Orchard Notes: February 2021


The 2019/20 California Prune Board annual report is now available. Copies are being mailed now but you can also view online to get a comprehensive look at the 2019/2020 crop year. If you haven’t received a copy yet, send your mailing address to: klocy@prunes.local. To access the report online, along with highlight videos and other industry statistics, log into the password-protected “Reports & Resources” section of the website.

View Annual Report


Franz Niederholzer, UCCE Farm Advisor, Colusa, Sutter & Yuba Counties

Luke Milliron, UCCE Farm Advisor, Butte, Tehama & Glenn Counties

Katherine Jarvis-Shean, UCCE Farm Advisor Sacramento, Solano & Yolo Counties

Emily J. Symmes, former UCCE Area IPM Advisor, Sacramento Valley


  • Forecast = cold at bloom: a closely mowed orchard floor is warmer than one with tall weeds/cover crop, while freshly disked soil is the coldest.
  • Forecast = hot at bloom: If temperatures climb above 81-82° F during or soon after full bloom, fruit set may be reduced and crop loss can occur. To cool the orchard as much as possible when hot weather (80°F plus) at bloom is predicted, run sprinklers during bloom (especially full bloom and the next 2-3 days after full bloom) when temperatures reach 75°F and keep them on until they drop below 75° Evaporation of sprinkler water as it moves through the air provides some small temperature reduction (usually just one or two °F). If the weather is hot at bloom, taller orchard floor vegetation may keep the orchard cooler during the day.
  • Brown rot: A single bloom spray for brown rot, applied at 25-40% bloom, is recommended to protect flowers from brown rot even when skies are clear during bloom. Use locally systemic fungicide(s) (FRAC Group 3, 9, and/or 11) in a single-spray brown rot program. A scab material can be included with this single brown rot spray. Dew can wet the flowers long enough to allow infection, even if there is no rain, so treating at least once for brown rot is recommended. If the weather outlook changes and rain is forecast during bloom, spraying twice is recommended; once at white bud (5% bloom) and again at full bloom. The full bloom spray is the most critical.
  • Russet scab: This disorder develops when significant rainfall occurs during or immediately after bloom. If a single bloom spray is applied for brown rot, before 50% bloom, scab material can be included in that spray. Once the fruit is through the jackets, the risk of scab is mostly gone. The suggested full bloom timing of captan or chlorothanil (Bravo®/Echo®) can harm bees, so spray in the late evening or night (when bees are back in the hive) or arrange with your beekeeper to remove the hives before spraying. The recommended timing for bee removal is when 90% of flowers are open.
  • Peach twig borer (PTB): Monitor during and after bloom. Chewing damage on buds during bloom indicates PTB activity and may warrant treatment. To protect bees, avoid any insecticide in the spray tank at bloom, except Bt (Bacillus thuringiensis formulations such as Dipel®, Javelin®, etc.). Begin post-bloom monitoring with pheromone traps (minimum 2 per block) no later than mid-March to determine biofix (moths caught on two consecutive trap checks) and begin accumulating degree days to inform when to begin fruit inspections. More on PTB at ucanr.edu/PMG/r606300211.html
  • Aphids: If control measures were not taken during fall or winter, two 440 oil sprays (4 gals/acre/spray) at bloom can be effective against mealy plum and leaf-curl plum aphids if applied at slow ground speeds (for example 1.5 mph) 7-10 days apart. Oil has a level II precaution for bee safety, meaning it should only be sprayed between sunset and midnight, ideally when temperatures have dropped below 55°F to avoid foraging bees. The safest option for bees is to consider utilizing an alternative management timing (spring, fall, or winter) for aphid control. Finally, oil should not be applied with or shortly before/after captan, chlorothalonil, or sulfur because the combination can be phytotoxic.

More leaf curl plum aphid info: ipm.ucanr.edu/PMG/r606301811.html

More mealy plum aphid info: ipm.ucanr.edu/PMG/r606301711.html


  • Got a crop? With a light crop in 2020 in many orchards in the state, if bloom-time maximum temperatures stay between 60-80° F, there is a strong chance the crop will be good to heavy and thinning needed once the reference date arrives. Get ready to line up shakers if bloom weather is good. Check for tip hardening starting in mid-April. If a sharp knife catches, even briefly, when cutting across the blossom end of the flower, the fruit has reached tip hardening. The reference date is usually 7-10 days after tip hardening. Thin early (once reference date is reached) for best size results.
  • Irrigation: In dry springs, pay special attention to orchard water status and if irrigation is needed.
    • If we continue to have a dry spring, irrigation may be needed much earlier than “normal.” If the orchard is allowed to really dry out in the spring, rewetting can cause end cracking on fruit, especially in May and/or June. Don’t let your orchards go into those months with water stress. Keep an eye on 1) crop needs and soil water levels and 2) the forecast weather for the coming week and beyond. The most direct measure of water status is the pressure bomb, read more at com/manuals/stem-water-potential/
    • Monitor orchard moisture (soil moisture sensors or pressure chamber readings) to track orchard moisture status and determine when to apply first irrigation. For more information on the approaches to timing the first irrigation, see com/blog/almonds-blog/early-season-irrigation-do-we-know-when-to-start.
    • Don’t apply irrigation before the crop has used more water than the first irrigation will apply. Irrigating too early can saturate soils, leading to leaf yellowing from iron chlorosis. Yellow trees due to wet soils in the spring should “green up”, but may not feed the growing crop as well as if they never became yellow at all. For more on diagnosing yellow prune trees see: com/blog/prunes-blog/why-are-some-prune-trees-yellow-in-the-spring-the-bicarbonate-blues/
  • Fertilization program starts: Crop load is the major driver of nitrogen (N) and potassium (K) use in prune trees. The bigger the crop, the more of these nutrients that are needed. Check crop load in mid-April and use this information to plan your fertilizer applications. To optimize uptake and avoid leaching, apply multiple N applications, avoiding a single heavy spring application. Consider an N application before the end of April if there is a good crop set. If considering foliar potassium nitrate applications as your K program or to supplement soil-applied K, begin spraying in late April and make additional applications every 2-3 weeks.
    • More than 50% of the annual N budget should be applied before June 1. A large prune crop (3-4 dry tons/acre) contains 40-50 lbs. of N and that N will leave the orchard in the fruit bins at harvest. Assuming an additional 30 lbs. N for the tree (shoot growth, spur growth, etc.) and 70% efficiency (0.7 lb. N into the tree for every pound of fertilizer N applied to the soil) the annual N budget/acre for a mature prune orchard with a good to heavy crop should be 100-115 lbs. N/acre. For best efficiency, make several smaller (for example, 25-40 lbs. N/acre) N applications through the season and inject liquid fertilizer late in the irrigation set and then flush with 1-2 hours of clean water.

More details on prune nutrition/fertility are found at apps1.cdfa.ca.gov/FertilizerResearch/docs/Prune_Plum.html

  • Aphid: Monitor for leaf curl plum aphid and mealy plum aphid since colonies can grow soon after bloom. Monitoring details at ucanr.edu/PMG/r606900211.html. Oil sprays anytime from petal fall to May 15 can reduce mealy plum aphid to acceptable levels with good to excellent coverage. Oil is not effective against leaf curl aphid during this period as the spray can’t reach inside the curled leaves. Other pesticides are effective in controlling aphids during the spring, but be careful to avoid flaring mites with pyrethroids (Asana®, Warrior®, etc). or neonics (Actara®, Provado®, etc.). Movento® and BeLeaf® can provide excellent aphid control when monitoring shows a need.
  • San Jose Scale (SJS): If dormant treatments were not applied, the dormant spray didn’t do a good job, or spring SJS pressure appears high, consider treating at 60°to 70° days after pheromone trap biofix to target emerging crawlers. (Traps should be up in February.) Alternatively, SJS crawler activity can be monitored using double-sided sticky tape around limbs beginning in April to detect crawler emergence and time spring treatments if necessary. Caution: If you use neonic pesticides for aphid control (Actara®, Assail®, Leverage 360®, etc.) scale populations may increase.
  • Peach twig borer (PTB): Continue monitoring for PTB biofix. (Traps should be up in March.) PTB biofix in prune orchards is often later than in almond orchards. PTB damage can give brown rot disease entry into fruit. If you set a heavy crop, beware of PTB populations.
  • Oblique banded leafroller (OBLR): Place pheromone traps (minimum 2 per block) at the beginning of April to establish a biofix (moths caught on two consecutive trap checks) and begin accumulating degree days to inform when to begin fruit inspections. More on OBLR at ucanr.edu/PMG/r606300511.html

Learn more about the efficacy of different fungicides, mentioned above, used to prevent brown rot, russet scab, peach twig borer, aphids, and more.

View Prune Fungicide Efficacy Data



A recent California Prune Board survey asked growers and handlers for their feedback on the Production Research program to gather insights on the areas that matter most to the industry. Responses have provided valuable input for the Crop Management & Sustainability Committee and will continue to guide discussions about the most effective use of resources that help improve profitability. Survey results were also shared at the Statewide Prune Day on February 24th.

View Survey Results



The Coronavirus Food Assistance Program has been under review with the onboarding of the new administration to evaluate the program. USDA suspended the processing of payments and halted implementation of additional assistance while under review.

While the review of the program in ongoing, the deadline of February 26 has been eliminated, and USDA’s Farm Service Agency (FSA) will continue to accept applications during the evaluation period.  Interested applicants will have at least an additional 30 days for producers to sign up after any decision is announced.
Payments under CFAP-2, which closed in December, have not been impacted in any way.

For more information, visit: https://www.farmers.gov/cfap 

Upcoming Events


April 19 – April 23, 2021
Registration will be closed after April 12

Understanding the fundamentals of tree biology is essential in making sound orchard management and business decisions in the tree fruit and nut industry.  However, access to educational courses on basic fruit and nut tree biology, and how it relates to agronomic practices, is limited. This course incorporates lectures, lab exercises, and field demonstrations to provide information on all aspects of basic plant biology and the relationship between plant biology and nuts and fruit orchard management.

For course content questions, please contact the Fruit & Nut Research and Information Center staff at fruitsandnuts@ucdavis.edu.

View More Information


It is now time to register for the 2021 MRL Harmonization Workshop Webinar to be held on May 26-27.  Registration can be accessed on the California Specialty Crops Council CSCC website at http://specialtycrops.org/mrlworkshop.html.

Session One: May 26, 2021, 8:00 am PST – 12:00 pm 

Session Two: May 27, 2021, 8:00 am PST – 12:00 pm

Our program booklet will be sent to the attendees before the webinar. All presentations will be posted on the CSCC website afterward. CEUs applied for pending CDPR approval.

Ms. Elisa Fertig with FAS-USDA will discuss EU Pesticide MRL Policies. She will be followed by Mr. Okisegere Ojepat from Kenya who will be discussing the “Impact of Changing MRLs Landscape on African Growers. We will also have several international speakers, representing South Korea, China, United Kingdom, European Union, Central America, and Codex.

View More Information & Register Now!




Send us your favorite ways to enjoy prunes and breakfast – or any other part of the day! Submit ideas to aconsulo@prunes.local to be a part of the heritage recipes featured on our website and social media.

Clare’s Prune, Nut Butter & Honey Sandwich 
Clare Thompson whipped up this twist on a PB&J while making lunch for her dad and brother! Her yummy creation includes crunchy peanut butter, sliced California Prunes, and honey on whole wheat honey bread.
View Recipe