Psyllid Resistance to Organophosphates Begins in Brazil

Josh McGill HLB Management, Pesticides, Psyllids

Psyllids are showing resistance to malathion in some areas of Brazil.

Research has confirmed the initial phase of resistance of the HLB-spreading psyllid to the active ingredient malathion in some microregions of the citrus belt of São Paulo and Triângulo/Southwest Mineiro. Malathion is from the organophosphate chemical group. The research was conducted by Fundecitrus in partnership with Luiz de Queiroz College of Agriculture/University of São Paulo (Esalq/USP).

This is the third chemical group psyllids have shown resistance to. The resistance of the HLB insect vector has already been verified for the ingredients bifenthrin and imidacloprid from the pyrethroid and neonicotinoid groups, respectively.

According to the ProteCitrus (Citrus Protection Products) list, only malathion appears as an active ingredient belonging to the group of organophosphates available for use in the field. However, there are other active ingredients registered for use in citrus that are not on the list. They include acephate, chlorpyrifos, dimethoate, phosmet, methidathion and pirimiphos-methyl.

The data are part of studies conducted by Fernando Amaral, a Fundecitrus agricultural engineer and post-doctoral fellow at Esalq/USP. To verify resistance to this molecule, Amaral evaluated psyllid populations in the laboratory from four regions of the citrus belt using subsequent generations of insects collected in the field.

According to Amaral, although resistance has been proven in these microregions, the occurrence has not yet reached the same parameters of ineffectiveness in combating the psyllid found in products from the pyrethroid and neonicotinoid groups.

“We can say that it is an initial phase in the resistance evolution process. This shows, once again, that there was a high frequency of use of this active ingredient without the correct rotation with other modes of action or a dosage below that indicated in the leaflet,” said Amaral. “If control failures are observed, the organophosphate must temporarily leave the citrus grower’s list of options for managing the insect. This should occur until susceptibility is reestablished in the future.”

Growers should use other molecules that show good effectiveness in combating the psyllid. In other Fundecitrus studies, insecticides from the diamide, carbamate, sulfoximine and spinosyn groups have been shown to be 90% or more effective in combating the psyllid. Diamide and carbamate, in particular, showed greater effectiveness in eliminating the psyllid in all areas evaluated. The use of mineral oil mixed with insecticides also helps in managing the psyllid.

Source: Fundecitrus

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