyami, meaning “to eat,” but its introduction has caused ongoing confusion over whether people are referring to the sweetpotato or to the yam, a tropical crop.

There are numerous differences between the sweetpotato and the yam. The sweetpotato, I. batatas, originated in the tropical Americas and is in the dicotyledenous morning glory family, Convolvulaceae, whereas the true yam, Dioscorea spp., originated in Africa or Asia and is in the monocot family Dioscoreaceae. Other important differences are that the sweetpotato produces storage roots that generally have thin, smooth skin and is short with tapered ends, whereas a true yam produces tubers that have a rough, scaly skin and are generally long and cylindrical. When cooked, sweetpotato storage roots have a sweeter taste and moister feel in the mouth than a true yam, which has a starchy taste and texture. When sweetpotatoes labeled as “yams” are sold in the United States, the label must also include “sweetpotatoes” in an effort to reduce confusion among consumers.

The word potato is thought to have been derived from the Incan name for sweetpotato, which is papa or bappa. However, Spanish expeditionary forces confused sweetpotato and potato and misapplied the derivative words bappata, patata, and eventually potato to Solanum tuberosum L. In recent years, controversy has also developed over the seemingly mundane issue of whether sweetpotato should be spelled as one word or two. The National Sweetpotato Collaborators Group—­consisting of research, extension, and industry personnel who work with sweetpotato in the United States—­adopted the one-­word spelling in 1989 for two primary reasons: (1) to reflect the fact that this is a unique crop and not a sweet version of potato (also known as Irish potato, white potato, and S. tuberosum) and (2) to be consistent with the multitude of other crops with compound names that use one-­word spellings (for example, eggplant, grapefruit, sugarcane, watermelon, etc.). The U.S. Department of Agriculture has also adopted the one-­word spelling, as reflected in its PLANTS Database and other publications.

For these reasons, the editors have chosen to use the one-­ word spelling of sweetpotato in this compendium. However, the International Committee on Taxonomy of Viruses, which approves virus names, has not yet been adopted the one-­word spelling for the host portions of virus names. Some other organizations also continue to use the two-­word spelling.

Schultheis, J. R., and Wilson, L. G. 1993. What is the difference between a sweetpotato and a yam? North Carolina Cooperative Extensive Service. Available online at www.ces.ncsu.edu/depts/hort/ hil/hil-­23-­a.html

(Prepared by C. Clark)

The Sweetpotato Plant The sweetpotato, Ipomoea batatas (L.) Lam., is a dicotyledonous plant in the family Convolvulaceae, the morning glory family, which also contains several important species of weeds and cultivated ornamentals. The sweetpotato is thought to have originated in Central America or South America, in the region between the Yucatan Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. Considerable evidence suggests a prehistoric spread to Oceania. Christopher Columbus is thought to have brought the sweetpotato to Europe. From there, the Portuguese are believed to have introduced the crop into Africa and into parts of Asia, and the Spaniards likely introduced it into the Philippines and into China, from where it was introduced into Japan.

The sweetpotato is a vegetatively propagated, perennial plant grown as an annual. Because it does not have a defined maturity, it can be harvested following growing seasons of varying lengths. Transplants produce adventitious roots mostly from nodes and, under certain conditions, from the cut ends (“wound roots”). The initiation of adventitious roots has been associated with transplant establishment (Fig. 1).

Under optimal field conditions, adventitious roots can be observed as early as 3 days after transplanting. In cultivated varieties, such as Beauregard, most of these adventitious roots have the capability of becoming storage roots. Within 9 days after transplanting, lateral roots can be observed growing from the main axes of adventitious roots. Lateral roots facilitate water uptake and transport and extraction of nutrients from the soil.

Selected References Averre, C. W., and Wilson, L. G. n.d. Sweetpotato—­W hy one word?

North Carolina State University, College of Agriculture and Life Sciences. Available online at www.cals.ncsu.edu/plantpath/ extension/commodities/sweetpotato-­one-­word.html Kays, S. J., Collins, W. W., and Bouwkamp, J. C. 1992. A response: The sweetpotato storage organ is a root, not a tuber. Pages 307-­ 313 in: Sweetpotato Technology for the 21st Century. W. A. Hill, C. K. Bonsi, and P. A. Loretan, eds. Tuskegee University, Tuskegee, AL.

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Fig. 1. Adventitious root development in a 15-­day-­old sweet­potato plant. (A) Adventitious roots generally arise from leaf gaps in nodes. (B) The main axis of each adventitious root gives rise to lateral or branch roots. (Drawn by Rachel Pagliocco da Silva)

The number of rows of lateral roots corresponds to the number of protoxylem elements. For example, adventitious roots with pentarch and hexarch steles have five and six rows of lateral roots, respectively.

In Beauregard, storage root initiation can be observed as early as 13 days after transplanting under optimal conditions.

Around this time, the primary cambium can be seen to form a continuous ring. Anatomically, storage root initiation is associated with the appearance of anomalous cambia around the central metaxylem cell, protoxylem arms, and secondary xylem.

Storage root initiation is associated with pentarch and hexarch stele configurations. Under optimum growing conditions, initiated storage roots are initially visible as localized swellings on Beauregard adventitious roots starting at 25 days (Fig. 2).

Storage root expansion results from the continued activity of the primary and anomalous cambia (Fig. 3). Adventitious roots that do not become storage roots typically have lignified steles.

These lignified adventitious roots have also been referred to as “pencil roots.” The ratio between initiated and lignified adventitious roots determines in part the potential yield. It has been demonstrated in experiments that extremely high air and soil temperatures, as well as a marginal level of soil moisture, can result in reduced storage root yield because of increased lignification of adventitious roots.

The molecular characterization of storage root initiation is progressing significantly. However, a molecular model for storage root initiation is not currently available. Identification and characterization of the genes that are involved in storage root initiation and development will lead to an enhanced understanding of the conditions for storage root induction.

The sweetpotato plant is predominantly prostrate, with a vine system that expands horizontally very rapidly and develops a relatively shallow canopy (Fig. 4). Genotyopes display extensive variation in branching pattern, internode length, and vine length. Three general types have been recognized: bunch (bush), intermediate, and vining. In addition, the leaves of different genotypes vary widely in size, length of the petiole, and shape, from deeply indented or lobed to broad and entire. The

Fig. 2. Adventitious root development in a 30-­day-­old sweet­potato plant: (A) initiated storage roots in the early bulking stage and (B) lignified adventitious roots. (Drawn by Rachel Pagliocco da Silva)

shapes and sizes of leaves may also vary considerably on a single vine.

Sweetpotato flowers are complete, with a compound and superior pistil, five stamens attached to the corolla but not attached to each other, and petals united into a trumpet-­shaped corolla. The corolla is usually white around the entire margin, with a pink to purple throat. Seed are borne in a capsule and have a very hard coat. Seed do not have a strong physiological dormancy but are generally scarified mechanically or with acid to promote germination. Seedlings have characteristically bilobed cotyledons, similar to those of many morning glories.

Sweetpotato is a hexaploid with 90 chromosomes, whereas most species of Ipomoea have 30 chromosomes. Given this difference, there has been considerable speculation and controversy on the genetic origin of sweetpotato. One suggestion is that it involved a cross between a tetraploid progenitor (possibly I. trifida auct. non (Kunth) G. Don. p.p.) and a diploid.

In favorable environments, sweetpotatoes set relatively few viable seed. Many genotypes do not flower readily, if at all.

Flowering can be enhanced by training the vines onto trellises or by grafting onto other Ipomoea spp. as rootstocks.

I. setosa Ker Gawl. and I. trichocarpa Elliott are frequently used for this purpose. Some genotypes are sterile, producing defective pollen. Self-­ compatibility, self-­ incompatibility, cross-­ compatibility, and cross-­ incompatibility all exist in sweetpotato; however, self-­incompatibility is the predominant condition. Several cross-­incompatibility groups exist among the available pool of sweetpotato germplasm. These factors, combined with the hexaploid constitution, make genetic studies difficult. Nevertheless, considerable improvements have been made in sweetpotato through breeding.

Selected References Edmond, J. B., and Ammerman, G. R. 1971. Sweet Potatoes: Production, Processing, Marketing. AVI, Westport, CT. Firon, N., Labonte, D., Villordon, A., McGregor, C., Kfir, Y., and Pressman, E. 2009. Botany and physiology: Storage root formation

Fig. 3. Progression of storage root development in a sweet­ potato plant: (A) a storage root in an advanced stage of development, (B) lignified adventitious roots, and (C) newly initiated adventitious roots. (Drawn by Rachel Pagliocco da Silva)

Fig. 4. Schematic of a sweet­potato plant. The root system is comprised of (A) storage roots that were initiated during the first 30 days, (B) late-­forming storage roots, and (C) lignified adventitious roots. (Drawing by Rachel Pagliocco da Silva)

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and development. Pages 13-­26 in: The Sweetpotato. G. Loebenstein and G. Thottapilly, eds. Springer, Berlin.

Kays, S. J. 1985. The physiology of yield in the sweet potato. Pages 80-­ 132 in: Sweet Potato Products: A Natural Resource for the Tropics.

J. C. Bouwkamp, ed. CRC Press, Boca Raton, FL. Togari, Y. 1950. A study of tuberous root formation in sweet potato.

Bull. Nat. Agric. Exp. Stn. Tokyo 68:1-­96.

Villareal, R. L., and Griggs, T. D., eds. 1982. Sweet Potato: Proceedings of the First International Symposium. Publ. 82-­J72, Asian Vegetable Research and Development Center, Tainan, Taiwan.

Villordon, A. Q., LaBonte, D. R., Firon, N., Kfir, Y., Pressman, E., and Schwartz, A. 2009. Characterization of adventitious root development in sweetpotato. HortScience 44:651-­655.

Wilson, L. A., and Lowe, S. B. 1973. The anatomy of the root system in West Indian sweet potato (Ipomoea batatas (L.) Lam.) cultivars.

Ann. Bot. (Lond.) 37:633-­643.

Yen, D. E. 1974. The Sweet Potato and Oceania. Bishop Museum Press, Honolulu, HI.

(Prepared by A. Villordon)

Cultivation and Storage Sweetpotato tolerates a wide range of growing environments.

However, the crop typically requires a minimum frost-­free period of 120–­150 days and thrives when the minimum daily temperature is above 24°C. Once storage roots have been initiated, sweetpotato can withstand periods of moisture deficit. Under irrigated conditions, it does well with approximately 2 cm of rain or irrigation per week, uniformly distributed during the growing season. Production is favored by well-­drained, fine, sandy loam soils. Sweetpotato grows well over a wide range of soil pH (4.5–­7.5). However, adjustment of pH may be necessary in areas where soil acidity or alkalinity contributes to other problems. For example, aluminum toxicity can be a problem in acidic soils. Conversely, reduction of the pH to 5.2 may be necessary in fields with a history of Streptomyces soil rot (pox), the disease caused by Streptomyces ipomoeae.

Cultivation strategies vary in tropical regions, where plants are produced and maintained in the field throughout the year, versus more temperate regions, where roots are stored during the winter months to serve as the source of “seed” for sprout production for the subsequent crop. Thus, production in temperate regions requires more extensive production inputs, such as storage facilities with the capacity to maintain a protected environment and additional land for the production of plants from roots.

Fig. 5. Sweet­potato beds in various stages of preparation. Part of the bed in the middle has been covered with soil, and the bed on the left has been covered with clear plastic mulch to heat it and promote earlier sprouting. (Cour­tesy G. J. Holmes)

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The propagative stock used to produce sweetpotato can accumulate systemic pathogens, especially viruses (see Part I, Infectious Diseases, the section Diseases Caused by Viruses), and somatic mutations can occur, causing changes in the color and shape of storage roots (see Part III, Noninfectious Disorders, the section Somatic Mutations). Cultivars may appear to “run out,” or decline, if a good-­quality “seed” program is not followed.

In many sweetpotato-­growing areas, universities, government agencies, or grower associations operate “seed” programs to provide high-­quality propagative material for growers. These programs follow strict protocols using meristem-­tip culture and micropropagation in tissue culture, combined with evaluation for trueness to type and indexing for pathogens to provide a nuclear stock of clean planting material that is further multiplied in greenhouses and field nurseries.

Stem pieces approximately 30 cm long are used as propagative organs. These stem pieces are often referred to as cut­ tings, slips, sprouts, or transplants. In tropical areas, where the sweetpotato crop is grown continuously throughout the year, stem cuttings are obtained directly from plants of the previous crop. In temperate regions, the production cycle begins by laying roots next to each other and covering them with 2–­5 cm of soil in long, rectangular plots (60–­80 cm wide) called plant beds (Fig. 5). For maximum sprout production, it is generally recommended that the roots be presprouted at 25–­30°C and 90% relative humidity for 2–­4 weeks prior to bedding.

Each root has the potential to produce many sprouts suitable for transplanting beginning 4–­6 weeks after bedding. Roots continue to produce sprouts for several weeks under favorable conditions. The sprouting potential of individual roots depends on the genotype and root size, as well as cultural conditions, including freedom from disease. Approximately 0.8–­1.5 t of roots is required to produce enough transplants to plant 1 ha of sweetpotato. For comparison, the yield of U.S. No. 1 roots in the United States ranges from 10 to more than 30 t/ha. This method of propagation requires a significant proportion of each crop for the production of the next crop. Plants cut above the soil surface (Figs. 6 and 7) and slips pulled from plant beds (Fig. 8) have been used for transplanting, but the use of cuttings is generally recommended to avoid carrying root-­and soilborne pathogens or pests to the field.

Transplanting can be as simple as pushing transplants into the soil with a notched stick, or it may involve transplanting machines, in which workers put the transplants in a machine that then places them in the soil at set distances (Fig. 9). In row-­ based production systems, the recommended planting density generally varies with the genotype and the agricultural machinery and implements used for planting and harvesting;

Fig. 6. Cutting crew harvesting sweet­p otato transplants from plant beds. (Cour­tesy G. J. Holmes)

the environmental variables, such as soil moisture and air and soil temperature; and the intended market of the crop. Typically, transplants are planted in rows 80–­100 cm apart, with 17–­26 cm between plants (Fig. 9). The rows may be prepared as level or raised beds, depending on local requirements. Raised beds are generally preferable to flat beds when it is necessary to improve drainage. The roots develop to a harvestable size in 90–­150 days, depending primarily on the genotype and environmental variables.

Fertilizer requirements for sweetpotato are dependent on cultivar, local soil type, previous condition of the soil, and environmental factors, such as leaching of nutrients in areas of high rainfall. In many areas, such as in the Gulf of Mexico production region of the United States, nitrogen and phosphorus are

used in relatively moderate amounts compared to potassium.

Local soils may require applications of minor elements. Boron deficiency is common in some soils, and if not corrected by the addition of borax, it may result in mild stunting and superficial necrosis on roots. (Further details on the nutritional requirements of sweetpotato can be found in Part III, the section Nutrient Disorders.)

Systems for harvesting and storing sweetpotatoes also vary significantly between tropical and temperate areas. In tropical areas, sweetpotatoes are often harvested piecemeal by hand or with a digging stick and only when needed. When they are stored, they may be placed in variations of field clamps or bunkers similar to those used in the United States many years ago (Fig. 10). The harvesting of sweetpotato roots has not been fully automated, particularly in regions where they are stored and used for human consumption. In many areas of the world, the roots are dug entirely by hand as needed. In the United States, they are dislodged from the soil by various implements, such as modified mold-­board or disc plows and chain diggers (Figs. 11 and 12). Hand labor is the predominant method of lifting the roots from the soil into containers for storage (Fig. 13), but in many cases, harvesters are designed to allow workers to work in the shade and at waist height (Fig. 14). However, recent developments in the processing industry have spurred research and development in bulk harvesting and handling through the use of mechanized equipment. The use of mechanical harvesters substantially reduces labor requirements and production

Fig. 7. Cuttings from sweet­potato plant beds.

(Cour­tesy G. J. Holmes)

Fig. 9. Transplanting sweet­potatoes via machine in the United States. (Cour­tesy G. J. Holmes)

Fig. 8. Slips pulled from sweet­potato plant beds with adventitious roots that formed below the soil surface. (Cour­tesy G. J. Holmes)

Fig. 10. A bunker or field clamp, used for storing sweet­potatoes many years ago in the United States. Storage roots were placed in layers of straw, covered with soil, and removed when needed.

(Cour­tesy P. Dukes)

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Fig. 11. Sweet­potatoes being turned out by a four-­row disc plow at harvest to be picked up by hand. The vines were mowed several days before harvesting. (Cour­tesy G. J. Holmes)

Fig. 12. Sweet­p otatoes being dug and dropped back to the ground using a four-­row chain digger for pickup by hand. (Cour­ tesy T. P. Smith)

Fig. 13. Hand labor is still widely used to collect marketable roots immediately after digging. When done properly, this method results in the least amount of wounding to roots. (Cour­ tesy G. J. Holmes)

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Fig. 14. A crew harvesting sweet­potatoes using a riding chain digger. Chain digging is often combined with field grading to provide shade for and reduce stooping by field laborers. (Cour­tesy D. Ferrin)

Fig. 15. A sweet­potato bulk harvester requires minimal labor but does not allow for grading sweet­potatoes. (Cour­tesy T. Smith)

Fig. 16. Palletized 40-­ bushel bins filled with sweet­ potatoes.

Fresh-­market sweet­potatoes are stored in this type of bin, which can be moved with a forklift. (Cour­tesy G. J. Holmes)

Fig. 17. Curing and storage room for sweet­potatoes. Fans on the back wall draw air through the storage bins and discharge it back into the room for uniform heating and cooling. (Cour­tesy G. J. Holmes)

Fig. 18. Sweet­potatoes in bulk pile storage. (Cour­tesy Theresa Arnold)

Edmunds, B., Boyette, M., Clark, C., Ferrin, D., Smith, T., and Holmes, G. 2008. Postharvest Handling of Sweetpotatoes. N.C. Coop. Ext. Serv. Bull. AG-­413-­10-­B,

costs. Mechanically harvested sweetpotatoes are subsequently subjected to bulk handling to support the capacity and speed of processing plants (Fig. 15).

In both harvesting scenarios, the cultivars that now enjoy wide acceptance in the United States (and presumably, the cultivars popular in many other parts of the world) are susceptible to significant injuries from handling. These injuries predispose the roots to many organisms that require wounds for infection.

The most common among these organisms are Rhizopus and Fusarium spp. Curing the roots immediately following harvest and before storage reduces the likelihood of disease developing. Harvested roots are cured by promptly moving them into storage maintained at 30°C and 90% relative humidity for 5–­7 days. This environment stimulates the rapid synthesis of a periderm layer on the root surface. Any wounds are “healed” by the curing process and protected from invasion by pathogens. To prevent further wounding of the periderm, roots should not be moved after placement in storage. They should be held in storage at 16°C until marketed or used as a source of propagating material for the next cropping cycle.

Sweetpotatoes should not be stored at temperatures less than 15°C. In traditional U.S. production, sweetpotatoes are stored in bins holding 20–­40 bushels or more (Figs. 16 and 17), but sweetpotatoes for processing are sometimes stored in bulk piles, similarly to how potatoes are stored (Fig. 18).

In summary, sweetpotato production can be divided into six major operations: (1) the acquisition and production of vegetative propagation material, (2) the planting of transplants, (3) the growing of plants for root production, (4) harvesting, (5) curing, and (6) storage. Disease management should be integrated into each operation.

Selected References Edmond, J. B., and Ammerman, G. R. 1971. Sweet Potatoes: Production, Processing, Marketing. AVI, Westport, CT.

(Prepared by C. Clark; revised by A. Villordon)

Sweetpotatoes as Ornamental Plants Sweetpotato is well recognized as a staple food crop for human and animal consumption. Although many species of Ipomoea have been used as ornamentals—­including moonflower (I. violacea L.), cypressvine (I. quamoclit L.), and numerous cultivars of morning glory—­the sweetpotato was not used much as an ornamental plant before the 1990s. Since then, ornamental sweetpotatoes have become quite popular and can be found cascading from hanging baskets and planters or being used as ground cover in many locations.

The availability of cultivars for these purposes has expanded from the original Blackie, with purple to black leaves, and Margarita, with chartreuse leaves, to include plants with an array of leaf shapes, growth habits, and colors, including tricolored bronze-, red-, and green-­leafed cultivars (as portrayed on the back cover of this compendium). Certain cultivars may also produce attractive flowers.

Ornamental sweetpotatoes may carry some pathogens (such as Sweet potato leaf curl virus) or insect pests (such as sweetpotato weevil) that can have detrimental effects on the production of vegetable sweetpotatoes. Even so, diseases and pests do not yet seem to have a serious impact on the use of ornamental cultivars in the landscape.

Selected Reference Armitage, A. 1999. Specialty annual series: Sweet potato. Greenhouse Grower, Mar., pp. 103-­104.

(Prepared by C. Clark)

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