Orchard Considerations for Bloom and Beyond

Franz Niederholzer, UCCE Farm Advisor, Colusa, Sutter, and Yuba Counties
Emily J. Symmes, UCCE Area IPM Advisor, Sacramento Valley
Katherine Jarvis-Shean, UCCE Farm Advisor Sacramento, Solano & Yolo Counties
Luke Milliron, UCCE Farm Advisor, Butte, Tehama, and Glenn Counties


Late February

  • Bees: Order bees, generally at a rate of 1 hive/acre. Employ best management practices for maintaining hive health and actively communicate with your beekeeper about the fungicides you may use at bloom. Refer to the article in this issue for more information on bloom pest management activities and honey bee protection.
  • San Jose Scale (SJS): Dormant to delayed-dormant is the preferred management timing for applying pesticides to treat damaging levels of San Jose Scale. Use spur monitoring to determine if treatment is needed. For detailed directions for taking a dormant spur sample, see ucanr.edu/PMG/r606900511.html. Place pheromone traps by mid- to late-February to establish a biofix and begin accumulating degree days for crawler treatment timing (if dormant treatments were not applied) and to monitor parasitic wasp levels. More on SJS: ipm.ucanr.edu/PMG/r606302111.html
  • Irrigation Maintenance: Maintaining and checking the distribution uniformity of your irrigation system is key to preparing for possible heat at bloom, as well as the coming irrigation season.
  • Calibration: Calibrating your spray equipment and replacing nozzles, checking spray filters, and other worn parts are part of preparing for bloom disease sprays.
  • Protect new trees: For both replants and new orchard plantings, protect trees from sunburn and herbicides with white interior latex paint diluted 2:1 water to paint, plus tree wraps. If tree wraps are used without painting trees, the boxes should be flattened (à from the top, not □) to avoid “wrapper burn”.


  • Cold at bloom:  A closely mowed orchard floor is warmer than one with tall weeds/cover crop, while freshly disked soil is the coldest.
  • Heat at bloom: If temperatures climb above 81-82 F during bloom, fruit set may be reduced and crop loss can occur. Crop failures have occurred with maximum temperatures above 83 F at full bloom in a fast bloom year. To cool the orchard as much as possible when hot weather at bloom is predicted, run sprinklers when temperatures reach 75 F and keep them on until they drop below 75 F. Evaporation of sprinkler water as it moves through the air provides some small temperature reduction (usually just one or two degrees). If the weather is hot at bloom, taller weeds may keep the orchard cooler during the day.
  • Brown rot: A single bloom spray for brown rot, applied at 25-40% bloom, is needed 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, spray 2x, once at white bud (5% bloom) and again at full bloom. The full bloom spray is the most critical. See fungicide timing and efficacy data in this newsletter.
  • Russet scab: This disorder develops when there is significant rainfall during and/or immediately after bloom. The suggested full bloom timing of captan or chlorothalonil (Bravo®/Echo®) can be risky for bee health. 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.
  • 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.). More on PTB at ucanr.edu/PMG/r606300211.html
  • Aphid: If control measures were not taken during fall or winter, two oil sprays (4 gal/acre/spray) at bloom can be effective against mealy plum and leaf-curl plum aphids if applied slowly (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, the 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? If the weather stays dry and warm, we may have early bloom followed by an early reference date. 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. We are hearing reports of experienced thinning operations getting calls for thinning reservations before bloom even starts. Check for tip hardening earlier than usual. The reference date is usually 7-10 days after tip hardening. Thin early for best size results.
  • Irrigation: In dry springs, special attention to orchard water status and irrigation is needed.
    • Monitor soil moisture sensors or pressure bomb readings to track orchard moisture status and determine when to apply the first irrigation. 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/
    • If we continue to have a dry spring, irrigation may be needed much earlier than in previous years (last year?!). 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. The trick is to keep an eye on 1) crop needs and soil water levels and 2) the weather for the coming week plus. We have seen leaf yellowing (“iron chlorosis”) when irrigation is applied and then the weather turns cool and tree water use is less than expected and the soil stays too wet. The most direct measure of water status is the pressure bomb, read more at com/manuals/stem-water-potential/
  • Fertilization program starts: With crop load being the major driver of nitrogen (N) and potassium (K) use, measure the crop 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 details at cdfa.ca.gov/FertilizerResearch/docs/Prune_Plum.html
  • San Jose Scale (SJS): If dormant treatments were not applied, efficacy not achieved, and/or spring SJS pressure appears high, consider treating at 600 to 700 degree 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.
  • Peach twig borer (PTB): 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. PTB biofix in prune orchards is often later than in almond orchards. Use prune PTB trap data to determine biofix in prune orchards.
  • 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
  • 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.


  • Rust: Monitoring commences with the start of the month, surveying 40 trees every 1-2 weeks, paying close attention to non-bearing replants, exceptionally vigorous trees, and previous hot spots. Consider treating when the first leaf with rust is found. For more on rust, see: ucanr.edu/PMG/r606100611.html
  • Peach twig borer (PTB) and Oblique-banded leaf roller (OBLR): These worms feed on the fruit surface later in the season, “opening the door” for fruit brown rot infection as sugar increases in the fruit. Don’t assume earlier sprays worked. Inspect fruit at 400 degree days after the first biofix. In the orchard, look for larval entry points on the fruit (ideally 15 fruit from 80 trees), especially where fruits contact each other or touch leaves. Treat if 2% or more (24+ of 1,200) of the fruit have damage. For OBLR, begin fruit inspections at 930 degree days after biofix for that pest, following the same sampling protocol and treatment threshold.
  • Aphids: While monitoring for leaf curl plum aphid comes to an end in mid-May, continue monitoring for mealy plum aphid until mid-July.
  • Irrigation: Continue monitoring soil and/or plants or tracking ETc to determine irrigation needed. May and June are the most critical months for end-cracking. Stay on top of orchard water status since irrigation is critical during the spring.
  • Fertility: Continue with nitrogen and potassium fertilization program if a good crop is set. More than 50% of the annual N budget should be applied before June 1st.