Macronutrients

Nitrogen
Deficiency: Symptoms appear as reduced top growth with short spindly shoots that have pale green to yellow leaves. Generally speaking, symptoms first become evident in the older leaves at the base of shoots. In stone fruits deficient leaves appear reddish and may exhibit a “shothole” effect as the condition worsens. Fruits, especially stone fruits, tend to be smaller and to mature earlier.

Toxicity: Symptoms appear as an excessive amount of shoot growth accompanied by dark green foliage and delayed leaf drop in the fall. As nitrogen increases above the optimum, fruit color is reduced and maturity is delayed. Red cultivars are less red, and yellow cultivars tend to remain green. In apples and pears flavor and storage life are reduced. Besides direct toxic effects, other physiological problems, such as corking and bitter pit, can occur in apples and pears because of higher nitrogen levels that are not in balance with calcium levels.

Phosphorus
Deficiency: Deficiencies severe enough to produce visual symptoms are rare in fruit trees. When they do occur, symptoms may appear first as limited and slender terminal growth with young expanding leaves that are abnormally dark green. The young leaves’ lower sides, especially along the margins and main veins, frequently show purplish discoloration. The leaves may have a leathery texture and form abnormally acute angles with the stem. Leaf symptoms are most often seen early in the growing season and diminish later in the season. When soil moisture is low, lower levels of phosphorus are common in leaf analysis results.

Toxicity: Effects of excess phosphorus are usually expressed as deficiencies of one or more of the essential heavy metals, such as zinc, copper, iron, and manganese. Since deficiency symptoms of these elements may also be induced by excesses of phosphorus, visual foliar symptoms of phosphorus toxicity are not reliable.

Potassium
Deficiency: Symptoms generally develop first on older leaves at the base of the current season’s shoot growth. They are characterized by a marginal scorching of the leaves. In stone fruits an upward lateral curling and chlorosis may also become evident with the development of scorching. A heavy fruit crop usually accentuates the appearance of symptoms. Research suggests there is an inverse relationship between leaf potassium and crop load. Therefore, the lighter the crop the higher the demand for potassium. As with phosphorus, under conditions of low soil moisture, lower levels of potassium are common in leaf analysis results.

Toxicity: No known visual symptoms are directly attributable to high levels of potassium. However, magnesium deficiencies tend to appear when there are high levels of potassium.

Calcium
Deficiency: Specific foliar deficiency symptoms of a lack of calcium are rare in orchards. More common are symptoms induced by high levels of other nutrients. If deficiencies are present, they are first noticed in younger leaves as an upward cupping of leaf margins and a uniform veinal and interveinal chlorosis of the expanding leaves. Fruit often shows symptoms associated with a low level of calcium even when there may be sufficient levels in the leaves. (See section on bitter pit and corking.)
Toxicity: No known symptoms are associated with toxic levels of calcium.

Magnesium
Deficiency: In their severest stages, symptoms may look similar to the marginal scorching associated with potassium deficiency, although this is very rarely observed in Pennsylvania. More characteristic is a fading of the green color at the terminals of older leaves, progressing interveinally (between veins) towards the base and midrib of the leaf and giving the typical “herringbone” appearance. In pears, dark purplish islands of tissue surrounded by chlorotic bands may develop in the interveinal areas. As the growing season progresses, symptoms develop on progressively younger leaves and the older leaves fall off.

Toxicity: Symptoms of excessive magnesium levels are not specific but usually appear as a deficiency of either potassium or calcium.