Effects of Several Herbicides on Shoot and Root Growth of 'tifdwarf Bermudagrass

Tifdwarf bermudagrass (Cynodon sp. (L.) Pers.) sod-plugs were treated with two rates of five herbicides (DCPA, Benefin, Bensulide, Terbutol and Kerb) to determine effects of these chemicals on shoot and root growth. Ap plication rates were those commonly used for weed control and twice this recommended rate. Herbicides were applied on top of the sod and below the sod to simulate surface treatment and soil treatment with subsequent placement of sod on treated soil. Three replications were employed in a completely randomized block design. Turf was evaluated visually each week and shoot and root yield determined after 30 days. Initial herbicide damage appeared as a gen eral thinning of sod. However, final foliage yield under greenhouse conditions showed no signif icant difference between treatments. Root yield was greatly affected by herbicides. Surface appli cations of DCPA and bensulide and subsurface Florida Agricultural Experiment Stations Journal Series No. 5104. treatments of all herbicides significantly reduced root growth. Several chemicals completely in hibited root development. Numerous preemergence herbicides are avail able which effectively control a variety of annual weeds in established turf grass sods. However, the more important factor to consider in weed control is tolerance of turfgrasses to the chemical. Com plete eradication of weeds is of little value if the herbicide severely limits growth of the turf or weakens it to such an extent that it is more su sceptible to diseases or environmental stresses. The loss of turfgrass sods caused by herbicides is often overlooked. Injury may not be observed for weeks or months after treatment. If the injury is restricted to damage of the root system, as is often the case, loss of stand may not occur until the grass is under severe stress, i.e., lack of moisture, heavy traffic or disease. In these too frequent oc currences, turf injury is often ascribed to other causes when actually the herbicide had directly or indirectly damaged the turfgrass. This concept of herbicide injury has been recently elucidated to by Callahan (1). Despite numerous reports that herbicides have injured turfgrasses, few investigators have deSMITH: HERBICIDES FOR 'TIFDWARF' BERMUDAGRASS 435 fined the specific type of injury. Foliage damage has frequently been reported but effects of various herbicides on root and stolon growth of warm-sea son turfgrasses has not been adequately deter mined. Restricted root development of turfgrasses has been observed where preemergence herbicides have been used (3, 4). Duble and Holt (2), studying effects of preemergence herbicides as they influ ence establishment of 'Tifgreen' bermudagrass, found that simazine and bensulide retarded the spread of newly planted sprigs; trifluralin, DMPA and DCPA restricted growth of stolons. Smith and Callahan (5) have shown that benefin, trifluralin, DCPA, terbutol and bensulide restrict growth of 'Emerald* zoysiagrass. Reduction in root growth of common Kentucky bluegrass sod-plugs treated with benefin, DCPA, bensulide and terbutol has also been demonstrated (6). The purpose of this study was to investigate effects of several commonly used herbicides on root and shoot growth of 'Tifdwarf bermudagrass. Materials and Methods A greenhouse study was initiated September 1, 1970, to determine the effects of selected herbicides on the regrowth of 'Tifdwarf bermudagrass (Cynodon sp. (L.) Pers.) sod-plugs. Herbicides used were DCPA (Dacthal), Benefin (Balan), Bensulide (Betasan), Terbutol (Azak) and Kerb. Rates of application were those com monly used for control of Poa annua in Florida and twice this recommended rate (See Table 1). 'Tifdwarf bermudagrass sod-plugs 4.5 inches in diameter and 0.5 inch thick were mounted in plastic pots having a top diameter of 4.5 inches and bottom diameter of 3.5 inches. Containers were first filled with washed builders sand to within 0.5 inch of the pot rim. Half of the pots received the herbicide treatments directly on top of the sand layer and sod-plugs were then mounted Tnhle 1. Mean foliage weight of 'Tifdwarf' btTT.iidai:rass sodplugs surface treated with five herbicides, Gainesville, 1970.