GROWING CHERRIES ORGANICALLY IN MONTANA
By James Sagmiller
There are three types of cherries grown in home gardens and commercial orchards in Montana. Sweet cherries (Prunus avium) are grown in Montana’s mildest climates (USDA Climate Zone 5; hardy to about -20 degrees F.) and do well around Flathead Lake. Tart Cherries (Prunus cerasus) are hardier trees (USDA Climate Zone 4, to about -30 degrees F.) and are grown over much of the state, though are not really hardy enough for parts of Montana in USDA Climate Zone 3. Canadian bush cherries are a new kind of bush cherry with tart-sweet fruit made from crosses of tart cherries and Mongolian bush cherries (Prunus fruticosa). These are hardy to -40 degrees F. Sweet cherries grow to 30 or 40 feet tall on standard rootstocks, though are usually pruned to be shorter for easier picking. Tart cherries grow 18 to 20 feet tall and Canadian Bush cherries 6 to 8 feet tall. Most cherry trees live and produce for about 35 years.
SOIL AND SITING:
Cherries prefer sandy or sandy loam soils; with a pH of 6.0 to 7.0 (6.2-6.8 is ideal). Clay soils would need to be significantly lightened with gypsum and organic matter and still might be too heavy. If soil is too heavy the trees can be prone to diseases, such as Phytophthera. Siting of a cherry orchard is important, especially for sweet cherries. A sloping site is best, because cold air is heavier than warm air and can drain away from the trees when in bloom. Better air circulation also helps prevent foliage diseases, such as powdery mildew, and fruit diseases such as brown rot. In winter, a sloping site will be slightly warmer than low spots and this might protect bark from freezing and thawing. On a site sloping to the south or southwest, bark is especially susceptible to winter damage, which can lead to bacterial canker. All tree trunks should be painted with N.O.P. approved whitewash (no latex paint for organic growers). Here in Montana we do not have to worry about the number of chilling hours, because of our long cold season. Our relatively cool summers, lower summer humidity, and drier conditions around harvest time are all benefits to growing top quality cherries.
Cherries have been grown grafted onto rootstocks since ancient Greek and Roman times. The oldest rootstock is ‘Mazzard’, which dates to Roman times, is still used, and makes a 15 to 20 foot tree with high yields. ‘Mahaleb’ rootstock is slightly dwarfing and was first used in the 1700s in France. It is still used today. The ‘Gisela’ series of rootstocks, developed in Europe, have not proved reliable in the Western U.S., except perhaps on the Pacific coast. Some of the ‘Gisela’ rootstocks are very dwarfing, creating a tree that only grows 8 to 10 feet tall. These very dwarf trees need more consistent irrigation than standard types and staking because of heavy yields. The rootstocks are patented also, so a large scale grower cannot produce them legally without paying expensive royalties. ‘Colt’ and ‘Performer’ rootstocks grow trees about 70% and 80-100% the size of ‘Mazzard’, respectively. These two have proven moderately resistant to bacterial canker and are somewhat tolerant of heavier soils. ‘Colt’ is resistant to Phytophthera, moderately resistant to viruses, but is moderately susceptible to Armillaria. Spacing for trees on ‘Mazzard’, ‘Mahaleb’, should be 15 to 20 feet, slightly less for ‘Performer’ and ‘Colt’. Very dwarf trees on ‘Gisela 3’ and ‘Gisela 5’ could be planted 9 to 12 feet apart.
There are many sweet cherry varieties available. When choosing from those available, keep in mind that most sweet cherries require another named variety for pollination. Some kinds are self-fruitful, but most require another pollinizer, while others cannot be pollinated by certain specific varieties. I will list popular cherry varieties below with their characteristics and pollinizers:
‘Bing’ is an older variety with large, flavorful fruit. The cherries crack easily if watered too much when nearly ripe, the tree is not quite as winter hardy as others, but the fruit is among the highest in anthocynins. ‘Bing will not pollinize ‘Kristin’ or ‘Emperor Francis’.
‘Black Tartarian’ is a robust, early-bearing variety that bears red-purple-black fruit with great flavor. It is also a very good pollinizer.
‘Emperor Francis’ has yellow fruit with a red blush and bears early in the season.
‘Kristin’ is a very winter hardy sweet cherry with large, dark red fruit. The tree is resistant to bacterial canker. ‘Kristin’ will not pollinate ‘Bing’.
‘Lapins’ is self-pollinating (self-fruitful), a heavy bearer, and the tree is resistant to bacterial canker. The fruit is large, firm, dark red and crack-resistant with a good, sweet flavor.
‘Rainier’ has large yellow cherries blushed with red. The tree can be pollinated by ‘Bing’, ‘Van’ and ‘Black Tartarian’.
‘Royal Ann’ (‘Napoleon’) makes a large, spreading tree with yellow fruit blushed red.
‘Stella’ is a self-pollinating (self-fruitful) sweet cherry with very dark red, elongated fruit.
‘Van’ is a heavy bearer, tasty and reliable, with cherries somewhat smaller in size than ‘Bing’.
Several tart cherry varieties are grown in Montana. All of them are self-pollinating:
‘Montmorency’ is an heirloom variety grown primarily for pie or juice. It is a heavy bearer.
‘Morello’ is another heirloom tart cherry, from England. Fruit is heart-shaped and ripens late.
‘Northstar’ is a heavy producer of tart cherries. The tree is disease-resistant.
The Canadian bush cherries are so new that is difficult to find them in catalogs and local garden centers.
‘Carmine Jewel’ is one variety available now. It is self-fruitful, with semi-tart cherries on dwarf, bushy plants. It ripens earlier than other tart cherries and is hardy to USDA climate zone 3.
After an orchard site is chosen, a soil test has been made, and organic amendments have been added, it is time to plant. Spring planting is most common, but late fall (early November) is a good time also. Amendments and techniques used need to follow organic certification requirements if certification is desired. Dig a hole larger than the root span and add some organic compost to the bottom of the hole. Make sure the bud union (graft) is at least three inches above the soil level. Fill the hole with soil and water the tree well. Paint the trunk with whitewash to protect it from freezing and thawing during winter. Place a tree guard made from a rolled piece of ¼” hardware cloth around the trunk, extending from the soil level to at least 18”. This will protect the bark of the tree from being stripped in winter by voles. Stake young trees with a stake pounded 18” into the soil and extending about 18” high. Place the stake at a 45 degrees angle next to the tree with a soft tie made from a rubber hose or cloth attached to the tree. The stake is best placed in a direction so that prevailing winds will drive it deeper into the soil. Do not use wire or hard twine to tie the trunk to the stake because they will damage the bark. In growing cherries, it is important to always avoid any injury to bark, to avoid bacterial canker. In terms of irrigation, a drip system is probably the most efficient and water thrifty. Some seasons in Montana can be very dry and a person needs to be prepared. Watering is usually not needed until sometime in June and watering too much or too early can promote powdery mildew.
There are two periods in the year when you can prune cherries. Several sources recommend spring pruning (after flowering) as a way to avoid bacterial canker. The other time to prune is in late winter, while trees are dormant. Always prune cherries in dry weather and sterilize tools before and after each tree. If cutting out diseased wood, sterilize tools between each cut. A 10% bleach or Lysol solution in water is effective; or isopropyl alcohol. Prune cherry trees into a vase shape with a central leader. Leave alternate, staggered branches as if you were making a tree that would be good to climb. The aim is to give branches air circulation and light, and prune out all branches shooting straight up, except the central leader. Seal all pruning cuts.
INSECT PESTS AND ORGANIC CONTROLS:
In Montana the most serious pest on cherries is the western cherry fruit fly (Rhagoletis indifferens Curran). The species is native to the Pacific Northwest and occurs only on cherry. The public, and therefore packing houses/wholesalers, have a zero tolerance for cherry fruit fly maggots in cherries. Packing houses check all incoming fruit for maggots; if one maggot is found in a shipment the whole truckload is refused. Cherry fruit fly larvae are rarely found; in Washington State for example, larvae are found perhaps one to ten times a season from over 35,000 acres of cherries grown for commercial sale. Western cherry fruit fly has only one generation per year. Pupae overwinter in one to six inches deep in soil under cherry trees. The first flies emerge in late May and the number of flies emerging peaks about cherry harvest time in July. Adults feed on micro-organisms, pollen and bird droppings, aphid honeydew, and wounds on cherry fruit. This feeding and mating period lasts about 10 days. Females can lay 100 to 300 eggs over a period of 30 days, placing one or two eggs per fruit. Most flies stay on the host tree, but a few may travel as much as several hundred yards to neighboring cherry orchards or isolated trees. Eggs hatch in about eight days and the fly maggot eats the pulp of the cherry for 15 or 17days, or longer if weather is cool. At the end of feeding period, the maggot exits the fruit and drops on the ground. The larva burrows into the soil one to six inches deep and pupates for about 10 months, until next season. A few pupae overwinter twice and emerge the second season.
Most cherry fruit flies are found on home garden sweet or tart cherry trees. This highlights the importance of controlling and preventing this pest in home gardens. It is important to protect our Montana cherry industry. Prevention is one way of helping control western cherry fruit fly. If all fruit is picked from trees before flies emerge to drop on the ground, and this is undertaken at least two years in a row, the tree will be free of this pest until reintroduced. It is best to not allow fruit to be left on isolated trees. Beneficial nematodes have been used to control pupae, but they are only about 80-88% effective, so must be augmented with other organic controls. Yellow sticky traps are used to monitor fly populations, but are not really successful in controlling them.
An N.O.P. approved bacteria marketed as Spinosad is an effective control of western cherry fruit fly. A bait known as GF-120NF contains bait for newly emerged adult flies to feed on plus Spinosad. The bait is sprayed or squirted on the leaves after emergence (or when fruit is straw-colored) and again every ten days. The bait is rather thick when mixed, and a sprayer must be cleaned well after use. It is highly effective. Another effective product is Entrust, also made with Spinosad, and it is sprayed every seven to ten days after flies emerge. At the end of harvest, pick every single cherry and leave none on the tree or on the ground.
The plum curculio is an insect problem on cherries in the Eastern U.S. Organic controls include: PyGanic (a pyrethrum-based product), and Surround (a crop protectant made with kaolin clay. The American plum borer is another pest affecting tart cherries in the eastern half of the U.S. Infestations are common on trees with mechanical damage to bark and branches. Borer larvae have to be dug out of the bark and no organic controls are available yet.
Spotted-winged drosophila is an invasive species of vinegar fly from Japan. It has become established on the east and west coast and is moving inland. It is another fly that lays eggs in the fruit that hatch into maggots. Lure traps by Trece and Scentry available for this pest. For organic cherry orchards, use a combination of GF-120 bait plus Entrust and/or PyGanic. Read label directions of all products carefully because the treatment schedule can be complicated. In organic pest control, it is sometimes required to alternate product applications.
For pear slugs (cherry leaf skeletonizers) a forceful blast of water will wash them off trees; or diatomaceous earth is an effective control. Aphids can be washed off tree leaves also, and controlled with insecticidal soap. A dormant spray in winter with horticultural oil will smother aphid eggs. Tent caterpillars can be controlled with BT (Bacillus thurigensis) a bacterium that affects caterpillars.
Bacterial canker is by far the most important disease affecting cherries. The bacteria Pseudomonas syringae affects cherry roots, bark, branches, twigs, leaves and fruit. This disease can appear after any one of several stresses on trees, including: drought, frost, pruning wounds, nematodes and other diseases. As with many other organic pest controls, prevention is very important. Resistant rootstocks and resistant cherry varieties help. Older trees can harbor disease, so it is best not to plant new trees among old established trees. Avoid allowing irrigation water to hit bark, branches, or leaves. Try not to damage bark or branches and paint trunks with whitewash to prevent freezing and thawing in winter. Prune in summer if possible, rather than in winter, and only in dry weather. Keep weeds down, especially grasses, as they host the bacteria. White Dutch clover or a low growing vetch is better as a groundcover in a cherry orchard. Test for harmful nematodes before planting. A control most often used for bacterial canker is copper, but several strains of Pseudomonas syringae have become resistant to copper, especially in California and Washington.
Black Knot, caused by Apiosporina morbosum is a fungal disease that shows up as knot-like structures on branches and twigs. These should be pruned out of the cherry trees as soon as noticed. Cut three to four inches below the knot with sterilized tools (10% bleach or Lysol in water, or isopropyl alcohol). Sterilize tools again after each cut. A lime-sulfur spray in the dormant season will help control black knot.
Phytophthera root rot is very common problem for cherries on heavy poorly draining soils. Try to plant cherries on sand or sandy loam and do not plant cherries on clay soils. Affected trees will show loss of vigor. The cadmium layer will be reddish-brown in color and root growth will be poor and shallow. ‘Mahaleb’ rootstock is the most susceptible to root-rot, while ‘Mazzard’ and ‘Colt’ are somewhat resistant.
Armillaria mellea is the organism that causes a fungal disease called oak root rot or honey rot. It can affect cherries on any kind of soil, and is sometimes present in old roots from dead trees or shrubs. Recently cleared land can harbor this disease. The only known control is to avoid planting on newly cleared sites or sites known to have Armillaria.
Brown rot (caused by Monilinia fructicola and M. laxa) can appear if weather conditions are wet, warm and humid. Here in Montana, we historically did not have much of that type of weather, but as the climate changes, we are having more and more such days each summer. Brown rot affects blossoms, fruit and twigs. A first indicator of brown rot is blossom blight; if left unchecked, symptoms will reappear anytime during the period from about three weeks before harvest through harvest and storage. Temperatures in the 70s F. with rain and higher humidity favor development of brown rot. Keeping the orchard clean of fallen twigs, leaves and fruit helps discourage brown rot. A sunny site or slope with good air circulation is helpful. An open area planted with clover or vetch between the orchard and woods is helpful also. Thinning out branches on the cherry trees in summer and during dormant season will increase air circulation as well. Sulfur is the traditional remedy for brown rot and organic growers can use it. The first application is best done before the first flower petals open. Follow up with another spray 7 days later, at petal drop and a third time about 10 days later at sepal drop. More applications might be necessary in the case of frequent and heavy rains.
Another disease affecting cherries is botrytis blossom blight, but this is rare here in Montana and more common near coastal areas. To prevent botrytis, keep the orchard clean, pick up all “mummy’” fruit.
Powdery mildew, a fungus caused by Podosphaera clandestine, is occasionally seen on cherry leaves and twigs. It is more prevalent in high heat with humidity, so more common in the eastern U.S. Powdery mildew will cause loss of vigor and yield. Open pruning, creating a central leader with alternate branching, discourages mildew. Resistant varieties will help with this problem; ‘Bing’, Black Tartarian’ and ‘Rainier’ are especially susceptible to powdery mildew. Most tart cherries are susceptible, too. Sulfur made into a spray will also control powdery mildew, but also will a spray made with baking soda.
Leaf spot, another fungus primarily affecting tart cherries, is caused by Blumeriella jaapii. This fungus causes leaves to turn yellow and later, holes to form in the leaves. It is more common in humid climates than here in Montana, but sometimes is seen. Orchard sanitation is a good preventative. The fungus overwinters on fallen leaves, so these should all be raked up and destroyed in fall. Copper fungicide sprays will control this disease. Spray at petal fall, again when dead flower petals fall off fruit (shuck fall), and again two weeks later. Copper sprays can damage tree foliage, especially in temperatures above 80 degrees F., so should be used in cooler weather for best results.
Birds love cherries as much as we do, so measures must be taken to protect fruit. Netting is very effective, but expensive for large-scale growers. A combination of noise-makers and visual deterrents are used by organic cherry growers. Stationary electronic devices are available that emit loud distress calls that scare birds away. Also available are gas cannons, bird whistles and bird-bombs. Old CDs or metal pie plates tied among tree branches, and scare-eye balloons all are effective in frightening birds away. Usually one or another of these deterrents works for a week or so. Then you must use a different deterrent or rearrange them because birds get used to them.
Deer will browse on cherry trees in winter and eat leaves and fruit. The best way to prevent damage from deer is an eight foot fence. Repellents have only limited effectiveness. Gophers have become a problem in recent years and the best way to control them for an organic grower is to trap them. Voles can be trapped also, and be sure to place hardware cloth tree guards around trees before winter. If commercial plastic tree guards are used, remove them within two weeks after snow melts because condensation will take place between the plastic and the bark, creating conditions that promote bacteria.
Yields from each cherry tree 3 to 5 years after planting will be from 40 to 120 pounds of fruit. Pick cherries gently when fruit is ripe. Twist the cherry lightly and move your hand in an upward motion to separate the stem from the spur. Be careful not to tear off the fruit spur as that is where next year’s flowers and fruit will form. If you are harvesting for immediate home use, you can pick the cherries without stems. Cherries are picked commercially with stems attached because they last longer after picking. Harvest fruit every other day, for about a week, from each tree. Keep picked fruit cool. Cherries last for about 10 days in the refrigerator.
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