Torpedograss has invaded fine turfgrasses in the Southern U.S. due to its tolerance to most commonly used turfgrass herbicides. Research was conducted to determine torpedograss and ‘Tifway’ bermudagrass tolerance to quinclorac and tank-mix combinations with other turf herbicides. Quinclorac rates in excess of 2.2 kg ai/ha were required for control (≥ 80%) of torpedograss. Sequential applications were more effective than single applications. Generally, sequential applications made 3 wk after the initial were more effective than delaying sequential applications until 4 wk after the initial application. Tifway bermudagrass injury from quinclorac applied at 4.5 kg/ha, or at 2.2 kg/ha followed by a sequential application of 1.1 or 2.2 kg/ha, was observed at 4 to 10 wk; however, turf recovered thereafter. Sequential applications of quinclorac plus imazaquin (1.1 + 0.6 kg/ha) increased torpedograss control (approximate 35%) as compared to quinclorac plus MSMA (1.1 + 1.1 kg/ha) but also decreased turf quality versus quinclorac applied alone or in combination with MSMA. Quinclorac applied at 2.2 kg/ha followed by 1.1 kg/ha applied 3 or 6 wk after the initial controlled torpedograss best with least reduction in bermudagrass quality. Quinclorac is the first herbicide reported to selectively control torpedograss in bermudagrass turf.

Greenhouse, growth chamber, and laboratory studies were conducted to determine anatomical and morphological characteristics and cultural practices limiting the distribution of cogongrass, torpedograss, and johnsongrass in the United States. Cogongrass did not produce axillary buds along most of the rhizome nor regenerate when apical six-node-long rhizome segments were buried deeper than 8 cm. Both torpedograss and johnsongrass produced axillary buds along the entire lengths of their rhizomes. Torpedograss shoot emergence decreased at burial depths between 8 and 16 cm. Shoot emergence from johnsongrass rhizomes was not affected by burial as deep as 16 cm. Rhizomes of all three species were tolerant of desiccation. Cogongrass grew better in soil at pH 4.7 than in soil at pH 6.7, whereas torpedograss and johnsongrass grew equally well in either pH. It is postulated that cogongrass spread is limited by lack of axillary bud formation on most of the rhizome and the inability of rhizomes to send up new shoots if buried deeper than 8 cm. These factors could account for the intolerance of cogongrass to cultivation. Torpedograss appears to spread only vegetatively due to the lack of viable seed production.

In glasshouse experiments, Panicum repens rhizomes with more than two nodes emerged from soil depths of 1 to 20 cm. Emergence from one-node rhizomes was greatly reduced at depths more than 5 cm. In contrast, culm emergence from ginger like rhizomes decreased when burial depth (BD) was greater than 20 to 30 cm. P. repens emerged from deeper soil levels with an increasing number of nodes per cutting. Culms emerged from 36% of total underground regenerative organs. About 75 and 95% of the emerged culms were recorded 30 and 60 d after burial, respectively, and 91% emergence was recorded from 20-cm BD. In field studies, only 9% of nodes produced culms following cross-plowing. About 61 and 67% of the emerged culms were recorded 50 and 60 d after land preparation, respectively. Results indicate that mechanical and chemical control methods could be most effective for P. repens when applied approximately 50 d after land preparation. Burying deeper than 30 cm by deep plowing and reducing rhizome length by cross-plowing might effectively reduce emergence of P. repens.

Greenhouse, growth chamber, and field studies were conducted to determine effects of temperature on the potential of cogongrass (Imperata cylindrica L. Beauv. # IMPCY) and torpedograss (Panicum repens L. # PANRE) to spread beyond present distribution in the Lower Coastal Plains of Southeastern United States. Johnsongrass [Sorghum halepense (L.) Pers. # SORHA] was included in the study for comparative purposes. Growth of each species was greater with day/night temperature regimes of 30/25 C than with 27/22 or 24/18 C. Apical six-node-long rhizome fragments of all three species were killed by a 24-h exposure to −4.5 C. Johnsongrass produced at least three to five times more dry matter than either cogongrass or torpedograss. Order of interspecific competitiveness under 30/25, 27/22, and 24/18 C day/night temperature regimes was johnsongrass > torpedograss > cogongrass. After 2 yr, johnsongrass and torpedograss competition reduced common bermudagrass [Cyndon dactylon (L.) Pers. # CYNDA] yield by 99 and 37%, respectively, while cogongrass competition did not affect common bermudagrass yield. It is concluded that cogongrass and torpedograss are unlikely to spread into more temperate regions of the United States. However, both species are apt to become even more widespread and troublesome in the Lower Coastal Plains of Southeastern United States.

Leaves of torpedograss and American black nightshade were extracted with chloroform at room temperature. A 2-s dip was sufficient to remove most of the epicuticular wax from torpedograss. However, epicuticular hydrocarbon weight represented only 6.4% of the total extract weight and 6.94 μg g−1 fresh weight of chlorophyll were found in the 2-s extract. This represented 25% of the chlorophyll detected in the 232-h extract. In American black nightshade, epicuticular hydrocarbons continued to be removed from the leaf surface up to 6 h of extraction. Epicuticular hydrocarbons represented 0.6% of total extract weight. In the 6-h extract, 4.02 μg g−1 fresh weight of chlorophyll were found. This represented 17% of the chlorophyll detected in the 232-h extract. Evaluation of leaf surfaces using scanning electron microscopy indicated that epicuticular wax was being removed from torpedograss leaves up to 1 h. However, there was little visible evidence for wax extraction from the surface of American black nightshade leaves.

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin + oryzalin, imazapic, imazapic + 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin + oryzalin and imazapic + 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control.