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Yellow Wheat Part II - Causes and Corrections

Author: Keith Reid- Soil Fertility Specialist/OMAFRA, Stratford
Creation Date: 22 May 2009
Last Reviewed: 22 May 2009


A number of growers are reporting patches of yellow in their winter wheat fields. There are many potential causes for this discolouration - wet soils, low pH, nutrient deficiencies, disease - any of which may be exacerbated by backwards spring weather and slow root growth. The first step will be to diagnose the cause of the yellowing so an effective treatment can be applied. A quick guide is found in the following table.

Suspected Nutrient Deficiency Plant Symptoms Soil Conditions Corroborating Tests
Nitrogen Stunting and yellowing of entire plant, starting at lower leaves Often associated with wet soils, where denitrification has caused N loss Plant tissue tests (compare good with poor areas) will confirm if the yellowing is due to low N or low oxygen to roots
Magnesium Yellowing from the base of the plant, with distinct interveinal chlorosis Generally associated with sandy, low pH soils with low Mg. High K levels will make deficiency worse. Soil test to confirm low Mg levels; Squirt test can give quick diagnostic
Manganese Yellowing from the top of the plant, sometimes with faint striping of the leaves Patterns in field often more diagnostic than leaf symptoms; appears on high pH knolls, and in hollows with muck soils Plant tissue test (compare good with poor areas); Squirt test can give quick diagnostic
Iron Rare in Ontario; similar to Mn, with yellowing on younger leaves first, but with more distinct interveinal striping Saturated, high pH soils Plant tissue test (compare good with poor areas); Squirt test can give quick diagnostic
Low pH Stunting and poor vigour, may look like nutrient deficiency Most often associated with sandier soils and lower slope positions (exception: Niagara, where the clays are naturally acidic) Soil test for pH

Once the deficiency has been identified, steps can be taken to correct it. Magnesium deficiency will require soil applications of Epsom Salts or Sulphate of Potash-Magnesia (K-Mag™), or dolomitic limestone if it is associated with low soil pH. Micronutrient deficiencies can be corrected with foliar applications. The product of choice for correcting manganese deficiency is manganese sulphate, applied to provide 2 lb/ac of actual Mn (8 lb/ac of product). This should be applied in high rates of water (40 gal/ac), with a spreader-sticker to help carry the manganese through the cuticle of the leaf. Chelated manganese is much easier to use, and is more compatible with herbicides if they are mixed, but much more expensive. Scientific opinions on the effectiveness of chelates range from about 2X as effective as the sulfate (U. of G.) to equally effective (Michigan State), but the cost is roughly 10X higher for the chelate per pound of manganese. Very low rates of chelated product are not effective.

Squirt Test Protocol

The "squirt and see" approach can often give results quicker than the turn-around from a lab. Mix ½ teaspoon of nutrient with water in a one liter hand spray bottle, adding two drops of a spreader sticker (dish soap will work in a pinch). Lightly wet foliage with the mixture in one metre strips in the affected area(s), marking the sprayed area with flags. If the crop responds to the application within 48 hours, you have identified the problem.

Suspected Deficiency Nutrient Source
Magnesium Epsom Salts (MgSO4)
Manganese Manganese Sulphate
Iron* Ferrous Sulphate


*Note: Iron is known to give plants a darker green colour, so interpret these results with caution.

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