Crop Production Guidelines |
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By: Randall T. Hamasaki, Hector R. Valenzuela, Dick M.Tsuda, and Janice Y. Uchida
University of Hawaii, Cooperative Extension Service, Associate
County Extension Agent, Associate Extension Vegetable Specialist,
Research Associate, and Assistant Professor of Plant Pathology,
respectively
INTRODUCTION
Basil (Ocimum basilicum) is a popular herb grown for the fresh
market or for its dried aromatic leaves which are used as a spice
or flavoring. This herb, a member of the mint family, is a native
of Central Asia and North West India. It is a perennial, adapted
to warm growing conditions, but is typically grown as an annual.
It is commonly used in tomato dishes, pesto, and as a flavoring
in soups, salads, minced beef, and sausages. North America
annually imports about 2,000 tons of basil. Basil is produced
commercially in Egypt, France, Hungary, Israel, Mexico,
Indonesia, and the United States. In Hawaii, basil is grown on
about 55 acres with an estimated annual farmgate value of $1.2
million. Many types of basil are available varying in size, leaf
shape, flavor, and in leaf color ranging from green to purple.
Product quality is determined by appearance (color and absence of
decay or insect damage), flavor, and moisture content for the
fresh market, and volatile oil content and total insoluble ash
content for the processing market. Basil markets include local
hotels and restaurants, local wholesalers and retailers, mainland
produce wholesalers, and processors of pesto and other products
using basil. Basil for export from Hawaii is mainly grown during
the winter months.
CULTURE AND MANAGEMENT
Propagation
Basil seed should be obtained from a reputable source to assure
that the seed is true to type. The soil should be worked well to
allow for proper germination. Basil is direct seeded to a depth
of 1/4 inch or transplanted into the field when about 6 in tall.
When direct seeding, over-seed expecting an 80-90% germination
rate. Optimum temperature for germination is 70oF (20oC), but the
seeds will germinate well between 65-85oF (15-30oC) in about 7
days. Basil can be grown year-round in Hawaii in well-drained
soils at elevations below 700 ft (250 m), and from May to October
at higher elevations.
Spacing
Rows are spaced 24 to 36 in apart, and plants are spaced 6 to 24
in in the row depending on culture. Basil can also be planted in
beds with a spacing of 24 to 36 inches between bed centers. Three
rows are planted per bed with a spacing of 12 inches between
rows. In large scale operations, basil may be planted at a high
density for once over harvesting. In smaller operations, basil is
planted at a lower density and harvested over a long growing
season.
Mulches and Windbreaks
Basil requires adequate soil moisture throughout the growing
season to maintain quality and yields. The field may be mulched
with organic material between the rows to help control weeds and
conserve moisture. A mulched field will also reduce the amount of
soil splashing onto the leaves which will simplify the washing of
foliage at harvest time and help reduce the incidence of certain
diseases. High winds can damage foliage and cause rapid moisture
loss in the field. The use of windbreaks may be beneficial under
high wind conditions.
Fertilization
Fertilizer practices may vary depending on the previous crop and
on the current fertility of the soil. Use soil tests to determine
the levels of available plant nutrients in the soil.
Over-fertilization will diminish the quality of sweet basil at
harvest and may increase the soluble salt content of the soil to
undesirable levels. Plants overfertilized with nitrogen often
show dark discolorations in the cooling rooms after harvest.
Pre-plant fertilization rates of 120-120-120 lbs per acre of
N-P205-K2O are recommended for soils deficient in these
nutrients. Basil does best when soil pH is between 6.0-7.5.
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. Growers who plan to market basil labeled as
"organic" should check with Federal and/or State
guidelines for organically grown produce.
PESTS
Basil is a specialty crop with only a few pesticides registered
for use on the crop. Therefore, growers should develop and follow
a pest management program to minimize the incidence of pests and
diseases in their field and follow strict measures during and
after harvesting to ensure that live insect and mites do not
infest shipments. Field plantings of basil generally have a
healthy population of beneficial arthropods such as parasitic
wasps, spiders, and other general predators which can help keep
pest populations to moderate levels. Learn to recognize both
pests and beneficials and regularly monitor their populations.
The early detection and management of pest problems can often
prevent major problems. Growers producing basil for export should
pay particular attention to insects that are quarantine pests or
are likely to remain on harvested basil, and remove them before
export.
Growers should also be careful that their product is not
contaminated with pesticides that are not registered for use on
basil. Properly labeled shipments and record keeping help to
protect the industry as a whole and to identify the source of
contaminated products.
Insect, Mite, and Mollusk Pests
At least 30 known insects and mites are found on basil grown in
Hawaii. Although only a small portion of these cause significant
crop damage, growers shipping to the continental U.S. have to
comply with strict quarantine regulations which essentially
require arthropod-free shipments. Therefore, growers should also
monitor insects which may not be economically important in the
growing of the crop, but which could pose quarantine problems
later. Identification of the pests attacking your crop is
simplified by classifying them based on the type of symptoms
typically observed in the field.
Chewing Type Damage
Chinese rose beetle, Adoretus sinicus Burmeister. Chinese rose
beetles cause heavy damage to basil when population levels are
high. Adult Chinese rose beetles are brown, about 1/2 inch long,
and are nocturnal. The chewing type damage may appear as leaves
with holes or a lace-like appearance when the areas between leaf
veins are eaten. Chinese rose beetles leave small, dark colored
particles of frass which are excreted on the plant while feeding.
Chinese rose beetles feed on a wide variety of ornamental and
food crops in Hawaii. The larvae feed on decaying plant material
and do not damage basil.
Slugs, various species. Slugs are nocturnal mollusks which thrive
during wet weather but can also be troublesome during dry weather
in irrigated fields and greenhouses. Their feeding damage appears
as entirely eaten leaves or foliage with holes or missing parts,
girdling or scraping of the bark, or the entire destruction of
seedlings. Slugs leave a shiny slime trail as they move about.
They hide during the day under plants, rocks, mulch, pottery,
fallen leaves, or in loose soil.
Celery leafminer, Liriomyza trifolii (Burgess). The leafminers
infesting basil are yellowish larvae (maggots) of tiny flies.
Leafminer larvae feed inside the leaf tissue causing tunnels or
mines within the leaf. Leafminer populations have usually been
relatively light on basil and have not resulted in significant
in-field crop losses. However, because leafminer larvae live and
feed inside of the leaf tissue, they cannot be dislodged by
shaking or rinsing the harvested basil. For basil grown for
export, the leaves containing live larvae must be plucked off
before packing. The adult fly is mostly black with some yellow
and is about 1/16 inch long. Adult flies makes tiny punctures on
leaf upper sides while feeding and laying eggs. Leafminer
populations in Hawaii are usually kept below damaging levels by a
number of parasites. Beneficial parasite field populations may be
significantly reduced when broad-spectrum type insecticides are
applied. Because biological control does not provide total
leafminer control, grower/shippers must carefully inspect the
harvested basil to avoid noncompliance with quarantine
regulations.
Beet armyworm, Spodoptera exigua (Hubner). The destructive stage
of the beet armyworm is the larva or caterpillar which causes a
chewing type of damage on basil. The younger leaves are most
commonly infested with more than one of the small, recently
hatched caterpillars. The 1 1/4 inch long caterpillars are light
green with pink to red stripes on their sides. The caterpillars
develop into moths which are nocturnal.
Pinkwinged grasshopper, Atractomorpha sinensis Bolivar. Basil may
be attacked by several grasshopper species. The pink winged
grasshopper commonly feeds on basil and other herbs. Both nymphal
and adult stages cause a typical chewing type of damage to the
leaves. Grasshoppers are more of a pest in home gardens than in
commercial plantings where they are of minor importance.
Sucking Type Damage
Brazilian leafhopper, Protalebrella brasiliensis (Baker).
Brazilian leafhoppers commonly infest herbs such as basil,
perilla (shiso), and mint. The adults are black and yellow,
whereas nymphs are light green. Both stages are capable of
hopping or jumping when disturbed but only the adult, with its
fully developed wings, are capable of flying. Brazilian
leafhoppers are sucking type insects which can cause leaf
scarring, sometimes confused with the mines of leafminers.
Several other leafhopper species attack basil. These insects
generally cause no significant in-field damage even with high
populations levels. However, leafhoppers have resulted in
noncompliance with quarantine regulations, especially with the
eggs and small nymphs which are not easily detected.
Banded greenhouse thrips, Hercinothrips femoralis (O.M. Reuter).
Several thrips species infest and cause significant problems on
basil grown for export. Thrips are small, slender insects which
in the adult stage generally have wings with hair-like fringes.
The banded greenhouse thrips is very common on basil and can
usually be found on the lower leaves of established plants. Their
feeding leaves whitish scars or a silvered appearance on the
leaves. The fecal spotting left by thrips is also noticeable.
Live thrips in harvested basil can be easily overlooked because
of their small size and cryptic habits. Because it is difficult
to identify immature thrips to the species level, the presence of
live thrips in basil shipments has been of great concern to the
local fresh herb export industry.
Silverleaf (sweetpotato) whitefly, Bemisia tabaci
(Gennadius) and greenhouse whitefly, Trialeurodes vaporariorum
(Westwood). Both whitefly species infest basil. The nymphs and
adults feed on plant sap and produce a sticky substance called
honeydew which can serve as a substrate for sooty mold. Whitefly
immature stages, which tightly attach to the leaf undersides,
have caused problems with basil grown for export.
Other Pests. Other pests which cause sucking type damage to basil
foliage include:
Southern green stink bug, Nezara viridula (Linnaeus)
Broad mite, Polyphagotarsonemus latus (Banks)
Red and black flat mite, Brevipalpus phoenicis (Geijskes)
Diseases of Basil
Information on basil disease etiology, epidemiology, or control
is very limited. Although basil is plagued by many diseases, no
fungicides or bactericides are currently registered for this crop
in Hawaii. Growers, therefore, must rely on early disease
recognition and use of cultural practices such as the use of
windbreaks and rain shelters to prevent and manage diseases. By
recognizing the first symptoms of disease, growers can remove
diseased plants and continuously monitor fields for signs of
pathogen recurrence or spread. For disease control: 1) use clean
seed; 2) grow the crop in disease-free soil; 3) maintain
disease-free fields; 4) rotate basil with non-susceptible crops
such as oats, buckwheat, and sunhemp; 5) remove diseased leaves
or plants to reduce field inoculum levels; 6) control moisture
since high humidity or free water on plants strongly favors
disease; 7) increase the spacing between plants to improve air
movement and reduce leaf wetness periods; and 8) increase the
organic matter in the soil which will enhance microbial activity
and favor pathogen reduction. Laboratory analysis is recommended
to identify the causal agent(s) when diseases are first
encountered.
Leaf Spots
Various organisms cause leaf spots on basil in Hawaii. Some of
these are new causal agents, and research on identification,
pathogenicity, and spread of these organisms has been initiated.
These include the following organisms:
Colletotrichum sp. This fungus causes dark leaf spots,
defoliation, tip dieback, stem lesions, and sometimes loss of
entire plants. At times, dead tissue within leaf spots fall away,
producing holes in the leaves. Like most leaf spotting fungi in
the tropics, it is especially troublesome during wet and humid
weather. Fungal spores are produced on diseased plant parts,
splash to healthy leaves or plants, and initiate new spots.
Cornyespora cassiicola. This fungal pathogen produces numerous,
small gray to black specks or leaf spots on basil. Small spots
coalesce and produce larger diseased areas. Older leaves are lost
following heavy spotting. Stem lesions are light brown to brown.
Bacterial pathogens. Bacteria cause water-soaked, dark, angular,
or irregular leaf rots, and brown to black, wet stem rot. When
dry, diseased areas are brittle and easily cracked. Bacterial
diseases are extremely severe during wet weather and also cause
stem rots. Quality and total production will be greatly reduced.
Postharvest losses are also very high.
Aphelenchoides sp. (foliar nematode). These microscopic round
worms cause angular leaf rots during wet weather. Spots are
large, water soaked, and black. Aphelenchoides sp. swim in the
thin film of water covering the plant surface in high humidity or
rain. This nematode penetrates the leaves through stomates, then
feeds and multiplies in the internal leaf tissue.
Wilt, Die-back or Decline
Fusarium sp., causes a major production-limiting disease in
commercial farms and in home gardens. Early signs of this fungal
disease include slow growth and yellowing of the young shoots.
Advanced symptoms include wilting, die-back, and discolored
stems. Infected plants may show a darkened discoloration of the
stem beneath the bark. Longitudinal slices in the stem will
reveal this symptom. Under moist conditions, a light white to
pink, cottony, growth can be observed along the infected stem
areas. Fusarium can persist in the soil for many years, thus,
growers must prevent contamination of their farms or new fields.
The spread of Fusarium can be reduced by quick removal of all
diseased plants and leaves. Do not bring infected plants or soil
onto the farm from contaminated areas. Avoid planting in wet,
poorly drained areas.
Other soilborne pathogens such as Rhizoctonia solani,
Pythium spp. and Phytophtora sp. have been associated with
diseased plants. Further research is needed to establish their
roles in root disease.
Decline Caused by Nematodes
Basil is very susceptible to root-knot nematodes, Meloidogyne
spp. These microscopic round worms damage the roots and impede
the plant's ability to take up water and nutrients from the soil.
As a result, affected plants may show symptoms of nutrient
deficiency, wilting, and yield decline. Galling and root rot
occur on plants that are heavily infected. Growers should check
with agricultural chemical representatives, County Extension
Agents, or Plant Disease Specialists for chemicals that are
registered for soil treatments for nematode control. The addition
of organic matter such as chicken manure (1 lb per hill) may
improve soil conditions and reduce the effect of nematodes and
other pathogens. Other cultural practices for disease control
include rotation with non-susceptible plants and soil
solarization. Soil solarization techniques employ a clear plastic
sheet placed over tilled soil for six or more weeks. The plastic
cover retains heat in the soil and reduces nematode numbers. Soil
solarization is effective only if sufficient sunlight is received
to accumulate heat beneath the plastic cover.
Tomato Spotted Wilt Virus
Tomato spotted wilt virus is spread by several species of tiny
insects called thrips. This disease is not a major problem with
basil but is currently a severe problem in many other crops grown
in Hawaii such as tomato, pepper, lettuce, and chrysanthemum.
Infected plants may have dark colored, ring-like spots on the
leaves, especially on younger ones.
Postharvest Problems from Infected Fields
Unhealthy fields produce leaves of poor to marginal quality.
Leaves harvested from fields with disease problems are rapidly
rotted by bacterial and fungal pathogens following packing. A
minor field problem involving low levels of bacteria can result
in major postharvest losses. Avoid harvesting from fields with
known bacterial pathogens present. Select clean leaves from the
tips only and avoid branches near the base of the plant.
Weeds
High density plantings and physical or mechanical weed control
are the most common practices used to prevent weed problems in
basil. Weed control is enhanced with proper field preparation
prior to planting. Both plastic and organic mulches may also be
utilized to minimize weeds in the field. Check with your County
Extension Agent, Department of Agriculture, or chemical sales
representative for herbicides which may be registered for use on
basil.
HARVEST AND POSTHARVEST PRACTICES
Product Quality
Hawaii relies on the high quality of its horticultural products
to maintain competitiveness in the local and export market. High
quality, including rich flavor and attractive dark green or
purple foliage, is achieved by following proper cultural and
postharvest handling practices. Proper field culture is essential
to obtain a quality end-product. Growers should determine the
product characteristics desired by particular market outlets.
When growing basil for export maintain a line of communication
with Department of Agriculture personnel to determine acceptable
and unacceptable cultural and postharvest management practices
which may have an effect on the quality of your product.
Harvest Operation
Basil is ready for hand harvest about 30-35 days after planting.
In Hawaii, 4-6 inch shoot tips with two to four sets of true
leaves are picked. However, because variations exist depending on
the intended use of the product, check with your buyer for
desirable product characteristics (stem length, etc.). Basil
fields are picked daily when plants are rapidly growing, or every
3-5 days. Heavier picking (tips > 6 in) will delay the timing
between harvests. Regular harvesting prevents flowering and seed
setting and encourages vegetative growth. Basil will grow about
one inch per day under the proper environmental conditions.
During the picking operation try to hold the tips from to stem,
to minimize contact with the fragile foliage tissues.
Handling and Packing
Fresh basil is very tender and is easily damaged by rough
handling, desiccation, and chilling. To ensure and maintain
product quality, minimize bruising when harvesting and packing.
Harvested basil is usually dipped in cool water to reduce the
"field-heat" and to help dislodge soil particles and
some of the insects pests that are not strongly adhered to the
plant. It is important to drain off the free water prior to
packing the product. Basil may be packed in bulk or packed in
twelve bunches to the pound in polypropylene bags placed in paper
cartons, sometimes lined with moist paper. For the local market,
basil is packed in 1-2 oz plastic bags.
Storage and Transportation
The shelf-life of basil is relatively short as compared to other
herbs such as rosemary, oregano and thyme, and 30% losses during
shipment are not uncommon. Basil is susceptible to chilling
injury and should not be stored below 40oF (5oC) for extended
periods. Basil that has been damaged by cold (chilling injury)
turn black and are rendered unsuitable for sale. Store and ship
fresh basil at 45 to 55oF (5-13oC) and 95% relative humidity.
Diseases affecting basil in the field will likely reduce the
shelf-life of the harvested product. Basil for export must be
carefully inspected before packing to help ensure that it is free
from live insects which will result in noncompliance with Federal
and State quarantine regulations.
Other Postharvest Tips for Basil Include:
_ Harvest early in the morning when temperatures are lower.
_ If packaged in bags to reduce moisture loss, maintain at a
constant temperature to prevent condensation.
_ Packages may be perforated for ventilation or may be of a
polymer which is partially permeable to water vapor.
_ Do not store or ship with fruits or vegetables that release
ethylene.
REFERENCES
Cantwell, M. 1992. Handling of fresh culinary herbs. Small Farm
News. Univ. California Small Farm Center, Davis. July/August.
Dostal, D. L. 1990. Postharvest Storage of Sweet Basil. M.S.
Thesis. Michigan State University.
Flavin, D.J. 1987. Tropical herb production and marketing. pp.
77-79. In: J.E. Simon and L. Grant (eds.) Second Nat. Herb
Growing & Marketing Conf. Proc. Indianapolis. 19-22 July.
Purdue Agr. Expt. Stat. bull. 530.
Hamasaki, R. T. and D. M. Tsuda. 1993. Survey of Arthropod Pests
on Commercial Herbs Grown In Hawaii. Unpublished.
Hawaii Agricultural Statistics Service. 1992. Hawaii Herbs: Fresh
Production, Farm Price, and Farm Value.
Joyce, D. and M. Reid. 1986. Postharvest handling of fresh
culinary herbs. The Herb, Spice, and Medicinal Plant Digest 4(2):
1-7.
Uchida, J. Y. 1991. Disease of Herbs In Hawaii. Presentation at
the Third Annual Hawaii Herb Association Conference.
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