Citrus Fruits:Guidelines

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GUIDELINES: CITRUS PRODUCTION



STATISTICS

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OUTLINE OF MANAGEMENT ACTIVITIES

Cultural Practices

_____ Test soil for nutrient status and pH every year. Maintain records of test results and fertilizer applications. _____ Apply fertilizer according to test results. _____ Apply nitrogen to the soil or foliage in late winter or early spring. _____ Light pruning may be necessary to remove dead, broken or diseased limbs. _____ Make necessary precautions to avoid frost damage to the trees.



Pesticide Management

_____ Use approved and registered pesticides according to label. _____ Maintain application records including date, location, applicator, target pest, pesticide name, EPA registration number, formulation, rate and number of acres treated are maintained. _____ All sprayers are calibrated at the start of the season. _____ Minimize pesticide drift. _____ Develop and implement a resistance management plan. _____ Select pesticides which will preserve natural enemies of pests. _____ Use separate sprayers for herbicides and insecticides. _____ Check sprayer(s) calibration at least once during the season. _____ Recalibrate each sprayer as needed. _____ Maintain records of planting dates for treated fields. _____ Keep records of stage of crop of treated field. _____ Use water-sensitive spray cards to test coverage of leaf surfaces.



Insect Pest Management

_____ Scout "SUSPECT INSECTS" .. Armored Scales .. California Red Scale and Yellow Scale .. Purple Scale .. Soft Scales .. Black Scale .. Brown Soft Scale .. Citricola Scale .. Cottony Cushion Scale .. Thrips .. Citrus Thrips .. Greenhouse Thrips .. Lepidoptera (Orangeworms) .. Amorbia (Western Avocado Leafroller) .. Beet Armyworm .. California Orangedog .. Cutworms .. Fruit tree Leafroller .. Loopers .. Omnivorous Leafroller .. Orange Tortrix .. Pink Scavenger Caterpillar .. Western Tussock Moth .. Mites .. Broad Mite .. Citrus Bud Mite .. Citrus Flat Mite .. Citrus Red Mite .. Citrus Rust Mite (Silver Mite) .. Sixspotted Mite .. Yuma Spider Mite .. Miscellaneous Pests .... Ants .... Aphids .... Brown Garden Snail .... Fuller Rose Beetle .... Katydids .... Mealybugs .... Potato Leafhopper .... Whiteflies

_____ Keep records of monitoring results, weather, and management activities. _____ Start sampling before populations begin to build and continue through the damaging stages. _____ Monitor individual orchards for insects and their natural enemies when they are likely to be present. _____ Keep scouting a record.

_____ Identify control measures and implement according to thresholds.



Disease Pest Management

_____ Identify major disease pests and estimate losses. _____ Keep a scouting record. _____ Identify control measures and implement according to thresholds.



Weed Pest Management

_____ Scout "SUSPECT WEEDS" .. barley, hare (Hordeum leporinum) .. barnyardgrass (Echinochloa crus-galli) .. bermudagrass (Cynodon dactylon) .. bindweed, field (Convolvulus arvensis) .. bluegrass, annual (Poa annua) .. bromegrasses (Bromus spp.) .. canarygrass (Phalaris canariensis) .. chickweed, common (Stellaria media) .. clovers (Trifolium spp.) .. cockleburs (Xanthium spp.) .. crabgrass, large (Digitaria sanguinalis) .. cudweeds (Gnaphalium spp.) .. dallisgrass (Paspalum dilatatum) .. fescue, red (Festuca rubra) .. fiddlenecks (Amsinckia spp.) .. filarees (Erodium spp.) .. fleabane, hairy (Conyza bonariensis) .. foxtails (Setaria spp.) .. goosefoot, nettleleaf (Chenopodium murale) .. groundsel, common (Senecia vulgaris) .. henbit (Lamium amplexicaule) .. horseweed (Conyza canadensis) .. johnsongrass (Sorghum halepense) .. knotweeds (Polygonum spp.) .. lambsquarters, common (Chenopodium album) .. lettuce, prickly (Lactuca serriola) .. lovegrasses (Eragrostis spp.) .. mallow, little; cheeseweed (Malva parviflora) .. miner's lettuce (Claytonia perfoliata) .. mullein, turkey (Eremocarpus setigerus) .. mustards (Brassica spp.) .. nettle, burning (Urtica urens) .. nightshades (Solanum spp.) .. nutsedge, purple (Cyperus rotundus) .. nutsedge, yellow (Cyperus esculentus) .. oat, wild (Avena fatua) .. pigweeds (Amaranthus spp.) .. pineapple-weed (Chamomilla suaveolens) .. polypogon, rabbitsfoot (Polypogon monspeliensis) .. puncturevine (Tribulus terrestris) .. purslane, common (Portulaca oleracea) .. radish, wild (Raphanus raphanistrum) .. redmaids; desert rockpurslane (Calandrinia ciliata) .. rocket, London (Sisymbrium irio) .. ryegrass, Italian (Lolium multiflorum) .. sandburs (Cenchrus spp.) .. shepherd's-purse (Capsella bursa-pastoris) .. sowthistles (Sonchus spp.) .. speedwells (Veronica spp.) .. sprangletops (Leptochloa spp.) .. spurge, spotted (Chamaesyce maculata) .. thistle, Russian (Salsola tragus) .. witchgrass (Panicum capillare)

_____ Prepare weed maps in mid-to-late season, indicating significant weed species and their location. _____ Use last year's scouting records to begin this year's scouting. _____ Base all herbicide rate, selection and spot or strip sprays on weed survey results. _____ Weeds may be controlled by cultivation, with no herbicide applied. _____ Use reduced rates of herbicide through banding of herbicides and cultivation. _____ Do not use herbicides of the same class on the same field in succeeding years. (Use crop rotation and corresponding herbicide selections.) _____ Prevent weeds within the field, alleys and roadways from going to seed. _____ Use an experimental plot to test different weed management techniques and record the results.



Weather and Crop Monitoring

_____ Monitor weather and crop parameters _____ Keep daily records.

Date: - Min/max temperatures: - Rainfall: - Hours of leaf wetness: - Stage of tree development (by cultivar, weekly):



CITRUS DEVELOPMENT

The objective

Citrus growers strive to achieve a large harvest of firm juicy fruit. Each piece of fruit should have the desired sweetness or tartness and appropriate aroma. The key to an abundant harvest is large, healthy trees.


The Seasonal Cycle of Citrus

Trees of most citrus cultivars (except coastal lemons) stop growing during the winter and resume growth in late February and March. Most citrus cultivars produce flowers in the spring and are self-compatible, meaning that they can be fertilized by their own pollen. The Clementine mandarin is an exception and requires pollination by another mandarin or tangelo cultivar. Citrus trees usually bloom abundantly but most flowers and young fruit drop due to a combination of environmental and physiological factors that determine which flowers develop into fruit that persist to harvest. Usually persistent flowers are those borne on leafy inflorescences with a low flower-to-leaf ratio.


GROWTH REQUIREMENTS

Healthy trees require light, water, nutrients, and appropriate temperatures. All plants require light, which supplies the sugars for the plants to grow through a process called photosynthesis. In order for the plant to produce these essential sugars, they need water. Most of the water that the plant takes up is lost through the leaves during the process of transpiration. Transpiration is the method by which water can be taken in by the roots and climb to the leaves in a very tall tree. Climatic factors greatly influence how much water a tree will need. Most trees will also require some nutrients to be added, the most common nutrients to be replenished are nitrogen and zinc and occasionally manganese. A beneficial fungi called mycorrhizae lives on the roots of many trees and assists in the uptake of water and nutrients. The optimal conditions of growing citrus is under a mild subtropical climate with wide fluctuations between day and night temperatures. These conditions produce a rich flavor and the bright orange or yellow color of the rind.


MANAGING PESTS

The most successful pest management system incorporates pest identification, field monitoring, control action guidelines, and effective methods for prevention and control. Anticipating and preventing future problems will increase the overall control of pests.


Pest Identification

Correctly identifying the pests is extremely important because in many cases symptoms caused by pests closely resemble those of nutrient deficiencies or other growth problems. There are many resources available to aid with pest identification.


Field Monitoring

Regularly monitoring the status of pests, weather, and soil moisture can help predict or evaluate problems. The things to check are the pest species present, the maturity and health of the crop, the weather, plant environment, and the populations of pests present. These records can help forecast possible outbreaks of future pest generations. Monitoring methods for insects include checking a certain number of fruit or leaves, shaking foliage into a sweep net, or using traps. Monitoring diseases may require checking fruit, leaves, or trunks for symptoms or digging up some feeder roots for inspection. Acquiring accurate weather forecasts from reliable sources are important in controlling pest activities and cultural operations.


Accumulating Degree-Days

The concept of degree-days is important for understanding crop and pest development. Degree-days are used to predict citrus bloom and to time controls for pests. To use degree-days for keeping track of crop or pest development, you must know the number of degree-days (amount of heat units) required to complete each growth stage. At high temperatures, degree-days accumulate faster, and organisms develop faster. You can estimate degree-days from the daily minimum and maximum temperatures from the following formula. This is only an estimate and more precise degree-days can be calculated with the use of computers. Add daily minimum and maximum temperatures and divide by 2 to get the average daily temperature. Then subtract the lower threshold temperature from the average daily temperature and the result is the number of degree-days accumulated that day.


SCION CULTIVAR AND ROOTSTOCK SELECTION=

The most important cultivars grown today are the Washington navel and Valencia orange, Eureka and Lisbon lemons, Marsh (seedless) grapefruit, and mandarin types. The choice depends on climatic conditions and on desired market qualities. The navel orange matures in about 9 months and is harvested from late fall through early spring. The Valencia orange yields a high flavor fruit with few seeds and a tough, firm rind with superior juice qualities. Lemons bloom most of the year and can be harvested over a 9 month period, as well. Marsh grapefruit yield high quality fruit with few seeds and is harvested in the winter and early spring. Rootstocks are selected for improving tree vigor, fruit size and quality, cold hardiness, adaptability to soil conditions, and resistance or tolerance to diseases and nematodes.


SOIL AND WATER MANAGEMENT

Proper water management takes into account soil texture, root depth, water requirements, and irrigation methods. It is important to avoid compacting the soil and permitting it to become waterlogged, which will cause root and crown diseases, ground water pollution, and reduce the effectiveness of herbicides. However, allowing trees to become stressed for water causes them to lose more fruit early in the summer due to a natural thinning of the young crop.


IRRIGATION METHODS

Whether furrow, sprinkler, or low-volume irrigation is used depends on the availability and cost of water, installation and operation costs, soil texture, slope of the land, and frost hazard.


Furrow Systems

In normal furrow systems, three to five furrows are made between each row of trees in mature orchards or one small furrow on either side of the tree, close to the trunk on young orchard trees. Furrow systems may encourage weed growth as seeds move through the water.


Basin and Flood Irrigation

Basin and flood irrigation is mostly used on sandy soils where little of the water remains close to the surface. The water penetrates too quickly and the demand for water is high because most sandy soils are in desert locations. Basin irrigation can increase the spread of disease or weeds through the surface water. It may also promote the development of crown diseases if the trunks remain wet for too long.


Sprinkler Irrigation

Sprinkler irrigation systems are used in all soil types because the amount of water used can be easily controlled, avoiding standing water and runoff. Overhead sprinklers can be advantageous for pest controls such as removing dust from foliage, but they are not widely used.


Low-volume Irrigation

Low-volume irrigations are those that include drip, mist, and mini-sprinklers which consists of emitters located near the trees to supply the trees' daily water requirements. In many ways these systems are advantageous in that fertilizers can be injected into the irrigation water and the amount of water applied can be regulated by time clocks and water meters. However, these systems are quite expensive to operate because of the installation and energy costs, as well as the high maintenance to avoid plugged or broken lines.


Scheduling Irrigations

Knowing when to irrigate is an important factor in maintaining healthy trees. This can be done by knowing the soil content and when it reaches field capacity and knowing the amount of water that is available to the tree. A successful estimate is to water when 50% of the available water has been depleted, but a more accurate estimate can be reached by consulting with a local farm advisor. It is important to remember that water is lost through the soil but also through the leaves due to transpiration. Having accurate evapotranspiration (ET) data is valuable to know how much water was lost through transpiration by the plant and through evaporation from the soil. These figures will help in determining how much water should be used during each irrigation.


FERTILIZING

It is essential that trees are properly fertilized so they are strong and can withstand pest and disease problems as well as produce a healthy crop. Most citrus orchards require yearly applications of nitrogen and zinc, and many will need additional applications of manganese, potassium, and iron. Proper nitrogen levels in the early spring are critical for good growth and fruit set, but are less important in the summer and early fall. A leaf analysis can also be performed in a laboratory to determine if the nutrients are deficient or in excess. If nutrients are deficient, they can be applied either to the soil or to the foliage, or both. Healthy roots will absorb the nutrients more efficiently than damaged or small roots. The timing of nitrogen fertilizer applications is sometimes critical, for example, nitrogen should be applied to oranges and grapefruit in late winter or early spring but can be applied to lemons at any time of the season. Most other nutrients can be applied at any time of the year.


FROST PROTECTION

Citrus crops can be damaged by two types of frost: frost due to heat radiation, and frost due to a cold air front moving through an area. Damage done by heat radiation occurs when the orchard soil and lower air layers in the orchard cannot maintain enough heat from the daytime sunshine to keep the orchard frost-free during the night. When cold air gets trapped under a warmer layer of air, a temperature inversion occurs. When this happens, wind machines can mix the warm and cold layers of air, helping prevent frost damage but can also be very costly if not used efficiently. Areas at greatest risk of frost damage are on valley floors or at the bottom of a slope. There are some protective measures that can be taken to avoid potential frost damage. These include growing healthy trees that are well supplied with water, avoid fertilizing during late summer or early fall to suppress new growth, avoid pruning in the fall or winter to keep as large a canopy as possible and to suppress new growth, wrap trees with insulating materials, and keep the soil moist. For most citrus growing areas, a frost protection service operates from November through February.


HARVEST

Citrus does not have a defined time for harvest because it varies greatly among crops. Navel oranges, grapefruit and mandarins are usually harvested from November to May or June, after a minimum soluble solid to acid ratio has been met. Valencia oranges are harvested between February and November and grapefruit between July and August. Lemons must reach a certain juice content and are harvested during the winter months.


PRUNING

Pruning is generally not needed or recommended for citrus except to remove sucker roots, open up a crowded tree center, reduce the tree height for harvest, or remove diseased wood. Pruning should be kept to a minimum and if possible, done manually. Manual pruning is the preferred method because it allows selective removal of dead or undesirable branches close to a lateral or scaffold.


GROUND COVER

Ground cover is generally not needed or recommended since many ground covers provide food and shelter to many citrus pests and require extra water, fertilizer, and management. However, ground covers can reduce problems with soil erosion on sloped land and increase water penetration and aeration of some soil types.


BIOLOGICAL CONTROLS

There are several biological controls that can be used in orchards. By contacting a local farm advisor, it can be determined which biological controls are used in a particular area for certain trees. However, the environmental conditions must be sufficient to support the biological controls, for example avoiding particular pesticides or herbicides and keeping dust in the orchard to a minimum.


PESTICIDES

Pesticides include all chemicals called insecticides, herbicides, fungicides, rodenticides, and nematocides, even though each has very different properties. In many circumstances one chemical will be able to control several pests at the same time, but this is determined on the degree of control needed, the type of application, weather conditions, and effect on other beneficial organisms that may occupy the same area. Oils are valuable insecticidal materials in citrus because they have little residual toxicity for beneficial insects and effectively control a number of scale and mite pests. Using the correct dosage, choosing the appropriate application technique and equipment, and calibrating the machinery properly are necessary for effective pest control and preventing tree damage. Always read the pesticide label because it outlines safety precautions, legal requirements, and registered uses for each product.


Pesticide Application

For achieving the most efficient pest control, choose the correct pesticide and coverage, ground speed, gallonage, and type of equipment. Timing is critical depending on the cultivar that is planted.


Coverage

The method of applying the pesticide is determined by the size of the pest that is being targeted. Pests that are small and do not move much will require a more thorough coverage of spray than pests that are larger and more mobile. Thorough coverage also requires more gallonage than low volume spray systems.


Ground Speed

The speed at which the pesticide is applied can significantly affect its effectiveness. If you drive too fast, much of the spray will not reach the target and if you drive too slow, the spray will overlap and be wasted.


Gallonage

Gallonage refers to the amount of spray mixture applied per acre or per tree. Required gallonage varies with application method and required coverage. Different methods of applying pesticides include oscillating boom sprayers, air blast sprayers, and low volume sprayers. Hand spraying is used for spot treatments, dense plantings, and trees next to buildings, borders, or on hilly terrain.


Aircraft Spraying

Aircraft spraying is sometimes used for certain outside coverage treatments, but drift is a major problem with this type of spraying. For all equipment, proper maintenance and calibration is necessary for good pest control. Check nozzles regularly for plugging and wear, and replace those that are worn.