Masters Theses

Date of Award

8-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Thomas C. Mueller

Committee Members

Donald Fowlkes, G. Neil Rhodes Jr.

Abstract

Morningglories (Ipomoea spp.) have been persistent and difficult to control weeds in tobacco (Nicotiana tabacum) production. In 1997 sulfentrazone was labeled for use in tobacco. Sulfentrazone provides excellent control of morningglories and many other broadleaf weeds. It also provides partial control of annual grasses. Tobacco injury from sulfentrazone had not been noted during several years of research. In 1997, however, numerous producers using sulfentrazone experienced unexpected tobacco injury.

Studies were conducted at Greeneville and Springfield, TN to determine the influence of incorporation on tobacco injury and weed control. Treatments of sulfentrazone plus clomazone (352 g/ha + 840 g/ha) or sulfentrazone plus pendimethalin (352 g/ha + 1156 g/ha) were either surface applied or preplant incorporated to depths of 5 or 10 cm. Weed control was excellent at both locations and with all treatment combinations. Weed control was 90% or greater for smooth pigweed (Amaranthus hybridus L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], goosegrass [Eleusine indica (L.) Gaertn.], Pennsylvania smartweed (Polygonum pensylvanicum L.), carpetweed (Mollugo verticillata L.) and yellow nutsedge (Cyperus esculentus L.). Weed control was not influenced by depth of incorporation.

Crop symptoms associated with sulfentrazone include stunting and chlorosis. In 1997 at Springfield, all injury was 20% or less at 14 days after treatment (DAT) with a slight increase in injury with both incorporation depths. At 64 DAT all treatments exhibited less than 10% Injury. In 1998 and 1999 at Springfield, stunting and chlorosis were both less than or equal to 10% from 16 DAT to 27 DAT. No injury was observed later in the growing season. At Greeneville in 1997 stunting was less than 21% at 26 DAT and increased with depth of incorporation. By 59 DAT all stunting was less than 11%. Chlorosis in 1997 was 23% or less at 26 DAT and increased slightly with incorporation depth. Chlorosis had diminished to less than 15% by 59 DAT. At Greeneville In 1998 stunting injury was 13% at 33 and 69 DAT. Chlorosis was less than 21% at 33 DAT with no chlorosis evident at 69 DAT.

Tobacco injury was slight (less than 10%) in most cases and diminished as the season progressed. Injury from sulfentrazone + clomazone in both 1997 and 1998 increased with depth of incorporation. The influence of incorporation depth of sulfentrazone + pendimethalin was less clear. Injury was greater with the 5 cm incorporation depth than the 10 cm incorporation depth. In 1997 the 5 cm depth resulted In more injury than the other depths, and in 1998 the 0 and 5 cm resulted In more injury. The dark fire cured variety tended to exhibit less Injury than the burley. Tobacco injury caused by incorporation depth of either herbicide combination did not affect tobacco yield or quality when compared to the untreated hand weeded check.

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