Season Update August 2018: Western Australia

August 2018

Seasonal outlook

The outlook for September to November is in and will more likely be drier than average for the southwest of WA. For the remainder of the state there is an equal chance for either a wetter or drier-than-average three months.

There is a 50% chance that the minimum and maximum temperatures for August to October will exceed the long-term median daily temperature for most citrus growing regions of the state. Chances of exceeding the median are higher for the far north.

Evaporation and irrigation

Average daily evaporation rates and water use for the coming months of August to September for locations within WA are listed below.

Ave daily evaporation2.5mm3.2mm2mm2.5mm4.8mm6.6mm
Daily water use by large citrus tree (14m sq canopy)19.5-24.5L31L19.5-24.5L47 L65L

Grower tips

Some comments from a few local WA growers on what they are doing and planning:

  • Monitoring for early fruit drop in some late Navels
  • On-going pruning after harvest
  • Start of the fertiliser program for 2019 season has commenced, including foliar fertiliser on harvested blocks
  • Still doing snail control
  • Weed control.

Crop status and management

Pre-bloom to flowering is a critical period for spring flush and flower development and is a high demand period for nutrients. The key management goal for this stage is to ensure the trees are well supplied with all required nutrients leading into flowering and fruit set.

Tag the spring flush to ensure you collect the correct leaves for nutrient analysis in February/March. The buds that have burst (as shown in the photo) will form your spring flush.


From August through to October is the pre-bloom to flowering stage.

Keep an eye out for bud break (pictured in photo) in your orchard and record when it happens for each variety and block.


After harvest, consider foliar applications of urea and micro nutrients to promote flowering for the coming season, particularly if you suspect a light flowering year. Further foliar micronutrient sprays applied to the new spring flush when it emerges will also boost tree nutrition and help improve fruit set and fruit size. Apply the spring micronutrient spray when leaves of the new spring flush are at least 1.5 cm long – large enough to absorb a good proportion of the applied nutrients.

Aim to apply 40 to 50% of annual nitrogen requirements in the pre-bloom to flowering period (August to October). Nitrate forms of nitrogen such as calcium nitrate and potassium nitrate are the best forms to use during this stage as they are quickly and easily taken up by the roots. Ammonium and urea forms of nitrogen can be too slow to convert to nitrate in the soil and can therefore be lost before they are taken up by the roots. Apply nitrogen in split applications to avoid loss to leaching.

Phosphorus is also important at this time and should be applied just before and during the bloom period. Apply the bulk of phosphorus now and the remainder at monthly intervals. Apply 30 to 40% of annual potassium during the pre-bloom period.

For more information on citrus nutrition:


Your trees need adequate water in their root zone to take up nutrients. Monitor irrigation requirements very closely. Although your soil may appear moist, if you have a dig around, you may be surprised that the soil is not as wet as you think.


Pruning after harvest encourages new growth that will bear bigger fruit. Good canopy management will also allow for more efficient application of foliar nutrient and GA sprays and assists in reducing crop load in an “on” year. Pruning will also significantly help a tree to cope with water restrictions and depending upon pruning severity, save water. Note, pruning late navel varieties from flowering to fruit set has been known to result in excessive fruit drop.

Mulch and compost

Now is a good time to consider applications of compost and mulch as part of your nutrition, irrigation and pest management strategies. Compost has been shown to be highly effective in the control of Kelly’s citrus thrips.

Pests and diseases

Citrus gall wasp

Check your orchards for signs of citrus gall wasps, a new pest in WA. You will see distinctive galls, or swollen woody areas, along the last year’s growth. Prune off any galls and destroy the material. Visit the DAFWA website for more information.


Baby snails are on the move so now is a good time to apply copper sprays to control snail populations. Apply the spray early in the morning on a predicted fine day for best effect. Affected snails will dehydrate in the warm sun before they have a chance to recover from the spray. For more information:

Fruit fly

Continue monitoring and bait spray programs for fruit fly until after harvest.

Red scale

If red scale is a problem, consider the release of Aphytis melinus as a biological control. Plan for the release of Aphytis now and order early for the first release in October/November. Keep an eye out for scale crawlers (the juveniles) and apply oil sprays only when crawlers are active.


Maintain a good weed control program to reduce the incidence of Fullers Rose Weevil (problem in export markets) and to help control snail populations.

This Seasonal Update for Western Australia has been prepared by Bronwyn Walsh, WA Citrus.