18 



EFFECT OF CALCIUM CHLORIDE ADDITION ON SOLUTION pH 

 AND ON HYDROLYSIS OF CERTAIN PESTICIDES 



William M. Col i , John M. Clark and Matt Brooks 

 Department of Entomology 



Commercial apple grov/ers in Massachusetts typically apply an average of 

 6-10 insecticide and 8-12 fungicide dosage eguivalents annually to produce a 

 marketable crop. Up to four dosage equivalents of miticide are applied in 

 problen blocks and small amounts of aphicides and herbicides are used as 

 well, as are various plant growth regulators for fruit thinning, to promote 

 early ripening or delay preharvest drop. 



Most growers apply CaCl2 sprays to Mcintosh apple trees, generally as 

 additions to their pesticide cover sprays. Technical flake CaCl2, used for 

 foliar application, contains 77-80% CaCl2 as well as sizable amounts of 

 water, and small percentages of sodium chloride and calcium hydroxide (free 

 lime). Many pesticide labels contain warnings about mixing pesticides 

 with alkaline materials. Captan, for example, is reported to have a half 

 life of less than one hour in pH 8.5 water at 70OF. We became interested in 

 what effect, if any, use of CaCl2 would have on solution pH and potentially 

 on hydro ''ysis of pesticides and thus on pest control. 



In our earlier tests we monitored the pH of solutions containing the 

 equivalent of 5 lbs/A of technical or analytical grade CaCl2, with or 

 without the insecticide Guthion*. Concentrations tested ranged from dilute 

 to lOX, to simulate a variety of application conditions. It was evident 

 that technical grade CaCl2 at 6 and lOX resulted in a moderately to strongly 

 alkaline solution pH. The addition of the acidic material Guthion* reduced 

 the pH of analytical grade solutions below potentially troublesome levels; 

 however, pH of technical grade solutions remained high except at the most 

 dilute concentrations. Analytical grade CaCl2 had a less dramatic effect on 

 pH due to the presence of less Ca(0H)2 contaminant. We also showed that pH 

 of CaCl2 solutions tended to drop over time as the Ca(0H)2 contaminant com- 

 bined with CO2 in the air to form calcium carbonate, with an overall reduc- 

 tion in solution alkalinity. This reaction can be speeded up by bubbling 

 CO2 through the solution. 



Here we report the results of a laboratory study to measure any effect 

 of solution pH on hydrolysis of certain representative pesticides. Field 

 rate concentrations of azinphosmethyl (Guthion*), methomyl (Lannate*), for- 

 metanate hydrochloride (Carzol*) and benomyl (Benlate*) were prepared in 250 

 ml of distilled, deionized water containing technical grade CaCl2 at 1,5, 

 and lOx concentrations. A control solution containing no CaCl2 and one 

 containing lOx CaCl2, which had been saturated for one minute with CO2 prior 

 to pesticide addition, were also included. Solutions were sealed and stored 

 at 75" F in the absence of light. 



Addition of technical grade CaCl2 resulted in substantial alkaliniza- 

 tion of all treated solutions. Although pH of most solutions had returned 

 to near neutrality within 24 hours, those containing lOX CaCl2 were still 

 moderately alkaline even after 24 hours, as seen in Table 1. Our earlier 



*lrade name 



