Cherries - Spring Rains and Fruit Harvest

 

 

For fruit growers, harvest is their final exam. It is the “acid-test” of how well their plans and efforts paid off. To get close to harvest and not be able to pick due to crop failure is devastating. Avoiding that is a big challenge.

 

There are many details involved in producing cherries. While an early variety can be very lucrative, you only have about a 60 and 90 day timeframe to work within (depending on region and variety) to “make the magic” happen. Invariably there are weather events; sometimes rain and sometimes worse. These bring challenges to the potential yield, planning for them beforehand can be in your best interest. Let’s discuss pre-harvest rain.

First, let’s consider some common concepts and ideas:

Rain assumptions and facts:

Has an average pH of 5.4-5.6

Not necessarily. This tends to differ regionally, especially since there are less sulfur compounds, in the air, due to clean air restrictions, so check rainwater to confirm.

Assumed to be perfectly distilled water.

Not necessarily. In California, for instance, there is a good amount of sodium found in rainwater because of the close proximity to the Pacific Ocean; check to confirm.

A 1” rain event can add 15-20 lbs. of NO₃-N per acre.

I have found this to be fairly accurate, but again, check your field to confirm. The key here is to offset the adverse nitrate effects to the fruit. When harvest is within 2-4 weeks, nitrate levels, in the fruit, should be very low. A nitrate application (planned or unplanned) shifts nutrient proportions out of balance and delays fruit maturation. Nutrient focus should be placed on K, Mg, Mn, Zn and a little P (all in “plant-ready” forms) to stimulate photosynthetic efficiency. The byproduct of photosynthesis is sugar (C₆H₁₂O₆). Sugar is a carbon source. Carbon is needed ASAP to correct the imbalanced C:N ratio, due to the nitrogen influx, from the rain. The fastest way to get these into the plant and fruit is with a foliar nutrient spray. Check with your certified crop adviser for the best options available to you.

Irrigate the field to saturation prior to or during the rain event to lessen rainwater uptake.

The concept: a “full vessel” cannot and/or will not take absorb more fluid. Makes sense; right? Here are few details to keep in mind:

·         Turgor Pressure: Plants drink water. In fact, if supplied to them, they will “bloat up” on water.

·         At Preharvest Stage: Plant focus shifts to “finishing” the crop. That means the movement of liquid is already going into the fruit…adding more probably won’t help as much as you’d think.

·         Osmatic Gradient Differential:

o   The pressure difference between the rainwater “outside” and the (concentrated) sugar content “inside” the fruit tends to "pull" water into the fruit (dilution effect). This creates immense pressure on the skin (from within) and a high likelihood of cellular rupture.

o   Fruit damage: It turns a brown to black color, just like freeze damage. In a freeze event, the cells swell (due to ice expansion) and rupture...it's the same in a rain event. The cells expand beyond their capacity to “flex” and burst.

So what is needed, by the fruit, when it rains close to harvest? Cell Elasticity. Your cherries need to be strong enough to flex and bend. Larger, thicker, stronger (nutrient-rich) cells, fruit cell walls and leaves help cherries more readily manage the adverse effects of rain; because larger cells have more volume capacity and thicker cells are stronger and less permeable and therefore less prone to “stretch marks” or “growth cracks”.

Applications can be made prior to the rain and even immediately afterwards, but “spoon-feeding” nutrition while growing the crop is ideal. Your nutrient plan should include traces like copper, manganese, boron, in regular, small amounts. This will have your crop “front-loaded” before a rain (or weather) event takes place and will have positive benefit on next seasons fruit bud development. Ideally, traces should be included within the product formulation, because a “finished” product is more manageable and less likely to have elevated phytotoxic risk. The less ingredients added to a foliar spray mix, the less the risk of “new chemistry” (phytotoxicity) forming and becoming a problem in the field.

These are some things that have worked for me and while not an exhaustive list of cherry and weather issues, it does give you a starting point for discussion with your crop adviser. And as I mentioned earlier, seek their counsel for sound advice on plant nutrition treatment options.