He said that combined with a recent soil test, a leaf test can indicate whether crops, particularly deep-rooted crops, are tapping into nutrients accumulated in the sub-soil. Williams said it is important to note that a leaf analysis report will indicate any nutritional problem the plant may be experiencing, but it will not specifically identify whether the problem is disease-based. “A general rule of thumb is that if a problem is patchy then disease is a likely cause. If a problem is more widespread then a nutritional cause is likely,” Williams said, adding that taking a leaf test soon after the application of an input can help verify the effectiveness of the input.
Williams said once the sample area is defined, one should pick the last fully mature leaf but not the youngest or the oldest. A farmer should limit any potential contamination by wearing gloves and sampling at least a week after foliar spraying. “Use a paper sandwich bag to pack leaves for analysis so the leaves don’t sweat,” he said, adding that the bag should be labelled clearly. Farmers should use the same block name each year to enable easy tracking of changes over time. Contact Justin Platt on 083 264 6816.