Question of the Week
Answer: I am pleased to provide you with information on cherry tree integrated pest management and fertility.
Please refer to the ATTRA publication Organic Tree Fruit Production. This publication provides a good introduction to the principles of organic tree fruit production. Many of the general principles of organic weed management, soil fertility, and general pest management apply to organic cherry production, so I would encourage you to look at this publication as a resource. This publication also emphasizes that ecological management of the orchard floor can have positive impacts on tree health and pest management. I will address some specific pests for organic cherry production in this letter, however.
Pest Management: Disease
Choosing disease resistant cultivars is a good starting place for minimizing reliance on pesticides. To begin with, sweet cherry varieties are much more susceptible to brown rot and bacterial canker than tart cherries. Some sweet cherry cultivars--Angela, Chinook, and Early Burlat--are resistant to buckskin disease (1), a virus-like disorder which may or may not be a serious disease in your area.
Both powdery mildew and leaf spot can be controlled with regular sprays of sulfur (sulfur is considered "organic" by most certifying organic growers' groups). Bordeaux mix (also considered organic) may be more effective for leaf spot than sulfur.
Brown rot can be a severe problem on sweet cherries if favorable conditions (high heat and humidity) occur. An organic control program for brown rot should probably include the following:
* Encourage air movement with site selection and open pruning.
* Prune out all dead wood and cankers and destroy them.
* Remove mummies--the shriveled, rotted fruit from last season.
* Remove and destroy infected fruit promptly.
* Apply wettable sulfur every 10 to 14 days from petal fall until harvest. Spray more often during wet seasons. Sprays may not be needed in dry seasons or dry climates if the other steps are followed.
Control of brown rot involves the integration of several tactics. Cultural practices and orchard sanitation are the first line of defense. Planting-site selection and pruning are critical to providing sufficient air circulation within the canopy. Good air circulation through the tree facilitates rapid drying of the foliage and flowers after rain or overhead irrigation. Thinning branches to open the center of the tree is a good practice—this can be done in July, as well as during the regular dormant-season pruning. Orchard sanitation practices include pruning and removal of infected twigs and cankers and disposal of dropped, culled, or mummified fruit.
University of California researchers determined that excessive nitrogen fertilization increases fruit susceptibility to brown rot. They also found that pre-harvest sprays of calcium reduced brown rot infection over non-sprayed trees but were not equal to fungicidal control. (3)
Organic growers have traditionally relied on sulfur to control brown rot. The first application of sulfur should be done at the "pink" stage, just before the petals open. This should be repeated at seven-day intervals, especially if rain occurs, for a total of three applications. Two other applications should be made—one at petal drop, the other at sepal drop (usually about 10-14 days after petal drop). The crop is still susceptible to infection later in the season, but treatments during the early "critical" stage will reduce the amount of crop loss without leaving a sulfur residue at harvest. When the weather is hot and dry, the need to spray is not as great.
A promising organic control strategy for brown rot, according to Dr. Michael Glenn at USDA's Appalachian Fruit Research Station in Kearneysville, West Virginia, is to combine sulfur with Surround™ WP Crop Protectant. Derived from processed kaolin clay, Surround is an OMRI- (Organic Materials Review Institute) approved pest control product shown to control or suppress certain insects and diseases. The mechanism by which Surround suppresses powdery mildew, sooty blotch, fly speck, and fire blight (but not scab) in apples. While no studies have been conducted on cherries, I imagine that the response would be quite similar. (6)
Carl Rosato of Woodleaf Farm, Oroville, CA, consulted with ATTRA about his techniques in managing brown rot on his organic peach orchard. He relies primarily on a spray mixture of micronized sulfur + rock dust (e.g., Azomite™). However, for a dynamic foliar spray that provides both nutritive and pest-control benefits, Rosato likes to blend a foliar "brew" for all pre-bloom, bloom, and post-bloom sprays. A common tank mixture (per acre) may include: 6-8 lbs Azomite; 5-15 lbs micronized sulfur; 5 lbs soluble potassium sulfate; 1 lb Solubor™ (boron); 5 lbs kelp; and a yucca extract for a sticker. For the pre-bloom spray, he adds copper specifically for brown rot control. Bloom sprays begin at one-third bloom and proceed every 5-7 days all the way through petal fall, for a total of 3-4 sprays altogether. Post-bloom sprays depend on the weather. When rain or humidity approaches, he religiously applies a brew spray as a prophylactic before weather arrives, again every 5-7 days depending on environmental conditions. Brown rot pressure decreases dramatically when it is hot and dry—around 85-90° F. (7)
Bacterial canker is a serious bacterial disease which affects cherries. Bordeaux mix, or other copper-containing fungicides, will exert some control over bacterial canker. However, this control will probably be imperfect, which points out the importance of taking whatever steps possible in eliminating the predisposing factors to bacterial canker--primarily freeze damage. Whitewashing trunks and avoiding drought stress or nutritional stress (especially as the trees are preparing for dormancy) should help to minimize the risk of freeze damage.
Choice of cherry rootstocks may also have an impact on disease management. The two most commonly used rootstocks are Mahaleb and Mazzard. Mahaleb is susceptible to phythophthora root rot in heavy or poorly drained soils. Mazzard is better suited to heavier soils, but it is susceptible to crown gall and several viruses.
Dwarfing rootstocks are also being evaluated in the US to make cherry production more efficient. Recently some new rootstocks such as Colt and the Gisela series produce fruit trees from standard size down to 45% of normal. These new root stocks are not yet widely tested in B.C. Semi-dwarf cherry trees may be kept at 12 ft high (3.6 meters). At the present time dwarf sweet cherry trees are not as small as dwarf apples. Gisela 5 seems to be the most widely used of the two and is about half the size of Mazzard. It is also more susceptible to pests than Gisela 6, something to consider when using organic production practices (4). Referenced below is a publication that lists the more commonly-used cherry rootstocks and their characteristics. This will help in determining what is best for your farm and preventative strategies in organic production.
One of the major insect pests of cherry is the cherry fruit fly (Rhagoletis cinulata and R. fausta). Failure to adequately control this pest can cause severe crop loss due to the presence of fruit fly larva (maggots) in the cherries at harvest. Both federal (USDA) regulations and consumers demand a zero tolerance for maggots in fruit at harvest. Regarding insect pests, if you plan to wholesale the fruit, you may have few non-chemical options available to you since cherry processors and wholesalers maintain what amounts to zero tolerance for cherry fruit fly maggots. Recently the use of Spinosad has been quite effective at controlling Cherry Fruit Fly. Spinosad is derived from a naturally-occurring bacteria and it is approved for use as a pesticide in cherry production. It has been used in combination with bait as well as applied as a foliar insecticide. While it has not proven to provide 100% control of Cherry Fruit Fly, it has reduced population numbers significantly. A bait (GF-120NF) is an attractive substance with spinosad as the active ingredient. It is lethal to flies that feed on it while "grazing" on the tree. This bait is "squirted" and spattered on the trees weekly at 20 fluid ounces per acre diluted in about 1.5 to 2 gallons of water per acre. Entrust is a spinosad-based product that kills flies both by contact and residue. It is generally applied by air-blast sprayer every 7-10 days and has had excellent results. (5)
Lastly, for diseases and pests, sanitation is always helpful. Removing and destroying prunings, cutting out disease-infected wood, and roguing out wild plum and cherry trees in the orchard vicinity are all examples of good orchard sanitation practices.
Grower profiles and networking is always very helpful in transitioning to organic. I have listed contact information for an organic cherry grower, Cynthia Lashbrook, under “resources” below. She is also an organic crop advisor and would be an excellent resource for organic cherry production.
1) Stebbins, R. L. and L. Walheim. 1981. Western Fruit, Berries, and Nuts. HPBooks, Los Angeles, CA. p. 96.
2) Hall-Beyer, Bart and Jean Richard. Ecological Fruit Growing in the North, Jean Richard Pub., Trois Rivieres, Quebec, 1983, p. 78.
(3) Hansen, Melissa. 1996. No Magic Bullet Exists for Brown rot Disease Control. The Good Fruit Grower.
(4) Hansen, Melissa. 2006. Growers Worldwide Choose Productive Rootstocks: the perfect cherry rootstock has yet to be found. The Good Fruit Grower. V. 15 No. 10. May 15th, 2006.
(5) Smith, Timothy. (no date). Western Cherry Fruit Fly (Rhagoletis Indifferens Curran) and its Management in The Pacific Northwest United States. Washington State University Tree Fruit Program.
(6) Glenn, D. M., T. van der Zwet, G. J. Puterka, E. Brown, and P. Gundrum. 2001. Efficacy of Kaolin-based particle films to control diseases in apples. Plant Health Progress an online journal. doi : io. 1094/PHP-2001-0823-01-RS.
(7) Peach Brown Rot Control. Organic Farming Foundation Research Report, Grant 92-26. Carl Rosato, Woodleaf Farm, Oroville, CA. Accessed July 2002. (PDF / 3 M)
Stromnes, John. 2006. Bugged to death by flies—Growing organic cherries is tough but getting easier. Western Montana InBusiness Monthly. Vol. 4, No. 7.
Hansen, Melissa. 2006. Growers Worldwide Choose Productive Rootstocks: the perfect cherry rootstock has yet to be found. The Good Fruit Grower. V. 15 No. 10. May 15th, 2006.
Cynthia Lashbrook – PCA and Org. Grower
Four Seasons Agricultural Consulting & Riverdance Farm
12230 Livingston-Cressey Road
Livingston, CA 95334
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