Extension Briefs for October and November 2019

INTEGRATED PEST MANAGEMENT
T.G. GROUT and S.D. MOORE

Thrips management
During October and November, citrus fruit is highly susceptible to damage from citrus thrips and orchards should be scouted at least once a week for this pest, being sure to look under the sepals. Citrus thrips larvae cause more serious damage than adult thrips, so low numbers of adults in the absence of larvae may not require immediate intervention. The intervention threshold for citrus thrips larvae on fruit is 2% for the first four weeks after petal fall, 3% for five to six weeks after petal fall, then 4% for seven to eight weeks after petal fall. These thresholds can be approximately doubled if the population comprises mostly adults. Citrus thrips are genetically predisposed to developing resistance to pesticides, so avoid spraying two consecutive sprays of the same active ingredient. Treatments that give six to eight weeks thrips’ control will eliminate natural enemies of false cod-ling moth, mealybug and scale insects for a month or more, so if this degree of control is required it’s best to spray these at petal fall and to follow up with softer options when necessary.

Parasitoid releases
Growers planning to augment parasitoids for mealybug (i.e. Coccidoxenoides perminutus or Anagyrus sp.) or FCM (i.e. Trichogrammatoidea cryptophlebiae) control, should initiate releases as early in the new season as possible. Augmentative releases of parasitoids are not a corrective option. Therefore, growers should not wait until the pest reaches a problematic level. Research trials with both mealybug and FCM parasitoids indicate that better suppression of the pest is achieved with releases initiated as early as October. However, first ensure that sufficient time has lapsed since application of pesticides that would be detrimental to parasitoids. This information is available from the biocontrol agent producers.

Preventative sprays for mealybug
Pre-harvest blemish analyses or winter inspections of trees might have indicated that preventative spraying for mealybug is unnecessary. This can be confirmed or refuted by inspecting fruit in October and November for the presence of mealybug. Sprays applied before calyx closure will most likely be more effective than those applied thereafter. An infestation level in excess of approximately 5% at petal fall, or up to 20% six weeks after petal fall, requires immediate chemical intervention. Anything short of an absolutely thorough full cover film spray will compromise the effectiveness of a chemical treatment. If citrus mealybug is not the dominant species, augmentative releases of Coccidoxenoides perminutus should be considered unsuitable.

Bollworm
In many regions, it might already have been necessary to treat bollworm during September. However, routine spraying for bollworm is generally not necessary. By monitoring the percentage of blossom clusters infested, it will be possible to determine whether a spray is necessary. A treatment should be applied when more than 20% of blossom clusters are infested with larvae or mature eggs. Enlarged navel end problems in navel oranges can be further exacerbated by bollworm attack. In such an instance, a threshold of 11% of infested clusters should be used. Four biocontrol options are available for the control of bollworm. These are DiPel (Bt), Helicovir, Bolldex and Graboll (all viruses). In order to be effective, these biological products should be applied imme-diately after egg hatching and certainly not once larvae are more than a centimetre in length.

Lemon borer moth
Lemon borer moths (or citrus flower moths), Prays citri, are attracted to lemon blossoms. Growers should inspect these blossoms in spring to determine whether they are infested with larvae or pupae. These can be identified by their colouration – which is usually greenish – and the association of webbing with pupation. Even if the damage to, and loss of blossom is not considered sufficiently severe to justify control measures, no intervention will allow the development of a second generation. It is the moths of this second generation that lay their eggs on the lemon fruitlets. Hatching larvae can potentially cause severe damage. It is therefore more effective to control the first generation. No plant protection products are registered for use against the lemon borer moth. However, there are a number of pesticides which are registered for other pests on citrus that are effective, including Bt (DiPel) and mevinphos.

False codling moth
N.B. As was the case last season, all growers intending to export citrus to the EU must implement the FCM Management System (FMS), which includes the FCM Systems Approach. Effective control of false codling moth (FCM) from early in the season is critical. If this is not done, FCM could escalate to undesirable levels, which will be far more difficult to bring under control. As soon after harvesting as possible, all out of season fruit should be removed from trees and destroyed. These fruit can act as a reservoir for FCM and fruit flies, enabling particularly the former to carry over onto the new crop set in spring. Do not neglect orchard sanitation early in the season. Infested fruitlets can contribute significantly to the buildup of FCM populations later on and any extra labour required is well worthwhile.
FCM pheromone traps should not be hung later than November. It’s imperative that these traps be hung strictly according to the recommendations on the label.
Growers wishing to control FCM with Cryptogran, Cryptex or Gratham (FCM granulovirus) should apply the first treatment no later than the end of November, or early December – applied shortly after the flight peak, which occurs at this time in all production areas.
If mating disruption (e.g. Isomate, Checkmate, Splat, X-Mate) is being used, there are a few very important principles to be aware of. Firstly, application must be initiated early in the season (preferably October, but no later than November), before FCM levels begin to rise; secondly, the product must be applied (or hung) as high as possible in the tree; lastly, large areas (at least 5 ha, but preferably even larger) must be treated.

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

Fruit set treatments need to be applied according to cultivar requirements. Treatments include the application of gibberellic acid (GA3) and girdling, especially for parthenocarpic cultivars. General guidelines cannot be given as fruit set treatments differ by cultivar and orchard. Moisture stress should be avoided during full bloom, fruit set and early fruit growth. Fruit growth must be optimised during stage 1 of fruit development, with optimal nutrition and irrigation practices. The rind (flavedo and albedo) is formed during this phase of fruit development. Importantly, ensure optimal uptake of essential nutrients such
as Ca and Mg, which play an important role in the structural integrity of cell membranes. In addition, fruit thinning practices need to be applied to reduce inter-fruit competition and to optimise fruit growth. The acidity of fruit at harvest is largely determined within the first six weeks of fruit growth and devel-opment. Thereafter, only minor modifications to acidity can be achieved. Under conditions of antic-ipated high acidity mono-ammonium phosphate
(MAP) or mono-potassium phosphate (MKP) can be applied at 1% (i.e. 1 kg per 100 litres of water, six weeks after full bloom). Please note that these phosphate sources have not been tested on all cit-rus cultivars; until now 1% MAP or MKP has reduced acidity on valencia orange and temple tangor, but not on grapefruit. Pruning of late cultivars should be done as soon after harvest as possible. All of the following should be re-moved during pruning: old, broken and dead shoots/ twigs, weak and entangled shoots crossing each other or hanging downwards as well as any rootstock regrowth. Regrowth on the inside of the tree should be thinned out, cut back or removed. Light levels above 30% are necessary for optimal photosynthesis. Enough windows should be cut to allow for adequate light distribution and improve bearing wood within the tree. This will lead to increased fruit size and internal fruit quality (Brix°), better fruit colour, increase in rind integrity as well as a more uniform fruit size distribution. Pruning can be used as a thinning tech-nique: prune more heavily after a light crop when the orchard has a history of alternate bearing. A follow-up prune of regrowth in the summer is of critical impor-tance. Lastly, pruning tools should always be sanitised with 10% Jik.

GRONDGEDRAAGDE SIEKTES
M.C. PRETORIUS and J.M. VAN NIEKERK

Aalwurms
Grond- en wortelmonsters kan nou in die lente getrek word en na die Diagnostiese Sentrum in Nelspruit gestuur word vir ontleding, sodat die status van die aalwurmpopulasie in die wortels bepaal kan word. Die resultaat sal dien as ʼn bestuurshulpmiddel om ʼn kostedoeltreffende aalwurmbeheerstrategie daar te stel.
Die gebruik van chemiese aalwurmdoders vir die beheer van die sitrusaalwurm word nie aanbeveel alvorens ten minste 30 mm reën geval het nie (Oktober). Elke aalwurmdodertoediening behoort op nat (veldkapasiteit) grond toegedien te word en met ʼn behoorlike besproeiing opgevolg te word, om daardeur te verseker dat die middels deeglik in die grondprofiel ingewas word. Toedienings behoort slegs volgens etiketaanbevelings toegedien te word. Afwykings van die geregistreerde dosisse, om kostes te bespaar, is glad nie ʼn effektiewe benadering nie.

Phytophthora
Phytophthora wortelvrot – die gebruik van fos-fonaat produkte wat sistemies is, is ʼn uiters effektiewe en bekostig-bare beheermaatreël wat suksesvol deur produsente gebruik word. Dit is van uiterste belang dat die etiket en waarskuwings deeglik bestudeer word voordat die produk gebruik word, om effektiwiteit te verseker en fitotoksisiteit te voorkom. Indien kraagvrotletsels voorkom kan ʼn stamverf of blaarbespuiting aangewend word, drie aanwendings per seisoen met ses tot agt weke intervalle.
Vir wortelvrotbeheer word ʼn blaarbespuiting van ten minste twee of drie blaarbespuitings met intervalle van ses tot agt weke aan-beveel. Fosfonaat-behandelings behoort jaarliks op nie-draende bome toegedien te word.

FRUIT AND FOLIAR DISEASES
P. MOYO and B.D.X. MABUNDA

Alternaria core rot
Alternaria core rot, also known as navel-end rot or black rot, is prevalent on citrus cultivars such as navels and Clementines, which are characterised by the presence of a secondary fruitlet (navel) located within the stylarend of the primary fruit. The navel can vary in size and usually results in the development of navel-end openings. Fruit with large navel-end openings are more susceptible to Alternaria core rot and physio-logical disorders such as fruit splitting These provide entry points through which fungi can penetrate into locules of the primary fruit and form infections that remain quiescent until favourable environmental conditions stimulate further fungal growth. Fungicides registered for the control of Alternaria core rot include Score (50 ml/100 L water) and Folicur (80 ml/100 L water).

Black spot
Usually the first ascospore releases take place during November, but there can be deviations from the norm with early rain events during September or October. Therefore, spray programs should commence early in October and the first spray round must be completed before mid-October according to the selected

POSTHARVEST PATHOLOGY
W. DU PLOOY and K. LESAR

By now most of the crop has been harvested, packed and shipped. Now is the time to consider what changes need to be done to improve disease management next season. Here are a few factors to consider:

1. How long did it take from harvest to the first fungicide treatment? The shorter this period, the less likely it is to have latent infections developing and rotten fruit arriving at the packhouse, which will reduce the strain on your sanitation protocol.
2. Was the flow of your drench applicator strong enough? Were you able to apply at least 250 ℓ per minute? A more effective drench application will lead curb disease development, resulting in fewer rotten fruit arriving at the packhouse, and again, less pressure on the sanitation protocol.
3. Is there enough packline facility for sorting and removal of rotten fruit in the very first part of the packline, just after tip? Most packhouses have insufficient sorting in the beginning of the packline, which allows for rotten fruit to enter the packhouse, con-taminating the rest of the packline.
4. Consider installing a second sanitation treatment. This should be a total loss system and it should be situated in the packline after rotten fruit has been removed from the export fruit. This will protect the packline from contamination.
5. Sanitation of dip tank: do you have a pasteurisation protocol (heating overnight)? Heating the solution to 60°C and letting it cool down overnight will reduce the build-up of bacteria, as well as Rhizopus and other pathogen spores in the solution. Coliform counts that seem to skyrocket can often be traced back to poor sanitation of reused water.
6. The end of the season is the time to thoroughly sanitise the entire packhouse from roof beams to the floor, but this should be done only after all fruit (rotten or healthy) is removed from the packhouse environment. A quaternary ammonium product can be used, after which it should be ensured that the surfaces where fruit will make contact with the cleaner used, are rinsed off with clean water. Do not postpone this cleaning until next season, as the pressure of preparing for the new season always leads to unsatisfactory sanitisation.