HORTSCIENCE 51(11):1339–1343. 2016. doi: 10.21273/HORTSCI11157-16 The Potential of Greater Chinese Chestnut (Castanea mollissima) Production in the Central Region of the United States Michael A. Schnelle1,2 Department of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater, OK 74078-6027 Additional index words. food crops, specialty crops, Castanea sp., nutrition, flowering, fruiting Abstract. Although many areas of the United States are suitable for chestnut (Castanea sp.) production, less than 1.0% of chestnuts are domestically produced with most U.S. orchards less than 30 years old. Furthermore, the majority of U.S. citizens are not accustomed to chestnuts as a mainstream nut crop but rather associate them with winter holidays. Because nearly all chestnuts are imported, agricultural producers have a significant incentive to expand U.S. chestnut production and command top dollar because of their crop being locally produced and potentially certified organic. With cultural and postharvest practices becoming more refined, growers are poised to seize this niche crop opportunity.
The United States imported 3781 t of central region of the United States, due to its given year would be worthy of a grower’s chestnuts in 2011 valued at U.S. $12.4 million pest and disease resistance as well as supe- resources and financial inputs (Michigan State (Rock Bridge Trees, 2015). Chestnut produc- rior cold hardiness when compared with University, 2015a). tion is worldwide with producers and their other chestnut species (Warmund, 2011; market share being China 40%, Korea 15%, Hunt et al., 2012). Chinese chestnut is also Italy, Turkey, and Japan about 10% each; grown with varying success in other areas of POLLINATION France, Spain, and Greece 4% and the United the Continental United States (Payne et al., Chestnuts are primarily self-sterile and thus States, Australia, New Zealand, Chile, and 1983). It continues to be favored due to its at least a second cultivar is required (Gold, Argentina, less than 1% each (Olsen, 2000). superior cold tolerance (as low as –30 C) and 2014). In chinese chestnut orchards, where all Fewer than 1600 ha of chestnut trees were in greater resistance (Warmund, 2011) (not im- trees produce pollen, the recommended or- production in the United States in 2011 (USDA munity) to chestnut blight [Cryphonectria para- chard design is to establish alternating double 2012 Census of Agriculture). Chestnuts are sitica (Murrill) Barr.] relative to other chestnut rows of a given cultivar in a repeated pattern a novelty crop for U.S. consumers and the nuts species. Chinese chestnut, while less sweet and (needing at least two cultivars). This double are primarily imported from other countries. flavorful than american chestnut, is considered row method provides diversity in the orchard United States’ consumers are not as inclined to by those most familiar with this species as better and results in excellent pollination if the purchase Castanea nuts as are consumers in tasting than European or Japanese chestnuts. nearest pollen source is no more than 20 m other regions of the world. Consumption figures Chestnut cultivars share several common sen- away. The pollen parent may influence the are 1.8 kg per capita in Korea, 0.9 kg per capita sory attributes yet differ in intensity ratings of pollinated nut, especially as it pertains to nut in China, 0.45 kg per capita in Europe, and 0.05 six descriptors. Sweetness has been associated size (metaxenia). Historically, chestnuts are kg per capita in the United States (Olsen, 2000). with consumer acceptance and can be promoted considered to be primarily wind pollinated, Various chestnut species (Castanea sp.) are in the marketplace (Warmund et al., 2011). native to all three continents of the Northern although many insects visit their flowers and Hemisphere. American producers are cur- aidincrosspollinationtoensurefruitset rently growing seedlings and cultivars of PLANTING PROCEDURES (Payne et al., 1983). Fruits are contained in chinese chestnut (Castanea mollissima Bl.), spiny cupules (involucres), 5–11 cm in diam- european chestnut (Castanea sativa Mill.), Because chestnuts bear on current sea- eter, also called burs. Burs are often clustered and interspecific hybrids of European and son’s growth, shading is detrimental to nut on the branch and typically contain up to three Japanese (Castanea crenata Mill.)selec- production. Generous spacing or aggressive nuts in chinese chestnut if all ovaries are tions. Cultivars of interspecific hybrids of pruning must be employed with the former pollinated. When producers fail to plan for chinese, japanese, and american chestnuts being more desirable. Mature chestnut trees, trees’ pollination requirements, burs may still aged 15 and above, need at least 13 · 13 m form without pollination (parthenocarpy) but [Castanea dentata (Marshall) Borkh.]also · can be found growing in the United States. to 15 15 m spacing between them. Growers without chestnuts inside. Pollinator trees are However, chinese chestnut has proven to be that elect to initiate their orchards with seed- spaced 10 to 20 m of each other to ensure cross the most reliable species particularly in the lings, either from direct seeding or young pollination and optimal nut set throughout the liners, should ideally plan on later top grafting orchard (The Center for Agroforestry at the young trees with select scion wood from University of Missouri, unpublished data). named cultivars to create uniformity and early Consequently, growers balance pollination Received for publication 12 July 2016. Accepted bearing in the orchard. With already budded or needs with chestnuts’ requirements for maxi- for publication 18 Aug. 2016. grafted cultivars directly planted in the field, mum sunlight. Ideally, chestnuts will not grow This paper was part of the colloquium ‘‘Alternative however, initial spacing is wider since fewer into one another as shading reduces flowering Specialty Crop: Opportunities and Challenges,’’ pre- trees are removed, if any, over time. Profitable and nut set and fosters overall tree decline sented at the 2015 ASHS Conference, New Orleans, commercial chestnut growers use grafted trees (Michigan State University, 2015b). Seedlings LA, on 4 Aug. 2015, and sponsored by the Working for uniformity. While chestnut growers may bear fruit, often erratically, in 4 to 7 years Group of Asian Horticulture, Tropical Horticulture experience successful yields from seedling- whereas cultivars may start bearing within 2 to Working Group, and Pomology Working Group. derived orchards, research indicates that named 3 years (Fulbright, 2012). Grafted cultivars at This paper is partially supported by the Oklahoma cultivars are often prudent and a worthwhile 9 · 9 m centers with 125 trees/ha, may yield at Cooperative Extension Service, Oklahoma State Uni- –1 versity, Stillwater, OK. investment for consistently achieving supe- least 840 kg·ha between the 6th to 9th year 1Professor and Extension Specialist rior and precocious yields. Researchers at after grafted selections are planted (Hunt et al., 2Corresponding author E-mail: mike.schnelle@ Michigan State University (MSU) estimated 2012). Once the orchard is 12 to 15 years old, okstate.edu. that only 10% of seed-grown chestnuts in any the grower may harvest up to 2240 kg·ha–1.
HORTSCIENCE VOL. 51(11) NOVEMBER 2016 1339 Trees are pruned with the goal of a standard whereas bearing chestnuts should produce from the ground at least every other day is central leader. As trees start to shade one 30 to 38 cm new growth per season (Hunt helpful. Additionally, harvested nuts bathed another at 15 years, every other tree is removed et al., 2012). Nitrogen rates, in particular, in 49 C water for 30 min effectively kills on the diagonal to leave trees on a 13 · 13 m could be adjusted based on annual average weevil eggs, followed by immediate cool spacing or 64 trees/ha. A second thinning may vegetative growth. down at 0 for storage (Gold, 2014). Japanese be necessary before chestnuts attain their final beetles (Popillia japonica Newman) are also spacing of 15 · 15 m or 42 trees/ha. BIOTIC AND ABIOTIC CHALLENGES a significant pest. They can destroy as much as one-third of the upper canopy if left uncon- CULTURAL NEEDS Biotic challenges such as mammalian trolled (M.R. Warmund, unpublished data). In pests including but not limited to deer, feral summary, chestnuts are susceptible to a num- While chinese chestnut withstands –30 C hogs, gophers, voles, mice, and rabbits are all ber of pests, diseases, and abiotic disorders when fully dormant, buds near the terminal possible to encounter in chestnut orchards. only a few of which were listed above. end of shoots may be injured by temperatures Deer are a particularly significant threat in However, the fact that some growers are slightly warmer, should a rapid temperature most chestnut-growing areas of the United successfully growing the species in an organic decrease occur. Chestnuts are early to leaf out States. Graft failures on selected cultivars fashion or a nearly pesticide-free environment in the spring following a mild winter and thus have been reported as late as 7 to 8 years after (Hunt et al., 2012) indicates that many of the are susceptible to cold injury particularly in initial grafting (e.g., with ‘Eaton’) (Hunt challenges are avoidable altogether or are the eastern United States. Researchers sug- et al., 2012). Sunscald (southwest disease or otherwise manageable through appropriate gest not planting them in frost pockets but southwest injury) may occur on young trees cultural practices such as strict sanitation. rather using sloping land to enhance cold air with thin bark. Tree trunks can be damaged drainage. Heat issues are not as critical with when temperatures rise above average for HARVEST/POSTHARVEST chinese chestnut growing down into Florida a few days in the winter followed by a sudden CONSIDERATIONS and other regions to at least USDA hardiness drop in temperature. This temperature differ- zone 9. Chestnuts are tolerant of a myriad of ential results in bark being killed often on the Most growers with 4.0 ha or less use hand soil types as long as they are reasonably well south side of the tree (Schnelle et al., 2003). labor and/or various devices to pick up nuts drained. Preferably, sandy to clay loam soils Growers can mitigate damage by painting such as the commercially available Nut with pH ranging from 5.0 to 6.5 should be young trunks with diluted (50% water/50% WizardÒ (Nut Wizard, 2016), which helps sought for a planting site. Slightly lower pH paint) white latex paint for at least their first 2 gather nuts of the orchard floor. Mechanical soils are tolerated while trees subjected to years in the field or by using white tree wraps pecan harvesters can be considered but are alkaline soils may have depressed yields. that also reflect sunlight keeping the bark usually not economically viable except for Heavy clay soils or otherwise chronically cooler and less susceptible to sunscald. Fi- growers with 4.0 ha or more (Missouri Nut wet sites are not viable planting areas. Root nally, two flowers commonly appear on Growers’ Association, 2016). Additionally, rots (Phytophthora cinnamomi Rands) are chinese chestnut in the summer without the mechanical harvesters may dislodge nuts common place otherwise although C. molli- resulting chestnuts having enough time to before they are physiologically mature result- ssima shows moderate resistance. Future hy- mature before freezing temperatures. The ing in depressed yields. Pecan (Carya illinoi- brids of chinese chestnut and other chestnuts additional nuts can overload branches caus- nensis L.) harvesters can be problematic in may be phenotyped for P. cinnamomi re- ing breakage. When two burs are removed, orchards with sod or groundcover since sistance based on lesion progression rate one nut weight is enhanced (Warmund et al., chestnuts have a flat side. When the flat side which is easily measured (Santos et al., 2010). Researchers have not yet been suc- faces the ground, the machine fails to pick up 2015). While chinese chestnut is drought cessful with chemical sprays to abort late the nuts or those buried in the groundcover. tolerant upon establishment, supplemental summer fruits nor is it practical for growers to Consequently, maximum yield potential is irrigation will be necessary when planting physically remove two flowers throughout an lost. Vacuum systems may, however, prove the orchard and during dry seasons before nut orchard of a commercial scale. useful for future mechanization. Warmund set. Drip, microsprinklers, and surface means Besides abiotic disorders, biotic chal- et al (2012) showed that with minor modifi- of irrigation are used to supplement inade- lenges such as pests and diseases can occur cations to a paddock vacuum, individual nuts quate rainfall. Even when rainfall is ade- on occasion. Chestnut gall wasp (Dryoco- were harvested 2 s faster vs. time needed per quate, first-and second-year plantings benefit smus kuriphilus Yasumatsu) is well estab- nut with mechanical harvesters. Harvesters from supplemental irrigation to ensure estab- lished in many U.S. states (Sartor et al., using a vacuum system are the best option in lishment. Nut expansion/maturation con- 2015). Researchers evaluated the effects of the eastern United States where the chestnuts tinues into the last 2 weeks before chestnuts jasmonic acid (JA) on insect galls and de- typically drop on to mowed turf. Therefore, drop to the ground. Limiting moisture before termined that cultivated chestnuts selected the chestnuts are sucked into the harvester harvest ends (normally after October) may for early budbreak and leaf expansion con- regardless of position on the orchard floor. result in depressed yields (Vossen, 2000) current with parasitoid emergence from over- Rather than planning for harvest consider- with nut weight compromised and burs wintering sites could aid in chestnut cultivars ations, some growers have begun to experi- sometimes not opening normally. Growers that promote parasitism (Cooper and Rieske, ment with U-pick days to significantly reduce practice weed control by clean tillage, mulch, 2011) Although some control has been labor inputs and sell their crop immediately. herbicide tank mix typically consisting of achieved with the parasitic wasp (Torymus Growers should wash chestnuts, discard glyphosate and pre-emergent chemical, mow- sinensis Kamijo), it is prudent to avoid floaters, and cool immediately to 0 to 0.5– ing or a combination of the above. Preplant purchasing trees or budwood in geographic 1 C for storage. Ertan et al. (2015) found that soil fertility and foliar nutrient recommen- areas heavily infested by the chestnut gall low temperature was the main factor that dations are largely based on research from wasp. However, scion wood can be heat positively affected chestnut quality. Relative other fruit and nut crops (Hunt et al., 2012). treated before grafting to eliminate gall wasp humidity should be as high as possible, but Growers often apply 112 kg·ha–1 of actual N larvae (Warmund, 2014a). Small chestnut even still protective packaging may be on a mature orchard (Olsen, 2000). Recent weevil (Curculio sayi Gyllenhal) and large needed to avoid desiccation. Growers have work on pollination treatments of chinese chestnut weevil [(C. caryatrypes) Boheman] been successful in storing chestnuts for up to chestnut (Zou et al., 2015) may help growers both damage nuts by creating entry and exit 3 months by placing them in a cool water bath make better decisions for spraying nutri- holes. Keesey and Barrett (2012) found that for 7 to 9 d and then into cold storage at –2 to ents such as N, P, and K during ovary chestnut plant volatiles can be used as attrac- 0.5 C and 70% to 80% relative humidity development to bolster nut yields. It is tants in a semiochemical-based monitoring (RH) (Vossen, 2000). Because chestnuts are recommended that nonbearing trees should trap for small chestnut weevil. Proper sani- high in carbohydrates and water, they are produce 46 to 61 cm new growth per year tation in the form of promptly harvesting nuts subject to molding and decay. Beyond 3
1340 HORTSCIENCE VOL. 51(11) NOVEMBER 2016 months of cold storage, nuts can be treated/ vitamin C, with about 40 mg per 100 g of raw times more likely to choose locally produced bathed in disinfectants such as hydrogen product, which is 65% of the U.S. recom- chestnuts (Missouri) and five times more peroxide, sorbic, propionic, or peracetic acid, mended daily intake. However, nuts exposed likely to select chestnuts anywhere else from natamycin or ozonation to prevent mold to heat will lose 40% of their vitamin C the United States compared with imported (Panagou et al., 2005). A number of micro- content (Li et al., 2016). nuts (Aguilar et al., 2009). Furthermore, organisms are often present on shells and Chestnut flour is sweet, nutty, and gluten a postpurchase evaluation of U.S. preferences kernels of fresh chestnut including Penicil- free making it a viable choice for 1 out of 133 for chestnuts revealed that consumers were lium, Sclerotinia, Botryotinia, and more U.S. citizens that suffer from Celiac disease 5.2 times more likely to choose organically (Donis-Gonzalez et al., 2016). Refrigeration or gluten intolerance (Beyond Celiac, 2015). grown chestnuts over conventionally grown is imperative regardless of storage period. A Pancakes, pastries, muffins, and other food- nuts and that the odds of choosing pesticide- radio frequency (RF) protocol was develo- stuffs are all possible from chestnut flour free chestnuts over conventionally grown ped involving heating (55 C) a single layer which retailed for at least $33.00 per kg or ones were 4.3 times higher (Aguilar et al., of chestnuts followed by forced room air when roasted $44.00 per kg or more in 2014 2009, 2010). All imported chestnuts must be cooling in a single layer for chestnuts. Chest- (Chestnut Growers of America, Inc., 2016). fumigated and thus cannot be certified or- nut quality was not significantly affected by Nutritionally, chestnut flour is comparable to ganic. This lends a competitive advantage to the RF treatments, suggesting viability as wheat (Triticum aestivum L.), rice (Oryza U.S. growers who are able to tout ‘‘healthier’’ a practical postharvest disinfestation method sativa L.), and potato (Solanum tuberosum nuts. As better cultural practices are discov- (Hou et al., 2014). Donis-Gonzalez et al. L.) (Vossen, 2000). Chestnut/rice (O. sativa) ered and breeding efforts in the United States (2014) developed postharvest noninvasive blends of 30/70 with xantham gum and for disease and insect resistance continue assessment methods for fresh Castanea sp. emulsifier can be used for gluten-free breads (Anagnostakis, 2012), the anticipation of in- to sort out nuts with internal decay via (Demirkesen et al., 2010). Because nuts have creased hectares and higher yields appears computer tomography imaging. Similar ef- very little protein or fat, their calories are plausible. Chestnut trees could be paired with forts are being conducted by other chestnut mainly derived from carbohydrates (Hou vineyards in agritourism settings (Cernusca researchers working with interspecific hy- et al., 2016; McCarthy and Meredith, 1988). et al., 2012) to further accentuate the impetus brids (Moscetti et al., 2014). Chestnuts have 40% carbohydrates, 40% water, for adding chestnut orchards in the United Harvesting season can be cumbersome in 5% to 10% protein, and less than 5% oil States. Breeding efforts continue but cur- older orchards given that chinese chestnut (Vossen, 2000). However, researchers have rently a limited number of chestnut cultivars can mature heights at 12 to 18 m. Conse- shown that different geographic growing re- are commercially accessible to growers. quently, researchers are investigating the gions result in variations of carbohydrate and There is significant diversity among chinese possibility of dwarfing rootstocks or using protein content (Yang et al., 2015). Chestnuts chestnut cultivars, many of which have not interstems between the rootstock and scion to are considered a health food given the fact been thoroughly trialed in states where the reduce overall height while maintaining or that they are low in fat vs. other nuts that chestnut industry is in its infancy such as improving yields (Warmund, 2014b). sometimes contain well over 50% fat. Re- Oklahoma and other U.S. locations. Al- searchers found that consumers need addi- though not all cultivars are commercially USES OF NUTS tional information to be informed of the low available to date, there are at least 65 types fat content of chestnuts compared with other being observed for their worthiness in U.S. Chestnuts are nutritionally ideal for nuts and the gluten-free attribute of chestnut orchards (Metaxas, 2013). Graft failures are a number of reasons. Chestnuts may be flour (Cernusca et al., 2012). Besides flour, common and the price of grafted trees often roasted, boiled, or steamed. Kan et al. roasted chestnut beer chips are used for gluten- exceeds U.S. $25.00 wholesale to U.S.45.00 (2016) found that roasting may be an alter- free brewing for beers such as ales, stouts, and retail United States (Forest Keeling Nursery, native industrial thermal processing method porter (Associated Press, 2015; Urban Chestnut personal communications). Another chal- for chestnut kernels vs. boiling or steaming. Brewing Company, 2016). Chestnut honey is lenge is cash flow with the average orchard Some growers opt to cure or dry out a per- also a sought-after product relatively new to being 10 to 15 years old before producers centage of their fresh crop (Schmutz et al., the United States (Healthy with Honey, begin realizing a net profit. Understory crops 2014). Michigan State University personnel 2015). Chestnut shells (e.g., burs), which with a more rapid turnaround have been aided in developing peeled frozen chestnut otherwise are considered a waste product, suggested (Red Fern Farm, 2015), particu- packs (inner ‘‘skin’’ or pellicle removed) are being researched for their water-soluble larly while waiting for chestnuts to mature. with the intent of appealing to fast lifestyles pigments demonstrated to possess antimicro- During the first 6 years of orchard establish- and chefs and consumers wanting a ready-to- bial qualities (You et al., 2014). ment, alley cropping with light-demanding use product. Zhou et al. (2015) determined crops is a viable option. Corn (Zea mays L.), that salicylic acid prevents browning on CONCLUSIONS soybean [Glycine max (L.) Merrill], and fresh-cut chestnuts. High moisture and low especially winter wheat (T. aestivum) are oil content render chestnuts virtually fat free The U.S. chestnut industry has grown by successfully grown between young chestnut (Chestnut Growers of America, 2016). Fur- 13.5% from 1350 ha reported in 2007 to 1531 ha trees with very little loss in crop yield. Shade- thermore, chestnuts have a high concen- reported in 2012 (Gold, 2014). Although much tolerant pawpaw [Asimina triloba (L.) Dunal] tration of complex carbohydrates, a low of the world’s production is collected from matures much earlier with its specialty fruit glycemic index, are cholesterol free, and natural chestnut populations, there clearly in demand. However, pawpaw requires contain one-third the caloric content of are tangible rewards for U.S. growers to full sun for maximum yield. Shade-tolerant peanuts (Arachis hypogaea L.) and cashews capture some of the market share currently vegetables/greens could also be grown within (Anacardium occidentale L.) and as much held by imports. The United States imported and between chestnut rows. During the fall, ascorbic acid as their equivalent weight of 4910 t of in-shell chestnuts (Castanea sp.) financial inputs are even higher for success. lemons [Citrus limonum (L.) Burm. f.]. valued at $12.7 million in 2010 primarily For example, irrigation must be considered at Structural and functional properties of from Italy (60%) and South Korea (25%) least 1 to 2 months before nut maturation for starches from C. mollissima vary among (USDA, 2011). With premium retail prices, maximum yield. Irrigation should cease once cultivars with researchers determining differ- particularly when grown organically or the crop begins to mature and drop to the ences regarding swelling power, pasting nearly pesticide free, great potential for high orchard floor. Daily harvest of chestnuts is characteristics, thermal and structural prop- gross income per hectare is possible. Global ideal due to their need for immediate re- erties, and freeze-thaw stability (Liu et al., chestnut production is over 450 t annually frigeration and their predisposition to weevils 2015). Information on chestnut starches with the United States constituting about and other pests if not gathered in a timely would be useful in food industries. This 1.0% of production. A consumer preferences fashion. Local wildlife quickly hone in on genus yields the only ‘‘nuts’’ that contain survey indicated that consumers were 10 chestnut farms necessitating the installation
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