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Micronutrient Chlorosis

Micronutrients are essential for plant growth but are only needed by plants in small quantities. The are usually classed as amendments (not fertilizers) and include chemicals such as magnesium sulfate (Epsom salts), limestone (calcium carbonate), gypsum (calcium sulfate), and iron, zinc, manganese, copper chelates or sulfates.

Micronutrient deficiencies that are common in trees growing in our southwestern soils. Trees that most frequently show micronutrient deficiencies are queen palms, eucalyptus, bottle trees, silk oak, ash, citrus, pecan and pines. An arborist can advise you on which micronutrients that are lacking and identify your problem for effective treatment.

The most common micronutrient problems are caused by lack of iron, manganese, zinc, and magnesium. Low levels of these cause "chlorosis" or leaf yellowing. The type of chlorosis is unique for each micronutrient and can be determined by a skilled arborist. For example, chlorosis due to low iron or manganese affects young leaves, while low magnesium, nitrogen or potassium affects old leaves. Also, the pattern of yellowing in leaf veins is different for each element. The photos above show some examples.

Often a leaf tissue or soil analysis can verify the element that is lacking and whether more than one element is involved. Also, trees that suffer from salt damage, excess fertilizer or have insect, disease or root problems can exhibit chlorosis symptoms that mimic nutrient deficiencies. This is where a professional arborist can help you.

Micronutrients come in two forms, as chelated or non-chelated sulfates or oxides. The sulfates are cheaper but often less effective because the micros get tied up as insoluble precipitates when soil pH is high. Sulfates should be applied with humic acid or humates to keep them soluble. Chelated micros are much more effective and should be used where possible. They can be applied to the soil, to the foliage or by trunk microinjections. Soil applications can be made by surface application of dry chemicals or subsurface liquid injections (preferred) to roots under the tree crown. Tree roots MUST be adequately aerated for soil applications to be effective. If tree root zones are restricted, then trunk injections or foliar spray applications of chelated micronutrients can be used. Never use sulfates for foliar applications, as they will burn foliage. Often, the best solution is to use trunk injections with Mauget microinjections for a rapid response.

Chelated micronutrients are sold singly, as iron, manganese, zinc and magnesium chelates or as mixtures. The best chelating agent is EDDHA, followed by EDTA. MICROPLEX, is a mix of iron, manganese, copper and zinc chelates. SEQUESTAR and FERRIPLUS are single item products either with iron or manganese. One of the best mixtures on the market is Peter's S.T.E.M (for Soluble Trace Element Mix) which is used as a foliar spray. It is high in manganese, iron, zinc and magnesium and also contains copper and molybdenum. Another highly recommended soil only treatment is HEALTHY START 5-2-2 (Plant Health Care, Inc) that contains chelated magnesium, iron, manganese and zinc combined with beneficial microorganisms that colonize roots to give long-term relief. An alternative are the STEMIX line of Mauget trunk injection systems that contain mixtures of iron, zinc, manganese and copper.

These chemicals are inexpensive and recommended for large projects where many trees need to be treated. However, they are hit-or-miss. They include iron sulfate (which typically gives poor results), manganese sulfate and zinc sulfate. One sulfate that works well is magnesium sulfate or Epsom salts and is a good treatment where magnesium is lacking. Never use sulfates as a foliar application because they can burn leaves. A popular micro sulfate for trees are LUTZ Tree Stakes. These come as 5"-long stakes that you bury 5 per tree at the base of trees. FERT ALL Iron, another treatment, is a liquid iron oxide with humates to give benefit. The most effective way to apply micro sulfates are with INJECT-A-MIN Mauget trunk injectors containing mixtures of iron, zinc, manganese, copper and magnesium. With them you don't have to worry about soil conditions that might tie up the micros, because you introduce them directly into the tree trunk. INJECT-A-MIN MANGANESE is particularly good for treating low manganese in queen palms.

Artistic Arborist carries all of the health care chemicals described above. Check out Catalog #2 for prices and descriptions or visit our store on 4915 N. 7th Ave, Phoenix to pick up the ones you need.

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