TECH-SPRAY Hi-K is one of our best-selling products because it is so effective for so many needs. As this winter is shaping up to be a cold one, we have been talking to many growers and PCA’s about freeze protection programs and how micronutrients can play a role in frost recovery and cold hardiness. Below is some information on how to protect crops from freeze damage.
FOR FREEZE RESISTANCE
ON TREE CROPS
| TECH-FLO ZMC:
TECH-SPRAY Hi-K: |
2 quarts per acre.
2 quarts per acre. |
Timing:
- On citrus and avocados, apply shortly before freezing weather which normally can be expected around the second week in December.
- On deciduous fruit and nut trees, apply post-harvest and in early spring at the time a freeze is anticipated or predicted.
ON GRAPES AND BERRIES
| TECH-FLO ZMC:
TECH-SPRAY Hi-K: |
1 quart per acre.
1 quart per acre. |
Timing: Apply just prior to anticipated freezing temperatures.
ON FIELD AND ROW CROPS
| TECH-FLO ZMC:
TECH-SPRAY Hi-K: TECH-SPRAY COPPER: |
1 quart per acre.
1 quart per acre. 1 pint per acre. |
Timing: Apply just prior to anticipated freezing temperatures.
The use of foliar nutrients as frost protectants was being promoted even before publication of the research by Dr. Steven Lindow at the University of California, Berkeley, which showed that certain naturally occurring bacteria such as Pseudomonas syringae and Erwinia herbicola act as nucleating agents for ice formation. The presence of these ice-nucleation-active bacteria results in the formation of ice crystals in plant tissue at temperatures several degrees higher than in their absence. When water in plant cells freezes, it expands and ruptures the cell walls, leading to cell necrosis. The bacteria can be killed or prevented from acting as nucleating agents, thus providing several degrees of frost protection.
This discovery provided a plausible explanation for the previously observed positive effects of foliar nutrients on freeze tolerance. While the mechanism can be explained, there is no general agreement on which chemicals are most effective in controlling the ice-nucleating bacteria. Several specially formulated products are commercially available, but in controlled tests these have generally not given better results than copper-based fungicides or micronutrient mixtures.
Just as low temperatures are not the only factor involved in freeze damage, it is likely that control of ice-nucleating bacteria is not the only factor involved in improving freeze resistance. Gradually lowering temperatures promote cold hardiness. Trees under long term water stress are less cold-hardy(1). Plant growth regulators play an active role in influencing freeze resistance. High gibberellin levels have been reported to increase susceptibility to environmental stress(2). During chilling, a precursor of auxin has been shown to accumulate in buds, followed by the gradual appearance of auxin(2).
Plant nutrients are capable of influencing these factors. Copper, because of its inherent fungicidal properties, is considered the most effective element for control of ice-nucleating bacteria. Zinc also has mildly fungicidal properties and has been shown to be a co-enzyme for the biosynthesis of tryptophane, a precursor of auxin(3). Potassium, Calcium, and Phosphate play important roles in freeze protection and recovery as described.
For more detailed information on how a freeze program can help your crops, contact your Nutrient TECH Rep or talk to your PCA.
REFERENCES
- Parsons, L. R. Interactions among Environmental Stresses. HortScience 25(11):1363 (1990).
- Seeley, S. Hormonal Transduction of Environmental Stresses. HortScience 25(11):1369 (1990).
- Bennett, J. P. and F. Skoog. Preliminary Experiments on the Relations of Growth-Promoting Substances to the Rest Period in Fruit Trees. Plant Physiol. 13:219-225.
