Jonagold Culture in Western Washington

INTRODUCTION

The Jonagold apple, a high quality bicolor variety, was developed in Geneva, New York, tested at WSU Mount Vernon, and proved well adapted to a cool maritime climate. The first commercial plantings of Jonagold in this area were made in the 1970s. It is a leading commercial variety in Europe, particularly in the cooler climates of Belgium and Holland. Jonagold has not adapted as well to warmer climates, because of its susceptibility to sunburn. It is grown in eastern Washington, but performs best at higher, cooler elevations. Evaporative cooling has been used with some success in warmer sites to produce better fruit with more red skin color.

As Jonagold production has increased in western Washington, growers have found that it has some specific needs for nutrition and culture that must be provided in order to produce top quality fruit for the market. This bulletin is aimed toward helping growers to achieve the best results.

MARKETING AND ECONOMICS

Before starting an orchard operation, it is very important to decide how the crop will be marketed. If the fruit is intended for the wholesale market only, then choose a variety that packing houses want to handle and that will give good returns. Jonagold has been the main western Washington variety attracting attention that is acceptable to wholesale packing houses; however, other varieties such as Gala have also been favorably received. If marketing will be done on-the-farm, several varieties should be grown to stretch out the marketing season (see bulletin EB0937 Tree Fruit Varieties for Western Washington for variety descriptions).

The economics of Jonagold production have been compiled in a bulletin by Richard Carkner (EB 1763, Carkner et al), who consulted with area growers to establish actual costs and returns. Apples are a high per-acre investment, so it is necessary to look closely at the cost breakdowns and capital outlay. An orchard is a long-term commitment that requires year-round attention. The prospective grower needs to examine the degree of commitment required, and determine what is practical. It is essential to bring a high quality product to the market, and this 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, there is variability in the amount of red blush on an 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. There is some controversy about this grading system, with claims that there is too much emphasis put on red color, along with suggestions that a separate category of grading be established 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 from Japan is no redder in color thanstandard, and is not widely planted.

Slightly better than standard -- Jonica and Nicobel appear to have a percentage of red color marginally better than standard. Field experience so far with Jonica has been limited.

Moderately colored -- King (Jored) 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.

Highly colored -- Strains in this category may reach nearly 100% red color. In some areas, Jonagored has sometimes been criticized for too deep or dark a color. It appears from our observations to be more striped and earlier coloring than the DeCoster strain. DeCoster has been the most planted strain, and develops good color. 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 one may be slightly better. Other new strains that may be worth planting as a limited trial are Jomured, Rubinstar, and Jonagold 2000.

POLLINATION

Jonagold is a triploid variety and produces pollen with low viability. Therefore, if another commercial variety is planted as a pollinizer for Jonagold, that variety will also need a pollinizer. Most growers have been planting solid blocks of Jonagold using crabapples as pollinizers. There are several varieties of crabapples that can be used; normally both an early bloomer and a mid season bloomer are planted in the block so that the entire Jonagold bloom period is covered.

Manchurian has been the early blooming variety most commonly used to set the king bloom. Snowdrift, a mid season bloomer, is used to cover the rest of the bloom. However, in some years it may turn out to be the main pollinating variety. Other varieties with compatible bloom period, such as Donald Wyman and Simpson, can also be used. Manchurian can be susceptible to winter low temperature injury and disease, so an early-blooming replacement is being sought. Others that may have promise are Sugar Tyme, M. Zumi calocarpa, Bob White, Evereste, and White Angel. These may need to be on 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 them 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 wood, trees are pruned hard after bloom, encouraging new upright regrowth. Normally, a pollinator tree is planted every 50-100 feet in every row (approximately 5-10% 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. The two pollinator varieties should be alternated down every row.

SITE PREPARATION AND SOIL FERTILITY

In site selection, it is preferable to plant Jonagold in an area with lighter soils, and plant other varieties on the heavier ground. The soil should be well drained, and it is very important in establishing a Jonagold block to start with properly amended soils before the trees are planted. Fertilizer recommendations for Jonagold in western Washington are drawn from Stiles and Reid's Orchard Nutrition Management, from field observations, and from information on other area crops.

Of first importance is a good soil sample that is properly taken. One sample should be taken at topsoil depth (to 8"), and a second in the subsoil (8" -16"). This covers the main areas that will be occupied by the tree roots. Preplant soil applications are the best opportunity to amend the entire soil profile, and may be the only time that the subsoil can be significantly altered. Send samples for analysis to a reliable testing company, one that other growers are using.

The three primary factors to look at in a soil analysis are the soil pH, the cation exchange capacity (CEC), and the base saturation. These data will provide information on whether application of lime is needed (pH), which management group is closest to the soil sample tested (CEC), and what percent of the CEC is made up of calcium (Ca), magnesium (Mg), and potassium (K) (base saturation). Generally speaking, sandy soils will have a lower CEC, while heavy soils have higher CEC. Greater amounts of organic matter will raise the CEC, and incorporating manure can improve the CEC, particularly on very sandy soil.

Table I. Calcium and Magnesium Requirements for Preplant (PP) and Established (EST) Orchards for Different Soil Management Groups. (Stated in pounds of element/acre at 8" depth for topsoil and 8"-16" depth for subsoil.)

A soil pH of 6.5 allows most elements to be available. Before planting, Stiles and Reid recommend adjusting the soil pH to approximately 7 in the topsoil and 6.5 in the subsoil. In a preplant situation, amend topsoils to 67% Ca and 13% Mg (% of total CEC.) In established orchards or preplant subsoils, 58% Ca and 12% Mg are adequate. The table shown above groups the soils by CEC. After obtaining the results of a soil sample, compare the CEC number shown in the sample to the numbers shown in Table I in order to determine in which management group that specific soil belongs.

Next, figure the pounds of Ca contained per acre of soil at 8" deep. This is done by taking the Ca reading (given in meq./100 grams of soil) and multiplying by 532: 1 meq. Ca/l00g soil = 532 lbs. Ca/acre at 8" deep. Subtract this Ca number from the amount recommended for your soil management group, and the result will be the amount of Ca you will need to add to the top 8" of soil before planting. Repeat the same procedure for the subsoil.

The subsoil application should be spread and plowed down first, then the topsoil application added and harrowed in. In an established field, go through the same procedure but use 58% as the rate for the top 8" of soil, applying lime on the surface and scratching it in if possible. Pay attention to soil pH and don't let it rise higher than 7. Leaf levels of Ca should be in the range of 1.2-1.6.

Determine the rates for magnesium in the same way; Dr. Stiles recommends a preplant rate of 13% Mg 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/l00g of soil = 323# Mg/acre at 8" deep. As above for Ca, subtract the result from the Mg reading for your soil management group to find the amount of supplementary Mg that must be added to the topsoil. Repeat this procedure for the subsoil and apply the Mg with the Ca using the same application method. When you add the percent of base saturation of Ca (67%) and Mg (13%), the overall rate is about 80% (58% Ca and 12% Mg for established orchards). The remainder ought to comprise mostly K, Na, H, and Al. Magnesium in the leaves should read at least 0.3 -O.5.

Potassium levels are usually given in ppm (parts per million.) To convert that number to pounds per acre in 8" of soil, multiply the soil reading by 2.66. Compare the result with the numbers in Table I that are given for the appropriate soil management group to find how many pounds of potassium need to be added. In a preplant situation adjust the subsoil as well. It may be advantageous to apply additional potassium when high nitrogen levels have been noted, particularly for a variety like Jonagold that appears to be a heavy potassium user. The fertilizer guide prepared by Ron Tukey in 1975 suggested that a reading of less than 200 ppm of K should be amended, using at least 120 pounds of K2O per acre. Leaf potassium should read 1.8-2.0.

When determining soil phosphorus, readings will vary according to the method being used by the soil testing company. Be sure to find out what is defined as "normal range" for the specific company doing your test; it is important to know what the soil lab considers to be "low" and "high" readings. Stiles and Reid's formula takes the ppm reading of phosphorus and multiplies by 2.66 to get a result for pounds of P/acre of soil at 8" deep. This number is subtracted from 9 lbs.; if the remainder is a negative number it is treated as zero, otherwise it is multiplied by 10, and 40 lbs. added to the result. This is the amount of P2O5 to be added to the soil before planting. Since P is so immobile, a preplant amendment is the best chance to incorporate it throughout the soil profile. Therefore, in preplant situations an additional 40 lbs. of P2O5 is applied even when the soil readings are high. Leaf readings of P should be at least 0.1-0.4%.

Availability of trace elements is often highly affected by soil pH. Foliar sprays are frequently the best way to supply adeqate trace elements to the tree. However, the soil should still be amended with a sufficient amount to maximize adequate uptake, particularly at the preplant stage. Boron readings above 1 ppm in the soil test require no additional amendments; with readings of 0.5-1 ppm add 2 lbs. B/acre, and below 0.5 ppm add 4 lbs./acre. Remember that boron is an element that can go from deficiency to toxicity quite easily if overapplied. It is in high demand at bloom time from pink to petal fall, and effective responses have been observed from foliar sprays mixed with fungicides, starting at pink stage. Leaf levels of boron should be from 25-50 ppm.

Zinc should have a soil reading above 2 ppm to be considered adequate. Soil surface applications on established orchards have not been effective. Studies incorporating zinc sulfate at 120 lbs/acre have been beneficial. A delayed dormant spray has been most effective in raising the level of zinc in the leaf tissue. Stiles indicates that a post-harvest spray has also increased leaf readings of zinc the following year. Where a deficiency occurs in an established orchard, zinc should be applied both in the fall and in early spring. Zinc in leaf tissue should be in the range of 15 to 60 ppm. Stiles indicates his preferable level of zinc in the leaf at about 50 ppm.

Copper levels in the soil analysis should be 2 ppm. According to Stiles, preplant incorporation of copper sulfate providing 90-120 lbs. of elemental copper per acre has increased both tree growth and the amount of copper in leaf analysis. Leaf copper should be in the range of 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 post-harvest have significantly raised levels of leaf copper. In the spring, copper sprays should not be applied later than 1/4" green tip stage, because of the danger of foliage injury and fruit russeting.

Manganese should read approximately 5 ppm to be considered adequate; if below this level it should be adjusted. At readings of 3 to 5 ppm, apply 15 lbs./acre of Mn; for readings of 0.5 to 3 ppm apply 30 lbs./acre, and if readings are below 0.5 ppm apply 50 lbs./acre. Soil pH is a factor in uptake of manganese; when the pH is lower, manganese becomes more available to the tree, and at low pH levels can actually become toxic. In most soils commonly found in western Washington, manganese needs to be carefully monitored and periodically adjusted. Applied 7-10 days after petal fall, a dilute spray (2-4 lbs. manganese to 400 gallons of water) has effectively reduced problems of low manganese. Leaf levels of manganese should range from 25-100 ppm.

PLANTING, LAYOUT, TREE DENSITY, ROOTSTOCKS, TRAINING SYSTEMS

After the soil is properly amended and the materials incorporated, the trees are planted. 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 ten years ago 200-400 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, and thus far is the most successful. However, some orchardists are testing M27 on sites with heavier soils where M9 seems too vigorous.

There are several possible orchard layouts, with spacing that ranges from 10'-12' between rows, and in-row tree spacing from 3'-6'. 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, a support system is required. Some plantings use individual posts to support each tree. Others use large posts approximately every 50', with a single wire about 7' off the ground, with a stake about 8' 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. Other support systems use large posts 50' apart with 4-5 wires to support the trees; this method is the most economical, but access to the area around each tree is impeded.

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

PRUNING

Have 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, however, 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. Prune the trees as little as possible, and aim for a good balance between leaf and fruit; make sure light gets in to all areas of the tree.

Maintain vigor in the lower branches of the tree while keeping the top branches small to facilitate light penetration. Don't let large limbs get established in the top of the tree. Limb diameter should be largest at the bottom of the tree and get 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 remove only a portion (1/3 to 1/2) of each shoot or branch. Use mostly thinning cuts, and minimize heading cuts, especially into one-year wood. Thinning cuts open up light channels without stimulating too much new growth. Heading cuts tend to produce excessive new growth and delay fruiting. Remember that pruning is a dwarfing process and will reduce overall yield.

Everyone will have slightly different objectives and variations within each training system. However, try to picture how the tree should look 5 years from now, and direct the training and pruning to achieve those objectives. Don't make major changes in tree training from year to year. Have 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).

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 going to fertigation, particularly because of the seasonally high demand for specific nutrients within certain time windows. Fertigation helps enable a small root system, typical of dwarfing rootstocks, to meet high nutritional demands. Irrometers are used to monitor soil moisture and determine irrigation schedules. Even though the soil may be properly amended, the amount of soluble nutrients available to the tree within the emitter zone of the drip line is the important factor, especially during dry periods. Enough nutrients must be supplied to the emitter zone to meet the tree's demands.

Fertigation guidelines from different sources have been used. Some of the higher demands are as follows: phosphorus is generally fertigated in the beginning of the season, starting at full bloom. Nitrogen (if needed) can be fertigated at this time, but this usually is not recommended in western Washington. Also at this time boron is applied in 1 to 4 sprays from pink through petal fall, and manganese is applied with fungicides in foliar sprays 7 to 10 days after petal fall. Zinc and copper applications are actually most effective somewhat earlier, in the delayed dormant period.

At petal fall there is a higher demand for magnesium, and Stiles suggests it be applied both through the fertigation system and as a foliar spray with fungicides. Most tree fruits require double the amount of magnesium needed for other crops. Large amounts of Epsom salts, up to 15 pounds per hundred gallons of spray, are suggested as beneficial. Furthermore, during the period from petal fall to 40 days following, the fruit is most susceptible to russeting. At that stage, avoid spraying any potentially damaging material, and avoid spraying in conditions when the spray material would dry slowly, so as to reduce the possibility of russeting.

It is important to take leaf samples during the latter part of this period (40 days after petal fall) to see how much of each element is present, and where a quick compensation can be made through the fertigation system if nutrients are lacking. Chelate sprays and/or fertigation applications of both copper and zinc can be made at this time if leaf analysis indicates they are low. It is noteworthy that in an experiment on citrus, zinc chelates in the fertigation system were taken up more effectively than zinc sulfate; in the case of copper it was the reverse, the uptake of copper sulfate being more efficient than copper chelate.

About 45-60 days after petal fall, the demand for potassium begins to increase geometrically as the fruit gains 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. Fertigation, once a week using 6-7 pounds of K2O and 31/2 to 4 pounds of magnesium, is usually 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 soil is dry, particularly in sandier soils. Fertigate with potassium and continue with magnesium at least until harvest. Again, monitor the elements with a leaf analysis and adjust fertigation accordingly. Many growers prefer to take 2-3 leaf analyses a year. At about 45-60 days after petal fall, calcium foliar sprays should be started and applied every 2-3 weeks.

In western Washington, irrigation is supplemental. 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 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, those elements must be added back every year, more if the crop is larger and less if the crop is smaller.

In summary, 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, replenish the soil with nutrients taken out by the crop. Finally, know when particular elements are in higher demand so that supplementary nutrient sprays or fertigation can be employed in a timely manner.

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 herbicide combination that gives the best weed control. Contact herbicides are often combined to kill existing weeds, but can also be used during the growing season. It is important to make sure that the herbicide you plan to use is compatible with the age of the trees. Be sure to follow all label instructions.

As March approaches, order codling moth traps. If any trunk or limb cankers are observed during pruning, late March is a good time to treat them with copper. As buds begin to reach stage 2-3 (green tip to 1/2" 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. This spray is normally applied separate 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 2-3) start the first scab and powdery mildew sprays. Mildew overwinters in the bud so early control is important. Scab sprays are normally applied on a protective schedule every 10-14 days for the first month. As the weather improves, a scab monitor is used to determine when and if sprays are needed. Boron can be added to the spray formulation (always check for compatibility of materials). Scab and mildew sprays are continued through the bloom period, and the presence of insects is monitored. Often a spray at full bloom is needed to control campylomma bug and leafrollers. Care must be taken to use appropriate materials, so as not to kill bees.

Codling moth traps must be out before full bloom. As petal fall approaches, traps must be observed and maintained carefully, and the catch of moths recorded, to correctly determine the date of biofix. Biofix is the day of 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 (approximately 45 calendar days) after biofix. Refer to WSU Extension Bulletin No. 1072 for specific details about timing of codling moth sprays.

Petal fall is also the time to apply finish enhancers to be followed by one to three additional applications at 6-10 day intervals. Provide can improve fruit finish and reduce russeting. Chemical thinning can also be started at petal fall, as the weather dictates (see below). Scab and mildew sprays are continued, often mixed with Epsom salts for magnesium and some micronutrients. The first codling moth spray is usually mixed with the first calcium spray. If codling moth was a problem in previous seasons, a second spray should be applied 2-3 weeks later. If mites have previously been a problem, population levels should be monitored regularly. Introduction of predator mites in some orchards have eliminated the need for spraying.

If trees exhibit excessive vigor, ethrel used approximately 60 days after full bloom has slowed down growth, increased fruit color, and increased return bloom the following year. This product should be used with caution. Throughout the rest of the season, pests should be monitored regularly but often little or no control is needed if a good spray program was implemented early in the season. If any cankers have been observed in the orchard after harvest and as leaves fall, a spray should be applied. The must-have bulletin for pest management is EB 0419, Crop Protection Guide for Tree Fruits in Washington.

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. 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 are different 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 the last three years in Skagit and Whatcom counties, supplemented by input and observations from individual apple growers, some guidelines have been developed to improve success of thinning sprays.

Do not rely on blossom thinners. Tests with Will-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 three consecutive days in which temperatures are above 60F) the spray program can begin. The closer to petal fall an application is timed, the better. This provides a longer period in which to assess the results and to apply additional sprays if needed. Also, in varieties like Gala that tend to produce small fruit, earlier thinning can enhance fruit size.

Be aggressive. 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 aggressively on them. Use XLR Plus or Sanit 4F formulation of carbaryl to reduce hazard to bees.

Let the weather be your guide. It's hard to over-thin on the first try, but if the forecasts predict very hot weather (85F 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 Golden Delicious rate recommended in EB 0419, 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 fruits and in most cases turn off the bottom nozzles.

Assessment takes at least 16 days. In eastern Washington it takes approximately 10 - 14 days to evaluate the effectiveness of a given thinning spray; in western Washington at least 16 days are needed to determine if further thinning is required. Fruit sprayed with Amid-Thin has continued to fall for a longer time period (compared with NAA), and it takes even longer than 16 days to assess the results. A second spray is sometimes needed, lthough in many cases this second spray should be directed 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

HARVEST

As fall approaches, apples must be monitored for maturity. In western Washington conditions, Jonagold normally begins to reach full harvest maturity in late September. Multiple harvests, at least two and sometimes more, are necessary for this variety.

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

The second parameter is starch content. To determine this, specimens are cut horizontally and sprayed 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 harvest. Normally 1/2 to 2/3 starch clearing is necessary for Jonagold to attain a desired harvest maturity and still have enough starch to store long-term. Soluble solids, measured with a refractometer, is a third parameter. Jonagold fruit should contain at least 13% in sugars, preferably 16-17%, for good quality.

Fruit color is the fourth consideration. It is most 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, a slight increase in pressure may also be noted. 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 2-3 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, and if proper nutrition hasn't been given to the trees, the quality of the later picked fruit is decreased and may not reach proper maturity. Crop loads need to be regulated, and further studies need to be done 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 anyone seeking further information, the following publications are helpful:

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

Carkner, Richard, Dyvon Havens and Craig MacConnell. Costs of Establishing a 10-Acre Jonagold Apple Orchard in Northwest Washington. EB 1763, published January 1994 by Washington State University Cooperative Extension, Pullman, WA.

Norton, Robert A., Jacqueline King and Gary A. Moulton. Tree Fruit Varieties for Western Washington. EB 0937, revised 1992, published by Washington State University Cooperative Extension, Pullman, WA. 12 pp.

Oberhofer, Hermann. Pruning the Slender Spindle. Originally published as Schnitt der Schlanken Spindel (1987). Published 1990 by the 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. Published 1989 by Good Fruit Grower, 1005 Tieton Drive, Yakima, WA 98902. 187 pp.

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

Washington State University. Crop Protection Guide for Tree Fruits in Washington. EB 0419, published annually by Washington State University Cooperative Extension, Pullman, WA..