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Integrating GWSS Insecticide Treatments with Citrus IPM

Dr. Beth Grafton-Cardwell  
Department of Entomology, UC Riverside, stationed at the Kearney Agricultural Center, Parlier

               The purpose of the glassy-winged sharpshooter (GWSS) area-wide treatment program is to reduce the overall number of GWSS in citrus so that they do not move into neighboring crops (especially grapes) and to prevent transport of the pest to uninfested areas of the state.  Yellow sticky cards are used to trap adult GWSS and when adults are found treatments are initiated.  Research has shown that if this is done on an area-wide basis, GWSS numbers will remain low in the years following treatment.  Researchers have studied the effects of various insecticides on both the pest (GWSS) and the parasites needed for other pests of citrus.  While much of this research is still underway, the current treatment program is tailored to minimize the effects of insecticides on Aphytis and other natural enemies (predatory mites, parasitic wasps, lacewings and predatory beetles) through careful choice of the insecticide, insecticide rate, the water volume applied, as well as the method and timing of application. 

The current plan uses the systemic insecticide Admire as the first line of defense.  The foliar insecticide Assail is used during times of the year or in situations when Admire can not be used (usually late fall).  Treatments of either of these insecticides should be delayed in situations where vedalia beetle is actively feeding on a cottony cushion scale infestation. 

Admire 2F (32 oz):

Application: Due to bee toxicity, Admire is applied in the spring just prior to bloom or just after petal fall if it is daytime but can be applied during bloom if the treatment is conducted at night.  Use 2 hours of pre and 2 hours of post irrigation (the amount of time varies according to soil type).  Admire requires 4-6 weeks for uptake into the tree, but lasts for many months providing long-term control of GWSS.  Admire applications are usually administered through the irrigation system, but they can be can also be done by handspraying the ground in the area where the sprinklers wet the soil.  Shanking the insecticide into the soil and following up with furrow irrigation is a less effective method of application. 

Selectivity:  Because Admire is systemic, it is relatively nontoxic to most natural enemies because they don’t feed directly on the plant.  The exception to the rule is vedalia beetle, which is killed when it feeds on cottony cushion scale that have ingested but are not killed by Admire. 

Assail 70 WP (2.0 oz):

Application: applied in 100-500 gpa.  Used in late fall as a clean up before harvest or in the spring in situations where Admire will not work fast enough. 

Selectivity: Assail is fairly broad spectrum killing most natural enemies it comes in contact with, however, it is fairly short-lived (about 4-6 weeks).  While fresh residues kill most of the adult Aphytis, about 50% of Aphytis that are inside the scale when the spray is applied survive that treatment when they emerge.  Assail is toxic to vedalia beetles for 1-2 months after treatment. 

Other Approved Insecticides

     There may be situations where growers prefer to use an insecticide other than Admire or Assail perhaps because that insecticide has a shorter preharvest interval.  Examples include Baythroid, Danitol, Dimethoate, Dibrom, Lorsban, Evergreen, Sevin, Lannate, or Provado.  Some of these insecticides are not as effective against GWSS and/or are less favorable for natural enemies.  Be aware that many new insecticides do not have Maximum Residue Limits (MRLs) established, preventing treated fruit from being shipped to some foreign countries.

  Should you Release Aphytis in Orchards Affected by Glassy-winged Sharpshooter Treatments?  

The short answer is yes!  It is critical to establish Aphytis in orchards in early spring (Feb-Mar) when 3^rd instar scale are available for parasitism.  These early releases are creating small insectaries in the orchard that will later expand throughout the orchard.  GWSS treatments are likely to occur later in the season and while they will have some negative effect on Aphytis, they will not eliminate them.  Aphytis releases can be resumed immediately after an Admire treatment and about one month after an Assail treatment.  Admire is most effective against scale infesting leaves and fruit and so Aphytis releases are needed for scale infesting twigs and wood. 

  Are there any treatments available for organic citrus?

Pyganic (pyrethrum) can be used in organic situations to reduce GWSS.  Because it is very short-lived (it lasts a few days), the populations may not be completely eliminated and re-infestation may occur if neighboring orchards are not treated.