Smutgrass is an invasive warm-season perennial bunch-type grass native to tropical Asia. The two varieties of smutgrass prevalent in Florida are small smutgrass and giant smutgrass. Laboratory seed germination experiments were conducted on both smutgrass varieties to determine the effect of various environmental factors on germination and emergence. The average germination rate for both varieties was 88% at 30/20 C day/night temperatures. Seed germination for both varieties was greater under simulated temperature flux than at constant temperatures. Seed of both varieties germinated at four simulated Florida temperature fluxes (22/11, 27/15, 33/24, and 29/19 C day/night), although the germination of small smutgrass and giant smutgrass was reduced at 33/24 and 22/11 C, respectively. Germination of small and giant smutgrass under dark conditions was 27 and 53%, respectively. Both smutgrass varieties germinated over a wide range of pH values. Small and giant smutgrass germination was inhibited at water potentials below −0.2 MPa and when small smutgrass seed was placed below the soil surface. Emergence of giant smutgrass seed did not occur below 3 cm. Both smutgrass varieties germinated over a broad range of environmental conditions, indicating their capability of year-round germination; however, germination is only likely to occur under field conditions during the summer growing season when rainfall is prevalent. These results indicate that both species have the ability to germinate over a wide range of environmental conditions but that germination is inhibited by moisture stress and depth of burial. Considering that giant smutgrass prefers higher temperatures than small smutgrass, the advent of rainfall from June through September is conducive for germination. Practices that focus on the germination pattern of smutgrass could lead to better long-term management of smutgrass in Florida.

Cadillo is an invasive species commonly found in pastures, rangelands, and disturbed areas. It is becoming a significant problem weed in Florida pastures and natural areas. The objectives of this research were to determine effective techniques to break seed dormancy and the effect of light, temperature, pH, water stress, and depth of seed burial on Cadillo germination. Cadillo seeds had significant levels of innate dormancy imposed by a hard seed coat; chemical scarification was the most effective technique for removing dormancy. Seeds germinated from 15 to 40 C, with an optimal temperature of 28 C. Germination was unaffected by pH levels. Water stress below −0.2 MPa reduced seed germination. Cadillo germination was not light-dependent and seeds emerged from depths up to 9 cm, with the greatest occurring emergence near the soil surface. Considering that Cadillo seed can germinate under a wide range of environmental conditions, it is not surprising that it has become a serious invasive weed in Florida.

Common teasel is an invasive and widespread weed in Argentina. Germinationexperiments were carried out from 2011 to 2014 to determine the effect ofvarious environmental factors on germination and emergence. Germination ofrecently dispersed seeds was 12% in darkness at constant temperature. Incontrast, seed exposure to light and alternating temperatures enhancedgermination to 95%. The requirement of light and alternating temperaturessuggest that common teasel has physiological dormancy. Several experimentswere carried out to determine whether (1) seed responses to light andalternating temperatures have a hormonal basis, (2) seed coats can suppressgermination, and (3) time and thermal conditions during seed storage reducelight and alternating temperature requirements. Germination was reduced (≤13%) by a gibberellin synthesis inhibitor. In contrast, the presence ofgibberellins and an abscisic acid synthesis inhibitor increased germinationto 95 and 38%, respectively. Results suggest that a higher ratio amonggibberellins and abscisic acid (GA/ABA) leads to a break in dormancy.Germination was 100% when embryos were excised, suggesting that seed coatsmay suppress germination by mechanical restriction. Likewise, germinationwas enhanced by hydrogen peroxide (70%). This compound is known to increaseGA/ABA ratio in agreement with a hormonal control of dormancy proposed forcommon teasel. An increment of storage time reduces light and alternatingtemperature requirements, allowing seeds to germinate in darkness. Takingthese results together confirms that common teasel has physiologicaldormancy. Seedling emergence was progressively reduced from 70 to 8% byincreased burial depth from 0 to 3 cm. Information from these experimentsmay facilitate development of effective management for common teasel.

Natalgrass is an invasive species that has become increasingly problematicin natural areas in Florida and other subtropical and tropical regionsaround the world. Natalgrass is a prolific seed producer, but littleinformation is available regarding its seed biology and ecology. Researchwas conducted to determine levels of seed dormancy and to examine theeffects of light, temperature, pH, water stress, and depth of burial onnatalgrass seed germination. In addition, seed persistence under fieldconditions was examined both on the soil surface and while buried. Seedsappeared to undergo afterripening. Seed germination was not light dependentand occurred from 15 to 35 C, with optimum germination occurring at 20 to 35C. Germination occurred at pH levels of 6 and 8 and was affected by waterstress; no germination was observed at osmotic potentials less than −0.2MPa. Seeds emerged from depths of at least 5 cm. Under field conditions,germination was reduced after burial; however, burial lengths of 3 to 15 modid not result in differences in germination levels. Seedling numbers fromseed deposits on the soil surface were greatly reduced after 1 mo, and noseedling emergence was observed after 4 mo.