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Sa Fruit Journal Aug Sept 2021 Citrus
October / November 2021

Extensions Briefs October and November 2021

SA Fruit Journal: October / November 2021

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

Integrated pest management (T.G. Grout and S.D. Moore)

Thrips management

During October and November, citrus fruit are 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 roughly doubled if the population comprises mostly adults. Citrus thrips are genetically predisposed towards 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 codling moth (FCM), mealybug and scale insects for a month or more. So, if this degree of control is required, it is best to spray these at petal fall and follow up with softer options when necessary.

Parasitoid releases

Growers planning to augment parasitoids for mealybug (i.e. Coccidoxenoides perminutus or Anagyrus vladimiri), red scale (i.e. Aphytis melinus) 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, and growers should therefore not wait until the pest reaches a problematic level. Research trials with 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 elapsed since application of pesticides that would be detrimental to parasitoids. This information is available from CRI and the biocontrol agent producers/suppliers.

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. At this later stage, the organophosphates and buprofezin with which we are so familiar, can no longer be used.

However, trial work indicates that some of the newer options, particularly spirotetramat and sulfoxaflor, are effective. 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, then augmentative releases of Coccidoxenoides perminutus should be considered unsuitable.

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