METHODS FOR EVALUATION OF SPRAY CHEMICAL PHYTOTOXICITY TO CITRUS

ALBRIGO, L. GENE

Abstract


For Florida citrus, pesticides, nutritionals and growth regulators are often sprayed together in tank mixes in order to reduce sprayer use when timings for efficacy are relatively coincident. Many individual spray components are marginally phytotoxic and can result in spray burns when used together or if applied with adjuvants that increase absorption. The toxicity level of many standard spray materials is unknown and new products are not routinely tested for phytotoxicity in citrus, particularly as tank mixes with other pesticides or nutritionals. Three test methods were developed to allow spray chemical phytotoxicity testing using cell cultures, peel disks and whole fruit. Cell suspension cultures initiated from 'nucellar derived' embryonic callus of 'Hamlin' sweet orange and 2) peel disks of orange or grapefruit were grown in culture and exposed to media incorporated test chemicals. Reduced weight gain (Method 1) or color changes and callus growth reduction (Method 2) were used to evaluate phytotoxicity. Dilute sprays and droplet applications to on-tree fruit (Method 3) were used to evaluate individual and combinations of chemicals with and without spray adjuvants. The three tests effectively determined thresholds for phytotoxicity and will be useful for testing new citrus production chemicals. These were preliminary evaluations and could be refined for statistical application. Chemicals tested and found to have some level of phytotoxicity by these methods included Aliette, Morestan, Pro-Gibb with 2,4-D, citric, phosphorus, and phosphoric acids, and some additional pesticides in combination with urea. Two herbicide grade adjuvants tested (Herbex and Induce) increased phytotoxicity in on-tree tests. Salty water often reduced the influence of a surfactant. Acidity, in itself, was phytotoxic to the peel of the fruit indicating buffering is important to minimize spray burn.

Keywords


urea; n-sure; unocal; aliette; morestan; tissue culture

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283