Masters Theses

Date of Award

5-2003

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Thomas C. Mueller

Committee Members

G. Neil Rhodes Jr, Gary E. Bates

Abstract

Grazon P+D®, a premix combination of 0 .24 kg / L 2,4-D and 0.06 kg / L picloram, has shown promise for horsenettle (Solanum carolinense) control. Experiments were conducted in 2001-2002 in Hamilton and 2002-2003 in Monroe County to evaluate Grazon P+D® for horsenettle control and clover (Trifolium sp.) tolerance in a tall fescue (Festuca arundinacea) pasture. Grazon P+D® treatments included 0.7 Kg acid equivalent (AE) / ha and 1.4 kg AE / ha at three timings in each study: early post (EPost)(10-15cm horsenettle height), mid post(Mpost) (early flower), and late post (LPost) (fruit initiation). In February 2002, separate 3.0 m strips of "Reddy" variety red clover (6.3 kg / ha seeding rate) and "Will" variety ladino white clover (11.2 kg / ha seeding rate) were drilled across all plots. Horsenettle control and density at season's end was determined for both locations. Survival of clover drilled the winter following application was evaluated in the spring and summer of 2002 at Hamilton County. Data were subjected to analysis of variance and means were separated using Fischer's Protected LSD test (P = 0.05). Reduction of ladino white clover existing at the time of application was >95% for all Grazon P+D® treatments. All early and late summer treatments at both locations provided >80% control of horsenettle. Horsenettle density in all treated plots in the experiment at both locations was < 1 stem / 10m2, while untreated plots contained >25 stems / 10m2. Both late season experiments exhibited a difference in stem density between late season LPost applications and all other applications. EPost and MPost plots contained > 1 stem / 10m2, while LPost plots contained between 2 and 45 stems / 10m2. This difference was due to the short time between the LPost applications and the stem counts. LPost applications eventually exhibited control similar to, or better than other application timings. Horsenettle density was measured in both Hamilton County experiments one year after application on 17 May and 13 June 2002 using the same methods as in 2001. All early and late season treated plots contained from 1 to 25 stems / 10m2 as opposed to between 20 and 125 stems / 10m2 in the untreated plots. Clover survival was evaluated at both Hamilton County experiments on 17 May 2002. Red and ladino white clover survival was lower in the Grazon P+D® treated plots of both the early and late summer experiments (22 - 50%) than in the controls (73 - 82%). Horsenettle control at both Hamilton County experiments was evaluated on 13 June 2002. All early and late summer experiment Grazon P+D® treatments controlled horsenettle between 45 and 75% with no control difference between treatments. Grazon P+D® reduced horsenettle growth immediately after application and provided suppression of horsenettle the following year; however, treated plots showed reduced survival of clover drilled the winter following application. This reduced survival can be attributed to the herbicide. All applications of the herbicide controlled horsenettle equally well the year of application. Horsenettle control one year after application was less in EPost applications than in MPost or LPost applications in the late summer study. All other applications controlled horsenettle equally well one year after application regardless of timing or rate. An application of Grazon P+D® (0.7 Kg AE / ha) at either the flower or fruiting stage will provide excellent control the year of application and reduce horsenettle infestation one year after application. It will, however, reduce survival of clover drilled the winter following application.

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