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December 2021 / January 2022

Extension Briefs for December 2021 and January 2022

SA Fruit Journal: December 2021 / January 2022

By J.J. Bester, Mathys Pretorius, Wayne Mommsen and Catherine Savage (Citrus Research International)

Integrated pest management

False codling moth (S.D. Moore)

It is utterly imperative that the FCM Management System (FMS) for citrus, including the FCM Systems Approach, be implemented as diligently and thoroughly as possible. No lapse in the implementation of comprehensive and effective management practices can be afforded by growers or by the industry as a whole. The details of all of these practices are described in the FMS, with reference to CRI’s 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, including lemons. In the hotter summer months the FCM larvae exit the fruit faster to pupate in the soil. Therefore, for effectiveness, orchard sanitation should be increased to at least twice weekly. 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. Fruit must NOT be mulched inside the orchard.

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. Only initiating control measures 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 in ascertaining FCM risk. Monitors must be trained and proven competent for this very important task.

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 in the northern production areas and during January in the Cape production areas. If mealybug infestation does not decline during early January and late January to early February, respectively, suppression with a chemical treatment is advisable on early maturing cultivars.

Unfortunately, buprofezin can no longer be used at this stage, due to residue restrictions. However, there are a couple of relatively new options that can now also be used correctively for mealybug, and which are effective i.e. spirotetramat and sulfoxaflor. 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 Coccidoxenoides perminutus (which is only effective against citrus mealybug) and Anagyrus vladimiri (which also attacks at least oleander mealybug, in addition to citrus mealybug) should be initiated as early in the season as possible for optimal efficacy. The phytosanitary status of certain species must also be borne in mind.

Citrus thrips (M. Gilbert)

Thrips can still cause damage on citrus fruit between December and February, particularly in hotter production areas such as the Lowveld and Sundays River Valley. Damage generally declines with increasing fruit size from January onwards, but one should still be vigilant. Later-flowering cultivars such as Valencias and lemons, whose fruit are still relatively small at this time of the year are susceptible, and scouting should therefore continue to be carried out at least twice weekly, particularly on new flush, to prevent a build-up of numbers, and avoid possible late damage known as “scribbling” or “browning” on the sides of the fruit. Applications of thripicides at this time of the year should preferably not leave a long residue, as we do not want to disturb the activity of mealybug and scale parasitoids too much.

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