When establishing a new orchard, growers are usually very diligent in identifying all the components needed for rapid tree establishment, including performing soil tests to determine fertilizer needs. Additionally, the results will indicate whether the pH needs to be adjusted with the goal of attaining pH 6.5.

Professor Eric Hanson, from the Horticulture Department at Michigan State University, said that checking soil pH is even more vital when replanting old orchards. Growers want to prevent over-fertilizing. Not only does it waste time and money, but it can generate as many issues as under-fertilizing.

Consider foliar, rather than soil, tests

Monitoring the nutrient status of the orchard as trees grow is critical as lack of adequate nutrients will affect tree growth and orchard productivity. However, once trees are planted, foliar tests, rather than soil tests, are more accurate in gauging orchard nutritional health. Performing routine tissue analysis can be economically worthwhile as it can enable deficiencies to be identified before symptoms or yields decline. Routine foliar samplings are normally taken between mid-July and mid-August.

Apples with symptoms characteristic of boron deficiency

Hanson recommends tissue sampling every two years in young orchards. “Once the orchards are older, changes occur more slowly and sampling can be less frequent,” he said.

How to strategically sample is a question that each grower needs to decide for himself. Separating leaf samples by variety, rootstock, maturity, soil type and management would be ideal, but Hanson said that this may not be economically or logistically practical.

“If the grower isn’t going to manage the blocks separately it isn’t worthwhile doing the separate sampling,” Hanson said.

Normally, the two most significant variables are tree age and soil type. Growers with trees of different ages in the orchard are advised to sample the different aged planting separately. If there are different soil types in the orchard, it is recommended that growers keep leaf samples from trees in those zones.

Nationwide many laboratories can perform foliar analysis. (Hanson uses A & L Great Lakes Laboratories in Fort Wayne, Indiana. Visit (http://www.algreatlakes.com/). In addition, your local extension educator can direct you to laboratories that provide the service.

After a grower has identified a laboratory, the grower should read the protocol for sampling, packing samples and shipping, as these conditions vary from laboratory to laboratory and, if not performed correctly, may compromise results. It is recommended a grower continue to use the same laboratory each year to allow easy comparison of results.

Determining deficiencies

A lab test will tell a grower how much boron or calcium to apply. Boron and calcium deficiencies have characteristic symptoms. For many deficiencies, however, symptoms alone are not reliable for a definitive diagnosis. Such is the case when trees are deficient in more than one nutrient. Under these circumstances sending leaf samples from apparently healthy and problematic trees for analysis is necessary to identify specific nutrient issues.

“Honeycrisp” apple with calcium deficiency known as bitter pit

Some foliar deficiencies may be regional, and can be related to soil type, weather conditions and fruit varieties, whereas others may be due to management history or other factors. Regional information is available through extension and grower organizations, so growers can understand which nutrients are likely to be deficient in their orchard.

In Michigan for example, nitrogen and potassium are common foliar deficiencies, and in the Pacific Northwest, boron deficiencies are commonly observed. These deficiencies can be diagnosed fairly accurately by symptoms that include poorly developed stamens in the blossom, inadequate fruit set, low seed numbers, bark necrosis in apple, fruit cork, and sometimes fruit cracking. It is often made worse by the dry soil conditions in this region that frequently occur in the fall. Over-treating to correct for boron deficiency can lead to serious outcomes such as loss of the crop or trees. It is not recommended to use more than 3 pounds of actual boron per acre unless indicated from soil tests. Soil applications should last for up to three years. A spray application is an alternative. A low maintenance annual rate of boric acid or polyborate-based spray product should be used; use of higher rates is only advised for very sandy soils.

Spotting calcium deficiency in fruit

Calcium deficiency in fruit impacts most apple-growing regions worldwide. Although calcium results from a foliar analysis test will nearly always indicate that there is an adequate level in the leaves due to limited calcium mobility, the fruit may be calcium deficient and, if so, will show characteristic symptoms. This deficiency can cause significant reduction in fruit quality, resulting in economic loss.

Some varieties are more susceptible than others. For example reports have been found in which fruit from young plantings of “Honeycrisp” had more than 50 percent of the fruit develop bitter pit prior to harvest or during storage.

Calcium sprays applied to fruit during the growing season may reduce the problem but seldom eliminate it. Calcium chloride is most commonly used – either food-grade product or products specifically formulated for use as a foliar spray. Construction-grade should be avoided because it contains impurities that can severely damage fruit. Calcium chloride is not entirely problem free; it can cause leaf burn and fruit injury and should be checked for compatibility with pesticides being used.

Another option is calcium nitrate, but it is more likely to cause fruit injury than calcium chloride. Both calcium chloride and calcium nitrate can cause fruit russet, but incidence can be reduced by using low rates and dilute sprays. The goal is to reduce the likelihood of pooling on the fruit’s lower part. Five to eight applications of calcium chloride or calcium nitrate from June to late August may significantly reduce bitter pit development depending upon variety, location and season. Foliar sprays of calcium sulfate may increase bitter pit and should not be used.

Iron is important in chlorophyll synthesis and therefore deficiencies result in bleached leaf color. In addition, the fruit is often poor in color and taste with yield being reduced. Applying chelated iron may help, but the problem is often related to over-irrigation and below-optimal organic content of the soil.

Visit the following links for more details on apple tree nutrition and management:

http://apples.msu.edu/uploads/files/Applenutrition-EricHanson.pdf

http://www.uvm.edu/~fruit/?Page=treefruit/tf_horticulture/AppleHortBasics/fruittreenutrition.html&SM=tf_submenu.html

COVER AND ALL PHOTOS BY ERIC HANSON.