MAGNESIUM DEFICIENCY
Magnesium is an essential part of chlorophyll and aids in the formation of sugars, oils and fats. Magnesium deficient vines have older leaves that are pale in colour. Leaf analysis is the best way to evaluate magnesium requirements.
Identification
Magnesium is mobile within the plant and deficiency usually appears first on the older leaves as it translocates from older to newly growing tissue,
Early Season
- Usually before bloom small brown-green spots near the margins and in the interveinal tissues of young, growing leaves
Summer
- Straw yellow tissue between the main veins developing from the leaf margin toward the attachment of the petiole in the shape of a wedge
- Some of the affected leaves will maintain a halo of green on their margins
- Symptoms progress to dead blotches on the leaves, which may be a rusty-red in red cultivars
- Leaf margins will curl and with severe deficiency the leaves may drop prematurely
- Fruit matures early, is highly coloured and may shell or drop prematurely
- Fruit bud initiation for the following year may be reduced
Often Confused With
Manganese deficiency - yellowing pattern between the veins occurs as “islands” of yellow areas rather than a continuous discolouration of the leaf
Zinc deficiency – deformed leaves, poor fruit set and on younger leaves
Boron deficiency – small cupped leaves, poor fruit set and bulges in internodes
Scouting Notes
Symptoms occur on older leaves and are most pronounced in mid- to late summer.
Management Notes
High applications of potassium or ammonium can induce magnesium deficiency symptoms on soils that originally contained enough magnesium so avoid excess nutrient applications.
Foliar sprays may be used but deficiency should be confirmed with tissue analyses before use. Apply foliar magnesium sulphate (Epsom salts) or chelates beginning immediately after bloom. Depending on severity of deficiency, there may be need for multiple foliar applications.
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