It is time for us to take leaf tissue samples in pecans. UGA Extension Pecan Specialist Dr. Lenny Wells has this information:
The general recommended period for leaf sampling is July 7-August 7.
Why does it matter when you sample?
Concentrations of N, P, and Zn on a leaf dry weight basis start off relatively high early in the season, decline rapidly, reach a fairly steady state after mid-June, and then decline near leaf fall. K tends to start high, then decreases and plateaus at about the same time as N, P, and Zn. Most of the P and Zn that accumulates in the leaves have done so by the time the leaves reach full size. Calcium (Ca) accumulates in the leaves as the season progresses, peaking in August-September. Magnesium (Mg) Manganese (Mn), and Boron (B) also tend to increase as the season progresses, but to a lesser extent than Ca.
How do we sample?
- Collect 50- 100 middle-pair of leaflets from the middle leaf of this year’s growth (right). Use terminal shoots exposed to the sun. Avoid twigs from the interior of the tree. Collect leaflets from all sides of the tree. Avoid leaflets damaged by insects and diseases.
- Abnormal trees or trees not representative of the area should be sampled separately. A complete and accurate description of abnormalities should accompany these samples.
- Sample trees of the predominant variety in a given block. If Schley is the main variety, sample Schley; etc.
- Immediately upon collection, wipe leaves (entire surface, both top and bottom) with a damp cellulose sponge or cheese cloth to remove dust and spray residue. Do not allow the leaves to come into contact with rubber or galvanized containers. Partially air dry and place in the large envelope of the mailing kit.
- If recent soil test data is not available, it would be advisable to collect a soil sample and have it sent to a soil testing laboratory. By sampling the same trees each year, growers can more readily see the results of any changes to their nutritional programs.
**Some growers have taken leaf samples throughout the growing season to determine the fertility needs of the tree. This is really unnecessary. Leaf analysis does not necessarily reflect the actual use pattern of mineral nutrients, but instead indicates concentrations of those elements in the leaf at the time of sampling. The tree knows what it needs and when it needs it.
Concentrations of mineral nutrients in the leaves change as leaves emerge, expand, and finally senesce in the fall. For many elements, the least change in concentration occurs from early July-early August.