July 2018

Grower tips

  • Winter maintenance on irrigation system
  • 2nd copper sprays, with the recent wet weather
  • Same for 2nd Stop Drop on late varieties of navels
  • Update crop forecasts and size profiles on later varieties
  • Pruning on harvested varieties
  • Prepare for winter foliar nutritional program
  • On-going snail baiting between heavy rain events.
  • On-going maturity testing of varieties prior to harvest to ensure they exceed Brima requirements.

Seasonal outlook

There is an equal chance of a wetter or drier season for citrus production in WA for August to October. Temperatures by comparison are likely to be warmer than average for days and nights for WA, particularly August to October.

Evaporation and irrigation

Average daily evaporation rates and daily water use for the month of July and August are in the table below.

Ave daily evaporation Daily water use by large citrus tree

(14m sq canopy)

Harvey Karnet Carnarvon South-west Carnarvon
July 2.3mm 1.8mm 3.7mm 17-25.5L 36
August 2.5mm 2mm 4.8mm 19.5-24.5 47

A loamy soil (with no rock component) can hold around 20 mm of water that is readily available a citrus tree. With below average August evaporation rates of 2.5 mm per day (as seen in Harvey), a loamy soil profile full of water can supply enough water without irrigation or rainfall for a maximum of 11 days straight.

A sandy soil like those of West Gingin can hold 9 mm water that is readily available to a citrus tree. With below average August evaporation rates of 3.5 mm per day a sandy soil profile full of water can supply enough water without irrigation or rainfall for a maximum of 3.7 days straight.

Crop status and management

Phenology

Fruit is ‘colouring-up’ well with Afourer, Hicksons and Mystique mandarins at or nearing full colour.

For next season’s fruit, July is usually still in the floral induction stage where buds in the tree are making the transition from vegetative to floral buds. The maximum number of flowers your trees can produce is determined during this phase. Cooler temperatures during winter induce citrus buds to flower. The number of flowers produced and the proportion of different types of flowers is strongly influenced by crop load in the previous season. Most flowers are produced on shoots that grew during the previous year.

Heading into August, buds will be swelling and moving towards bud break. Keep an out for bud break and record when it happens. This is entering the pre-bloom to flowering stage (August-October).

If you would like a chart of the key phonological stages for citrus please contact Bronwyn, industrymanager@wacitrus.com.au.

Harvest timing

Think carefully about the timing of harvest as this can have a significant impact on the rind quality of the current crop and on flowering and fruit set next season. A late harvest for any given variety will reduce flowering the following season, particularly in many mandarin varieties. For mandarins, have an early select pick, taking the largest and most coloured fruit first. This takes the load off the tree and allows the remaining fruit to increase in size.

Internal maturity

Good results have been seen with pre-harvest testing and market testing for WA oranges and mandarins. Keep monitoring fruit maturation rates closely for new varieties to ensure it meets Australian Citrus Standards before harvest. Hickson mandarins have been variable in results in previous seasons so be vigilant. Fee-for-service payers can have the internal quality of fruit independently tested without charge (two samples per variety per grower). Just drop your samples to any agent at Market City.

Oleocellosis

Oleocellosis is rind damage resulting from rough picking and handling of fruit. Damage does not fully appear for up to 4 days after the injury/damage occurred and can significantly reduce the value of your fruit. To minimise oleocellosis, harvest in the warmest part of the day and pick from the northern side of the tree first. As a rough guide, ambient air temperatures should be above 12°C, however a wet bulb temperature and rind oil release pressure test should be conducted to provide a more reliable guide. It is best not to harvest if fruit are wet.

For next year’s crop

The long-term management goal during the floral induction stage is to achieve consistent levels of flowering with a high proportion of leafy inflorescences carried on strong bearing shoots.

Light crop loads (for oranges < 3.5 to 4.0 fruit per 0.5 m quadrat); drought or water stress and good vegetative growth in the previous season can all result in excessive flowering. To achieve balanced flower numbers and good fruit size next season it’s important to act now by applying winter Gibberellic Acid (GA) and ensuring a well-pruned canopy. Good management of keeping trees stress-free can also help reduce granulation. 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.

Flower manipulation (Winter GA)

Application of GA in the form of Ralex during floral initiation will reduce the number of leafless inflorescences (white blossom) and increase the proportion of leafy inflorescences. Leafy inflorescences set more fruit and have a higher initial growth rate, resulting in larger fruit at harvest. The first opportunity to apply Ralex was in mid-June however there will still be an effect if applied up to bud break. The timing of bud burst varies depending on variety and location, occurring between early August and mid-September in different varieties in WA. Apply Ralex in sunny conditions in the middle of the day, allowing trees to dry before nightfall to avoid the risk of marking fruit.

Pruning

A well-pruned canopy with a good distribution of strong bearing shoots close to main scaffold branches promotes leafy inflorescences. Pruning after harvest therefore assists in balancing crop load if heavy flowering is expected.

Nutrition

After harvest consider foliar applications of urea and micro nutrients to promote flowering for the next season particularly if you suspect a light flowering year. Do not apply urea if you expect a heavy flowering. Management of nutrition, irrigation and pruning now may prevent granulation issues next season.

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 adsorb 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: https://www.agric.wa.gov.au/citrus/citrus-nutrition

Irrigation

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.

Pests and diseases

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: https://www.agric.wa.gov.au/pest-animals/snail-and-slug-control

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

Monitor for pests such as scale and mealy bug in the orchard whilst harvesting and record observations. This will help you take the correct action when determining control programs for the spring and summer period when juveniles of these pests are active.

Keep an eye out for any galls along the stem of your trees, particularly in last year’s growth and in lemon trees. Citrus gall wasp will be emerging in the spring so pruning over winter is a good opportunity to remove the pest from your orchard.

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