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Exstention Table1
June / July 2020

Extension briefs for June and July

SA Fruit Journal: June / July 2020

INTEGRATED PEST MANAGEMENT

False codling moth (FCM) | S.D. MOORE

All fruit remaining on trees after harvest must be removed and destroyed within 14 days of harvesting being completed in the orchard. This is because FCM activity does not cease during winter, and any remaining fruit can therefore serve to facilitate this activity. In addition, this winter fruit creates a reservoir of inoculum of FCM for the following spring. Conversely, removal of all fruit after harvest can dramatically reduce FCM levels in the following season. Fruit fly numbers can also build up on unharvested fruit.

Packhouses must continue to implement all aspects of the FCM risk management system (FMS) for fruit destined for the EU, as diligently and accurately as possible (e.g. grading of fruit on the packing line must be conducted as stringently as possible). Packhouses should not hesitate to slow down the line speed to enable more careful scrutiny of fruit. Additionally, a designated inspection table should preferably be installed just before final grading and sizing of fruit. These should be equipped with excellent lighting and staff appointed to conduct such inspections and grading must have 20/20 vision, and should be properly trained and incentivised to do the most reliable and accurate job possible. Realise also that PPECB pallet inspections are a critical component of the FMS in assisting to filter out infested fruit and therefore, full cooperation must be given for this to be conducted thoroughly and accurately.

Red scale

T.G. GROUT

Those growers who have experienced red scale problems during the past season should consider applying narrow distillation range horticultural mineral oils as these comprise the most IPM-compatible treatment option for red scale. The optimal period to apply this treatment is from budswell to budburst (mid-July to mid-August). The concentration to be used is dependent on the grade of the oil to be applied (generally 1.0 – 1.25% medium grade oil). When spraying oil, care must be taken to apply the oil as a full cover, film wet spray. Trees to be sprayed must also not be under any stress. Other treatments for red scale would normally be applied in August, September or after petal fall and will be discussed in later editions of Extension Briefs.

Ant control

T.G. GROUT

Ants are usually indirect pests on citrus and interfere with the behaviour of natural enemies, sometimes protecting and even transporting pest species. The winter months are a good time to control ants before honey-dew-producing pests such as aphids increase on the spring growth flush. Trees should also be skirt-pruned to prevent branches from touching the ground later in the season when bearing fruit.

NA-OES PRAKTYKE

P.J.R. CRONJÉ

Vir die voorkoming van na-oes fisiologiese afwykings is die korrekte produksiepraktyke, soos bemesting en besproeiing, asook snoei, uiters belangrik. Daar is egter gedurende die oes en pak-proses kritiese faktore waarop gelet moet word wat die voorkoms van skil-defekte, asook algemene vrugkwaliteit kan beïnvloed. Bepaal die optimum plukvenster vir elke kultivar per boord deur ʼn maand voor die beplande oesdatum met ryp-heid-indeksering (interne kwaliteit en skilkleur) te begin. Daar moet gepoog word om die temperatuurlading op die vrug te beperk vanaf die plukproses tot in die pakhuis, deur die vrugte se veldhitte so gou as moontlik te verwyder (bv. deur vrugte gouer te “drench”). Die paklyn het ʼn invloed op skil-toestand, asook die voorkoms van skil-defekte, en dit is belangrik dat detail aandag aan alle bewegende dele, bv. rollers en borsels, asook waks-tipe en aanwending geskenk word. Ontgroening is ʼn belangrike aspek van die sitrus na-oes hantering en moet optimaal bestuur word. Dis belangrik om te besef dat daar ʼn interaksie tussen kultivar, vrugrypheid en die effektiwiteit van ontgroening bestaan. As vrugte te vroeg (onvoldoende kleur-ontwikkeling aan boom) in die ontgroe-ningskamer geplaas word, sal die wenslike kleur nie ontwikkel nie en vrugte neig om dan ʼn geler of bleker voorkoms te kry. Gedurende ontgroening is daar egter aspekte wat streng be-heer moet word, nl. etileenkonsentrasie (1-3 ppm), temperatuur en relatiewe humiditeit (95%+).

Optimum ontgroeningstemperatuur

Satsuma-mandaryne – 18 tot 21°C
Clementine- en Nova mandaryne – 19 tot 22°C
Nawel-lemoene – 21 tot 23°C
Ander lemoene – 23 tot 24°C
Pomelos en suurlemoene – 24 tot 25°C

Ontgroen altyd meer sensitiewe vrugte teen die laagste temperatuur. Die etileenbehandeling is die effektiefste as vrugte van dieselfde kleur gelykertyd behandel word. Die tydperk van die behandeling moet ook so kort as moontlik wees. Hou die CO2 vlakke onder 0.3% (3000 dpm) deur die lugtoevoer sodanig te stel; hoë CO2 vlakke verleng die ontgroeningsproses deur as kompeterende inhibeerder teen etileen op te tree. ʼn Stadiger ontgroeningstempo sal ʼn verlenging van die tydsduur in die ontgroe-ningskamer vereis en ’n verkorte rakleeftyd tot gevolg hê. Vir meer inligting, raadpleeg die
“Common defects associated with degreening of citrus” deur Krajewski en Pittaway, wat by CRI in Nelspruit bestel kan word (kontak Bella 013 759 8000).
Die koueketting se invloed op die vrugkwa-liteit is van kardinale belang en sal nie net die voorkoms van skil-defekte beïnvloed nie, maar ook algemene kwaliteitsaspekte soos vrugferm-heid en rakleeftyd. Die belangrikste faset van die koueketting is dat dit nie onderbreek mag word nie, m.a.w. as vrugte tot op die wenslike temperatuur verkoel is, mag die temperatuur nie weer styg nie.

CROP AND FRUIT QUALITY MANAGEMENT

P.J.R. CRONJÉ

Maturity indexing:
Maturity indexing on mid-season to late cultivars should commence. Maturity indexing is done to predict the rate of change in fruit maturity, in order to harvest fruit at an optimal maturity. The aim is to define changes or rate of change in acids and sugars, and to build up a database over a number of years. Random weekly sampling of fruit from each of 10 representative trees should start four to six weeks before the expected harvest date. Titratable acidity is determined by titration with sodium hydroxide, sugar content (Brix) is determined using a refractometer, the sugar:acid ratio calculated, and fruit colour should be read from a colour chart. All the parameters men-tioned above should be plotted on a graph, over time. Once plotted, trends will become apparent, harvest dates can be estimated, and problem areas in internal and external quality parameters can be identified and manipulated. Degreening and postharvest rind disorders: The two publications; Common Defects Associated with Degreening of Citrus by Andy Krajewski and Tim Pittaway, and Postharvest Rind Disor-ders of Citrus Fruit by Paul J. R. Cronje are a must for any grower. Both are available from CRI (contact Bella Thulare 013 759 8000, bella@cri.co.za).

Training and monitoring of pickers:
Picking bags should always be carried on the side of the waist to avoid crushing of fruit between the body and the ladders, bins or trees. Picking bags should at all times be free of leaves, shoots or sand and kept dry throughout. To avoid lesions on fruit, pickers’ fingernails should be short and scissors and ladders handled correctly, i.e. no long stems and limited con-tact between ladders and fruit. Avoid picking of low-hanging fruit, as well as collecting of dropped fruit. Two sorters should be stationed at each bin, wearing gloves and the fruit quality of each picker monitored by an appointed team leader via the sorters.

Pruning:
Pruning for early and mid-season cultivars should be done soonest, after harvest. All of the following should be removed during pruning: old, broken and dead shoots/twigs, weak and entangled shoots crossing each other or hanging downwards and any rootstock regrowth, water shoots and excessive regrowth from main frame shoots on the inside of the tree. Light levels of full sunlight above 30% are necessary for optimal photosynthesis – at least one “window”-cut should be made to allow adequate light distribution and improve bear-ing wood. Increase in photosynthesis and light distribution will lead to increased fruit size and internal fruit quality (Brix°), better fruit colour development, increase in rind integrity, as well as more uniform fruit distribution across the tree. Pruning can also be used as a thinning technique: prune more heavily after a light crop if a heavy crop is expected, and when the orchard has a history of alternate bearing. A follow-up prune of regrowth in the summer is of critical importance. Pruning tools should always be sanitised with 10% Jik (100 ml Jik topped up to 1 L with water) when moving from one orchard to another. Pruning also ensures better spray penetration, which improves target effects during pest and disease control and is far more cost-effective

Flower induction:
Citrus trees require a rest period of about six weeks to ensure that adequate flower induction takes place. The two mechanisms engaged in floral induction in citrus involve (i) low temperature, or (ii) controlled-drought stress, both to ensure no root activity. In the absence of low-tempera-ture rest, citrus trees should be exposed to controlled-drought stress for a four to six week period during June and July, if possible.

BEMESTING / FERTILISATION

P.J. RAATH & J.G.K. COETZEE

Blaarontleding/Leaf analysis
The very last opportunity to get leaf analyses done is in June and July. Leaf analysis is still the best diagnostic method to measure the nutritional status of the trees. Blaaranalise kan egter nie as enigste norm vir die daarstelling van ’n bemestingsprogram gebruik word nie, maar moet as ’n aanvulling tot grondanalises gesien word. Dit kan ook nuttig vir diagnostiese doeleindes gebruik word, waar blare vanaf “siek” bome vir ontledings gemonster word, om vas te stel of voedings-wanbalanse ‘n rol kan speel in die voorkoms van hierdie bome. Die gesonde/beter bome se blare dien dan as direkte kontrole, sodat die tyd van monsterneming en al die ander veranderlikes, minder krities of nie ter sake is nie. Geen norm word gebruik nie, maar wel die relatiewe verskille tussen die twee monsters.

Grondontledings/Soil Analyses
Soil analyses should be done annually and preferably during the same time as leaf analyses. A good practice is to take soil samples from the same spot every year to ensure that an accu-rate historic dataset is developed for the soils. Sampling areas can be marked with GPS coordinates. Sections where trees are performing poorly should be sampled separately. Gereelde grondontledings word benodig in bestaande boorde om te verseker dat optimale groeitoestande gehandhaaf word. Die belangrikste voordeel van grondontledings in bestaande boorde is dat veranderings in grondvrugbaarheid bespeur kan word, en dat daar korrektief opgetree kan word voor voedings-probleme wat boomprestasie benadeel, kan ontwikkel.

Other analyses
If manure or compost is used, it should be analysed to deter-mine the nutrient value and occurrence of unacceptable ele-ments (e.g. heavy metals) in the organic material. The amount of organic material applied is determined by the concentration of nutrients in the compost or manure. The nutrient content of organic material is much lower than inorganic fertilisers, and often in an inappropriate ratio compared to what the trees’ nutritional requirement is. Therefore, be careful not to apply excessive amounts of nutrients that are out of sync with the trees’ requirement.

Bemesting/Fertilisation
Potential yield is used as an indicator for the amount of fertiliser to be applied. Use historic yield data to determine a realistic target yield and basis from which the fertilisation requirement is compiled. The fertilisation programme should then be tweaked, using results of both soil and leaf analyses. The fertilisation programme for each season starts in July or August of the previous year, depending on the production area. Due to the properties of the specific nutrient, the properties of the soil and the physiological requirements of the trees, certain basic rules should be adhered to when applying fertilisers to citrus.

Blaarbespuitings word gebruik om tekorte reg te stel, of om die bome se fisiologie te manipuleer.
Vir manipulasie is dit hoofsaaklik lae biuretureum of kaliumnitraat wat gebruik word. Indien nodig, moet beide bespuitings ses tot agt weke voor die 50% blomstadium toegedien word (gewoonlik in Julie of vroeg Augustus).

POSTHARVEST PATHOLOGY

W. DU PLOOY AND L. MAMBA

While most packhouses are now entering their peak period, important and basic practices such as sanitation and fungicide application must not be neglected.

Packhouse sanitation

The main aims of this practice are:

  1. To remove any infected fruit from the packhouse environment.
  2. To sanitise surfaces with appropriate treatments.

These actions will reduce the inoculum (spore) levels, and the risk for future infections and fungicide resistance development.

Surfaces that should be considered for sanitation
• Packline surface: treat daily with QAC, but rinse with clean water afterwards; alternatively use chlorine or another suitable sanitiser.
• Fruit surface: one of the first steps when entering the pack-house, should be a fruit disinfectant treatment. Chlorine (CI) is the most popular active for this step. Remember to manage the Cl concentration, pH and ORP. Suitable alternatives such as liquid or powder Perasitic acid (PAA) formulations can also be used, with the precaution that the PAA levels must be managed carefully. In the case of PAA there is no need to adjust the pH.
• Floors and walls: wash weekly with a registered quaternary ammonium compound (QAC), or a registered soap. These include the packhouse, degreening rooms and cold rooms.
• Degreening rooms and cold rooms need to be washed and then, where possible, fumigated with a suitable product that can reach into crevices and folds.
• Orchard bins and picking bags: wash regularly.

Sources of inoculum (spores)

•Waste fruit: have a protocol in place to remove the fruit a.s.a.p. and to keep it in sealed containers.
• Juice fruit: this fruit is often treated with fungicides and remains in the packhouse area for some time until shipping to the juicing plant. Therefore, any decay that develops on such fruit poses a resistance risk.
• Retention samples: fruit was also treated with fungicides and holds a similar resistance risk as above.
• Post-degreening fruit: degreening conditions are hugely favourable for disease development and unfortunately, some sporulating fruit is often tipped into the packhouse system.

Recommendations that can reduce the risk for infection and/or resistance development
• Treat all harvested fruit within 12 – 18 hours, as most fungi-cides cannot control infections older than a day. This is now more important than ever with the loss of guazatine.
• Don’t let fruit stand from Friday afternoon to Monday morn-ing, without any fungicide protection. In this case it would be prudent to drench the fruit on Friday.
• Degreen fruit for the absolute minimum period of time.
• Do not exceed the volume limit of your packline: ex-ceeding the limit will result in accelerated agitation and movement of the fruit, which, in turn, will result in bruising and injuries, and will reduce the efficacy of sanitation and fungicide treatment.
– Fruit will move too quickly through the various control points:
– The chlorine treatment = poor disinfection, spores surviving The fungicide dip tank = loading suboptimal residue, poor infection control
– The wax applicator = poor wax deposition on the fruit = suboptimal residue loading, poor moisture retention, negative impact on quality
• Limit the time from harvest to pack and eventual introduction to the cold chain.

Some advice in managing retention fruit
• Have a dedicated person managing this task.
• Fruit should be evaluated every day, with decayed fruit noted on the carton and removed:
– The infected fruit should be placed in a plastic bag immediately, and the bag sealed tightly
– this is to reduce the risk of releasing inoculum (spores) into the packhouse atmosphere.
– Fruit in retention samples have been treated with fungi cides, and poses a serious resistance risk if spores are spread into the packhouse.
– Green mould sporulation inhibition is a very important criterion to note, as the loss of sporulation inhibition is indicative of either fungicide resistance or poor fungicide application. To prevent spores from spreading from the infected fruit, fruit exhibiting sporulation inhibition should be kept in sealed transparent plastic bags and incubated for another week to rate sporulation inhibition.
– When the sporulation inhibition rating is concluded, the bagged fruit must be destroyed (along with the bag), well away from citrus orchards and packhouses to prevent spores from entering any production area.
• Do not keep fruit for longer than the shipping period.

Ideally, the retention room should be some distance away from the clean area in the packhouse and should be totally enclosed with controlled access. This room should be cleaned and treat-ed with a suitable soap and sanitiser at least once a month. ✤

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