Site selection:-
The three major environmental factors to consider in selecting a site to grow papayas are temperature, moisture (rainfall and soil drainage), and wind. The hermaphrodite papaya plant preferred for commercial orchards is more sensitive to the growing environment than the female papaya plant, and therefore selection of a suitable site is critical. Another condition to consider is the amount of sunlight the site receives to support plant growth and fruit production. Insufficient sunlight results in low yields and fruits with inadequate sugar and encourages plant diseases affecting papaya production.
Temperature:-
The temperature of the site is the most important factor. Commercial papaya production in Hawaii is generally limited to low-elevation areas where the minimum temperature is above 60°F. Temperatures below 60°F cause carpeloidy, which results in “cat-face” deformity when floral stamens develop abnormally into fleshy, carpel like structures.
Moisture:-
A minimum monthly rainfall of 4 inches (100 mm) and an average relative humidity of 66 percent are suggested as “ideal” for papaya growth and production. In low rainfall areas irrigation should be provided via drip-type or mini-sprinkler irrigation systems.
Papaya requires good soil drainage. Where soil drainage is restricted, papaya is susceptible to fungal root diseases. The plants are severely affected by water logging and can be killed when subjected to puddle conditions for even a few hours.
Wind:-
Papaya plants must be protected from wind. Plants exposed to constant wind develop deformed, crinkled leaves. When wind stress damage is excessive, the plants have reduced growth, fruit set, fruit quality, and productivity. Wind-blown dust can cause sap bleeding that harms fruit appearance.
Land preparation:-
After existing vegetation is cleared, soil samples should be collected and analyzed to determine if there are any problems. Based on analysis results, recommendations are provided on adjusting soil pH and the amounts of soil amendments required to correct any deficiencies. Papaya grows well at a soil pH between 5.5 and 6.5.
Seedling production:-
Papaya can be either seeded directly or transplanted into the new field. The seeds are planted in a trench approximately 6 inches long dug parallel to the planting row. In soil areas, transplanting allows growers to place a larger plant (4 –8 inches tall) into the field. Seeds are direct-seeded into individual cells (2 x 2 inches) placed in full sunlight. The potting media should be sterile and well drained to minimize root rot.
Planting:-
Planting in “virgin” lands or fields in which papaya has not been grown before is preferred because of low disease and insect pressure. It is becoming increasingly difficult to find such fields.“Replant” fields in which papaya has recently been grown generally have high levels of Phytophthora palmivora spores due to the decomposition of infected papaya fruit, trunk, and root residues.
In fields with mineral soils, residual fungi and nematodes can be controlled with soil fumigants. The fumigant is injected under plastic mulch before planting and allowed to volatilize for 2–3 weeks to ensure that seedlings are not damaged when transplanted. Fumigation reduces the population of nematodes and residual fungi and allows young roots to grow free of pathogenic organisms.
Plant sex selection:-
Seeds from solo varieties produce plants of two reproductive types: female and hermaphrodite. Although there is no difference in the eating quality of fruits from these two types, the commercial market prefers the pear shaped fruits produced by hermaphrodite plants over the rounder fruits of the female plants. Female plants require cross pollination to produce fruit, and there can be gaps in production when pollination does not occur. The desired hermaphroditic plants have flowers that contain both an ovary (female organ) and pollen sacs (male organ); they are self-pollinating. Hermaphroditic flowers are more uniformly tubular than female flowers, which are bulbous at the base and pointed at the end (see illustration). Female flowers contain an ovary but lack pollen sacs, and they need to be pollinated.
Thinning:-
Thinning is done to reduce competition while retaining enough plants to ensure that a hermaphrodite plant is finally obtained. In direct-seeded fields, the plants are thinned three times. First, one month after germination, the number of seedlings is reduced to 6–10 per hole. Second, at three months after germination, the number of seedlings is further reduced to three plants for the standard commercial solo cultivars, which have a sex segregation ratio of 2:1 (two hermaphrodite plants for each female plant), ensuring a 97 percent chance of retaining one hermaphroditic plant.
Soil conditions:-
When papaya is grown in soil, the soil should be sampled in advance of planting to allow for incorporation of any amendments needed. The results will determine the form and application rate of liming material required to adjust the soil pH to the 5.5–6.5 range. Soil should be analyzed annually to determine if current practices are sufficient for maintaining production. If deficiencies are found, recommendations will be given by the soil testing laboratory.
Weed control:-
Weed control is a major cost in papaya production, particular in young fields. In “virgin fields,” the initial weed population may be low, requiring minimal hand weeding. The use of fumigation or the “virgin soil” technique reduces the need for hand weeding in replant fields. Before planting, irrigate fields to germinate weed seeds and then spray the weeds with a systemic herbicide .
It is advisable to shield the young plants when spraying. Older papaya plants with woody trunks are more tolerant of glyphosate-based systemic herbicides such as Roundup, but care in herbicide application should be emphasized. Herbicide applications are usually limited to a bimonthly or quarterly interval in mature orchards, where shading reduces weed growth.
Leaf trimming:-
Leaves of bearing plants should be trimmed to facilitate application of fungicide to the fruit column and minimize fruit scarring from petioles rubbing against the fruits. It is important to retain as many leaves as possible, because they produce the energy that supports the developing fruits. Trim only leaves with petioles that angle below horizontal. Trimming should be kept to a minimum in winter. Petioles should be cut at the halfway point between the leaf blade and base to minimize fungal infection.
Pest management:-
Papaya crops are affected by various disease, insect, and mite problems. Becoming aware of potentially injurious organisms and taking appropriate management measures are important for success. The following sections present a brief overview of the major pests of papaya.
Diseases:-
The diseases of papaya include those caused by a virus, fungi, and nematodes. The papaya ring spot virus (PRV) is the most severe papaya disease and is often the limiting factor in papaya production throughout the world. PRV is widespread on Oahu.
Papaya plants infected with PRV must be destroyed to minimize spread of the virus. Virus problems can be avoided by planting genetically resistant cultivars.
PRSV is not transmitted via seeds, but it can be spread to areas where it is not present by transporting infected seedlings. To avoid introductions of the virus, do not transport papaya seedlings between islands. On islands where PRV is already present, raise seedlings in nurseries close to the planting site to minimize the possibility of spreading the virus further.
Fungal diseases are a major problem in papaya production. The strategy for fungal disease management is prevention through the application of fungicides at regular intervals. Proper timing, deposition, and coverage of the pesticide application is critical for effective control. Once the disease is established, the fungicides have minimal impact on control. Under high-rainfall conditions, high-volume sprays (75–100 gallons per acre) are required at 2–3 week intervals. Under drier conditions, low-volume sprays (40–50 gallons per acre) at 3–4 week intervals are adequate to protect the exposed fruit surfaces.
The use of a surfactant is important to ensure good distribution and adherence of the fungicide spray. Currently, the most effective fungicide for protecting fruits is mancozeb, which can be used in combination with a copper product to increase efficacy.
Powdery mildew can cause premature loss of foliage, resulting in reduced fruit quality and yield. Wet-table sulfur is effective for powdery mildew control but only when thorough coverage of the foliage is achieved. Nematodes can be controlled by fumigating the soil before planting.
Insects:-
Insects can be a major problem in papaya production. The Stevens leafhopper can be a serious problem when its populations build to high levels, which can occur under dry conditions. Infestation is recognized by the yellowing of terminal leaves and the exudate from feeding wounds on petioles. The phytotoxic reaction of the plant, termed “hopper burn,” is characterized by the browning (or “firing”) of leaf tips and edges.
The white peach scale is a recent introduction to Hawaii. The insects can form large populations at the base of the trunk, giving it a whitewashed appearance. They may move up the trunk and invade the fruit column. If this pest is on fruit intended for export, it becomes a quarantine concern.
Fruit flies are primarily a problem in fruits allowed to ripen on the tree; they are not a major problem when fruits are harvested mature-green for export sale. Papaya fruits for export need to be subjected to approved disinfestations procedures.
Mealybugs and white peach scale are occasional pests on the fruits and may lead to rejection at the packing plant. Thorough spray coverage is important in mealybug control, especially at the stem end of the fruit, near the trunk.
Miticides generally kill only adults and nymphs and have little effect on eggs. Timely chemical applications are necessary to control the emerging young, which can become egg-laying adults in 7–14 days. Proper spray coverage is essential to prevent “escapes” from reestablishing their population to destructive levels.
Mites:-
Mite infestation can affect both the fruit and foliage. It becomes a significant problem under hot, dry conditions. Mites usually feed on the underside of leaves and on young, developing tissues. Miticides generally kill only adults and nymphs and have little effect on eggs. Timely chemical applications are necessary to control the emerging young, which can become egg-laying adults in 7–14 days. Proper spray coverage is essential to prevent “escapes” from reestablishing their population to destructive levels.
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