Extension Briefs For December 2024 And January 2025

By Hannes Bester, MC Pretorius, Wayne Mommsen, Coenraad Fraenkel, André Combrink, Natasha Jackson, Jan Landman, and Rudolph Strydom (Citrus Research International)

Integrated pest management

False codling moth (S.D. Moore)

It is imperative that the False Codling Moth Systems Approach (now abbreviated as the FCMSA) be implemented thoroughly and diligently. Neither growers nor the industry can afford a lapse in the implementation of comprehensive and effective management practices. The details of all of these practices are explained in the FCMSA, with reference to the CRI IPM Guidelines for FCM Management (available on the CRI website). These Good Agricultural Practices (GAPs) must be followed as described. One of the most important practices is orchard sanitation, which must be conducted at least weekly in all orchards, as well as for lemons. This involves not only collecting and destroying fallen fruit, but also removing all hanging fruit that appear damaged or infested in any way. It has been shown that such a practice can effectively remove an average of up to 75% of FCM larvae from an orchard. In the hotter summer months, orchard sanitation should be increased to at least twice a week, in order to have the same effect. Fruit must not be mulched inside the orchard. Although lemons at the commercially ripe stage for export are not a host to FCM, very small and over-ripe lemons can host FCM, which can result in lemon orchards being a source of FCM for adjacent and nearby orchards of FCM-susceptible cultivars. This makes sanitation in lemon orchards as important as in orchards of other citrus types. The use of an area-wide control technique, such as the sterile insect technique (SIT) or mating disruption, from early in the season, will also provide effective suppression of the FCM population while it is still low. Initiating control measures only a few weeks or months before harvest is unlikely to be sufficiently effective. Finally, monitoring of fruit infestation, as described in the FMS is extremely important to ascertain FCM risk. Monitors must be trained and proven competent for this very important task. Colour plates are available from CRI, to assist with correct identification of FCM larvae and other insects that can internally infest citrus fruit. If there is any doubt as to whether a larva is FCM or not, it must be recorded as FCM, due to its phytosanitary status and the potential consequences of underestimating levels of incidence.

Fruit flies (A. Manrakhan)

Fruit flies are pests of phytosanitary concern. The fruit fly pests affecting citrus are: Ceratitis capitata (Mediterranean fruit fly or Medfly), Ceratitis rosa (Natal fly) and Bactrocera dorsalis (Oriental fruit fly).
Oriental fruit fly has a restricted distribution in SA and is regulated within the country. There is a zero tolerance of fruit fly eggs and larvae in fruit consignments for export. Monitoring and control are two important components in Fruit Fly Good Agricultural Practices. It is essential to initiate monito-ring activities for Medfly and Natal fly between December and mid-January, before the peak of fruit fly activities. Monitoring of Oriental fruit fly should be carried out throughout the year. Fruit fly control, using protein baits, should be initiated in middle to late summer (either January or February, depending on regions). However, for farms with either mixed fruit crops (such as mangoes, deciduous fruit or grapes) or near-fruit types prone to high fruit fly infestation, fruit fly control should already be implemented by December. In citrus production areas infested by Oriental fruit fly, the Male Annihilation Technique (MAT) must also be applied preferably by mid-January. All fruit fly control products should be applied correctly. Frequency of application of fruit fly control products should be adjusted based on fruit fly catches, which should not exceed threshold levels for registered traps. Orchard sanitation is also an important practice in managing fruit flies, and must be conducted at least weekly. Details of fruit fly monitoring and control practices are available in English and Afrikaans on the CRI website (register as a member for access to the guidelines). In all B. dorsalis infested areas a removal permit is required for movement of fruit outside those areas. Start application for removal permits early. The contact email for the removal permit application is: RemovalPermits@daff.gov.za.

Mealybug (S.D. Moore)

Apart from the obvious pest status of mealybug, it is also important to control this pest as it can attract carob moth and increase infestation of this secondary pest. Growers should be scouting regularly for mealybug by inspecting underneath calyxes and thereby determining the percentage of infested fruit. The most effective way of doing this is to break the fruit off from the calyx. Both the fruit and the underside of the calyx should then be inspected. Where mealybug is under good biocontrol, infestation should peak during December/January in the northern production areas, and during January/February in the Cape production areas. If mealybug infestation does not decline during January to March (region dependent), suppression with a chemical treatment is advisable on early maturing cultivars, particularly if the mealybug species present have phytosanitary status for export markets. Products such as spirotetramat and sulfoxaflor have been proven effective in this role. In addition, it is crucial that a full-cover film spray be applied. If it is necessary to spray for thrips during December or January, it is extremely important that only IPM compatible thripicides be used. Use of any harsh thripicides at this stage, will result in mealybug repercussions. Augmentative releases of parasitoids should be initiated as early in the season as possible for optimal efficacy: Coccidoxenoides perminutus, which is only effective against citrus mealybug, and Anagyrus vladimiri, which also attacks at least oleander mealybug, in addition to citrus mealybug. Initiation of releases later than December will be far less effective than early release programmes. Augmentation of predators, such as Cryptolaemus montrouzieri would be far more justifiable against high levels of mealybug infestation in mid to late summer, as these beetles are high density feeders.

Citrus thrips (T.G. Grout)

Thrips can still cause damage on citrus fruit in December, particularly in hotter production areas such as the Lowveld and on later-flowering cultivars such as Valencias, whose fruit are still relatively small at this time of the year. Therefore, scouting should continue to be carried out at least twice a week, in order to prevent a build-up of numbers, and to avoid possible late damage known as “scribbling” or “browning” on the sides of the fruit. Thrips control materials applied at this time of the year should preferably not have a long residue, so that the activity of mealybug and scale parasitoids is not unduly disturbed. From January the chance of thrips damage declines with increasing fruit size, but continued vigilance is advised.

Citriculture (P.J.R. Cronjé)

Fruit growth and size Citrus fruit development is divided into three distinct development phases, and fruit growth follows a sigmoidal curve. Phase I of fruit development (end of October–December) incorporates full bloom to the end of December. And it’s characterised by cell division and the formation of the majority of the total cellular structures of the fruit. During this period, the majority of the fruit diameter comprises the rind. In phase II (January–March), the different sections of the fruit pulp volume increase substantially and make up most of the fruit diameter until harvest. The biggest increase in fruit diameter occurs in summer, with very little to no increase in phase III, as temperatures decrease from autumn until fruit harvest (April–August) during this phase. Fruit growth during this period of fruit development is important, to achieve optimal size at harvest, and an individual factor or a combination of factors that are suboptimal, e.g., irrigation or ambient temperature may contribute to small fruit size. All the factors influencing fruit size should be considered and managed optimally and do use Cutting Edge No. 103 or chapters 5–8 in the CRI Production Guidelines (Vol. II, www.citrusres.com/category/chapter-5-crop-manipulation) for revision of the various lemon fruit size management strategies.

Fruit size and crop load prediction This exercise should commence after the physiological fruit drop period. Fruit size is inversely related to flower number and eventual fruit load. In contrast to fruit set treatments such as girdling and foliar sprays of GA3, producers can make use of various thinning practices to control flower intensity and eventual crop load. Except for hand thinning, foliar applications of synthetic auxins are particularly successful in this regard and are used to reduce fruit load in an “on year” and increase final fruit size. A reduction in the number of flowers will reduce the eventual percentage fruit set, reduce the inter-fruit competition, and increase fruit size. Fruit from trees bearing small yields experience increased growth rate. At high fruit loads, increased inter-fruit competition for nutrients and water, especially during the early stages of fruit development, lead to a decrease in potential fruit size. Do refer to chapters 5–7 in the CRI Production Guidelines (Vol. II, www.citrusres.com/category/chapter-5-crop-manipulation) “Fruit size and crop load prediction for citrus” or the SA Fruit Journal of Oct/Nov 2009 for details on how these predictions can be made.

Regrowth Control should commence as soon as possible while shoots are soft and easy to remove, especially after heavy pruning earlier in the season, as regrowth adversely affects fruit size and is antagonistic to fruit colour development, particularly for early maturing cultivars.

Creasing Gibberellic acid (GA) is applied in January to reduce the incidence of creasing. However, it should be noted that improper timing of GA delays colour development. When applying GA, ensure that the side of the fruit facing inwards is also covered by the GA, as this part of the fruit is more prone to creasing. A heavy fruit set could also promote the incidence of creasing.

Oleocellosis incidence Late summer vegetative growth of bearing trees should be kept to a minimum, as excessive vegetative vigour during this period is associated with high incidence of oleocellosis at harvest.

Rind colour development Avoid late nitrogen application and the use of high concentration, heavy summer oil sprays after December, as these treatments are antagonistic to rind colour development. In addition, GA treatment to reduce creasing incidence is also antagonistic to colour development and could reduce it, if applied later than middle January.

Disease management

Grondgedraagde siektes (J. Van Niekerk en MC Pretorius) Phytophthora beheer Alhoewel redelike goeie reënval gedurende Desember voorkom, is Januarie en Februarie gewoonlik droër en die dagtemperature heelwat hoër. Vandaar die waarskuwing dat indien daar van fosfonate gebruik gemaak gaan word om Phytophthora-wortelvrot te beheer, die middels met sorg en volgens gebruiks-aanwysings toegedien moet word. Dis van uiterste belang dat die middels nie toegedien word indien dagtemperature hoër as 28°C is nie, of wanneer die bome onder enige mate van droogte- of hittestres verkeer. Geen bespuitings moet gedurende warm bergwinde gedoen word nie. Geen wortelvrotbespuitings moet in bogenoemde warm maande op vroeë sagte-sitruskultivars, bv. Satsumas en Clementines, gespuit word nie.

Aalwurmbeheer Reën en besproeiingswater is nodig om die aalwurmdoders effektief deur die grondprofiel te was. Dien aalwurmdoders toe op nat gronde, direk na ’n goeie reënbui. Volg die toediening op met ten minste 35 mm besproeiing.

Wenk vir effektiewe bestuur van wortelgesondheid Neem grond- en wortelmonsters ten minste elke drie jaar as bestuurshulpmiddel om die aalwurm en Phytophthora-status in die grond en wortels van sitrusboorde te bepaal. Dit is uiters belangrik om monsters te neem voordat boord vir herplantdoeleindes verwyder word, om die aalwurm en Phytophthora-status vir toekomstige verwysings te bepaal. Inligting aangaande die metode van monsterneming is beskikbaar by die Diagnostiese Sentrum in Nelspruit. Monsters kan ook vir ontledings na die Diagnostiese Sentrum gestuur word.

Fruit and foliar diseases (P. Moyo)

Citrus black spot Continuous fruit protection throughout the season is critical for managing citrus black spot (CBS). Use CRI-PhytRisk to help plan your spray programme and avoid gaps in your treatment programme. Ensure consistent coverage throughout the recommended fruit protection period, because as fruit size increases and tree canopies become denser, achieving effective spray coverage becomes more challenging. Refer to the Recommended Usage Restrictions document (No. 57, August 2024) for specific fungicide guidelines by different export markets. For example, mancozeb may not be applied later than December for fruit destined for Canada or later than the end of January for Japan. Copper can be used as an alternative to mancozeb, offering longer spray intervals, but excessive use may cause phytotoxicity to fruit and foliage, especially when combined with low-pH products or applied in hot, dry conditions.