EB1804

G.A. Moulton

INTRODUCTION The Jonagold , a high quality bicolor variety, was developed in Geneva, New York. When researchers tested the apple at WSU Mount Vernon, it proved well adapted to a cool maritime climate. The first commercial plantings in western Washington were made in the 1970s. Jonagold is a leading commercial variety in Europe, particularly in the cooler climates of Belgium and Holland. In warmer climates it has not adapted as well, because of its susceptibility to sunburn. Although growers have planted Jonagold in eastern Washington, it performs best at higher, cooler elevations. Growers have used evaporative cooling with some success in warmer sites to improve fruit quality and red skin color.

As Jonagold production has increased in western Washington, growers have found that it requires specific nutrition and cultural attention to produce top quality fruit for the market. This bulletin is intended as a guideline to help growers achieve the best results.

MARKETING AND ECONOMICS Before starting an orchard operation, decide first how you will market the crop. If you intend to market the fruit wholesale, choose a variety that packing houses will handle and that will give good returns. Jonagold has been the main western Washington variety that wholesale packing houses will accept; varieties such as also have gained a favorable reception. If you will be marketing on the farm, grow several varieties to stretch out the season (see EB0937, Tree Fruit Varieties for Western Washington for variety descriptions).

Richard Carkner, Dyvon Havens, and Craig MacConnell have compiled a bulletin, EB1763, Costs of Establishing a 10-Acre Jonagold Apple Orchard in Northwest Washington. The authors consulted with area growers to establish actual costs and returns of Jonagold production. are a high per-acre investment, so look closely at the cost breakdowns and capital outlay. An orchard is a long-term commitment that requires year-round attention. The prospective grower must examine the degree of commitment required, and determine what is practical. It is essential to bring a high quality product to the market. This undertaking requires high levels of investment, not only of capital but of the grower's knowledge, time, and attention.

STRAINS Because standard Jonagold is a bicolor apple, the amount of red blush varies on each individual fruit. Currently in the United States, apples are graded higher if they have more red color, and growers are paid more for such fruit. Some claim that this grading system puts too much emphasis on red color. Others suggest establishing a separate category of grading for naturally

bicolored apples such as Jonagold. At this point the discussion is moot, and current grading standards are not expected to change in the near future. Therefore, growers putting in new plantings have been selecting the more highly colored strains that can attain the higher grades. The following is a summary of the strains planted:

Standard The original strain of Jonagold still constitutes the greatest number of trees in current production. Under proper conditions the percent of red color attained can

be quite high, but does not reach 100% red in any case. New Jonagold (Photo 1) from Japan is no redder in color than standard, and is not widely planted.

Photo 1. New Jonagold is similar to standard Jonagold in amount of red color developed.

Slightly better than standard Nicobel appears to have a percentage of red color marginally better than standard. Field experience so far

with Jonica has been limited but is thought to be similar.

Moderately colored King (Jored, Photo 2) develops significantly more red color than the above strains and appears to have a

slightly better fruit finish than most other strains. Plantings of King have been increasing.

Photo 2. King Jonagold (Jored) develops significantly more red

color than standard, and appears to have a slightly better fruit finish than most other strains.

Highly colored Strains in this category may reach nearly 100% red color. Some have criticized Jonagored (Photo 3) for too deep or dark a color. It appears from our observations to be more striped and earlier coloring than the DeCoster strain. DeCoster (Photo 4), which develops good color, has been the most planted strain. In western Washington

both have done well. In our few years of testing we have noted that in some years one is more successful, and in other years, under different climatic conditions, the other may be slightly better. Other new strains that may be worth planting as a limited trial are Jomured, Rubinstar, and Jonagold 2000.

Photo 3. Jonagored is highly colored and may reach nearly 100% red, sometimes criticized for too deep or dark red color.

Photo 4. DeCoster Jonagold is the high-color strain most planted

in western Washington; both it and Jonagored have done well.

POLLINATION Jonagold is a triploid variety that produces pollen with low viability. If you plant another commercial variety as a pollinizer for Jonagold, that variety also will need a pollinizer. Most growers have planted solid blocks of Jonagold using crabapples as pollinizers. They use several varieties of crabapples. Normally, growers plant both an early bloomer and a midseason bloomer to cover the entire Jonagold bloom period.

Manchurian is the early blooming variety most commonly used to set the king bloom. Snowdrift, a midseason bloomer, covers the rest of the bloom. However, in some years Snowdrift may turn out to be the main pollinating variety. Other varieties with compatible bloom period, such as Donald Wyman and Simpson, also can be used. Manchurian can be susceptible to winter low temperature injury and disease, so growers are seeking an early-blooming replacement. Others that may have promise are Sugar

Tyme, M. zumi calocarpa, Bob White, Evereste, Winter Gem, and White Angel. These may require M 27 or another rootstock of similar dwarf size.

Spacing of pollinator trees within the planting can vary. Some growers leave a full tree space, others plant pollinator trees in what is called a "half space," in between two trees, but only taking up half the space allocated for trees of the production variety. The pollinator trees are trained as upright as possible. Since crabapples bloom heavily on 1-year-old wood, trees are pruned hard after bloom, encouraging new upright regrowth. Normally, a pollinator tree is planted every 50 to 100 feet in every row (approximately 5% to 10% pollinizers in a block). In western Washington conditions, where cool cloudy weather at bloom time may result in less bee activity, 50 feet seems the better choice. Alternate the two pollinator varieties down every row. Table I. Calcium, Magnesium, and Potassium Requirements for Preplant (PP) and Established (EST) Orchards for Different Soil Management Groups. (Stated in pounds of element/acre at 8 inches depth for topsoil and 8 to 16 inches depth for subsoil.) Calcium Magnesium Potassium Soil Mgmt. Group CEC PP EST PP EST PP & EST I topsoil 25 8900 7800 1100 950 520 subsoil 17 5900 4600 700 550 300 II topsoil 20 7100 6200 850 750 450 subsoil 13 4700 3700 600 450 260 III topsoil 18 6400 5600 780 700 430 subsoil 12 4300 3300 500 400 250 IV topsoil 16 5700 5000 700 600 400 subsoil 11 3800 2900 450 350 240 V topsoil 12 4300 3700 500 450 330 subsoil 8 2800 2200 350 350 200 (from Stiles and Reid, Orchard Nutrition Management)

SITE PREPARATION AND SOIL FERTILITY When selecting a site, it is better to plant Jonagold on lighter soils. Make sure the soil is well drained and properly amended before you plant the trees. Fertilizer recommendations for Jonagold in western Washington are drawn from Stiles and Reid, Orchard Nutrition Management, from field observations, and from information on other area crops. Take good soil samples, one at topsoil depth (to 8"), and a second in the subsoil (8" to 16"). This covers the main areas that will be occupied by the tree roots. A good soil analysis provides information on soil pH (whether lime is needed), your soil management group type (CEC), and what percent of the CEC is made up of calcium (Ca), magnesium (Mg), and potassium (K) (base saturation). Sandy soils will usually have a lower CEC, while heavy soils have higher CEC. Greater amounts of organic matter will raise the CEC. Incorporating manure can improve the CEC, particularly on very sandy soil. Preplant soil applications provide the best opportunity to amend the entire soil profile; this may be the only time that you can significantly alter the subsoil.

Before planting, Stiles and Reid recommend adjusting the soil pH to approximately 7 in the topsoil and 6.5 in the subsoil. Amend topsoils to 67% Ca and 13% Mg (percent of total CEC). In established orchards 58% Ca and 12% Mg are adequate. The table shown above groups the soils by CEC. Compare the CEC number of your soil sample to the column of CEC group numbers shown in Table I to determine your CEC type. Next, figure the amount of each element to add. For calcium, take the Ca soil reading (given in meq /100 grams of soil) and multiply it by 532: 1 meq Ca/100g soil = 532 lbs Ca/acre at 8 inches deep. Subtract that number from the amount recommended for your soil management group, and the difference will be the amount of Ca to add to the top 8 inches of soil before planting. Repeat the same procedure for the subsoil. Spread the subsoil application first and plow down; add the topsoil application and harrow in. In an established field, apply lime on the surface and scratch it in if possible. Avoid raising the soil pH higher than 7. Desired leaf levels of Ca are 1.2 to 1.6.

For magnesium, Stiles recommends a preplant rate of 13% of the total soil CEC, and 12% for established orchards. This is double the amount used in most crops. The formula for calculating Mg is 1 meq Mg/100g of soil = 323 lbs Mg/acre at 8 inches deep. As above for Ca, subtract the difference between the Mg reading for your soil management group and your actual reading to determine how much Mg to add to the topsoil. Repeat this procedure for the subsoil and combine the application of the Mg with the Ca. Magnesium in the leaves should read at least 0.3 to 0.5.

Potassium levels are usually given in ppm (parts per million.) To convert to pounds per acre in 8 inches of soil, multiply the soil reading by 2.66. Compare the result with your soil management group to find the pounds of potassium to add. In a preplant situation adjust the subsoil as well. It may be useful to apply additional potassium when high nitrogen levels are present, particularly for a variety like Jonagold that appears to be a heavy user of potassium. The fertilizer guide prepared by Ron Tukey in 1975 suggested that growers amend soil having a reading of less than 200 ppm of K with at least 120 pounds of K2O per acre. Stiles recommends 1.35% to 1.85% K in leaves, but in western Washington readings should be closer to 1.8% to 2% because of high nitrogen levels.

Soil phosphorus (P) readings will vary according to the method the soil testing company uses. Ask what is defined as low, normal, and high range for the specific company doing your test. The Stiles and Reid formula takes the ppm reading of phosphorus and multiplies by 2.66 to get pounds of P/acre at 8 inches of soil. This number is subtracted from 9 lbs; if the remainder is a negative number, treat it as zero, otherwise multiply it by 10. The product is the amount of P2O5 to add to the soil before planting. Since P is so immobile, apply an amendment of an additional 40 lbs of P2O5 at preplant, even when the soil readings are high. Leaf readings of P should be at least 0.1% to 0.4%.

Availability of trace elements is affected by soil pH. Foliar sprays are frequently the best way to supply adequate trace elements to the tree. Nevertheless, amend the soil with a sufficient amount to maximize uptake.

Boron (B) soil readings above 1 ppm require no additional amendments; when readings are 0.5 to 1 ppm, add 2 lbs B/acre; below 0.5 ppm, add 4 lbs/acre. Remember, boron can go from deficiency to toxicity quite easily if overapplied. It is in high demand at bloom time from pink to petal fall, and growers have observed effective responses from foliar sprays. Boron leaf levels should be 25 to 50 ppm.

Zinc soil readings above 2 ppm are considered adequate. Soil surface applications on established orchards have not been effective. Studies incorporating zinc sulfate preplant at 120 lbs/acre have been beneficial. In established orchards, a late dormant spray (silver tip stage) has been most effective in raising the level of zinc in the leaf tissue. Stiles indicates that a postharvest spray also has increased leaf readings of zinc the following year. Where a deficiency occurs in an established orchard, you also might apply zinc in the fall. Desirable zinc leaf tissue levels are 15 to 60 ppm. Stiles prefers levels close to 50 ppm.

Copper levels in the soil should be at least 2 ppm. According to Stiles, preplant incorporation of copper sulfate providing 90 to 120 lbs of elemental copper per acre has increased both tree growth and the amount of copper in leaf analysis. Leaf copper should be 6 to 40 ppm. In established orchards surface applications of copper have not been effective. Foliar sprays of copper at both delayed dormant stage and postharvest have significantly raised levels of leaf copper. In the spring, avoid applying copper sprays later than 1 /4-inch green tip stage, because of the danger of foliage injury and fruit russeting.

Manganese (Mn) soil levels of 5 ppm are considered adequate. Given readings of 3 to 5 ppm, apply 15 lbs Mn/acre; when readings are 0.5 to 3 ppm, apply 30 lbs/acre; below 0.5 ppm, apply 50 lbs/acre. Applied 7 to 10 days after petal fall, a dilute spray (2 to 4 lbs Mn to 400 gallons of water) has effectively reduced low manganese problems. Leaf levels of manganese should range from 25 to 100 ppm.

PLANTING, LAYOUT, TREE DENSITY, ROOTSTOCKS, TRAINING SYSTEMS After properly amending the soil and incorporating the materials, it is time to plant the trees. Planting is best done from November to April, the earlier the better. Fall planted trees get a better start in the spring because some root establishment takes place during the winter months. If at all possible, plant before the 15th of March.

About 10 years ago, 200 to 400 trees per acre was considered high density. Today 800 trees per acre is the norm. These high-density plantings must be on a full dwarf rootstock. M9 has been the most common stock used in western Washington. Thus far, it has proved the most successful. However, some orchardists are testing M27 on sites with heavier soils where M9 seems too vigorous.

Several possible orchard layouts are effective, having spacings that range from 10 to 12 feet between rows, and in- row tree spacing from 3 to 6 feet. Most new plantings are single-row, patterned after the Dutch slender spindle training system. However, earlier plantings have been successfully trained to the central leader, palmette, or French axe. Because Jonagold is so precocious and fruits heavily, it requires a support system (Photo 5). Some plantings use individual posts to support each tree. Others use large posts approximately 50 feet apart, with a single wire 7 to 8 feet off the ground, and a stake 8 to 10 feet tall pushed into the ground next to each tree; the stake is then attached at the top to the wire. Each tree is supported by its own stake.

Photo 5. Because Jonagold is so precocious and fruits heavily, a

support system is required. This one uses large posts every 50 feet, using several wires and stakes to support the trees.

Another support system places large posts 50 feet apart and strings four to five wires to support the trees. This method is the most economical, but impedes access to the area around each tree.

Some growers are choosing to plant their trees on a raised bed (Photo 6). This practice allows closer control of soil nutrition (particularly of nitrogen) and soil moisture levels. The drawback to this practice is that it increases root exposure to winter injury, especially in colder areas.

Photo 6. Trees planted on a raised bed allow closer control of soil

nutrition. Note the drip irrigation line suspended on the low wire.

PRUNING Select a plan for pruning and training, and follow it consistently. Choosing the right spacing and rootstock are crucial. Using too vigorous a rootstock in a high density planting creates serious problems that may never be resolved even by the best pruning techniques. The target is to fill the tree space as quickly as possible while maintaining good light penetration. Allow the tree to begin fruiting as early as possible, usually in the second or third year after planting. Too early or too heavy a crop on a young tree may cause it to remain permanently undersized ("runt out"). Dwarfing rootstocks, particularly M9, begin bearing very soon after planting (precocious), and can produce a large amount of fruit from a relatively small tree volume (yield-efficient). Use training techniques such as branch bending to enhance early fruiting.

Maintain vigor in the lower branches of the tree while keeping the top branches small to improve light penetration. Do not let large limbs become established in the top of the tree. Limb diameter should be largest at the bottom of the tree and grow progressively smaller toward the tree top. Thinning cuts are those that remove an entire shoot or branch back to its point of origin, while heading cuts are those that 1 1 remove only a portion ( /3 to /2) of each shoot or branch. Use mostly thinning cuts, and minimize heading cuts, especially into 1-year-old wood. Thinning cuts open up light channels without stimulating too much new growth. Heading cuts tend to produce excessive new growth, close down light channels, and delay fruiting. Remember that pruning is a dwarfing process and will reduce overall yield. Prune the trees as little as possible, and aim for a good balance between leaf and fruit; make sure light reaches all areas of the tree.

Everyone will have slightly different techniques and variations within each training system. The most important thing is to picture how the tree should look 5 years from now, and direct the training and pruning to achieve those objectives (Photo 7). Do not make changes in tree training from year to year. Select a basic plan and stick to it. Use other growers' successful systems as models to follow. Also consult good references on the subject to serve as guidelines, such as Oberhofer's Training The Slender Spindle, Barritt's Intensive Orchard Management, and Intensive Orcharding, edited by Peterson (see reference list).

Photo 7.

Five-year-old tree pruned as a slender spindle.

IRRIGATION, FERTIGATION, NUTRITION In western Washington where irrigation is supplementary, drip or some other type of micro-irrigation system seems to be the best option. Most growers already use irrigation and some are including fertigation. This is due to seasonally high demand for specific nutrients within certain time windows, particularly during a dry period. Fertigation helps enable a small root system, typical of dwarfing rootstocks, to meet high nutritional demands.

Growers use instruments for detecting soil moisture, such as an irrometer, to monitor and determine irrigation schedules. Even though the soil may be properly amended, the amount of soluble nutrients available to the tree may be limited, especially during dry periods. Growers must add supplemental nutrients to the emitter zone (area of soil moistened by irrigation) to meet the tree's demands.

In preparing this bulletin, fertigation and nutrient spray guidelines from different sources have been used. Some of the elements in higher demand follow. Phosphorus generally is needed at the beginning of the season, so growers can start fertigation at full bloom. Nitrogen (if needed) also can be fertigated at this time, but usually is not recommended in western Washington. Apply boron in one to four sprays from pink through petal fall, and apply manganese with fungicides in foliar sprays 7 to 10 days after petal fall. Zinc and copper, applied as a spray, are actually most effective somewhat earlier, around silver tip stage.

At petal fall a higher demand for magnesium exists, and Stiles suggests applying magnesium both through the fertigation system and as a foliar spray with fungicides. Most tree fruits require twice as much magnesium as other crops. Stiles considers large amounts of Epsom salts beneficial, up to 15 pounds per hundred gallons of spray. Proceed with caution because during the period from petal fall to 40 days following, the fruit is most susceptible to russeting. To reduce the possibility of russeting, avoid spraying any potentially damaging material, and avoid spraying in conditions when the spray material would dry slowly.

Take leaf samples starting about 40 days after petal fall. This allows for a good assessment of each element, and improves chances of a quick compensation if nutrients are lacking, either through the fertigation system or with foliar sprays. This first leaf analysis allows correct assessment of both copper and zinc, and adjustments can be made using chelate sprays or fertigation if they are low. Use caution to avoid overapplying these compounds.

About 45 to 60 days after petal fall, the demand for potassium increases sharply as the fruit increases rapidly in size. Jonagold appears to require high levels of potassium as well as magnesium. Usually during this time (around July 1) the soil is dry and the primary uptake of nutrients into the tree is within the "onion" shaped area wetted by the drip line emitters. Stiles suggests that using 6 to 7 pounds of K2O and 3.5 to 4 pounds of magnesium each week may be very beneficial. This helps to meet the huge potassium and magnesium demand, since the area watered by driplines may be the only site of active nutrient uptake when the soil is dry. Fertigate with potassium and continue to apply magnesium until harvest. Continue to monitor elements with leaf analysis and adjust fertigation accordingly. Many growers prefer to take two to three leaf analyses a year. Also during this time (45 to 60 days after petal fall), start calcium foliar sprays and apply every 2 to 3 weeks.

Because irrigation is supplemental in western Washington, during much of the year the soil is moist enough for the tree roots to feed in other areas outside the drip line "onion." After harvest, test the soil and adjust as suggested above in Site Preparation. This is also a good time to replenish potassium and some micronutrients. According to discussions with J.E. "Ko" Reinhoudt, a fruit specialist in Holland, a crop of 40,000 kg/hectare of Jonagold takes out about 150 kg of K2O, 100 kg of NO2, 30 kg of P2O5, 20 kg of MgO, and 170 kg of CaO. To keep the soil in balance, add those elements back every year, using more if the crop is larger and less if the crop is smaller.

Summary. First, take a soil sample and amend soils properly before planting. Second, take frequent leaf samples to see if the plant is actually getting the proper nutrition. Third, know when particular elements are in higher demand so you can employ supplementary nutrient sprays or fertigation in a timely manner. Fourth, replenish the soil with nutrients taken

out by the crop. Remember that nutrition is most effectively managed by a combination of soil amendments, foliar feeding, and fertigation. Use leaf analysis as a guide. Maintain proper soil moisture levels, provide good pest control, and you will maximize the effectiveness of the nutrients you have made available to the tree.

PEST CONTROL AND SPRAY SCHEDULES The first spray normally needed in the calendar year comes in February or slightly earlier. This is the time to apply residual herbicide. Identify which weeds have been the worst problems and apply the registered herbicide combination that gives the best weed control. Contact herbicides often are combined to kill existing weeds, but also can be used during the growing season. Make sure that the herbicide you plan to use is compatible with the age of the trees. Follow all label instructions.

As March approaches, order codling moth traps. If you observe any trunk or limb cankers during pruning, late March is a good time to treat them with copper. As buds begin to 1 reach stage 2 to 3 (green tip to /2 inch green), apply a delayed dormant spray consisting of oil and an insecticide. This is probably the most effective spray for killing leafrollers, aphids, and mites. During the delayed dormant period most of these insects are hatching, or their eggs are softening, making the control more effective than a dormant spray. Apply this spray separately from, and about a week after, the most effective zinc spray. However, some new formulations of zinc sulfate allow it to be combined with oil and insecticide as one application. Use this formulation with caution and in accordance with product instructions.

At green tip (stage 2 to 3) start the first scab and powdery mildew sprays. Mildew overwinters in the bud so early control is important. It is common to apply scab sprays on a protective schedule every 10 to 14 days for the first month. As the weather improves, use a scab monitor to determine when and if sprays are needed. To reduce the number of trips through the orchard, add some nutrient sprays, such as boron, to the spray formulation (always check for compatibility of materials). Continue scab and mildew sprays through the bloom period, and monitor the presence of insects. You may need to use a spray at full bloom to control campylomma bug and leafrollers. Use appropriate materials, to avoid killing bees.

Place codling moth traps before full bloom. As petal fall approaches, observe traps and maintain them carefully. Record the catch of moths to determine the correct date of biofix. Biofix is the peak moth catch in pheromone traps. The peak worm hatch, and the most effective time to spray for codling moth, occurs 250 degree-days after biofix. Refer to WSU EB1072, Codling Moth Control: A New Tool for Timing Sprays, for specific details about spray timing.

Petal fall is also the time to apply finish enhancers such as Provide (GA4+7), to be followed by one to three additional applications at 7- to 10-day intervals. Provide can improve fruit finish and reduce russeting. Chemical thinning also can be started close to petal fall, as the weather dictates (see below). Continue scab and mildew sprays, mixed whenever possible with nutrients such as Epsom salts for magnesium, and micronutrients. Depending on the spray material used, you can sometimes mix the first codling moth spray with the first calcium spray. If codling moth was a problem in previous seasons, you may need to apply a second spray 2 to 3 weeks later. If mites have been a problem before, monitor population levels regularly. Introducing predator mites in some orchards has significantly reduced or eliminated the need for spraying.

Growers have observed that when trees exhibit excessive vigor, ethrel used approximately 60 days after full bloom has slowed growth, increased fruit color at harvest, and increased return bloom the following year. Use ethrel with caution and in accordance with the label instructions. Throughout the rest of the season, monitor pests regularly. Little or no control may be needed if a good spray program was implemented early in the season. If you observe any cankers in the orchard after harvest and as leaves fall, apply a spray. The must-have bulletin for pest management is EB0419, Crop Protection Guide for Tree Fruits in Washington.

CHEMICAL THINNING Proper thinning of the young fruit is crucial in determining overall profitability of a season's crop. A spray program that is too aggressive can leave the grower with insufficient fruit on the trees at harvest. This results in too-large fruit, often with high rates of bitter pit. On the other hand, poorly thinned trees will be overloaded with small, unmarketable fruit that may be of poor quality. Hand thinning can compensate for a failed spray program, but the labor is expensive and time-consuming.

Conditions for thinning apple orchards in cool maritime climates differ from those in warmer, drier areas. Suitable thinning practices in drier climates do not always prove effective in western Washington, and need some adaptation. Based on the results of on-farm experiments performed by WSU researchers over 3 years in Skagit and Whatcom counties, and supplemented by input and observations from individual apple growers, researchers have developed some guidelines to improve success of thinning sprays.

Do not rely on blossom thinners. Tests with Wil-Thin (D-88) up to this point have either been ineffective or have caused damage under normal orchard

conditions. Perhaps future blossom thinning materials may prove more successful.

Start early. As soon as the weather permits (at least 3 consecutive days in which temperatures are above 60°F) you can begin the spray program. The closer to petal fall you can make an application (in accordance with label instructions), the longer the period you have to assess the results and apply additional sprays if needed. Also, in varieties such as Gala, which tend to produce small fruit, earlier thinning can enhance fruit size.

Thin aggressively. The most aggressive program is recommended, using carbaryl plus either Amid-Thin in the early spray or NAA at the 10-mm stage. The more aggressive treatments tend to leave singles in each fruit cluster. However, if a softer approach is desired, use either Amid-Thin, NAA, or carbaryl alone. Young trees (fourth leaf or younger) and trees with low vigor tend to drop fruit more readily, so it is better not to thin them aggressively. Use XLR Plus or Sanit 4F formulation of carbaryl to reduce hazard to bees.

Let the weather be your guide. While it is hard to overthin on the first try, if the forecasts predict very hot weather (85°F or above), then cut the rate slightly. Remember that in most instances it pays to err on the aggressive side. In the early stages (at or near petal fall), Amid-Thin plus carbaryl is a good spray combination to use. When fruit begins to develop (10 mm diameter approximately), use carbaryl plus NAA at the rate recommended in EB0419, Crop Protection Guide for Tree Fruits in Washington. In the first spray cover the whole tree, provided you have good bloom and set in the lower branches. If a second spray is needed and can be applied, evaluate the distribution of remaining fruit and in most cases turn off the bottom nozzles.

Assessment takes at least 16 days. In eastern Washington it takes approximately 10 to 14 days to evaluate the effectiveness of a given thinning spray; in western Washington allow at least 16 days to determine if further thinning is required. Fruit sprayed with Amid-Thin has continued to fall for a longer time period (compared with with fruit sprayed with NAA), and it takes even longer than 16 days to assess the results. A second spray is sometimes needed. In many cases, direct this second spray to the tops of the trees only. This is followed by a touch-up hand thinning to finish off the job.

When chemical thinning, be sure to follow the labels and legal recommendations.

Photo 8. A successful program of nutrition, fruit thinning, and pest

control brings its reward at harvest time with a good crop of colorful, high quality fruit.

HARVEST As fall approaches, monitor apples for maturity. Under western Washington conditions, Jonagold normally begins to reach full harvest maturity in late September (Photo 8). Multiple harvests­at least two and sometimes more­are necessary for this variety.

Maturity specifications will vary slightly with each packing house, so stay in contact with the field staff as harvest approaches. Normally, four indicators are used in determining harvest maturity. First, fruit samples are collected and tested for pressure. Pressure readings that average 16 to 18 pounds are desirable. If pressures are below 14 pounds, market the fruit immediately.

The second parameter is starch content. To determine this, cut specimens horizontally through the core and spray with an iodine solution. When the fruit is immature, most of the cut area will stain black, indicating a high degree of starch. As the fruit matures and the starches are converted to sugars, the black stained areas become smaller and smaller. Test kits containing a spray bottle of solution, field log book, and diagrams illustrating the rating numbers of starch to sugar are available from various orchard supply outlets. Each packing house will designate its preferred ratings for each 1 2 harvest. Normally /2 to /3 starch clearing is necessary for Jonagold to attain a desired harvest maturity and still have enough starch to store long term.

Observations in some orchards have shown fruit that tests completely clear of starch long before the anticipated date of harvest. Such fruit often has poor color and insipid flavor. Evidence indicates the probable cause is deficiency of potassium and magnesium. Orchards that have received an aggressive program of soil amendments or fertigation supplements in these two elements have significantly reduced or eliminated this problem, resulting in more consistent starch test readings.

Soluble solids, measured with a refractometer, is a third parameter. Jonagold fruit should contain at least 13% in sugars, preferably 16% to 17%, for good quality. Fruit color is the fourth consideration. It is desirable to have as much red color on the fruit as possible, but the ground color (yellow) is a more reliable indicator to determine maturity. As the background color changes from green to yellow, you also may notice a slight increase in pressure. If the first three indicators are in the desired range, and the ground color changes to yellow, fruit is ready to harvest. Normally if all the above indicators are synchronous, a bright red blush follows. In red strains, the red turns from a dull to a bright color as the apple matures.

Because Jonagold is a multi-harvest fruit, the first one or two picks will selectively harvest only those fruit that meet the right criteria of good color, after a representative sample of fruit has been tested and shown to be within the required maturity indices. Pickers will have to be instructed to pick selectively, and educated to recognize that each tree of this variety may be picked two or three times over a 2- to 3-week period.

The early-harvested fruit have the best maturity parameters for long-term storage, while the later harvests are usually packed within a month or two after harvest. Jonagolds are picked several times in a season. If you have not provided the trees with proper nutrition, the quality of the later picked fruit decreases and may not reach proper maturity. Regulation of crop loads is needed, and further studies are anticipated in this area. With proper nutrition and chemical thinning, harvest windows can be narrowed and the number of picks reduced. If you plan to crop your Jonagold trees heavily, make sure you have healthy trees and aggressively maintain proper nutrition.

REFERENCES For further information, the following publications are helpful:

Barritt, Bruce. Intensive Orchard Management. 1992. Good Fruit Grower, 1005 Tieton Drive, Yakima, WA 98902. 211 pp.

Carkner, Richard, Dyvon Havens, and Craig McConnell. 1994. EB1763, Costs of Establishing a 10-Acre Jonagold Apple Orchard in Northwest Washington. Washington State University Cooperative Extension, Pullman.

Norton, Robert A., Jacqueline King, and Gary A. Moulton. 1992. EB0937, Tree Fruit Varieties for Western Washington. Washington State University Cooperative Extension, Pullman. 12 pp.

Oberhofer, Hermann. Pruning the Slender Spindle. 1990. Originally published as Schnitt der Schlanken Spindel (1987). Province of British Columbia Ministry of Agriculture and Fisheries, Victoria, B.C., Canada. 40 pp.

Peterson, A. Brooke, ed. Intensive Orcharding: Managing your high production apple planting. 1989. Good Fruit Grower, 1005 Tieton Drive, Yakima, WA 98902. 187 pp.

Stiles, Warren C., and W. Shaw Reid. 1991. Orchard Nutrition Management. Information Bulletin 219. Media Services, Cornell University Cooperative Extension, Ithaca, NY 14853. 23 pp.

Washington State University. Annual. EB0419, Crop Protection Guide for Tree Fruits in Washington. Revised annually. Washington State University Cooperative Extension, Pullman. 96 pp.

Waterman, Peter F. Fertigation Guidelines in High Density Apples and Apple Nurseries in the Okanagan-Similkameen. 1993. B.C. Ministry of Agriculture, Fisheries, and Food, Penticton, B.C., Canada. 21 pp.

Prepared by G.A. Moulton, M.S., Washington State University Scientific Assistant, WSU Mount Vernon Research and Extension Unit. Photos 5, 6, and 7 are by the author. Photos 1, 2, 3, 4, and 6 are by J. King, WSU Mount Vernon.

Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock. Washington State University Cooperative Extension bulletins contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a commercial product. Please reference by title and credit Washington State University Cooperative Extension.

Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published September 1995. Subject code 232. I

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