By Dr. Thomas T. Yamashita

Cool, rainy weather tends to have a number of deleterious effects on strawberries:

1. A tendency to reduce the overall metabolism (rate, scope, direction, completion, etc.) of the strawberry seedling.
2. A tendency to enhance wetness and length of wetness on canopy tissues.
3. Due to #2, increased opportunities for spore germination and bacterial activation, thereby increasing the chances of disease outbreaks.
4. Rains are not unlike distilled water, and rain events are known for their leaching of minerals and some soluble, carbon-based nutrients from the canopy tissues, resulting in:
   1. Overall reductions in tissue integrity.
   2. Reduced epidermal tissue stability and thus, an increased opportunity for pathogen colonization of tissues.
   3. Further reduction in the efficiency of metabolism for various reactions.
5. The cooler soil temperatures reduce the growth and development of the root tissues as well as canopy tissues.
6. The water-logged soil is reduced in oxygen, thereby inducing an expansion of the lenticels, which leak their cell contents into the soil, providing a preferred substrate for the attraction and proliferation of water mold species such as Pythium species and Phytophthora species.
7. The reduced evapo-transpiration rate and overall reduction in the movement of moisture through the plant reduces the opportunity to irrigate and thereby reduces the opportunity for delivering necessary minerals via the vehicle of additional moisture.
8. The overcast weather patterns reduces the opportunity to maximize photosynthetic harvest (PnH) and thus, has the potential harm of causing small flower development and reductions in size and sugar levels in the berries.
9. The overcast weather patterns also can lead to a minimal contribution from “Active Pn” of much needed carbon compounds, thereby causing the plant to draw additional carbon compounds away from the crown, a very dangerous proposition, indeed, as crown tissue with limited stored plant food and energy can lead to, among others, a severe reduction in berry quality, vine collapse and heightened susceptibility to various physiological and pathological diseases.
10. Other deleterious events and happenings.

Objectives for Strengthening Strawberry Plants’ Resistance to Wet Weather

Our goals are as follows:

1. Maintain the physiological functioning of the vines, without stopping or slowing down the physiological mechanisms.
2. Maintain a high level of photosynthetic efficiency (PnEf) that allows for substantial carbon and energy (C&E) harvest, thereby preventing the C&E drain on the crown, a phenomenon that invariably leads to the debilitation of the strawberry vine and is commensurate with eventual vine decline.
3. Overall, do not allow cool and wet weather patterns to reduce the growth and development of the vine, including the reduced rate of pollenization of the flower, which can ruin the quality of the berries, waste energy, and cost the growers much in the way of not having a viable product for sale in higher end markets.

Implementing a Wet Weather Solution for Strawberries

The effective management of these weather-related obstacles resides in defining the weather projections at least 3 to 7 days in advance of their happening. This factual information can be secured off the University of California IPM website for projected weather patterns.

Because of how distilled water leaching weakens tissues to pathogen colonization, and the need to construct additional tissue integrity and resilience to pathogen colonization, it will become necessary to supplement the slow release fertilizer with the broad array and proper concentrations of various micronutrients, as well as the proper proportions of macronutrients.

The importance of this emphasized need for mineral supplementation is substantiated from experiences demonstrating that the evapo-transpirational stream is largely responsible for the uptake and translocation of many minerals. These minerals move via mass flow from both the soil as well as from areas of the plant that do not demand so much of these nutritional factors, to areas that do require much more volume (e.g. the crown, flowers, and young developing flowers and fruit).

The sensitivity of the epidermal tissues to the further weakening effects from reduced uptake of Ca, K and Mg, not to mention a long list of micronutrients, must be mitigated with supplemental quantities of these nutrients. Further, during periods of overcast, cool, wet weather patterns, we need to provide preformed photosynthates, both through the soil program as well as by way of the use of superior foliars such as Fusion 360 Foliar FG-31, which holds the proper proportion of carbon-based precursor molecules as well as the appropriate species of carbon units.

It is extremely important for us to know that the indiscriminate use of these raw preformed photosynthate materials lends itself to weakening of the plant. Furthermore, our studies have shown that the indiscriminate use of carbon compounds results in symptoms reminiscent of poisoning or physiological shock and/or a physiological malady of grave proportions), all of which would lead to a dramatic reduction in yield and the eventual collapse of the vines.

As a very important example, let us utilize the delivery of nitrogen (N) as a means to visualize one of the most important obstacles we face when trying to achieve high performance strawberry culture while utilizing slow release fertilizers:

Note: What we are proposing is to increase the controlled delivery of balanced, blended fertility to the strawberry seedlings throughout the season:

1. To be able to adjust the nature, concentrations, ratios, balances, etc. of the nutrients based on the weather patterns and/or other environmental shifts.
2. At present, the grower is setting himself in a position that ties his hands, keeping him from truly reaching his potential for high yields and high quality fruit. Beds are oftentimes held together by plastic mulch. There is also the augmentation utilizing the gums produced by selective microbial activation. When the slow-release fertility is set in motion, the goal of achieving incrementation of balanced, blended fertilizers which is anticipated to occur does in fact never come to fruition. There is no control over the release of fertility from the slow release of the fertilizer. As a result, the grower is at the mercy of Mother Nature. If the grower was able to counter punch every potentially harmful weather event he would be able to avoid a long, long list of harmful events. The only way he can control environmental stresses at this time is to forgo the slow release fertilizer. In place of slow release of fertilizer, we are proposing a drainage facilitating system either using (1) sand and/or (2) thin plastic pipe with perforations (the pipes used for draining moisture away from the houses).

Figure 1: Enhancing the drainage of excessive water away from the bed using coarse sand placed beneath the bed in one of three shapes. Moisture will fill the sand conduit. Since the grade from top to the bottom of the field has a slope of about 6″ to 8″ per 100 feet of run, the collected excess moisture finds its way into the tile drains. From the tile drains, sump pumps placed at strategic locations will then pump the water to a drainage canal.

Note: The above drawings represent three scenarios of the drainage of excessive water into the sand conduit. The arrows in (1) point to a very efficient and even drainage. The arrows in (2) point to uneven drainage. In this model there will be excessive flow shown by netted lines. Consequently the sand conduit is overloaded quickly detracting from its primary focus which should be the planting bed. The arrows in (3) depict an excessive volume of soil to be drained such that the primary focus, the planting bed, is delayed in its drainage, thereby undermining the grower’s main reason for this conduit system, to allow for the use of the fertigation system.

The placement of the drainage conduit is extremely important. The reason for detailed placement is the complete and even drainage achieved when the conduit sits just beneath the base of the bed.

In this position indicated in (1), the “sweet spot” gains homogeneity, whereby the drainage excess attains an even direction and flow into the conduit without overloading its volume capacity. As a result, the rapidity with which the sweet spot is freed of excessive moisture allows the grower to control his fertility and to counter-punch environmental stress events which would otherwise result in such deleterious effects as photorespiration, a minimal defense response, continual fruit production and development, etc.

Notice how there is almost an overkill response of the saturated area. In other words, we will be remediating more saturated soil than is necessary. This is not a bad practice, but we must remember that we may be saddled with a limited area to drain our tile into.

Furthermore, we want to create a sweet spot which helps to retain the great majority of root volume within the sweet spot. It is important to know that a strawberry plant will only allow its root system to venture into a zone of soil that is replete with nutrients. If we are successful in creating a nutrient rich sweet spot, the great majority of the root system will be growing into that zone. This is very important for example in that we can achieve an higher degree of absorption efficiency by embellishing the sweet spot to a degree such as the plant will only generate its roots to reside in the sweet spot. This means that the roots will not venture out into the zones which may contain phytotoxic factors.

Hosting a unique volume of soil for each seedling is the ultimate luxury as this allows the grower to exercise his own personalized fertility program adjusted in time according to the direction of weather patterns. This control is an imperative direction if you want to enter the realm of high performance strawberry culture.

Synopsis of Desired Nutritional Programs in Strawberry Cultures

1. Ideally, omit the pre-plant, slow release nitrogen fertilizers.
2. To facilitate the beds with an ability to avoid waterlogging, place a large diameter layer or cylinder of coarser sand (then the existing soil) to act as a conduit for draining off excessive moisture.
3. Following the program and the format, we will have to generate a field specific program. I will leave this open with the message that each grower’s individual field will require definitive biological and chemical analyses testing and the fertility program will be done following the securing of your samples.

An Example of an Adaptive Remedial Program

This is the initial preview of a field-specific program developed following extensive characterization. The remaining portion of the program will be filled at a 3 month intervals. The 3 month interval is more practical as unforeseen weather patterns can alter the program quickly.

(Thumbnail source: Pixabay, public domain via CC0)