Citrus

Citrus are the most popular fruit bearing plants grown in Australia. Glossy green foliage, white scented flowers and colourful great tasking fruit make these trees a must for every back yard. Citrus trees are not only practical but make great ornamental and container growing trees. Citrus trees are all very easy to grow and will thrive under a variety of conditions. With proper care citrus will provided an abundance of fruit that can be left on the tree for long periods.

The best time to plant citrus is in the spring and autumn. When it comes to planting, select the site carefully, keeping in mind all heat and frost protection requirements.

Citrus love sunshine, they prefer open warm sunning position, receiving full sun for about 4-6 hours. Through most citrus will tolerate light frost, a position perfected from frost is advisable as frost can damage young blossom bearing shoots. Shelter from strong cooling winds is important as this can damage young growth, blossom and developing fruit.

Citrus preferred a light, well drainage soil, good drainage is vital for citrus as they are susceptible to rootrot. Citrus are heavy feeders and require a deep, friable, rich soil that is well prepared before planting.If you have a heavy, clay soil, you’ll need to dig in plenty of gypsum and S.A Compost. As trees can often struggle in heavy clay soil unless good soil preparing has been provided. Avoid planting in low lying areas that retain run-off in the winter months.

WATERING: Citrus are not deep rooted trees, regular watering is required, care must be taken to ensure they have adequate watering during hot summer months. Do not over water citrus trees. Good deep soaking once or twice a week, instead of small daily watering is much more beneficial for citrus when weather is warm. As weather cools down it’s important to back off on watering as citrus don’t like to have wet roots or their roots sitting in water for longer periods of time.


MULCH: When mulching citrus, only mulch in late spring to conserve moisture during hot summer months. Care must be taken not to build up mulch around trunk of trees as this may cause collar rot. It is advisable to remove mulch back from citrus over winter months, so to let them dry out and let sun warm soil. Lawn and citrus don’t mix, do not under plant citrus with lawn or plants.


FERTILISER: Like most plants, citrus trees need foods which contain essential nutrients for healthy green foliage and large juicy fruit. It is recommended when fertilising lemons, oranges, grapefruit, mandarins, limes and cumquats etc, to use a Fruit and Citrus Fertiliser. Spread the fertiliser 30 cm away from the trunk covering the whole area outwards to the edge of the foliage drip line (where the foliage ends). Water the fertiliser immediately into the ground after application.  NEVER apply more than is recommended.


PRUNNING: In general citrus need little or no pruning; there is no need to prune or trainee to particular shape. Citrus will naturally grow into bushy trees, however trees will be healthier, easier to manage and produce more reliable crops over the trees produced life, if trainee, shaped, and pruned. Citrus can be train to vase shape with well-placed main braches or to any shape you like. Why not have a go at espalier one, if you’re limited on space. Always prune out any dead, damage or disease branches, citrus can tolerate heavy cutting back if required. After harvest, in early spring is the best time to prune, or in late winter.


LIMITED AREA: Don’t have the room for a large tree? Short on space, try growing one in a pot or try your hard at espaliering.

As long as theirs a sunny position it’s possible to grow citrus in a pot, but be aware they need constant care, feeding and watering to produce a healthy crop. All that’s need is a good size pot, Half wine barrels (or pots of a similar size) and quality potting mix.


Espalier a citrus. This way trees provide an evergreen screen, but don’t encroach on the garden. There are many different ways to espalier a tree, the main objected is to grown one flat against a wall or fence. Plant citrus at about 1.5m intervals, and about 30 centimetres from fence or wall. Tie the stems to horizontal wires along fence, place wire about 20 centimetres apart.

PEST/INSECTS AND PROBLEMS:

ANTS

antsAnts run up and down the citrus trees, they are a secondary problems arising from another pest problem. The presence of ants is usually an indication that there is a Scale or Aphid problem. The Ants feed from the sticky exudate of the Scale and Aphids.

Control Methods: Control the scale or aphids and the ants will disappear.


APHIDS

aphidsAphids are small, soft-bodied insects, there are many different species of aphids which vary in color from green to yellow and black. Aphids often cluster on new young shoots and flower buds or underneath older leaves, particularly in spring and autumn. Buds may fail to open and leaves are twisted and distorted. New growth may be stunted. Aphids also transmit virus diseases.

Control Methods: Spray for aphids on citrus, but sprays that enter the plant and move in the sap are unsuitable. Spray with pyrethrum sprays or horticulture oils, like Pest oil, white oil or eco-oil.Also natural predators such as ladybirds and parasitic wasps will control numbers.


SCALES

scale

There are two main groups of scale insects, both of which spend most of their lives as immobile adults, sucking the sap from stalks, leaves and stems. Hard scale and Soft scale are usually found on the mid-rib of leaves and stalks of citrus. Scale can cause death of stems if infestation is heavy. Again, spring and autumn are the usual seasons when these are more prevalent.

Control Methods: Spray with horticulture oils, like Pest oil, white oil or eco-oil, making sure to cover the insects. If there are only small number it may be possible remove them by hand.


 

scale1SOOTY MOULDS

Sooty mouldSooty moulds are black and dry and look just like soot.Sooty moulds are a secondary problems arising from another pest problem.  Insects such as aphids and scales produce “honeydew” and where this substance falls provides an environment on which sooty mould can grow. Sooty moulds don’t directly damage but if it’s very thick or remains for a long time it may reduce photosynthesise.

Control Methods: Removing the source of the honeydew will usually solve the sooty mould problem. Control the insects like sales and aphids.


CITRUS GALL WASP

This insect is native to Australia; its host is the native finger lime, but has adapted to wider variety of citrus fruits.  Around September the wasp lays eggs into the soft new growth. The larvae grown within the soft stem for 9-12months , as the larvae develop, unsightly galls appear on the trees and gradually increase in size as the larva grow, gall are full-size by autumn. From mid-September to early November the adult wasps emerges from infested galls leaving small exit holes and live for about a week. Wraps are poor flyers so tend to re-fest the same tree, but can be move around by wind to nearby trees. Galls cannot be ‘cured’ or reversed.  Developing galls need to be removed cut out; therefore citrus gall is more damaging to younger citrus trees than older trees.

Plants Affected: All citrus especially lemons and limes. As well as the native Finger Lime.

Control Methods: Controlling citrus gall wasp can be difficult, there is not cure but damage can be minimized by:

  • Remove/cut out all new galls that don’t show signs of exit holes before August.
  • Destroying all infected stems by burning or bagging.
  • Hanging yellow sticky traps inside infected trees from mid-August to trap any emerging adult wasps.
  • Avoiding high nitrogen fertilizer in spring as this promotes soft sappy growth, perfect for the egg laying stage. Instead fertilizing trees in late autumn and early winter, so to reduce soft growth in spring time when gall wasp is around.

CITRUS LEAFMINTER

leafminerThe adults of this pest is a small moth, it is silvery-white in colour with fringed wings.  The moth lay eggs along the midrib of young leaves. Larvae are pale-green and difficult to see, they tunnel into the leaf and as they eat leaving silver trails over the leaves. The larvae are the damaging stage, attacking the young growth flush and causing leaves to twist and curl.

Plants Affected: All citrus varieties. New growth only affected, once leaves have hardened, they are resistant to leafminer attack.

Control Methods: Control of leaf minter can be hard as larvae are shielded within the leaf. But reduction of infestation can be achieved by:

  • Remove leaves that show signs of citrus leaf minter.
  • Spray horticultural oils to reduce numbers of egg laying. Moths avoid surface sprayed with oils. Two or more sprays may be required.
  • Reduce infestations by limiting production of new leaves when leafminer numbers are highest: Prune growth flushes. Fertilize in late winter to promote strong spring growth when the leafminer numbers are low.

IRON DEFICIENCIES

irondeficIron deficiencies are quite common in our lime rich soils, therefore the term ‘lime induced chlorosis. Young leaves are affected first, leaves appear light green, pale yellow or even white, while the veins remain quite green. New growth appears normal in mild cases, but in severe cases leaves may be smaller and dieback may occur. Also fruit crop yield will be reduced.

Control Methods: Foliage applications of iron in the chelate form in a solution to the soil around the plants or to the foliage.

WIND INJURY

Strong winds can effectively damage citrus trees. The wind can bashes new leaves against branches, which causes some cell damage.  Damage caused to leaves means a reduction in photosynthesis, therefore a reduction in the amount of sugars needed for maintenance of the tree for fruit production.

There is no real control for wind damage. When planting choose an area not exposed to strong winds.


ZINC DEFICIENCIES

zincZinc deficiently is first noticeable on the young leaves of the plant; the leaves appear small and grow close together. Also leaf tissue between the main veins will become mottled yellow.  In extreme cases of zine deficit, dieback and increased production of small, weak twigs will occur. Citrus trees suffering deficiency in zinc will certainly follow with a decline in the yield. In light, sandy soil zinc is leached out. In soils with high organic matter lime content zinc is present but unavailable to the plant.

Control Methods:Zinc is not very mobile in the plant so a foliage cover spray is essential to enhance fruit set. Zinc sprays should be applied prior to fruit set for maximum benefit. Also add urea as it will make uptake of zinc more efficient and supply extra nitrogen.


YELLOW LEAVES

Citrus leaves can turn yellow for a number of reasons wet or cold temperatures, lack of feeding and deficiencies.

Cold weather can cause citrus leaves to curl. Cold can cause the tissue in the leaves to dry out leaving a burnt appearance. If possible, cover citrus trees if you expect a freeze.

Sunburn can leave yellow or brown leathery spots on the fruit and leaves, likely on the south and west sides of the tree. Too much heat can cause leaves to curl.

Overwatering is another common cause of unhealthy looking leaves. Too much water can cause leaves to curl, turn yellow, and drop. If you suspect overwatering, reduce your watering schedule and look for signs of improvements. Also make sure your tree has proper drainage and there is no mulch around the trees.