Extension Briefs for April & may 2019

INTEGRATED PEST MANAGEMENT

False codling moth
S.D. MOORE

FCM activity continues during winter and can be facilitated by any fruit that remains on trees after harvest. Therefore, all fruit must be removed from trees after harvest, and destroyed. This winter fruit also creates a reservoir of inoculum of FCM for the following spring. What’s more, fruit fly numbers could multiply on unharvested fruit.

The removal of all fruit after harvest can dramatically reduce FCM levels in the next season. The PPECB pallet inspections are a critical component of the FMS in assisting to filter out infested fruit. Therefore, 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. Grading of fruit on the packing line, for example, must be conducted as stringently as possible.

Packhouses should not hesitate to slow down the line speed, if necessary, to enable more careful scrutiny of the fruit. Addition-ally, a designated inspection table should preferably be installed just before the 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 perform at an optimum.

Red scale
T.G. GROUT

Those growers who have experienced problems with red scale 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 it as a full-cover, film wet spray.

Trees to be sprayed must not be under any stress either. 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 they interfere with the behaviour of natural enemies, sometimes protecting and even transporting pest species.

The winter months are well suited 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 pakproses kritiese faktore waarop gelet moet word wat die voorkoms van skildefekte, asook algemene vrugkwaliteit kan beïnvloed.

Bepaal die optimum plukvenster vir elke kultivar per boord deur ʼn maand voor die beplande oesdatum met rypheidindeksering (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 velhitte so gou as moontlik te verwyder (bv. deur vrugte gouer te “drench”).

Die paklyn het beslis ʼn invloed op skiltoestand, asook die voorkoms van skildefekte, en dit is belangrik dat alle bewegende dele, bv. rollers en borsels, asook waks-tipe en aanwending noukeurig ondersoek word.

Ontgroening is ʼn belangrike aspek van die sitrus na-oes-hantering en moet optimaal bestuur word. Bewustheid rondom interaksie tussen kultivar, vrugrypheid en die effektiwiteit van ontgroening is belangrik.

As vrugte te vroeg (onvoldoende kleur-ontwikkeling aan boom) in die ontgroeningskamer geplaas word, sal die gewenste kleur nie ontwikkel nie, en vrugte neig dan om ʼn geler of bleker voorkoms te kry.

Gedurende ontgroening is daar egter aspekte wat streng beheer moet word, nl. etileen konsentrasie (1-3 ppm), temperatuur en relatiewe humiditeit (95%+).

OPTIMUM ONTGROENINGSTEMPERATURE:

Satsuma-mandaryne – 18 tot 21°C
Clementine-en Nova-mandaryne – 19 tot 22°C
Nawellemoene – 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 ventilasie sodanig te stel; hoë CO2 vlakke verleng die ontgroeningsproses deur as kompe-terende inhibeerder teen etileen op te tree. ʼn Stadiger ontgroen-ingstempo sal ʼn verlenging van die tyd in die ontgroeningskamer 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 vanaf CRI in Nelspruit bestel kan word (kontak Bella 013 759 8000).

Die koueketting se invloed op die vrugkwaliteit is van kardinale belang en sal nie net die voorkoms van skildefekte beïnvloed nie, maar ook algemene kwaliteitsaspekte soos vrugfermheid en rakleeftyd. Die belangrikste faset van die koueketting is dat dit nie onderbreek mag word nie, m.a.w. as vrugte tot op die gewenste temperatuur verkoel is, mag die temperatuur nie weer styg nie.

CROP AND FRUIT QUALITY MANAGEMENT
P.J.R. CRONJÉ

MATURITY INDEXING: 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 sampling of fruit every week from each of ten 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 read from a colour chart. All the parameters mentioned above should be plotted on a graph over time. Once plotted, trends will become apparent, harvest dates can then be estimated and problem areas in internal and external quality parameters can be identified and manipulated.

DEGREENING & POSTHARVEST RIND DISORDERS: The two publications; Common Defects Associated with Degreening of Citrus by Andy Krajewski & Tim Pittaway, and Post-harvest Rind Disorders of Citrus Fruit by Paul J. R. Cronjé are strongly recommended reading for any grower. Both are available from CRI
(contact Bella Thulare 013 759 8000, bella@cri.co.za).

PICKERS TRAINING AND MONITORING: 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 never contain leaves, shoots or sand and must be kept dry throughout. To avoid lesions on fruit, finger nails of pickers should be short and scissors and ladders handled correctly, i.e. no long stems, with limited contact between ladders and fruit. Picking
of low-hanging fruit, as well as collecting fallen fruit should be avoided. Two sorters wearing gloves are to be stationed at each bin, and the fruit quality from each picker needs to be monitored by an appointed team leader via the sorters. PRUNING: Pruning for early and mid-season cultivars should be done as soon after harvest as possible. All of the following should be removed during pruning: old, broken and dead shoots/ twigs; weak and entangled shoots crossing each other or hanging down-wards; and any rootstock regrowth, water shoots and excessive regrowth from main frame shoots on the inside of the tree. Light levels of above 30% of full sunlight are necessary for optimal photo-synthesis – at least one “window” cut should be made to allow adequate light distribution and improve bearing wood. An increase in photosynthesis and light distribution will lead to increased fruit size and internal fruit quality (Brix°), better fruit colour development, increased rind integrity, as well as a 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. Follow-up pruning of regrowth in the summer is of critical impor-tance. Pruning also ensures better spray penetration during pest and disease control, which makes for much more cost-effective spraying. Pruning tools should always be sanitised in a water solu-tion with 10% Jik, when moving from one orchard to another.

FLOWER INDUCTION: Citrus trees require a rest period of about six weeks to ensure that adequate flower induction takes place. Low temperatures and controlled drought stress are important for optimal floral induction in citrus, to ensure no root activity. In the absence of low-temperature rest, citrus trees should be exposed to controlled-drought stress for a 4-6 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 determine the nutritional status of the trees. Blaaranalise kan egter nie as die enigste norm vir die daarstelling van ’n bemestingsprogram gebruik word nie, maar moet as ’n aanvulling tot grondanalises gesien word. Dit is ook nuttig in gevallestudies waar blare vanaf ‘siek’ bome gemonster word, asook vanaf naburige, nie-geaffekteerde 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 selfs 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 accurate 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 korrektief opgetree kan word, voor voedingsprobleme wat boomprestasie benadeel, kan ontwikkel.

Other analyses

If manure or compost is used, it should be analysed to determine the nutrient value and occurrence of unacceptable elements (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 is 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 tree’s 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 chemical ion, 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 biuret ureum of kaliumnitraat wat gebruik word. Indien nodig, moet beide bespuitings ses tot agt weke voor die 50% blomstadium toegedien word. Dit is gewoonlik in Julie of vroeg in Augustus.

POSTHARVEST PATHOLOGY
DU PLOOY & L. MAMBA

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

Packhouse sanitation

This is mainly:
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 of future infections and fungicide resistance development.

SURFACES THAT SHOULD BE CONSIDERED IN SANITATION:

• Packline surface – treat daily with QAC and rinse with clean water afterwards; alternatively use chlorine or SOPP.
• Fruit surface – one of the first steps, when entering the pack-house, should be a fruit disinfectant treatment (chlorine is the most popular active for this step). Remember to manage the Cl concentration, pH and ORP. Suitable alternatives such as liquid or powder PAA formulations can also be used, with the precaution that the PAA levels must be managed carefully. When PAA is present, there’s 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 protocol in place to remove this fruit a.s.a.p. and to keep it in sealed containers.
• Juice fruit – this fruit is often treated with fungicides, and sits in the packhouse area for some time until it’s shipped to the juicing plant. Any decay that develops in such fruit presents a resistance risk.
• Retention samples – fruit that was also treated with fungicides, and bears a similar resistance risk as above.
• Post-degreening fruit – degreening conditions are hugely favourable for disease development and unfortunately, some sporulating fruit are often tipped into the packhouse system.

Recommendations that can reduce the risk of infection and/or resistance development

• Treat all harvested fruit a.s.a.p., but within 12-18 hours,
as most fungicides 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: exceeding 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: o The chlorine treatment = poor disinfection, spores surviving o The fungicide dip tank = loading suboptimal residue, poor infection control o 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 introduc-tion to the cold chain.

Managing retention fruit

• Have a dedicated person managing this task
• Fruit should be evaluated every day, and decayed fruit noted on the carton and removed o This infected fruit should be placed in a plastic bag immediately, and the bag sealed tightly, to reduce the risk of releasing inoculum (spores) into the packhouse atmosphere
· Fruit in retention samples have been treated with fungicides, and holds 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 spreading from these infected fruit, fruit that exhibit 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 treated with a suitable soap and sanitiser, at least once a month.