Title : Citrus Nursery Production
Visit Count : 3016 Time(s)
Upload Date : 6/1/2016 - 6 Year(s) ago
Category : agricultural technical notes
Wednesday, June 1, 2016
Visit Count : 3016 Time(s)
Upload Date : 6/1/2016 - 6 Year(s) ago
Category : agricultural technical notes
Citrus can be adversely affected by a number of virus diseases, many of which can be transmitted during budding. Many old-line selections of citrus have exocortis, xyloporosis and possibly other viruses. Moreover, a number of citrus trees in urban areas, have been illegally imported from other states. Random testing over the last several years has identified a significant incidence of citrus tristeza virus among these trees. Major objectives of this program are 1) to establish a foundation block of disease-free trees of all major commercial and non-commercial varieties of citrus grown in Texas, 2) to maintain a rigorous program of testing and retesting of foundation trees to assure continued freedom from disease, 3) to evaluate the horticultural characteristics of foundation trees to assure trueness-to-type and 4) to develop and maintain increase blocks for the production and sale of certified budwood for the production of disease-free citrus nursery trees.
Major advantages of container production include:
1. Smaller land area required, no need to change sites; 2. Growing in greenhouses/shadehouses provides climate control; 3. Sterile growing medium eliminates soil-borne diseases, insects, nematodes and weeds; 4. Production time of 15 to 18 months from seed, as compared to 24 to 30 months common to field nurseries; 5. Reduction of transplant shock because of transplanting entire plant with undisturbed root system.
Major disadvantages of container production include:
1. High initial capital investment for growing structures and climate control facilities and equipment; 2. Intensive management requirements; 3. Smaller caliper trees -3/8- to 1/2- inch rather than 5/8- to 3/4-inch; 4. Partial removal of medium necessary at transplanting; 5.More frequent irrigation during orchard establishment.
The use of virus-free propagation material requires sterilization of propagation tools. Sterilization of pruning shears and budding knives can be easily accomplished by cleaning the tools throughly with warm, soapy water, then spraying them with a 10-percent solution of chlorine bleach (one part bleach to nine parts water). A small spray bottle of the bleach solution is especially handy for periodic re-treatment of propagation tools during nursery operations.
Rootstock Production
As a general rule of thumb, most nurseries plant about twice as many rootstock seed as the ultimate number of budded trees that are expected to be produced, as total losses through the entire production process can account for about half. Initial losses are those seed which fail to germinate, as well as those that die before reaching liner size. The major loss occurs in the culling process of liner selection. Other losses include liners that die, budding failures and budling death or budlings which simply do not grow normally.
Seed. It is common practice to collect rootstock seed from fruit produced on root sprouts in existing orchards. However, it is recommended that seeds be purchased from certified sources or that nurserymen establish and maintain trees for rootstock seed production to assure uniformity of rootstocks year after year. Washed seed should be surface-sterilized in hot water maintained at 125o F for 10 minutes, then dipped in one percent 8-hydroxyquinoline sulfate, air dried and packaged for storage or planting. Properly treated and packaged in sealed plastic bags, seed can be stored in a refrigerator for several months with little loss in viability. Pre-plant soaking in aerated water maintained at 85o F for 24 hours will increase total germination, uniformity of germination and will shorten germination time. Germination and initial seedling growth in greenhouses can be further enhanced by using seedboxes designed and built to provide supplemental bottom heat to maintain constant 85o F temperature of the medium, supplemental lighting to provide 16 hours of light daily and use of polyethylene covering to maintain high relative humidity.
Seedlings. Seedlings for field nurseries are lined out in nursery rows in 4 to 6 months, at a spacing of about 12 inches. Row width is dependent upon mechanical equipment used in the nursery. Greenhouse-grown liners can be potted in sterile media in growing containers after 2 to 3 months. A number of containers are in use, including plastic bags and reusable plastic pots of various dimensions. Minimum dimensions of the various containers used locally are 4 to 6 inches wide and up to 14 inches deep. Standard 3-gallon and 4-gallon plastic nursery containers are also used. Seedlings should be graded critically at transplanting. Those few that are obviously much larger than average are probably of hybrid origin and therefore should be discarded as not true-to-type. Obviously-stunted seedlings should be discarded as they will probably never catch up to normal seedlings. Those having curved or crooked lower stems at or below the soil line should be discarded, as such stocks may take years to outgrow such deformities. Albino seedlings should also be discarded. Remaining seedlings may then be graded into two or three sizes and transplanted by size groups to establish blocks of uniform seedlings, both in field and in container operations. Thus, all seedlings within a block should mature together, thereby receiving uniform treatment, requiring less labor and producing a higher percentage of saleable trees from a given block at the same time.
Budwood. Under this legislation, citrus trees produced for sale in Texas must be propagated only from buds obtained from a certified source. Thus, the budwood will be cut, labeled and bagged by employees of the Foundation.
Budding. Budding height on the stock should be 6 to 8 inches, which normally provides ample height of the union to reduce the incidence of Phytophthora foot rot. Budders use the inverted-T method for inserting the bud into the stock.
Microbudding. Basically, the technique involves germinating rootstock seeds in test tubes, then decapitating them at a couple of months of age to insert a tiny bud into a small, vertical incision into the decapitated stem. Within another couple of months, the newly budded plant will have achieved typical liner size for transplanting into the field or into a container to be grown on to acceptable size for ultimate use. The relatively low insertion of the microbud resulted in a somewhat higher incidence of Phytophthora infections in field planting, but that should not be the case in container production. Fruit production occurred on microbudded trees in the second year post planting, which would certainly be advantageous for retail trees.
Aftercare. Rootstock sprouts below the bud should be removed periodically to avoid competition with the budling. Emerging buds can be easily rubbed off or broken off.
Cultural Practices
Irrigation. Container nurseries are normally established with automatic watering systems, using individual drip irrigation emitters in each container. Such systems are generally designed for daily operation.
Nutrition. In either case, water-soluble fertilizers are applied during irrigation, either during each irrigation or weekly.
Weed Control. Weed competition in field nurseries should be eliminated by the use of appropriate pre-emergence and post-emergence herbicides and/or by mechanical means.
Pests. Typical orchard pests can affect nurseries. Nurseries can also experience damage from caterpillars, cutworms, slugs, snails and rodents. Good pest control is essential to the production of high quality nursery trees.
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