1 citrus pruning

Citrus Pruning by Cindy Fake, County Extension (UCCE), California

1. Pruning Mandarins Cindy Fake University of California Cooperative Extension, Placer & Nevada Counties January 2012

2. Why Prune Mandarins? Improve fruit quality & marketable yields by: Increasing light in the canopy Pruning out non-productive branches (gourmands) Reducing risk of soil borne pathogens affecting fruit Reduce costs by: Facilitating weeding, mowing, & mulching Reducing tree height (also injury risk) Improve tree health Reduce insect and disease problems

3. Essential Pruning Tools Secateurs or hand pruners Lemon clippers for harvesting Loppers for branches >½” diameter (1.25 cm) Pruning saw

4. Pruning Tools for Larger Trees Pole pruner/saw Orchard ladder Chainsaw

5. Pruning Tool Care Tools need to be sharp & clean Sterilizing pruners is not necessary for most bacterial and fungal diseases For vascular diseases and those which form oozing cankers, pruning shears can transmit disease.

6. Sterilizing Pruning Tools Sterilization of pruners is important in orchards with virus diseases or wet cankers Sterilize with bleach Heat does not kill viruses

7. When to Prune? After freeze risk has diminished Before summer heat February/March is optimal Pruning too early may stimulate growth flush, late frost may then damage new growth Winter maintenance pruning should only be small branches <0.5 cm

8. When to Prune…after freeze damage After freeze damage, do not prune until the spring growth flush shows you where the damage is Pruning too early can cause more damage If the freeze has damaged fruit, however, remove as much of the fruit as soon as possible to prevent further injury

9. When to Prune…mitigate alternate bearing Alternate bearing = phenomenon where a tree carries a very heavy crop load one year and a very light crop the next Heavy crop depletes tree’s resources Produces less new growth, so only produces small amount of fruit the next year Pruning can mitigate alternate bearing – about 30% of difference at best

10. When to Prune…after a light harvest Heavy pruning is done after the light crop year Reduces bearing wood and potential fruit load for the next “heavy” year Major branch pruning and canopy thinning should occur at this time Prune heavily after a light year to: allow the tree to replenish its reserves reduce heavy crop so more moderate crop in off year

11. How to Prune… Carefully! Citrus bark is thin and easily damaged so avoid nicks Make pruning cuts with the blade toward the tree Cut cleanly and avoid damaging remaining branch

12. How to Prune… Do not cut branches flush with trunk Preserve branch collar = ridge in bark around base of branch Branch collar contains cells that make woundwood which grows over a pruning cut Branch collar also makes compounds to defend tree against decay Do not paint or tar wounds

13. How to Prune… When cut too closely, wound includes trunk wood Do not leave long stubs –+/-1 cm above branch collar is sufficient

14. How to Prune… Citrus has brittle wood Use a three-cut system for branches larger than 2.5 cm Prevents bark tearing or damage to remaining branch 1 st cut: 30 cm from branch union Cut 1 / 3 to ½ way through the branch from underneath (undercut) 2 nd : A few cm up, cut from above, removing the branch. Make the final cut just above branch collar

15. How to Prune… If previously shaded branches are exposed to sun, protect them from sunburn Sunburn causes bark cracking and cankers, which may kill the tree Paint exposed branches with whitewash or 1:1 mixture of interior latex paint and water

16. What to Prune? Best is to prune branches less than 5 cm in diameter Why? …because they are mostly living tissue and can protect themselves against decay better than larger branches This means pruning regularly, not leaving it until you need to take out large branches

17. Types of Pruning: Topping Top young trees at planting, esp. if they are tall and spindly Promotes side shoots which develop into a lower, fuller canopy The shorter the tree, the easier and more cost effective the harvest

18. Types of Pruning: Shaping young trees Prune downward growing shoots to allow upward growing buds to become dominant Cutting the shoot just above an axillary bud pointing upward will redirect growth upward Helps shape the tree for optimal future production

19. Maintenance Pruning Remove discolored, damaged, or dead wood from trees as necessary through the year Remove crossing branches or branches that shade out lower branches Remove branches infected with citrus blast ( Pseudomonas syringae ) when weather warms in the spring

20. Suckering Remove shoots below the bud union as soon as they appear They are growing from the rootstock and will not be productive For Trifoliate rootstocks, ( Poncirus trifoliata ) the rootstock thorns can be a hazard to workers and may damage fruit

21. Removing Gourmands Long, thick, very vigorous branches = water sprouts or gourmands Grow very rapidly, using large amounts of nutrients and water Typically remain vegetative for multiple years Produce poor quality, large, rough fruit, with dry segments Do not contribute to production, so should be removed at the base.

22. Reducing Tree Height Without regular pruning, fruit production is on top of the tree Increases harvest time and costs Cutting major branches back to the base is too hard on tree Only ¼ to 1/3 of tree height should be reduced at a time Leave a few branches with good foliage to photosynthesize and draw water through the plant

23. Canopy thinning Sunlight develops flavors and sugars in the fruit A dense canopy prevents sunlight from reaching fruit Thin canopy every 2-3 years Should see dappled sunlight beneath tree at midday Thin out center branches before they get large => increase fruiting wood in the center

24. Canopy thinning To facilitate thinning, divide trees into quadrants based on scaffold or primary branches Assess what is best in each quadrant Prune one section at a time

25. Canopy rejuvenation This tree has too much trunk and a very thin canopy, which means yields are low Canopy needs to be brought down so fruit is accessible Large branches with few leaves and low bearing potential need to be removed to stimulate new growth in center

26. Skirt Pruning Branches that hang to the ground “Skirts” impede weeding, and fertilizer or compost application Allow ants to access trees With heavy fruit loads, branches bend and fruit touches the ground Fruit may be contaminated by soil borne pathogens May cause plant disease, e.g. Brown rot Also potential food safety risk Skirt trees 50-75 cm above ground

27. Pruning for Pest Management Soft-bodied, sucking insect pests such as scale and mealy bugs thrive in dense canopies They like high humidity and little air movement The canopy protects pests from predators and parasitoids Thinning the canopy often reduces pest populations to the point that insecticide sprays are unnecessary.

28. Pruning for Pest Management: Citrus Blast Pseudomonas syringae bacteria cause disease Common where Satsumas grow Usually starts at the base of the petiole on small shoot Can move into larger branches Can cause cankers which kill limbs Prune out damage each spring to remove as much of the infection as possible Cut 15 cm below visible infection

29. What to do with Prunings? Significant amount of green material Could be returned to soil to the benefit of trees Difficult to leave prunings lie in orchard…hazard Burning loses all good benefits If prunings are not from diseased trees, Compost with cow or other manures Use compost as mulch along tree rows, under trees

30. Benefits of Pruning Improve quality through better flavor and color Increase yields Increase percentage of larger fruit As pesticides are restricted, need cultural practices to manage pests Cut costs by reducing labor for harvesting, weeding, and pesticide application

31. Benefits of Pruning Good Agricultural Practices (GAPs) may open more markets BUT, each grower must weigh the cost of pruning against the increased revenue from higher quality or higher yields Pruning must provide an increased return to compensate for the increased cost of production

32. Questions? Thank you!