Sorting out those yellowing leaves
Often during the drier, hotter mid summer days, leaves may show signs
of nutrient deficiencies. Sorting out the visual symptoms of nutrient
deficiencies can present a real challenge. Four easily confused visual
nutrient deficiency symptoms are magnesium, manganese, iron and zinc.
What makes them a challenge to diagnose is their similarity in symptoms:
leaf chlorosis or yellowing with the veins remaining green.
A good place to start sorting out the symptoms is by the leaf's location
on the plant. Magnesium usually appears on older leaves first. The other
three occur typically on younger leaves.
Magnesium
Common symptoms:
- lower, older leaves turn yellow (chlorotic) on leaf margins and between
the veins (interveinal)
- veins remain green resulting in a mottled appearance
- leaf veins have broad green margins
- leaf margins may remain green
- margins may curl up or downward giving the leaf a puckered appearance
- interveinal necrosis (dead tissues) develop late in the season
- necrosis between veins develops quickly
Magnesium deficiency, grape
Photo credit: International Plant Nutrition Institute
Manganese
Common symptoms:
- mosaic-like yellowing between veins (interveinal chlorosis)
- leaf has checkered or finely netted appearance; smallest veins remain
green
- the darker green colour next to veins and along the main veins gives
a "Christmas tree pattern" on younger and moderately old leaves
- no sharp distinctions between veins and interveinal areas as in an
iron deficiency
- necrotic (dead) spots usually present and scattered over leaf surface;
these may tear
Manganese deficiency, celery
Photo credit: International Plant Nutrition Institute
Iron
Common symptoms:
- youngest leaves become yellowish-green, later lemon-yellow or yellowish-white
- interveinal chlorosis with sharply contrasting narrow green main veins;
larger veins remain green; finest veins sometimes also remain green
- lower, older leaves remain a darker green
- necrotic (dead) spots are usually absent, but in extreme cases, leaf
margins and tips become necrotic; necrosis may extend inwards, developing
into a large area, spreading over the whole leaf blade
Iron deficiency, tomato
Photo credit: International Plant Nutrition Institute
Zinc
Common symptoms:
- characteristic irregular chlorotic (yellow) mottling develops rapidly
into variously sized necrotic (dead) blotches,
- leaf becomes yellow-ivory to white in colour
- younger leaves at growing tips are much smaller (little-leaf) than
normal leaves; often narrow in appearance and in a rosette like whorl
- the chlorotic mottling generally starts in the older leaves and spreads
all over the plant, but sometimes it is seen on the younger leaves first
- in perennial crops, stems are severely shortened resulting in formation
of numerous short stems at tip; extreme short internodes with a bushy
growth habit of the leaves, the terminal and lateral shoots ("rosetting");
tip die back may occur
- symptoms may occasionally appear on older leaves; older leaves may
drop
Zinc deficiency, corn
Photo credit: International Plant Nutrition Institute
These symptoms may indicate an acute or chronic nutrient deficiency problem.
What action to take, to reduce the symptoms depends on confirming the
deficiency and finding its cause. Use leaf and soil analyses to confirm
the deficiency. But the cause may not be a lack of nutrients in the soil.
Carefully check soil conditions, moisture, or damage from insects, diseases
or other animals. As well, review past weather conditions and spray records.
While it may look like a nutrient deficiency, it just may not be.
