New Crops News, Spring 1994, vol. 4 no. 1
To date, large-scale commercial nut production east of the Rocky Mountains has been limited to pecan and eastern black walnut. The pecan industry continues to grow at a slow but steady pace. Unfortunately, the black walnut industry has declined to the point where there is only one commercial processor left in the nation.
An attempt was made several decades ago to establish a sweet edible chestnut industry in the Southeast, but the accidental introduction of the oriental chestnut gall wasp destroyed that effort. Various trials on filberts and hardy strains of English walnut over nearly a century have produced some reasonable selections for midwestern conditions, but few growers have tried their commercial production. Other types of nuts, such as the butternut, heartnut, pine nut, hickory, and hardy almonds can produce decent crops in the Midwest, but their lack of any single noteworthy cultivar and limited market preclude their commercial planting at this time.
Aside from black walnuts and pecans, there is no other tried and true type of nut available for commercial production in the Midwest. Even pecan production must be limited to the extreme south. However, based on the trials of small plantings and solitary trees and cultivars arising from those trials, filberts, chestnuts, and hardy English walnuts, with all their flaws, are the most likely candidates for commercial production America’s heartland.
'Barcelona' is the leading commercial cultivar in the U.S. It was being replaced by 'Ennis', which recently has been found to be very susceptible to eastern filbert blight (EFB), resulting in premature tree death. 'Butler' and 'Hall's Giant', also susceptible to EFB but to a lesser extent, are used as pollinators for both 'Barcelona' and 'Ennis'.
Filbert breeder Cecil Farris, of Lansing, Michigan, has developed a series of hybrids that reportedly are EFB resistant. The best of his selections, named 'Grand Traverse', while producing a smaller sized nut than 'Ennis', reportedly has a higher quality kernel. Commercial trials of 'Grand Traverse' and Farris' other hybrids are just beginning in Michigan and Ontario, Canada.
The culture of filberts is like that of many fruit trees. They prefer a well-drained soil but one with good water holding capacity. On lighter textured soils, irrigation is suggested to reduce transplant shock and to optimize the opportunity for growth. The soil pH should be slightly acidic.
Unlike fruit trees, good air drainage is not as critical for frost protection during pollination of filberts. In the Pacific Northwest, they pollinate in January and February. In Michigan, pollination typically occurs in March but sometimes as early as February or as late as April. In Michigan, even though the ground might still be frozen, pollination occurs when daytime temperatures warm up to the 40°s or 50°s (F) for several days in a row. Once pollinated, temperatures of zero have little effect on the potential of the nut crop. Still, filberts should not be planted in frost pockets or similar areas as they might sustain frost or freeze injury to wood tissue.
Older groves in Oregon were typically set at 22'x22'. Newer plantings are at 18'x20' or 18'xl8' for permanent spacings or at l0'x20' with every other tree planned for removal at age 10 to 15. Newer plantings in the Midwest have been going in at 12.5'x20' (176 trees per acre). In the older plantings, usually every third tree in every third row is a pollinator. In the newer, higher density plantings, fewer pollinators would be needed.
Filberts usually begin to produce nuts by the third year after planting. Typically, commercial production should begin by the sixth year. By increasing the planting density, however, harvesting should become economical in the fourth or fifth year. Yields from a mature orchard range from 1000 to 4000 lb. per acre, depending on the cultivar, soil condition, and cultural care. Prices to growers have been in the 42-50¢ per lb. range, with 'Ennis' bringing upwards of a 5¢ per lb. premium.
Aside from the very debilitating to lethal EFB, there are few pests that should bother filberts in the Midwest. Leaf rollers, rose chafers, gypsy moth larvae, plum or peach borers, and possibly the hickory weevil might need to be controlled. Efforts are being made to find chemical controls for EFB, though the best line of defense is to plant blight tolerant cultivars. Control methods for the insect pests would require the use of generally available insecticides, but these are not yet labeled for use on filberts in this part of the country.
Pacific Northwest filbert production is all mechanized. Prior to nut drop, the ground is flail mowed so that nearly all vegetation is destroyed. If this does not also level the land, a land smoother or roller is used. The nuts begin to drop in August, and they are left on the ground till harvest in September or October. When harvested, the nuts are swept in windrows. A collector/cleaner picks them up from the windrows. Nuts are then taken to another cleaner and washer before the final drying process.
Under Midwest conditions, mowing to the point where protective ground cover is destroyed would increase the soil erosion potential. Also, leaving the nuts on the ground for two months or more would not only increase losses to animal depredation, but reduce the quality of the nut by staining and possibly mold.
The use of ethephon to hasten nut ripening is practiced to a limited extent in the Pacific Northwest. Its use in the Midwest could narrow the harvest window enough to allow the mechanical shaking or one-pass sweeping of nuts, thus overcoming these two cultural problems.
There is no organized commercial chestnut industry in the United States or Canada, although these two countries are capable of producing chestnuts. Present acreage of chestnuts in the U.S. is likely less than 1000 but growing. Most of that acreage is in California, the Pacific Northwest, and Michigan.
Compared to the 2 lb. per capita consumption of chestnuts in China and 1 lb. per capita in Europe, per capita consumption in the U.S. is only 0.04 lb. Despite this, in-shell imports of European chestnuts (Castanea salvia), primarily from Italy, have a wholesale value approaching $20 million. A less reliable estimate of the value of imported processed chestnuts is about $2 million to $5 million.
China and Korea are the world's largest growers of chestnuts, producing about 300,000 metric tons per year. About a third of that production is exported to Japan. France and Italy are Europe's largest producers. Switzerland, Germany, Australia, Spain, Chile, Argentina, New Zealand, and a few other countries have chestnut industries at various stages of development—some to the point of exporting.
Chestnuts are grown in temperate climate zones around the world. They have traditionally been grown on hilly land unsuitable for row cropping. They prefer sandy, somewhat acidic soil (pH 5.5–6.0). Once established, they are quite drought tolerant.
In the Midwest, chestnuts will bloom in late June or early July. They are monoecious (male and female flowers are separate but borne on the same tree). Cross pollination by a tree of different parentage is necessary. Trees are wind pollinated, though in Australia and New Zealand where bees are believed to enhance pollination, up to 10 hives per hectare are used.
Around the world, both seedling and grafted trees are used in commercial groves. Delayed incompatibility at the graft union has limited the use of grafted trees, but grafting onto progeny seedlings seems to reduce this problem. Tissue culture is being tried in several countries to eliminate the need for grafting. Success rates vary.
Most chestnuts grown in the Midwest are considered Chinese chestnuts (Castanea mollisima) or their hybrids. These tend to produce blight-tolerant trees which produce small to medium sized nuts. The nuts are quite sweet when properly cured. In Michigan, the interest has been more towards the Japanese or Korean chestnut (Castanea crenata) or its hybrids with Chinese chestnuts. This species tends to produce larger nuts than the Chinese chestnut, but they are reportedly not as sweet. It also has a high tolerance to chestnut blight. The blight susceptible European-type chestnuts can also survive in the Midwest, but their true winterhardiness is suspect. As a precaution, they should only be planted in areas with a tempered microclimate such as within the lake-effect area of the Great Lakes.
Few nurseries are set up to handle the quantity of trees necessary to start a commercial chestnut industry. Furthermore, the poor performance of grafted trees needs to be acknowledged and rectified. With that, the fledgling industry in the Midwest is based predominantly on seedling trees. As these trees come into bearing, the inferior ones will be removed and be replaced with newer superior selections, likely grafted, self-rooted, or tissue propagated.
At this stage of the industry, selecting which cultivars to plant is a gamble. Named selections in this country are often no better, and in some cases, much worse than seedlings from good parent trees. For clonal trees, 'Colossal' and 'Silverleaf' are two European hybrid selections worthy of trials on the proper sites and with a strict regimen of blight suppression. Based on very early trial evaluations, seedlings of the 'Dunstan' hybrids from Florida appear to warrant wider planting. They seem to be much hardier than the grafted 'Dunstan'. 'Paragon' and its hybrids have performed well in Michigan, but its availability is very limited. Otherwise, aside from the seedling trees of superior parents, it is premature to recommend any other cultivar at this time.
Chestnuts are subject to attack by at least 15 insect pests, though only a few present enough of a problem to require control. The ever present threat of chestnut blight must be dealt with. While there is no known control agent for blight, by selecting tolerant species and keeping tree stress to a minimum, blight will not be a factor in the commercial production of chestnuts. In planting blight susceptible varieties, the application of certain copper-based fungicides in a preventative program apparently reduces the spread of blight.
Worldwide, chestnuts are presently harvested by hand once they have fallen from the burr. Efforts are underway to mechanize this step. Once harvested, chestnuts must be processed or refrigerated until used. When stored at 32°F and 70–90% relative humidity, they can be kept up to one year. Before use or processing, chestnuts must be allowed to cure to allow starches to convert to sugar. This usually involves letting the nuts set at room temperature and humidity for several days before use or for longer periods of time under refrigeration. Sugar levels will be at about 2% at harvest and up to 25% after proper curing. If allowed to overdry, chestnuts must be rehydrated by soaking in water.
Most Americans recognize chestnuts as only being usable for roasting or as an ingredient in poultry stuffing. In reality, they are an extremely versatile commodity. They can be used in main dishes, soups, and desserts. They can be dried and then ground into chestnut flour, which is a superb additive or replacement for wheat flour. Taiwan even has chestnut flavored ice cream bars.
The potential for chestnuts in the Midwest is great. We possess the soils, climate, and knowledge of how to produce them profitably. Based on an import level of 5,000 metric tons, it would take 4,000 to 6,000 acres of chestnut orchards to satisfy the domestic consumption of in-shell nuts. Additional acreage would be needed to satisfy the demand for processed products, increased domestic consumption, and possibly exports.
While many of the selections of English walnuts grown in the Midwest are fully winterhardy, their resistance to spring frosts presents the most serious challenge for commercial production. Most walnuts break dormancy during a period when the probability of frosts is great. New growth that carries the pistillate blooms can be killed by below freezing temperatures. Therefore, the most frost-free sites are necessary for assured annual production.
Besides the good air drainage, walnuts require a good loam or clay-loam soil. The soil pH should be neutral to slightly alkaline for best growth. Sandy loam is acceptable providing the sub-soil has a reasonable water holding capacity. If not, irrigation is recommended.
While not entirely pest free, no unusual or uncontrollable pest or disease problems should plague Midwest growers. In the West, a viral disease called "black-line" is seriously affecting English walnuts grafted onto black walnut rootstock. The disease has not been observed in the Midwest.
Few suitable cultivars have been selected for the Midwest. 'Hansen' is a high quality but small nut. It produces large annual crops. Its best use would be for local sales, for confectionery use, or in a nut mix where a small nut might be acceptable. 'Holton', a seedling of 'Hansen', is a larger sized nut with a high quality kernel that has performed well in Michigan. Unfortunately, its availability is very limited. 'Somers' has proven to be a reliable producer of good sized nuts and is a more commonly grafted cultivar than 'Hansen'. Western commercial cultivars should be avoided since they are not likely hardy anywhere in the Midwest. Recent breeding successes by Cecil Farris have resulted in later leafing walnuts which are now being bred to increase nut size. It will still be a number of years before those will be available for release.
The spacing requirement of walnut trees is similar to that of chestnuts. Ultimately, a 40'x40' spacing is required (32 trees per acre). Even at that spacing, heavy pruning to control size will have to be done. Initially, planting trees on a 20'x20' or 20'x40' spacing is recommended, with their removal planned as the crowns begin to close in.
Yields in California average around 3000 lb. per acre with top yields upwards of 6000 lb. Known top yields in Michigan are slightly higher than one ton per acre.
Walnuts in the West are mechanically harvested and processed much like filberts, except mechanical shakers are usually used to get the nuts off the tree. Commercial growers in the Midwest are harvesting nuts by hand off the ground.
The potential for commercial production of walnuts in the Midwest is limited by the availability of good sites and planting stock. Modification of western harvesting methods to Midwest conditions must take place. As newer cultivars appear, older blocks must be replanted to eliminate frost sensitive clones and to increase annual yield potential.
Cultivar selection at this point will be by trial and error. Like any new agricultural crop, new and better cultivars must be planted as they become available. Current trials and breeding work should yield sounder recommendations.
Unlike the highly developed western markets, there presently is no marketing network for Midwest-produced nuts. Existing Midwest growers are now selling through niche markets. If and when large scale production occurs, alternate markets must be developed.
Joseph Lukasiewicz