Similar symptoms
Great care must be exercised when diagnosing nutrient deficiencies, and using visual symptoms alone can be very misleading. The diagnosis of problems must include using soil and tissue sampling and the analysis of affected and unaffected areas of a field to confirm a nutrient deficiency.
Sulphur deficiency can be similar to and confused with many other stressors that cause symptoms in canola similar to those caused by S deficiency. For example, Group 4 herbicides such as 2,4-D or dicamba (Banvel) at low, sub-lethal rates from wind drift, tank contamination or even precipitation can cause leaf cupping in canola (Figure 5a). However, the leaves in this figure lack the dark vein coloration associated with S deficiency.
Like S deficiency, Group 2 herbicides can cause purpling of canola leaves, but unlike the leaves of S-deficient canola, the purpling does not develop from the leaf margins.
Figure 5b shows Muster (ethametsulfuron-methyl) injury on canola. Muster is a registered herbicide (Group 2) on canola, but injury could occur if a heavy rainfall occurs shortly after spraying, facilitating the uptake of the herbicide via the roots.