Delivering the largest fruit possible this year.

Franz Niederholzer, UCCE Farm Advisor, Colusa and Sutter/Yuba Counties
Luke Milliron, UCCE Farm Advisor, Butte, Glenn and Tehama Counties
Drew Wolter, UCCE Hort Intern (supported by the CA Prune Board and the Almond Board of CA)
Rich Buchner, UCCE Farm Advisor Emeritus (Retired), Tehama and Shasta Counties

Many growers have been notified by their packers that there will be little to no value in fruit smaller than 72 ct/dry lb. (C’s and smaller) this year. With harvest around the corner, the only management options left to growers to maximize size of delivered fruit and increase net income will be harvest decisions, in particular harvest timing and field sizing.

Harvest timing: Fruit is mature when average internal pressure drops to 3-4 lbs. Above 4 lbs. pressure, sugar is still being moved from the leaves to the fruit and the fruit dry weight (what it will be after drying) continues to increase. If fruit pressure is above 4 lbs. when harvest starts, fruit quality (size and sugar) will be less than if harvested at a lower pressure.

Field sizing: In a year like this, deciding on field sizing practices will be very challenging. Each grower must make their own decisions based on the crop in their orchard and information from their packer.

Before we get into sampling details in a particular orchard, here is a critical point that growers must understand.  Perfect field sizing, delivering only certain size fruit, is an impossible task. Dry fruit size is related to fresh fruit size and sugar concentration (listed as % Soluble Solids in Table 1) in the fruit (see Claypool Table 1).  Fresh fruit sugar levels vary between fruit of the same fresh fruit weight and the range is particularly wide for small and medium sized fresh fruit (see Figure 1). In the field, the only tool currently available to grade fruit is fresh fruit size. A medium sized fresh fruit (27 ct, for example) is predicted to be anywhere from 71 ct (26% sugar) to 81 ct dried fruit (20% sugar).  One fruit has value this year whereas the next one may not, but it’s impossible to tell by fresh fruit size, alone, which will be which. Eliminating small and keeping large fruit is fairly straight forward, but growers must decide how aggressive they want to be with field sizing to separate medium sized fruit.

Here are some factors to consider when planning to field sort. First, know what the crop looks like in your orchard. Use the Claypool Table (Table 1) to estimate the average dry fruit size in your orchard. This table is not perfect and tends to predict larger average dry fruit size for lower sugar values, but it is all that is available. The following is a sampling program to estimate average dry fruit size in an orchard suggested by Bill Olson (UCCE Farm Advisor, Butte Co, retired) in a 1999 newsletter.

  • At the beginning of harvest, take several100 fruit samples from each orchard. Each sample = 100 fruit (20 fruits from each of 5 trees being sure to sample both fruit clusters inside and outside of the tree at eye level).
  • Weigh each fresh sample.
  • Divide the number of fruit in each sample (100) by the weight of the sample (in lbs.) to determine number of fruit per pound.
  • Determine percent soluble solids (a good way is to puree halves of all fruit from a sample in a blender and filter drops of juice through cheesecloth onto a refractometer). Ask your field man or dryer to help if you do not own a refractometer*.
  • Average the fresh count and soluble solids values for all samples to determine the orchard average. Different areas in the orchard could be treated separately if differences in crop exist that may require different harvest strategies.
  • Use the Claypool Table to predict your dry count/lb. based on your average fresh count/lb. and soluble solids for the orchard.

It will be important to check the results of field sizing before and during harvest. Set a chain size, collect the fruit dropped through that chain size at that pressure by placing a tarp on the ground under the sizer. Run a fresh fruit count and sugar check to compare with Claypool Table to see what size fruit is being dropped. Adjust chain size up or down as needed in that orchard. Once harvest has started, check size and sugar of fruit dropped through the chain several times during the season. This is especially important later in the season as the fruit softens and sugars increase so valuable fruit isn’t lost.

Growers who thinned in the spring should have less small fruit than if they hadn’t thinned. However, even if the expected average dry fruit count in an orchard is in the 50’s, there could still be a significant amount of medium and smaller sizes in the delivered crop.  For example, a thinned block in the Yuba City area several years ago had an average dry ct/lb. of 57 for a 2.6 dry ton/acre crop, with 15% of that crop, by weight, at 72 count or smaller. There was 6% C screen, 5% D screen and 5% undersized in that thinned orchard. At a 3:1 dry away, that’s an estimated $580 per dry ton for harvest, hauling and drying, that 15% of the crop would cost the grower $226/acre in 2019.  In a 50 acre block, that comes to $11,300 loss.

Finally, during harvest, make sure the belts feeding the sizing chain are runnning slowly enough that all the fruit is run across the sizer in a single layer — so it can be sized. If the sizing chain has too much fruit on it, all fruit will not be sized and some smaller fruit that should have dropped out will be delivered to the dryer.