Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/1996
Publication Date: N/A
Citation: Interpretive Summary: Methyl bromide is widely used as a preplant soil fumigant to control soil borne diseases in bareroot tree nurseries. It is also used in other nursery culture to control pathogens and other pests. Because methyl bromide is one of the class of chemicals with potential adverse impact on the ozone layer, it is mandated to be withdrawn from use in 2001. Dazomet is an environmentally benign chemical alternative to replace methyl bromide if reliability can be improved. Biocide reliability of dazomet was dramatically improved by use of a spade machine because the incorporation was deeper and distribution was more uniform than with rotary tillers--the method recommended by the manufacturer of dazomet. The improved method can now be tested for replacement in bareroot tree nurseries
Technical Abstract: Efficacy of soil fumigants in forest-tree nurseries requires evaluation of the incorporation tillage tool. Maximum depth and uniformity of incorporation of surface applied materials by three rotary tillers and a spading machine were compared in a loamy sand nursery using ceramic- sphere tracers (1-3 mm diameter) and dazomet micro-granules. Depth above which greater than 95 percent of ceramic spheres were recovered for the four implements were: 12.5 cm, Kuhn and Forbro rotary tillers; 17 cm, Northwest rotary tiller; and 21 cm, Gramegna spading machine. The spading machine produced a distribution of spheres through the soil profile closest to a uniform distribution. Inhibition of lettuce seed germination to a 12-cm depth in low and high dazomet rates indicated good incorporation of dazomet in that zone. Maximum depth (24 cm) for total inhibition of germination was observed for the spading machine regardless of chemical rate. Cone index values showed maximum penetration: 14 cm, Fobro rotary tiller; 22 cm, Kuhn and Northwest rotary tillers; and 27 cm, spading machine. All three measures of depth show a distinct superiority of the spading machine when the chemical fumigant must reach depths greater than 15 cm. The rotary tillers had much larger variations of sphere count among 5-cm**3 volumes in transects across the width of the implement.