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Low Spray & Organic Plum Production |
| By Guy Ames NCAT Agriculture Specialist Published 2001 ATTRA Publication #CT122 |
The
printable PDF version of the entire document is available
at: http://attra.ncat.org/attra-pub/PDF/plum.pdf 3 pages — 117K Download Acrobat Reader |
Abstract
This brief publication discusses organic and low-spray management options for disease and pest problems peculiar to plums.
Plums, apricots, cherries, peaches, and nectarines (fuzzless peaches) are all stone fruits (Prunus spp.) and share most of the same diseases and pests. Almost every peach pest is also a plum pest, so most of the pest and disease information in ATTRA's Organic / Low-Spray Peach Production publication is applicable to plums as well. The present document, therefore, will be limited to problems and considerations peculiar to plums. Organic fertilization and weed control techniques are covered in ATTRA's Tree Fruits: Organic Production Overview. Much of the basic information on tree fruit production will be the same whether the grower uses low-spray, organic, or conventional pest and fertility management. For instance, variety choices must be made with cold-hardiness and chilling requirements in mind. Also, pruning and training should be approximately the same for both kinds of culture. Since this type of information is readily available through conventional sources, it will not be touched on here. Local Cooperative Extension offices or State Extension Horticulture Specialists may be able to provide general plum culture information. You may also wish to consult one of the many books that are available on commercial fruit production. Enclosed are an article from National Gardening and a chapter from the book Ecological Fruit Production in the North, both of which discuss basic plum culture.
As the authors of Ecological Fruit Production in the North say, "Plums are affected by a variety of bizarre and somewhat disgusting diseases." (1) Black knot, bacterial spot, leaf scald, and plum pocket can all cause serious damage to the tree. Brown rot is the major disease of the fruit, and it can claim the entire harvest in a wet year if precautions are not taken. Regular sprays of wettable sulfur and the sanitation program outlined below are probably a must for any commercial venture (2):
On an encouraging note, there is progress being made in research on controlling brown rot organically. USDA researcher Dr. Michael Glenn (personal communication, July 2001) says that his preliminary research indicates that brown rot can be controlled with regular, protective sprays of Surround™ (a specific kaolin clay formulation registered as organic) mixed with sulfur and lime-sulfur. More on brown rot is presented in ATTRA's Organic / Low-Spray Peach Production publication. Black knot, another fungal disease, produces distorted, gall-like growths on branches. Trees should be checked several times throughout the season, and the knots pruned out by making cuts 3 to 4 inches below the knot. Pruners should be sterilized between cuts by dipping them in a 10% bleach or Lysol® solution. A single lime-sulfur spray before budswell (same material and timing as for peach leaf curl) will reduce black knot problems and also control plum pockets. There is some varietal resistance to most of the various diseases. However, there is no known resistance to leaf scald among the European plums. Moreover, there is no biological or chemical control for this bacterial disease. Luckily, leaf scald is largely restricted to the southeastern U.S., and there is resistance to leaf scald in certain Japanese, American, and Japanese-American hybrids. Researchers at Auburn University are focusing on detecting and incorporating disease resistance as part of their Japanese plum breeding program. For instance, they have found that 'AU-Producer', 'Morris', 'Explorer', and 'AU-Cherry' are all highly tolerant of leaf scald. (3) 'AU-Rosa', one of the more recent releases from the Auburn program, is resistant to leaf scald, bacterial canker, bacterial spot, and black knot. (4) The enclosed article titled "Plum Crazy" has an excellent discussion of plum varieties, including their relative disease resistance. In the eastern half of the U.S., plums share with apples and peaches one very important insect pest, the plum curculio. Without proper control, this pest can damage a large percentage of the crop. Wounds from curculio feeding also function as entry sites for the brown rot organism. Currently, the best organic control for the control of plum curculio is Surround, the kaolin clay product mentioned above. Although not acceptable for growers who have to meet organic standards, two sprays of Imidan® (a synthetic pesticide), one at petal fall and one 10 to 14 days later, usually provide excellent control. Other control strategies (including potential organic controls) are discussed in the Organic / Low-Spray Peach Production publication, as are other arthropod pests of plum, including oriental fruit moth, aphids, mites, and trunk borers. References
EnclosuresOlcott-Reid, Brenda. 1988. Plum crazy. National Gardening. July. p. 25-31, 59. Hall-Beyer, Bart and Jean Richard. 1983. Ecological Fruit Production in the North. Jean Richard Publishing Co., Trois-Rivieres, Quebec, Canada. p. 81-90. Low Spray & Organic Plum Production
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