19 - 



results indicating return of solution pH to less alkaline levels within 24 

 hours with addition of CO2 were confirmed, even in solutions which received 

 the highest CaCl2 rate. 



Benomyl and methomyl appeared to be most affected by CaCl2 addition, 

 because neither of these materials contains strongly acidic components. pH 

 of solutions containing either azinphosmethyl or formetanate were least 

 affected bv CaCl2 addition. This is because azinphosmethyl is a phosphoric 

 acid-containing ester, which would neutralize any added base such as calcium 

 hydroxide, while formetanate is formulated as a freely soluble HCl salt. 



As indicated by control values, azinphosmethyl does not appear to be 

 very susceptible to hvdrolytic dearadation over time. This material also 

 seems to be quite stable over a wide range of pH readings, ranging in these 

 tests from about pH 6 to about 9.4. It would seem safe in this case to 

 suggest mixing azinphosmethyl with CaCl2 in tank mixes. Formetanate also 

 appears to be reasonably stable over time in solution containing no CaCl2. 

 However, at the high pH levels resulting from addition of 5 and lOX concen- 

 trations of CaCl2, ma.ior loss of parent compound occurred at 6. 12 and 24 

 hours. 



In the case of metliomyl. substantial hvdrolysis occurred over time even 

 in the absence of CaCl2. Here, it seems that the buffering effect of adding 

 some Car.l2 enhanced this pesticide's stability up to a point, although in 

 lOX concentrate solutions there was still substantial loss of parent com- 

 pound at 48 hours. 



Benomyl also appeared to hydrolyse in control solutions over time with 

 only 26% remaining after 48 hours. Degradation was enhanced by CaCl2 addi- 

 tion with only about 1/3 of the parent compound and its carbendazim break- 

 down product (33%) remaining at 12 hours. 



V/hile the demonstrated substantial loss of parent compound in some "in- 

 ■.tances may represent a financial loss to growers, it is still unclear at 

 :his time that pH-induced pesticide hydrolysis would have any negative 

 effect on pest control, particularly since most materials are applied within 

 a relatively short time after mixing. However, tractor or sprayer break- 

 downs that delay application, or conditions of slow drying where pesticides 

 remain in solution for long periods of time may at least affect residues of 

 susceptible pesticide. Growers in the Pacific Northwest habitually buffer 

 alkaline spray waters, and workers in that region have reported improved 

 oest control from use of buffering aoents. 



We hope to look at pest control in the field as the next phase of this 

 work. We are particularly concerned about possible degradation of benomyl 

 and captan, another funaicide reported in the literature to be prone to 

 alkaline hydrolysis, as these materials are included in postharvest dips and 

 drenches to which Car.l2 may be added. In this instance, however, we have 

 two things going for us. One is the fact that FDA regulations allow only 

 use of briner's grade CaCl2. which is much more pure, beino composed of 97% 

 CaCl2, and thus would have a less dramatic impact on solution pH. Also, 

 since dips and drenches are agitated during application to harvested fruit, 

 mixing wi :h CO2 in the air would be expected to be af a maximum with a con- 

 sequent drop in pH over time. 



