Effects of Preemergence Herbicides on Hybrid Bermudagrass Root Growth and Morphology.

Preemergence herbicides can negatively affect establishment of hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy). However, little is known about the effects of preemergence herbicides upon root growth and morphology, which may limit growth and development of turf. Research was conducted in a climate controlled greenhouse during summer 2016 at Mississippi State University to evaluate the effects of  atrazine (1.12 kg ha^-1), atrazine (1.12 kg ha^-1) + metolachlor (0.86 kg ha^-1), dithiopyr (0.56 kg ha^-1), flumioxazin (0.286 kg ha^-1), indaziflam (0.033 kg ha^-1), liquid and granular applied oxadiazon (2.24 kg ha^-1), metolachlor (2.78 kg ha^-1), pendimethalin (1.66 kg ha^-1), prodiamine (0.594 kg ha^-1), and simazine (2.24 kg ha^-1) on ‘Latitude 36' hybrid bermudagrass. Grass plugs (31.6 cm²) were planted in a native Marietta silt loam soil in pots (126 cm² surface area, 1121 cm³ volume). Roots were cut to 2 cm before transplanting. Digital images were recorded weekly using a light box. Photos were analyzed for % green cover using SigmaScan^® Pro to estimate hybrid bermudagrass cover. Linear regression analysis was used to estimate time to 50% cover. Confidence intervals at α = 0.05 level of significance were used to detect differences compared to the nontreated. Roots were harvested and weighed 4, 6, and 10 weeks after treatment (WAT) and analyzed using WinRHIZO^® to quantify total root length, surface area, and average diameter. Separate roots were also harvested 6 and 10 WAT to determine free carbohydrate concentration. Means were separated using Fisher's protected LSD (α = 0.05). Liquid applied oxadiazon [48 days (d)], metolachlor (49 d), and atrazine + metolachlor (51 d) increased time to 50% cover when compared to the nontreated (33 d). At 4 WAT, flumioxazin, liquid applied oxadiazon, prodiamine, atrazine + metolachlor, and metolachlor alone reduced root weight, length, and surface area compared to the nontreated. Similarly, at 6 WAT, atrazine + metolachlor, liquid applied oxadiazon, dithiopyr, metolachlor, and indaziflam reduced root weight, length, and surface area compared to the nontreated. At 10 WAT, only metolachlor, indaziflam, and dithiopyr reduced root weight, length, and surface area compared to the nontreated. No differences in average root diameter were observed during the experiment. Effects upon carbohydrate concentrations, along with results from a second replication of the study, will be discussed.

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