Aldicarb application rates

Table I. Aldicarb Application Rates and Frequencies in the 9 Fields under Study...

In aerobic soils, aldicarb degraded rapidly (half-life = 7 d) releasing carbon dioxide. Mineralization half-lives for the incubation of aldicarb in aerobic and anaerobic soils were 20-361 and 223-1,130 d, respectively. At an application rate of 20 ppm, the half-lives for aldicarb in clay, silty clay loam, and fine sandy loam were 9, 7, and 12 d, respectively (Coppedge et al, 1967). Other soil metabolites may include acids, amides, and alcohols (Hartley and Kidd, 1987). 

According to recent estimates, some 35 chemical pesticides are currently used to control various pests on cotton (1). There is considerable variation across the USA cotton belt in seasonal pesticide application rates, ranging from a high average of 7.4 pounds per harvested acre in Florida to a low of 0.3 in Oklahoma. Currently, methyl parathion (21.0%), azinphosmethyl (13.0%), various pyrethroids (8.0%), chlordimeform (7.4%), propargite (6.8%), and aldicarb (6.8%) account for 63% of all insecticides applied to cotton (1). 

The fields were originally selected to allow comparison of aldicarb residue movement and persistence under the conditions pertinent to its prescribed (label) use and pre- and post-1982 maximum application rates [3 versus 2 lb a.i./A (3.4 v. 2.2 kg/ha)]. At the start of the study ... 

G formulation. In related work with aldicarb, Coppedge et al. (21) concluded that slow-release formulations may extend bioactivity over a longer time but not improve efficacy of compounds with moderate or low insecticidal activity at normal application rates. Pertinently, of the currently registered soil insecticides, carbofuran is the least toxic to CRW (22.), and therefore, rate of release would be critical to its bioactivity. 

Aldicarb is highly water soluble and soil application of this insecticide has the potential to result in runoff or leaching of the insecticide or active metabolites and contamination of surface or groundwater. Aldicarb is acutely toxic to bees, birds, and fish. Species-specific rates of bioactivation may influence the sensitivity of a particular organism to this insecticide. 

As a result, 3-5 times as much aldicarb leached below two meters with irrigation. Applications at potato emergence decreased the amount to leach by about one-half as compared to earlier applications at planting. The reasons for this are two-fold avoidance of some spring rain for later applications, and a more rapid rate of decay for later applications. 

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