Diagnosing is a detailed process.
A nutrient deficiency is one of numerous maladies that can affect evergreen and deciduous trees. The key word here is numerous. Many, many causes of odd-looking tree leaves and stems exist; the goal is to figure out the one or ones that are producing the symptoms and take steps to address it. Unfortunately, determining the cause often is difficult, but certainly worth the effort.
There are three main reasons for being accurate, for identifying the actual cause of the malady
Effectiveness: In order for an action to be effective, it must influence the problem. The old tale of a boy looking under a streetlight for a quarter that he lost somewhere else because the light is better there comes to mind. If the malady is poor soil drainage or winter injury, applications of nutrients won’t help, even though they may be easier to utilize.
Expense: Examples of this include unnecessary pesticide treatments for no problem at all or using fertilizer in an attempt to address a disease, insect or improper planting issue. Clients are much happier spending money that makes actual improvements in their trees’ health as opposed to ones that are more of a shot in the dark.
Legality: … and possibly fraud. Pesticides are designed to control pests — insects, diseases, weeds, rodents, etc. If a fungicide is applied to a tree when the actual problem is a borer infestation, it may be legal as long as the tree in question is listed as a site on the label, but no real positive results will occur.
The same is true for added nutrients. If a customers’ tree has yellow leaves due to being planted too deeply, and a quick fix seems to be the injection of a multi-nutrient solution, the action could be described as fraudulent, which the Nuance iPad dictionary app defines as “deceit, trickery, sharp practice or breach of confidence perpetrated for profit….” In other words, giving the impression of taking appropriate action when one knows that it’s not the right one, or that there may not be one.
How do you know?
The first step in determining if a nutrient deficiency exists is to identify the tree. Many trees have nutrient deficiencies that are commonly associated with them. For example, in the Midwest, pin oak trees growing in high pH soils often develop iron chlorosis. In these scenarios, iron exists in the soil in sufficient quantity to support healthy tree growth, but the alkaline pH ties it up and prevents it from going into the soil solution. Again, there can be many causes of odd-looking tree leaves and stems, so one reasonable place to start is with the known causes.
A good next step is soil sampling. Start by taking a representative sample from the tree that you suspect has a nutrient deficiency. What is “representative”? In the case of a soil sample for a tree, remove a trowel full of soil from nine or 10 sites at various levels of rooting. Since most will be in the upper 24 inches of soil, some should be taken at a 4-inch depth, some at a 12-inch depth, some at 18 inches and some at 24. As well, some samples should be a few feet away from the trunk, some under the drip line and some twice the drip line distance. Overall, the samples should be random in depth and distance from the trunk, and represent the active root zone of the tree. The extracted soil should be mixed together in a plastic (not metal) bucket and taken to a reputable soil-testing laboratory. As best as you can, remove small pieces of roots and rocks before submitting the sample.
Though the desirable amount of nutrients varies from species to species, the general ranges to consider for most trees are:
- (N) Nitrate nitrogen – 5 to 20 ppm
- (P) Phosphorus – 25 to 50 ppm
- (K) Potassium – 100 to 150 ppm
- (Mg) Magnesium – 200 to 400 ppm
- (Ca) Calcium – 300 to 800 ppm
- (S) Sulfur – 10 to 20 ppm
- (Zn) Zinc – 2 to 4 ppm
- (Fe) Iron – 50 to 150 ppm
- (Cu) Copper – 3 to 8 ppm
- (B) Boron – 0.5 to 1 ppm
- Desirable pH range – 5 to 7
Lastly, there are unusual visual symptoms of leaves, needles, stems and flowers. Gauging the presence of a deficiency based on the way that a plant looks is tricky at best. However, if you are experienced in caring for a particular species, then you should have a pretty good idea of how the overall appearance of the tree should look. Your previous encounters with healthy specimens then can be compared with the one that you suspect to be deficient.
There are three groups of nutrients required by plants for healthy growth: the macronutrients of nitrogen, phosphorous and potassium, the secondary nutrients of Ca, Mg and S, and the micronutrients of Fe, B, Cu and Zn. Some symptoms of nutrient deficiencies for each are listed here:
Broadleaf trees: Leaves are uniformly yellowish-green; this color is more pronounced in older leaves. The leaves are small and thin, have high fall color, and drop early. Shoots are short and smaller in diameter than usual. Shoots may be reddish or reddish-brown.
Conifers: Needles are yellowish, short and close together. Older plants exhibit poor needle retention. Lower crowns may yellow, while upper crowns stay green.
Broadleaf trees: Leaves are green to dark green. Veins, petioles, and lower surfaces may become reddish, dull bronze, or purplish. Foliage may be sparse, slightly smaller than normal, and distorted. Leaves drop early. Shoots are normal in length unless the deficiency is severe, but they may be small in diameter.
Conifers: Needles turn purple in young seedlings, starting at the tips of lower needles and progressing inward and upward. Few or no secondary needles may appear. Needles die, starting in the lower regions and spreading upward through the tree. Buds may set early or seedlings remain dormant longer than usual. Older trees take on a dull blue or gray-green color.
Broadleaf trees: Leaves exhibit marginal and interveinal chlorosis (yellowing), followed by scorching that moves inward between the main veins to the entire leaf. Older leaves are affected first. Leaves may crinkle and roll upward. Shoot tips die back late in the season. Shoots from lateral buds result in zigzag growth that is short and bushy.
Conifers: Older foliage takes on a dark bluegreen color that progresses to yellow and reddish- brown; finally, necrosis (death) occurs at needle tips. Needle retention is poor; needles are often stunted. Seedlings have short, thick, abundant buds; frost injury is frequent.
Broadleaf trees: Leaves become chlorotic and/or necrotic; young leaves are small and distorted with tips hooked back. Shoots are stunted with terminal dieback. Roots are usually affected first, with dieback of root tips severely reducing growth.
Conifers: Primary needles are usually normal, but secondary needles may be stunted or killed. Terminals are stunted and needles may hook at tips. Symptoms are most severe in the youngest foliage in the upper crown.
Broadleaf trees: Leaves are thin, brittle, and drop early. Older leaves may show interveinal and marginal chlorosis, reddening of older leaves, with interveinal necrosis late in the season followed by shedding of leaves. Shoot growth is not reduced until deficiency is severe.
Conifers: Needle tips are orange-yellow and sometimes red. Primary needles remain blue-green in young seedlings, but in older plants, older needles and the lower crown show symptoms first. In affected needles, the transition to green may be sharp.
Broadleaf trees: Leaves are entirely pale yellow-green in both young and old plants; they are small on some species and exhibit other symptoms associated with nitrogen deficiency. Shoots are stunted.
Conifers: Symptoms similar to those associated with nitrogen deficiency, needle tips may be yellow, red, or mottled, particularly on older needles. Necrosis may follow. Needle retention is poor.
Broadleaf trees: Young leaves are yellow with contrasting narrow green veins; older basal leaves remain darker green. Exposed leaves are bleached and eventually will exhibit apical or marginal scorch. Leaves may be small; symptoms will be severe in cold, wet springs. Shoot length is usually normal, but diameter will be small; twig dieback and defoliation will occur when the deficiency is severe.
Conifers: New growth will be very stunted and chlorotic. Older needles and the lower crown will remain green. In seedlings, cotyledons remain green.
Broadleaf trees: Leaves are occasionally bronzed or scorched. Young leaves are affected first. Leaves are small, thick, brittle and sometimes distorted. Shoots exhibit rosetting, discoloration, and dieback of new growth, which becomes zigzag, short, brushy, thick, and stiff.
Conifers: Shoot tips are bent and the meristematic tissue of the main leader may split. Necrotic blotches are visible on magnified cross-sections of buds and cause the death of terminal and some lateral buds. Plants may be more like shrubs than trees.
Broadleaf trees: Leaves are uniformly yellow, sometimes mottled with necrotic spots. Leaves are small (littleleaf ), very narrow and pointed; older leaves drop. Shoots of small diameter have tufts (rosettes) of leaves at their tips, which may die back.
Conifers: Branches and needles are extremely stunted; foliage yellows. Trees lose all but their first- or second-year needles; terminals die back.
There are many “look-alike” symptoms that may be confusing when trying to determine if the cause of a particular malady is due to a nutrient deficiency, an insect or disease organism, or some other agent. Some of the more common abiotic factors include construction damage, general slowdown in growth, herbicide injury, natural needle drop and leaf scorch. Some look-alike causes are more difficult to pin down than others, yet the same process should be followed — starting with the general and focusing on the specific using known information and diagnostic processes.