Proper irrigation can significantly improve grower returns by providing greater yield, higher fruit quality, and improved water and nutrient efficiency.
Inadequate soil moisture can lead to poor production from reduced flower formation, flower development, fruit set, and shoot growth, as well as from exacerbating alternate bearing and inadequate nutrient absorption. Poor irrigation can also lead to poor fruit size and shrivel.
Excessive soil moisture can result in poor shoot growth, yellow foliage and tree loss due to asphyxiation or root disease (phytophthora).
In California, mature table olives need about 36 acre-inches per acre of water per year to promote optimal fruit size and productivity. Oil olives require about 24 acre-inches of water per year.
Olive tree water needs are based on evapotranspiration (ETo) adjusted by an olive crop coefficient (Kc). ETo is the sum of evaporation of water from soil and transpiration of water from a reference crop then adjusted by the Kc to reflect the olive tree’s foliage transpiration.
Oil olives produce more oil with regulated deficit irrigation, while reduced irrigation in table olive orchards to 50 percent of normal from June through mid-August, did not have a significant negative effect on fruit weight, yield or gross revenue. See more information here.
Maximize water efficiency and orchard productivity by using information from site variables such as crop ET, rainfall, and irrigation system efficiency.
Olive trees need 16 essential elements to fulfill a cycle of growth. An olive orchard’s supplemental nutritional needs vary depending on soil fertility, orchard age, soil composition, nutrients in irrigation water, and cultivation practices.
Leaf nutrient levels vary normally throughout the growing season – some accumulate, some are relatively static, and some diminish. In addition, annual variations in nutrient levels can occur for other reasons, such as the crop load, water availability in the soil, crop management techniques, and interactions between nutrients.
Nutrient deficiencies observed in California olive orchards have been limited to nitrogen, and, rarely, potassium and boron. Nitrogen is the only nutrient supplement that might be needed on an annual basis. Investigate the cause of a mineral deficiency, because the solution is not always to simply provide fertilizer.
Determine orchard fertilization needs through annual leaf tissue analyses and visual deficiency symptoms. For annual leaf tissue analyses, collect at least 100 leaves from several trees in each homogenous area of an orchard from the middle of non-bearing, current-season shoots. Low nitrogen levels are visually indicated by poor shoot growth (less than 8 inches) and leaves with a light green-yellow shade, but must be verified by an objective, quantitative leaf tissue analysis.
Seek to achieve nutrient levels consistent with this table:
Table. Critical nutrient levels from July olive leaf tissue analysis from subterminal leaflets of current year’s non-fruit bearing growth.
Element | Deficient | Sufficient | Toxic |
---|---|---|---|
Nitrogen (%) | 1.40 | 1.50 - 2.00 | |
Phosphorus (%) | 0.10 – 0.30 | ||
Potassium (%) | 0.40 | > 0.80 | |
Calcium (%) | > 1.0 | ||
Magnesium (%) | > 0.10 | ||
Manganese (ppm) | > 20 | ||
Zinc (ppm) | unknown | ||
Copper (ppm) | > 4 | ||
Boron (ppm) | 14 | 19 - 150 | > 185 |
Sodium (%) | > 0.20 | ||
Chlorine (%) | > 0.50 |
Avoid applying fertilizers if leaf tissue nutrient levels are adequate. Excessive fertilization increases production costs, nutritional imbalances and environmental pollution.
Fertigation, the application of fertilizers dissolved in irrigation water, is the most efficient fertilizing method. Fertigation delivers nutrients to areas of greatest root activity and density, maximizing a tree’s nutrient absorption. Fertigation requires cleanliness and irrigation system maintenance, because some fertilizers can clog the system. Fertigation with some fertilizers can also increase soil salinity.
Organic fertilizers such as compost or cover crops have advantages in releasing nutrients slowly year-round, developing soil structure and aiding water infiltration, but also may require additional water (e.g. for a cover crop). Any fertilizer can leach nutrients during cold and rainy periods (when trees are not taking up nutrients) and allow nitrogen runoff into water resources.
The primary olive pests in California are Olive Fly and Black Scale. For more information on olive pests, see UC Integrated Pest Management.
The larva of olive fly, Bactrocera oleae (Gmelin), feed on olive fruit, leading to losses for table olive growers and potentially imparting a defective flavor to olive oil. Olive fly can be controlled but not eradicated in California.
Monitor olive fly with either yellow sticky traps containing a sex pheromone and/or ammonium carbonate, ammonium bicarbonate, or diammonium phosphate bait; or with MacPhail traps containing yeast hydrolosate and the same ammonia-producing chemicals as used with yellow sticky traps.
Control olive fly populations by collecting and destroying fruit on the ground and in trees after harvest, by use of bait sprays, and by “attract and kill” devices. Use Danitol late in the season if heavy infestations emerge after the summer. See more information about olive fly control here.
Black scale, Saissetia oleae (Olivier), feeds on olive leaves and twigs and excretes sugary honeydew that supports sooty mold growth impairing photosynthesis. Black scale infestation can reduce fruit bud formation, cause leaf drop and twig dieback and reduce the crop in the following year.
Monitor black scale in April by checking the inner canopy of about 40 trees per block for honeydew droplets on the leaves, and in May by checking at least 10 branches on 10 trees per 10-acre section for adult scale. Examine the terminal 20 inches of the branches, count the number of scale, and calculate the average per branch for the 10 trees.
Control black scale by pruning the trees to open up the canopy in the trees’ center. Heavy infestations (more than four scale per branch) also treat with insecticide in-season. See more information here.
Primary olive diseases in California are Olive Knot, Olive Leaf Spot (“Peacock Spot”), and Verticillium Wilt. For more information on olive diseases, see UC IPM.
Olive knot, Pseudomonas syringae pv. savastanoi (Smith 1908), is a bacterial disease that produces galls (knots) on twigs and small branches at wounds, even minor wounds such as leaf scars. Cracks in bark caused by freeze injury can also lead to severe damage from olive knot. Cultivars that are sensitive to freezing (such as Manzanillo) are more susceptible to olive knot. The disease can kill young trees, reduce productivity in more mature trees, and produce off-flavors in the fruit.
Infection almost always occurs with moisture, particularly rain but also humid conditions, and can be carried by pruning shears and harvest equipment.
Copper has traditionally been used to control olive knot but has had inconsistent and diminishing effectiveness in recent years. UC research is underway to identify new methods of control, and new chemicals are in the registration process. See more information here.
Olive Leaf Spot (“Peacock Spot”)
This fungal disease is caused by Spilocea oleaginea (Cast.) Hughes. Lesions most commonly appear on upper leaf surfaces, beginning as tiny sooty blotches and progressing to green or black spots, with some lesions developing a yellow halo, thus the name Peacock Spot. Infected leaves drop prematurely, weakening small wood and reducing productivity.
Most infections occur during the coldest part of the California winter, and it may take several years before the disease causes economic loss.
Control Peacock Spot by a spraying a copper-containing fungicide, once in late fall before winter rains begin. See more information here.
Verticillium wilt, Verticillium dahlia Kleb., is a soil-borne fungus infecting a wide range of crops grown in California, including cotton, melon, pepper, pistachio, stone fruit and tomato, and some indigenous weed species. The fungus persists in soil as microsclerotia, which resemble small grains of sand. Leaves suddenly collapse and die on one or more branches soon after the first warm summer weather, reducing productivity significantly.
There is no control method available for Verticillium Wilt. Conduct a soil test for microsclerotia prior to establishing a new orchard. Previously planted crops that harbor the Verticillium Wilt fungus are likely to leave high levels of microsclerotia. See more information here.
Weed management is essential for increasing orchard productivity (by eliminating competition for water and nutrients and increased frost protection, for example), facilitating harvest, removing fire hazards, and eliminating habitat for damaging insects and rodents.
The proper weed management strategy depends on many factors including weed species, soil type, irrigation method, amount of control desired and organic certification. Strategies include hand-weeding, mowing, disking, mulching, weed fabric, and spraying with pre-emergent and post-emergent herbicides.
Groves in the San Joaquin Valley are almost exclusively weed-free. Most California olive growers manage weeds by mowing the row middles and spraying herbicide in the tree row. Weed management is significantly more expensive in organic orchards. Begin weed management in new orchards to speed tree growth and productivity. See more information on weed management.
Reducing the fruit load (thinning) in heavy crop years may be necessary to achieve adequate table olive size and mitigate alternate bearing.
Chemical thinning is the most useful fruit thinning tool available to table olive growers. Post-bloom application of naphthalene acetic acid (NAA) regulates crop size to improve fruit size and results in better shoot growth for return bloom the following year.
Pruning is not ideal as a thinning method because pruning removes both leaves and fruit (leaf-to-fruit ratio is an important factor in fruit size). In addition, pruning is labor intensive. Pruning is, however, the most traditional method and is useful when chemical fruit thinning is not practiced or available.
Hand thinning is an effective method but is too labor intensive to be practical for most growers. When hand-thinning, wear gloves to protect fingers. Strip fruit from trees with both hands but be careful not to damage or remove leaves. Thin the twigs from which at least five or six olives can be removed from one pull. Complete within four weeks of full bloom.
Prune to optimize orchard productivity, mitigate alternate bearing, facilitate efficient fruit removal, manage crop size, rejuvenate productivity in older trees, reduce pests and disease, and reduce damage from mechanical harvesters.
Prune in spring and summer after winter rains have passed, to minimize diseases such as olive knot, attacks by pests, and susceptibility to freeze damage.
How a tree is trained and pruned is determined by the olive’s natural growth and crop-bearing pattern. Olives have “apical dominance,” where the central stem grows more strongly than lateral stems. The apical stem, which is vegetative rather than fruiting, produces several lateral buds that are almost exclusively fruiting buds. The two kinds of pruning cuts, heading and thinning, produce a different result with this apical vegetative and lateral fruit-bearing pattern:
- Heading cuts decrease apical shoot growth by removing the apical vegetative bud and may stimulate latent lateral vegetative growth further back on the shoot. If the tree is vigorous and the heading cuts are severe this strong response could be exclusively vegetative and therefore delay fruit production for two years beyond pruning.
- Thinning cuts remove a shoot where it emerges from the branch, producing a much weaker vegetative response and allow more light interception than heading cuts.
Moderate hedging cuts on alternate sides of the tree in alternate years will reduce the response of vegetative and fruiting shoots to produce consistent annual crops, thereby mitigating the alternate bearing tendency of many olive cultivars. Trees should be mechanically topped annually to maintain tree size and maximize fruit production on the lower lateral canopy (topping less frequently has been demonstrated to produce strong vegetative growth responses and erratic fruit production.)
Hand-harvesting.Hand-harvested orchards can be assisted with hand-held implements, hand-held pneumatic rakes, hand-held limb shakers, and by beating the trees with poles.
- Prune to achieve a lobular shape when viewed from above and to allow light channels into the trunk so that growth and fruiting is not restricted to the outer shell.
- Prune to maintain a safe tree height below 18 feet so that harvesters do not have to climb too high on ladders.
- Prune nonproductive parts of the tree, or not at all, during light-crop years, to minimize crop loss. Pruning can be more severe in heavy crop years but does not result in larger fruit desired by table-olive growers since fruit size is largely determined on each branch by leaf-to-fruit ratio.
- Prune mature trees from traditional orchards over several years so as to not dramatically reduce crop and stimulate excessive non-fruiting growth.
- Harvest by sliding a cupped, protected hand down an olive shoot in a milking action, removing olives into a container or onto a tarp. Avoid removing leaves as to minimize the potential for disease, and avoid stepping on olives in tarps.
Trunk-shaking equipment.
Trunk-shaking equipment includes side-by-side harvesters and umbrella trunk shakers. These harvesters operate most efficiently when the orchard is young enough that the shaking provides efficient fruit removal. Eventually the efficiency of trunk shaking will be reduced as the trunk grows thicker, making it necessary for the grower to switch to other harvest methods, such as limb-shaking or canopy-contact equipment.
- Direct the growth into stiff upright scaffolds, which efficiently transmit the shaking force. Top the trees at no more than 12 feet with scaffolds having no more than a 45° angle from the trunk. Prune with a combination of mechanical hedging and topping (or a single, gabled cut) with additional hand pruning to remove lateral branches extending from the scaffolds at less than a 45° angle.
- Decrease canopy density with hand thinning cuts, as a heavier canopy will dampen shaking and decrease removal efficiency.
- Prune generally to a V-shape with visibly filtered light.
- Remove branches extending laterally into the row middle, which can reduce harvester efficiency.
- Prune annually. If using a double-sided mechanical pruner, the annual pruning schedule can be every other row middle every other year. If using single-sided mechanical pruner, prune alternate tree row sides on alternate years. Top all trees annually.
Limb-shaking equipment. Limb-shaking equipment
- Prune to establish a maximum of five well-spaced, upright scaffold branches (more that five scaffold branches increases the harvest time for each tree).
- Decrease canopy density with hand-thinning cuts, as a heavier canopy will dampen shaking and decrease removal efficiency.
- Remove branches extending laterally into the row middle, which can reduce harvester efficiency.
Canopy-contact equipment. Canopy-contact harvesters come with one of two mechanisms. Some compress and agitate the canopy with a series of horizontal bars called bow rods, while others have a head with vertical rows of radiating tines that extend into the canopy and remove the olives with a horizontal whipping motion. Both removal methods remove the fruit on the outer canopy more efficiently than interior fruit, but, unlike trunk-shaking equipment, it is not necessary to thin the canopy as the removal force is applied directly to the canopy.
- Super-high-density (SHD) orchards in California typically have hedgerows spaced at 5-6 feet within the row and 12-13 feet between rows. High-density (HD) orchards with hedgerows spaced at 8-10 feet within the row and 16-18 feet between rows have been demonstrated to be optimal for harvesting and yield for California table olives.
- Train the tree into an upright narrow canopy, with primary scaffolds parallel to the tree row and with shorter branches extending into the row middle, to facilitate production of a continuous, flat, fruiting wall.
- Train SHD orchards to an espalier within the row. This can be accomplish by tying to a trellis or by simply weaving the branches through the trellis wires when adequately stiff. Train HD orchards to no more than 12 feet high after a season’s growth, 6 feet wide from row middle to row middle, with the bottom of the canopy 4 feet from the ground. Canopy width within the row will be a function of tree spacing within the row.
- Remove branches, which can reduce harvester efficiency and damage harvest equipment, and will probably be broken by the harvester.
- Prune annually. If using a double-sided mechanical pruner, the annual pruning schedule can be every other row middle every other year. If using single-sided mechanical pruner, prune alternate tree row sides on alternate years. Top all trees annually.