Fall & Winter Prune Orchard Management Considerations

Drew Alonso Wolter, UCCE Junior Specialist Horticulture Intern, UC Davis Graduate Student
Franz Niederholzer, UCCE Orchard Advisor, Sutter/Yuba and Colusa Counties
Dani Lightle, UCCE Orchards Advisor, Glenn, Butte & Tehama Counties
Emily J. Symmes, UCCE Area IPM Advisor, Sacramento Valley

Orchard clean-up:

  • Remove existing Cytospora cankers by cutting branches several inches to a foot below the symptoms. Information on identifying cankers and photos of a “clean” pruning cut can be viewed here.
  • Clean up “barked” trees damaged at harvest. Trunk/limb damage from harvester can result in Ceratocystis canker infection and possible tree death. Cut away any loose or damaged bark back to “tight” bark with a sharp knife or chisel and hammer. If you want to, paint the wound with commercial wound sealer. This can protect damaged trunks while healing.
  • Flag dying or weak trees for removal. Backhoe out old trees, making sure to get as many roots out of the hole as possible.

Pruning:

  • Avoid pruning immediately prior to rainfall events. Consider following pruning with a fungicide spray (Topsin-M® or Topsin-M + Rally®) to protect the fresh wounds from infection from rain-splashed spores.
  • Remove and burn prunings (if permitted) to reduce in-orchard inoculum levels of bark cankers like cytopsora.
  • If you skip pruning for a year as a significant cost-saving method, be prepared to shaker-thin, if needed, next spring. If thinning isn’t done when needed, the savings from not pruning may turn into a net-loss after setting a large crop of small fruit and suffering increased sunburn and broken limbs. Careful nitrogen fertilizer management during the growing season following winter pruning can help minimize vigorous regrowth and reduce subsequent pruning time and cost.
  • If you are training a young orchard, consider intermediate or long pruning for earlier yields, but be prepared to tie your trees to support the longer growth. See the article in this newsletter for more details.

Orchard topping:

  • If you are going to top your orchard, do this during the fall, with no rain in the forecast. This will allow cuts a chance to harden off before seasonal rains. Young, well-irrigated trees topped before mid-October will show some regrowth before leaf fall. Topping young, vigorous trees before a big wind will reduce risk of blow-over. If rain is in the forecast, be sure to protect fresh wounds from infection by rain-splashed spores with a fungicide spray (Topsin-M® or Topsin-M® + Rally®). This must be done before the rain!

Nutrition:

  • Soil applied potassium (K) should be banded in the fall. One dry ton of crop removes 26 lbs of potassium from your orchard. A common maintenance rate is 400-500 lbs/ac of K fertilizer (potassium sulfate). Growers can also opt to apply fertilizer K through a drip irrigation system (fertigation) and/or multiple foliar applications once a crop has been set.
  • Foliar zinc (Zn) can be applied at the beginning of leaf drop (late October/early November) to correct zinc deficiency. Applying 20 lbs of 36% zinc sulfate at 100 gallons water/ac may also hasten leaf drop, reducing the risk of blow-over and/or disrupting aphid reproduction.
  • Tree nitrogen (N) uptake is limited in the fall (there is nothing to feed) and trees will not take up N once leaf drop has begun. N should not be soil-applied after September to avoid N leaching by winter rains.
  • A fall foliar nitrogen (N) spray of 10-20 lbs N/acre may help reduce bacterial canker incidence next spring in young orchards, especially if summer leaf N levels are low.

Insects:

  • Aphids: Fall and winter can be an effective and ideal time to preventively treat orchards with a history of problems, particularly if no dormant sprays will be applied for scale or peach twig borer. Detailed articles on prune aphid management can be found here.
  • Scale: Obtain a dormant spur sample looking for San Jose scale and European fruit lecanium, as well as evidence of parasitism, in both species. More information on dormant sampling and treatment thresholds can be found here.
  • Peach twig borer: During the dormant period, a moderate rate of pyrethroid is effective on aphids and PTB (6-8 oz/acre of Asana) without the need to use the maximum labeled rate (14+ oz/acre).
  • Visit this page for a table of timing, efficacy, and other considerations for the treatment of these three pests.

Weeds:

  • Conduct weed scouting to evaluate your 2019 weed control program efficacy. See the article in this newsletter for more information.
  • Pre-emergence herbicide (combined with a post-emergence burn-down material, if winter weeds have already germinated) should be applied shortly before a moderate rain event (0.25”) to move material into the soil. Avoid application prior to a large rain event (> 1”), which can move the product too deep into the soil for good weed control. Avoid spraying root/trunk sucker leaves with any spray containing systemic herbicides such as glyphosate (Roundup, etc.) since those herbicides can enter the tree and cause damage next spring.

Gophers:

Because populations can be controlled before adults breed and create more gophers, late fall to early winter is prime gopher control time. Find gopher control strategies here.