Pruning Mandarins

Cindy Fake University of California Cooperative

Extension, Placer & Nevada CountiesJanuary 2012

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

Essential Pruning Tools

• Secateurs or hand pruners• Lemon clippers for

harvesting• Loppers for branches >½”

diameter (1.25 cm)• Pruning saw

Pruning Tools for Larger Trees

• Pole pruner/saw• Orchard ladder• Chainsaw

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.

Sterilizing Pruning Tools

• Sterilization of pruners is important in orchards with virus diseases or wet cankers

• Sterilize with bleach• Heat does not kill viruses

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

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

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

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

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

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

How to Prune…

• When cut too closely, wound includes trunk wood

• Do not leave long stubs –+/-1 cm above branch collar is sufficient

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• 1st cut: 30 cm from branch union• Cut 1/3 to ½ way through the branch from

underneath (undercut)• 2nd : A few cm up, cut from above,

removing the branch. Make the final cut just above branch collar

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

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

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

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

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

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

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.

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

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

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

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

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

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.

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

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

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

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

Questions?

Thank you!