The dispersion of ethylene in the soil after application from a backpack ethylene applicator (BPEA) was determined using a bioassay of witchweed [Striga asiatica (L.) Kuntze # STRLU] seed germination. Witchweed seed were buried in packets in ridged seedbeds under field conditions. Ethylene dispersion was better when injected into the furrow than into the ridge top. Injections 30 cm deep were more effective in causing seed germination than injections 15 cm deep. Seed germination induced by ethylene injection into the furrow 30 cm deep was 13% more than that obtained from the ridge top injection 15 cm deep. Seed germination as high as 90% was obtained at soil depths to 75 cm at a horizontal distance of 100 cm from the point of ethylene injection. Ethylene diffused up to 300 cm horizontally and to 75 cm vertically to cause at least 45% seed germination in a field of Lakeland soil (Typic Quartzisamment). The BPEA was found to be an effective application tool in witchweed control operations.

New or recently introduced weeds are biological pollutants in our natural and agricultural ecosystems. Unlike chemical pollutants, new weeds left unchecked often proliferate and pose problems that may not become apparent until eradication is too expensive or impractical. Management strategies for weeds should include: 1. prevention (from entering foreign commerce); 2. exclusion (detection of weed contaminants in imported products at ports of entry); 3. detection, containment, and eradication of incipient infestations; and 4. perpetual control (of widespread species that cannot otherwise be addressed). Appropriate legislative authority, modern weed technology, funding, and a renewed commitment to the concept of prevention are needed to prevent the introduction of new weeds. A national initiative to prevent the establishment of new weeds would be beneficial by saving on future losses and perpetual control costs. Actions taken now will prevent the continued introduction and spread of new weeds in the United States.

Ethylene-stimulated germination of witchweed [Striga lutea Lour. = S. asiatica (L.) O. Ktze.] seed first occurred after 13, 10, 6, 3, and 2 days of conditioning in moist sand at day/night temperatures of 20/14, 23/17, 26/20, 29/23, and 32/26 C, respectively. Maximum germination percentages in these regimes were 0.5, 3, 20, 24, and 37%, respectively. No germination occurred at 17/11 C. Witchweed seed survived in sand frozen for 7 weeks at −7 or −15 C and subsequently germinated in response to ethylene or in the presence of corn (Zea mays L., ‘DeKalb B73 × Mo.17H′) roots. The parasites emerged from the soil and flowered when maintained at 29/23 C after the termination of the freezing treatments. In other experiments, witchweed parasitized corn and/or sorghum [Sorghum bicolor (L.) Moench ‘DeKalb E-59+′] root systems in a sandy loam under 26/17, 26/20, 29/20, 32/23, and 32/26 C day/night regimes. Witchweed emerged from the soil with 26/20, 29/20, 32/23, and 32/26 C and flowered with 26/20, 32/23, and 32/26 C day/night regimes. Underground development and subsequent emergence of the parasites were substantially reduced with day/night temperatures below 29/20 C. Winter soil temperatures and growing season soil and air temperatures are unlikely to limit the spread of witchweed into important corn- and sorghum-producing areas of the United States.

Striga asiatica (Scrophulariaceae) is an obligate root hemiparasite of mainly C4 grasses (including cereals). It is the most widespread of the 42 Striga species occurring in many semi-tropical, semi-arid regions of mainly the Old World. Examination of herbaria specimens revealed that S. asiatica has a wider geographical distribution, is present at higher altitudes and occurs in a more diverse range of habitats than previously reported. The host range is also larger than previously reported and is likely to include a large number of C3 plants. Morphology of examined specimens revealed variation in size and corolla colour suggesting the existence of ecotypes. Climate may exert a significant influence on the distribution of S. asiatica given the diversity of potential host plants and their distribution beyond the current recorded range of S. asiatica.