Avocado Fertilization and Harvesting Part 2

CULTURAL PRACTICES

Trees should be spaced 25 to 35 feet apart, depending on the cultivar. In Kona, on the Big Island, avocados are often interplanted with coffee and macadamia nuts. But for the best management they should not remain interplanted with other fruit crops when mature. Organic mulches or herbicides are recommended for weed control. Cultivation for weed control should be avoided or should be done as shallow as possible to avoid damage to the avocado root system. Pruning is usually unnecessary except to shape young trees and remove dead branches.

FERTILIZATION

Specific nutrient requirements of avocado grown in Hawaii are not well known. Information on fertilization of avocado is based on avocado production elsewhere. For preplant applications, have the soil tested before planting and follow the recommendations. To make adjustments for soil pH and calcium (Ca) deficiencies before planting, soil from each distinct area of the orchard should be sampled. Soil type may be determined by the use of soil survey reports obtained from public libraries or the county USDA Soil Conservation Service offices. The University of Hawaii Cooperative Extension Service Circular No. 476, Soil Classification in Hawaii, may provide useful information on soil management.

The optimum soil pH for avocado is between 6.2 and 6.5. Lime (calcium carbonate) can be added to acidic soil to raise the pH to 6.5. Dolomite can be substituted for part of the lime requirement if magnesium (Mg) is deficient. Calcium nitrate or calcium sulfate (gypsum) may be used to provide calcium when soil pH is adequate. Also, adequate calcium may be provided by Phosphorus (P) applications when super phosphate (20% Ca) or triple superphosphate (14% Ca) is used. Lime, dolomite, and P fertilizers should be mixed with the soil thoroughly prior to planting to place the fertilizers at the root zone.

When avocado trees are transplanted into the field, a complete fertilizer containing nitrogen (N), phosphorus (P), and Potassium (K) should be mixed with the soil in the planting hole. Later fertilizer applications should be done by broadcasting fertilizer evenly over the root zone between about 1 foot from the trunk and 1 to 2 feet beyond the leaf drip line. Fertilizers may also be applied in solution by injection into drip irrigation waterlines, or in foliar sprays. Cultivation over the root zone to incorporate fertilizer should not be done because damage to the shallow roots may occur; mechanical damage to the roots may promote Phytophtora infestation. High levels of calcium in the soil, high levels of ammonium ions, and an increased amount soil organic matter help to combat Phytophtora.

Hawaii soils tend to be low in nitrogen and potassium. In addition, nitrogen and potassium are necessary to produce large high quality fruit. A 10-5-20 fertilizer is generally used after trees begin to bear fruit to provide the needed nitrogen and potassium. A 10-30-10 fertilizer is generally used during the early growth stages because phosphorus is needed in early stages to develop a strong root system. Zinc (Zn) is important to avocado and should be applied when zinc deficiency symptoms occur. Fertilizers should be used carefully because an excessive amount of fertilizer can cause root damage, leaf burn, defoliation and even death of the tree.

Leaves may be analyzed to determine any nutritional deficiencies. Leaf analysis is most reliable in mature orchards with trees over seven years old. Also, leaf analysis is often done in conjunction with soil analysis. Leaf samples should be healthy, full-sized, produced by the most recent growth flush, and taken from branches that are neither flushing nor fruiting. Six to eight leaves taken from each tree are combined to make one sample for each tree. Leaves may be taken from several branches if uniformity is maintained, and samples from uniform trees may be combined. Leaves should be gently wiped or rinsed (not soaked) in tap water to remove any soil or spray residues. Refrigerate leaves in plastic bags labeled with a permanent marker. The label should provide complete information on the sample source. Paper bags should be used if refrigeration is not available. The leaf samples should be transported to the laboratory as soon as possible.

HARVESTING

Avocados are harvested with hand-held poles and baskets. In flat areas in California, man-positioning machines are used to lift the pickers. Fruits are picked when mature but still hard. Determining when to harvest avocados can be difficult and may require experience. A slight change in skin color, loss of glossiness, or a brown seed coat is a sign of maturity. Pruning shears or special clippers should be used to harvest avocados. The pedicel should also remain attached to the fruit.

POSTHARVEST

The fruits are allowed to ripen off the tree. Softening of the fruit indicates ripeness. Determining ripeness of thick-skinned varieties may be difficult for the untrained. The fruit cannot be picked too early or the fruit will shrivel and fail to ripen. Fruits of some cultivars may be refrigerated for several days after ripening without damage.

DISEASES

  • Dodder (Cuscuta sandwichiana)
  • Avocado root rot (Phytophtora cinnamomi)
  • Stem-end rot (Phomopsis sp., Dothiorella sp.)
  • Fruit rot (Dothiorella sp.)
  • Anthracnose (Colletotrichum gloeosporioides)
  • Leaf tip-burn (various causes, not all disease related, including salt accumulation from over fertilizing)
  • Algal leaf spot (Cephaleuros virescens)
  • Scab (cause unknown; resistant varieties are available)

INSECTS

  • Red-banded thrips (Selenothrips rubrocinctus)
  • Armored scales (several species)
  • Chinese rose beetle (Adoretus sinicus)
  • Fruit fly (Ceratitis capitata and Bactrocera dorsalis)
  • Mites
  • Black twigborer (Xylosandrus compactus)
  • Mealybug (Dysmicoccus neobrevipes, Nipaecoccus nipae)
  • Plantbugs (Hyalopeplus pellucidus and other species)

For more information, contact:

Dept.of Agriculture
D.A. Compound, Elliptical Rd., Diliman,Quezon City
Tel. Nos. (632) 929-6065 to 67 / 920-3991 / 928-1134
Web: www.da.gov.ph

source: extento.hawaii.edu

Leave a Reply

Your email address will not be published. Required fields are marked *