The Influence of Changes in Concentration and Temperature upon the Bactericidal Activity of Formaldehyde in Aqueous Solutions
Although formaldehyde in aqueous solution (formalin) is an important and widely used disinfectant, there is very little information available concerning the exact effect of changes in either concentration or temperature upon its bactericidal activity. An experimental study was therefore made of the bactericidal activity of formaldehyde. This study was conducted along the lines of previous studies of the bactericidal activities of phenols and alcohols (Tilley, 1939, 1942).
An Experimental Study of the Influence of Temperature on the Bactericidal Activities of Alcohols and Phenols
A study of the relation between concentration of disinfectants and the time required for disinfection was described in a previous paper.' A number of alcohols and phenols were used in that work, and from the experimental datav obtained the concentration exponent of each of these was calculated and reported. More recently a study has been made of the relation between temperature of disinfection and the time required for disinfection. Most of the alcohols and phenols previously used were also used in the recent work. From the results obtained the temperature coefficients of the alcohols and phenols used were calculated by dividing the disinfection time in minutes at the lower temperature by the disinfection time for the same concentration at the higher temperature. The temperature differenees were in all cases 10°C. In most instances the temperature coefficient was determined for each of a series of successive concentrations of the same disinfectant, and the average coefficient calculated for the series is considered the temperature coefficient of the particular disinfectant. The experimental procedure was si-ilar to that previously described except that the relative effectiveness of the same concentration at different temperatures was studied instead of, as formerly, the relative effectiveness of different concentrations at the same temperature.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.