Diphenylamine (DPA) is applied postharvest to apples and pears to control scald development after storage. Using GC - MS analyses of hexane extracts of fruit surfaces, about 0.1 ug/g of DPA was measured on apples after 7 months of storage, even though no fruit in the storage were treated with DPA. Residues also were present on walls in the storage rooms. There is a report that DPA can be produced in plants. Therefore, fruit of 5 cvs. were harvested in mid-August and at commercial maturity and immediately extracted for measurement. A signal similar to that of DPA was detected in all extracts, but concentrations were too low for positive identification. Results show that presence of DPA residue on stored fruit is not proof that DPA was applied before storage. Extracts from freshly harvested fruit are being concentrated to try to ascertain the identity of the indicated material(s).
Flurprimidol is a plant growth regulator that can be applied as a granular formulation. Understanding flurprimidol release from a granular formulation and movement in various mediums will impact how it is used. Dissipation of flurprimidol from a granular formulation and movement through organic media and sand were evaluated in a greenhouse and laboratory experiment. Experimental variables included media type, depth, and irrigation event. Dissipation isotherms were determined by applying nonlinear regression. Mobility was evaluated using columns filled with media, which was surface-spiked with the granular formulation and then irrigated once daily for 22 consecutive days. Leachate was collected and analyzed by high-performance liquid chromatography–mass spectroscopy. Half-life (DT50), defined as time to 50% reduction, varied among sand, media, and media depth. Flurprimidol dissipation was rapid through sand with DT50 of 6 days. DT50 increased with increasing media depth from 5 to 10 cm for pine bark plus sand, 18 and 35 days, and hardwood bark plus sand, 77 and 173 days, respectively. Maximum flurprimidol leaching was a cumulative 71% of applied amounts over 22 irrigation events through the sand. Hardwood and pine bark media allowed less than 25% of flurprimidol to escape through the column. Data for all media indicated that flurprimidol was mobile through the substrates but exhibited hysteresis with pine bark and hard wood bark media. An initial pulse of flurprimidol will release slowly from this formulation over time. These results indicate that flurprimidol will dissipate from a granular formulation over time and that it will have movement through sand soil and pine bark and hardwood bark media to reach the roots of growing plants.