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Sweet basil requires a well watered soil throughout the growing season to maintain quality and yields. Because basil is sensitive to high humidity, drip irrigation in a plastic mulch production system may be preferable to over head irrigation. In addition the field may be mulched with organic material between the rows to help in weed control and to conserve moisture.
A mulched field will also maintain the foliage cleaner which may simplify the washing of foliage at harvest time. A clean foliage is also more likely to remain disease free as compared to a foliage with soil particles on it, resulting from rain drops splashing on the bare soil. Basil growth benefits from windbreaks in windy areas. Winds may damage the foliage and may also result in rapid moisture loss from the field. The basil plant will grow about one inch per day under proper environmental conditions.
Weeds
High density plantings and mechanical weed control are the most common practices used to prevent weed problems in basil fields. Weed control is enhanced with proper field preparation before planting. Both plastic and organic mulches may also be utilized to minimize weed problems in the field.
Sweet basil, Ocimum basilicum, is a popular herb grown for its dry or green aromatic leaves which are used as a spice or as a flavoring. The spicy herb, a member of the mint family, is a native of Central Asia and North West India. It is adapted to warm growing conditions and although it is a perennial, it is grown as an annual. It is commonly used in tomato dishes, and as a flavoring in soups, salads, pesto sauce, minced beef and sausages. North America imports about 2,000 tons of basil every year.
The plant is produced commercially in Egypt, France, Hungary, Israel, Mexico, Indonesia and Hawaii. In Hawaii basil is grown in about 55 acres with an estimated farm gate value of $1.2 million. The $1.2 million value, however, is probably highly underestimated. There are many types of basil varying in size, leaf shape, and in leaf color ranging from green to purple.
In Hawaii sweet and Italian basil comprise about 60% and 40% of the basil market, respectively. Basil destined for the fresh market has dark green leaves and a sweet taste. Quality of the product is determined by taste, flavor, moisture content, and cosmetic appearance for the fresh market, and volatile oil content and total insoluble ash content for the processing market.
Diseases that attack basil include Pythium, verticillium wilt, stem canker, tomato spotted wilt virus, stem die backs, leaf spot diseases and damping off. Little information exists on the effect of these diseases on basil and no pesticides are registered for their control. Growers should therefore rely on cultural practices, including crop rotation, sanitation, using clean seed, and growing their crop in disease-free soil, to minimize the incidence of pests and diseases.
Contact the Department of Agriculture for the latest marketing and shipment regulations, and your local county extension agent for the latest pest control techniques.
Nutrient needs
Fertilizer practices vary depending on the previous crop and on the current fertility of the soil. To find out the proper fertilizer rates soil samples should be tested at the University of Hawaii Diagnostic Service Center or other suitable laboratory.
Over-fertilization will diminish the quality of sweet basil at harvest and may increase the soluble salt content of the soil to undesirable levels. Pre-plant fertilization rates of 120-120-120 lbs per acre of N-P205-K2O are recommended in soils deficient in these nutrients. The soil should have a pH between 6-7.5.
Nitrogen may also be side-dressed at the rate of 20-30 lbs per acre soon after the first harvest. Experiments in Indiana showed that ammonium sources of Nitrogen may decrease petiole and stem yields, and leaf content of essential oils, when compared to nitrate-N sources.
Hawaii relies on the high quality of its horticultural products to maintain competitiveness in the export market to the mainland. High quality is achieved by conducting proper cultural and postharvest handling practices.
Basil is ready for harvest 45-70 days after planting. Harvest practices may vary from grower to grower depending on crop growth, handling, and product marketing practices. Leaves are picked above the bottom two to four set of true leaves. Sweet basil is picked twice a day under normal growing conditions. Well washed and drained leaves are stored over night. The leaves, with the terminals or shoots attached, are transported in wet newspapers or towels at temperatures of 40-42 oF (4-5 C), and relative humidity between 95-98. For the local market, basil is packed in 1-2 oz plastic bags.
Basil growers shipping to the mainland have to comply with strict quarantine regulations which require insect-free shipments. These restrictions are hard to meet because there are only a few pesticides registered for use in sweet basil. Growers should therefore follow a careful management program to minimize the incidence of pests and diseases in their fields. Growers should also be careful not to contaminate their product with pesticides which are not registered for use on basil. Proper labelling of the shipments and record keeping will protect the industry as a whole, and should help to identify the source of contaminated products. In the field, plants should be monitored throughout the growing season for the presence of insects or diseases.
Pests of economic importance include thrips; serpentine leafminers, Liriomyza trifolii (Burgess), and Liriomyza sativae Blanchard; Chinese rose beetle, Adoretus sinicus; greenhouse whitefly, Trialeurodes vaporariorum; carmine spider mite, Tetranychus vaporariorum; carmine spider mite, Tetranychus cinnabrinus; the stink bug, Nezara viridula; sweet potato whitefly (Bemisia tabaci); leafhoppers; and various mealy bugs, grasshoppers, and aphid species.
Leaves damaged by leafminers are removed prior to sale. Shipments to the mainland should be free of Thrips palmi. Foliage damage is also caused by the webbing of the Carmine spider mites, by the honeydew produced by feeding whiteflies, and by Chinese rose beetles feeding in the foliage.
Seed from basil should be obtained from a reputable source to make sure that the seed is true to type. Basil can be direct seeded or transplanted in the field. When direct seeded, overseed expecting an 80-90% germination rate. Optimum temperature for germination is 70 degrees Farenheit (21 C) but the seeds will germinate well with temperatures between 65-85 degrees (18-30 C) in about 7-15 days.
The soil should be well worked to allow for proper germination. Seed to a depth of 1/4 inches. A high density planting is recommended to help minimize weed growth in the field. Rows are spaced 24 to 36 inches apart, and plants are spaced 6-20 inches in the row. Basil can also be planted in beds with a spacing of 24 to 36 inches between beds. Three rows are planted per bed with a spacing of 12 inches between rows. When transplanted, basil is propagated by seeding in trays, then transferred to cell trays or pots. The plants are later transplanted in the field when about 6 inches tall.
Some growers also propagate by rooting basil cuttings, but the advantages of performing this practice has not been determined experimentally.
