A Short Guide to Prune Production 

Franz Niederholzer, UCCE Orchard Advisor, Colusa and Sutter/Yuba Counties

Nothing in life is as simple as it looks on paper, but this is a place to start preparing for the season.

To make money growing prunes you have to have prunes to sell.  The more large, high-quality prunes you have, generally, the more money you make (the higher your gross income).

To have prunes to sell, you have to set a crop.

To set a large, good quality crop, you need…

  • Good weather
    • Daytime highs between 60-80°(Max temperatures of 82+°F = bad set conditions within 3-4 days of full bloom.
    • A little rain helps fruit set. Some rain/clouds keep temperatures down, but days of wet and cool weather is bad (7-10 days at and after full bloom with highs around 55°F = bad set conditions)
  • Many, healthy flowers (flower number is set before bloom by conditions the year before and pruning practices)
    • One (or two) careful bloom sprays with effective materials for brown rot control (see UC fungicide efficacy charts in this newsletter)
      • Little to no rain: One spray with FRAC 3, 9, or 11 fungicides effective on brown rot
      • Lots of rain: two sprays with effective brown rot material, one at 5% bloom, one at 80-100% full bloom. The second spray works best if sprayed every row.
    • Good bee activity in the orchard (recommendation is one strong hive per acre).
    • Clean fruit skin
      • Consider adding captan or Bravo (check with your packer about which material is allowed) to help manage lacy scab. If the weather is looking dry and warm for 2 weeks after full bloom, you could gamble and leave out this material. We are in a drought year, this might work out (not needed, save money). Talk w your beekeeper about these materials (captan or Bravo) as they may harm bee brood.

Find out how big the crop is and decide if thinning is needed so the fruit left in the trees grows big and sweet.

  • Check fruit count at reference date (late April through early May, depending on the year).
  • If fruit per tree is more than the target you set, SHAKER THIN ASAP

Keep the trees healthy and control pests through the season.

  • Monitor orchard moisture (soil or plant measurement) and irrigate to maintain adequate moisture.
  • Apply nitrogen (N) fertilizer starting in April (into July). Frequent, small “shots” are recommended.
  • Keep adequate potassium (K) in the trees throughout the season.
  • Look for spider mites and rust every week starting in April or May. Spray to control those pests if enough (mites) or any (rust) are found.
  • Control weeds in the tree row so harvest is fast and efficient. Weeds use water and nutrients meant for the trees.

For the biggest, sweetest fruit in the bins, harvest when the fruit is ripe.

  • Track fruit pressure every week once the first purple color shows on the fruit skin (harvest is about 30 days from 1st color).
  • Turn off the irrigation water one to three weeks ahead of planned harvest, depending on orchard conditions (irrigation system, drought conditions, etc).
  • Prunes are ripe when internal fruit pressure is less than 4 pounds.
  • If feasible, wait to start harvesting until 3 pounds internal pressure for better dry away.
  • Run a sizer to drop small (and medium-sized fruit?) in the field when harvesting.

After harvest, irrigate immediately. The trees will be dry at the end of harvest (and a drought year) and bark disease (especially Cytospora) spreads faster in dry compared to irrigated trees.

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Top 3 Things You Need to Know About New Varietals

  1. Dry Away – the Solano and Yolo Gold have higher dry away ratios which can help reduce drying costs
  2. Bloom Time – These varietals can lengthen bloom to spread the risk of weather-related bloom issues
  3. Harvest – The most promising varietals spread the harvest over a longer period of time which may help with labor issues and other costs

Want more information about the prune breeding program? Contact Sarah Castro


Upcoming Events

N. Sacramento Valley Prune Day

February 24, 2022 | 8am-12 noon
Red Bluff Elks Lodge – 355 Gilmore Road, Red Bluff, 96080
Register here

S. Sacramento Valley Prune Day

March 1, 2022 | 8am-12 noon
Sutter County Ag Building – 142 Garden Hwy, Yuba City, CA 95991
No registration is required.

Principles of Fruit and Nut Tree Growth, Cropping, and Management Course

March 7-11. 2022
Virtual
Register here

2022 Meetings & Events


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