Pesticide Downward Movement in a Bermudagrass System Compared with Movement in a Fallow System.

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Title: Pesticide Downward Movement in a Bermudagrass System Compared with Movement in a Fallow System.
Author: Cummings, Hennen Dock
Advisors: Dr. Ross Leidy, Committee Member
Dr. Jerry Weber, Committee Co-Chair
Dr. Rick Brandenburg, Committee Member
Dr. Fred Yelverton, Committee Co-Chair
Abstract: Pesticide regulations based on pesticide mobility data derived from row crop systems may not appropriate for bermudagrass systems since organic matter binds pesticides and bermudagrass systems can have a thatch layer at the soil surface which is rich with organic matter. Downward mobility of pesticides in a fallow soil system was compared with movement in a bermudagrass system under field conditions when the bermudagrass was actively growing and dormant in a Candor sand. Soil column lysimeters (15 cm in diameter x 91 cm in length) were removed from the field after 140 days of summer or winter and analyzed by depth for either fipronil, fipronil metabolites (fipronil sulfone, fipronil sulfide, fipronil amide, desulfinylfipronil), imazaquin, prodiamine, pronamide, or simazine parent material using gas chromatography. In general, greater pesticide concentrations were reported for winter treatments. Pesticides tended to not move beyond the thatch layer of the bermudagrass system but were distributed more uniformly from 0 to 15 cm in the fallow soil system. The thatch layer of the bermudagrass system contained 300% more organic matter than the 0-4 cm depth of the fallow soil system which provided a greater potential to bind pesticides. In a second study, 14C-labeled simazine was applied to dormant bermudagrass and fallow soil in short lysimeters stored in a cold growth chamber and to actively growing bermudagrass and fallow soil in lysimeters kept in a greenhouse in late April. Following each clipping collection, lysimeters were irrigated with 5 cm of water every three to four days and leachate was collected 4 hours later. After 25 days, lysimeters were removed and divided into specific depth increments. Due to evapotranspiration, actively growing bermudagrass and warm fallow soil lysimeters yielded significantly less leachate than dormant bermudagrass and cold fallow soil lysimeters indicating less moisture was available for downward movement during summer. Simazine quantities in dormant bermudagrass leachate increased quickly indicating movement by channeling whereas simazine quantities in cold fallow soil leachate increased gradually over time indicative of herbicide front movement. There were no significant differences in the quantities of simazine in the roots or verdure of actively growing and dormant turf except for the 0-2 cm increment where dormant bermudagrass roots contained more simazine. The amount of simazine translocated in actively growing bermudagrass clippings increased from 14,377 disintegrations per minute (DPM) to a maximum of 62,003 DPM and then decreased to 21,314 DPM over a 21 day period. After the addition of 31 cm of irrigation (25% mean annual rain fall in NC), the greatest quantities of simazine were detected in the 0-2 cm increment of all treatments and concentrations decreased with depth. Although the greatest quantities of simazine in leachate were reported in dormant bermudagrass, the mobility index for simazine was greatest for cold fallow soil. Therefore, simazine is least mobile during periods of high evapotranspiration rates like summer. In a third experiment beginning in May 2003, fipronil was applied at the label rate to bermudagrass in pots in a greenhouse 120, 90, 60, 30, and 0 days before adding one tawny mole cricket nymph to each of 11 replicates in September 2003. The experiment was conducted twice. In Run 1, 10 days after adding nymphs and 4 days after adding nymphs in Run 2, cricket status was recorded as dead, absent, or alive. Run 1 included 11 non-treated containers, and Run 2 included 26 non-treated containers. Soil in the 0-4 cm increment was analyzed for fipronil and four fipronil metabolite residue concentrations. Fipronil residue concentrations (μg per g) decreased with time (0.00002x2 – 0.005x + 0.3675 where x =days after treatment, R2 = 0.9998). Two metabolites (fipronil sulfone and fipronil sulfide) concentrations increased as fipronil residues decreased. Each treatment's effect on the nymph was significantly different from the non-treated; however, there were no significant differences in nymph status among fipronil treated pots. Therefore, fipronil residues 120 days after application (0.047 μg per g) were high enough to affect mole crickets to the same extent as the 0 day treatment (0.368 μg per g). There was significant repellency with fipronil as the majority of nymphs evacuated the treated pots, but 35 out of 37 nymphs were found alive in the non-treated pots.
Date: 2004-11-29
Degree: PhD
Discipline: Crop Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/4068


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