Foliar Focus

Where do foliar sprays fit in a regenerative system?

Soil health is essential for a resilient plant, but we can also ramp up plant resilience and aid in building soil health by applying timely foliar sprays. For example, we can load up a perennial tree with reproductive inputs in a delayed dormant treatment prior to bloom and induce resistance to bloom-time diseases. We could also utilize an in-season foliar spray to increase photosynthetic efficiency and increase the sugars within the plant, about a third of which will be root exudates that feed soil biology. I have personally seen soil organic matter increases that far outweigh the pounds of compost or carbon we have applied, and I attribute much of these gains to my adoption of aggressive foliar applications. 

Under the conventional agricultural system, we would add some nutrition only when it was getting a “free ride” with either a fungicide or an insecticide application. Now, we are doing many applications without a fungicide or insecticide, because by enhancing plant performance, we’re able to achieve similar results with nutrition. I wish I would have listened to my early mentor, doctor Tom Yamashita, when he was preaching the value of foliar sprays to me over 20 years ago. I resisted his advice, only adding them with the so-called free rides. It wasn’t until about six years ago that I started utilizing foliar sprays more extensively. Soon after implementing this practice, plant health improved, along with more consistent yields due to increased carbon production.

When building a foliar application, my first rule is to make sure you stack the proper nutrients to create what you want. Do you want reproductive growth? If so, I use a stack of calcium, boron, phosphorus, zinc, manganese and cobalt. Or do you want a vegetative response? If so, I like using stacks with more of an emphasis on nitrogen, while also including humic, potassium, calcium, iron, zinc and silica. The nitrogen source varies depending on whether the crop is  organic or conventional. We can use plant-derived amino acids or even good old urea (low biuret) if it is sufficiently buffered with carbon. Other stacks I use help prevent disease and abiotic stress. These all include silica, selenium, iodine, manganese, zinc, copper and boron, and of course calcium and kelp. 

Another thing to consider when creating these nutrient stacks is the pH of the products. A perfect example is boron. I will use boric acid on my low-pH mixes, but then I use sodium borate on my high-pH mixes. I also feel foliar sprays are helpful where we have excesses in our soil that create some antagonistic issues with uptake. There are many examples of high calcium creating iron chlorosis and low magnesium. High magnesium antagonizes nitrogen, calcium and potassium uptake. High potassium creates low magnesium, high sulfur with phosphorus uptake, and vice versa. If phosphorus is high, sulfur uptake will be lacking. 

That’s why balancing ratios in your soil is so critical — so you’re not chasing low numbers but using stacks that create optimum performance. Salts (sodium and chloride) create challenges when they are in excess. You may have your soil in good order, but if your water source is marginal, then salt can become an issue. Carbon and silica are the most powerful when combating sodium and chloride. I will give examples of my success using these products when I discuss leaf tissue (sap) analysis in my next column.

Here are some does and don’ts when it comes to foliar sprays:

1. Make sure, when adding another product besides the nutrition, that it mixes without precipitation at the desired pH. I generally will do a jar test and see how it responds 48 hours later. I will also perform a small trial to ensure there is no phytotoxicity.
2. Do not spray drought-stressed plants, due to minimal stomata opening.
3. Spray early morning, even if dew is present, if you have ample time for the spray to dry without any possibility of rain or overhead irrigation. The longer the drying time, the more absorption you will get.
4. It is perfectly OK to spray perennial crops before the foliage pushes out. It is necessary for perennials that push bloom first before vegetative growth. The openings in the wood are larger than the openings on the leaf. I will use calcium and boron, along with phosphate, at this point. Calcium and boron are critical for pollen tube growth. This year, California had some unusually cold temps during the bloom — thus the reason for the smallest almond crop forecast in quite some time. Averages were estimated at 1750 lbs. per acre, when it should be 2350 lbs. per acre. Most experts think it was the lack of bee hours, but I believe suboptimal pollen tube growth also attributed to the poor crop. Why do I think this? We have some self-pollinating varieties that still have a poor nut set. The growers who implemented this delayed dormant application are not seeing their yield forecast as low. We are seeing ranges in the 2000- to 2900-lb. range.
5. I feel phosphites were overused again this year. During our cold, wet spring, many consultants in our area advised using phosphite to help battle phytophthora. The problem with that is the plant will not utilize phosphate as well, since phosphite triggers the plant as if it has enough phosphate — though the two molecules have different functionality in the plant. During bloom, and for at least three weeks after pollination, phosphate (along with calcium) is critical for cell division. Why would we want to trick the plant into thinking it has enough phosphate at this time? Tissue analysis of whole leaves or sap cannot decipher the difference between phosphate and phosphite. There may be a place to utilize phosphite, but I don’t think it is appropriate when you need peak reproductive response.
6. If you can, adjust your spray timing, starting at five days leading up to a full moon. This is when maximum sap movement occurs in the aboveground portion of the plant. Fertigation is also best to start five days prior to a new moon — this is when most of the energy moves in the roots. 
7. Use humic or fulvic acids to optimize the uptake of nutrients. Humic acid is a great partner with nitrogen applications such as urea. Fulvic is great on the lower-pH mixes, I’ve seen a much better response when adding these products versus when they are left out of the tank, along with the great buffering capabilities they have.
8. Do not be afraid to use products that enhance immune response, such as kelp, silica, triacontanol, chitinase and some bacillus strains of bacteria.
9. Use natural chelators such as fulvic, amino acids, lignosulfonates, etc. Do not use EDTA chelators. They do not break down easily in the plant or soil (they steal the plant’s energy to do so). They also will grab other trace elements after the original element it was carrying is released until it is broken down by the plant.

Jim Pingrey is an agronomic consultant in California’s Sacramento Valley.