Annual bluegrass (Poa annua L.) is an invasive weed producing copious amounts of viable seed that compete with seedling turfgrasses during renovation. These field studies were conducted to determine the effectiveness of dazomet (tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione), a granular soil sterilant that breaks down in soil to release methyl isothiocyanate (MITC), for controlling the soil seed bank of annual bluegrass during turfgrass renovation. Field trials in Urbana, Ill., and West Lafayette, Ind., in Spring and Fall 2000 and 2001 evaluated dazomet rate from 0 to 504 kg·ha-1 and soil preparation techniques to determine the most effective practices to reduce annual bluegrass reestablishment into a creeping bentgrass (Agrostis stolonifera L.) seeding. The interval, in days, between dazomet application and creeping bentgrass planting was also examined to determine the optimal seeding time as measured by the level of annual bluegrass reestablishment. Spring trials generally gave poor results that were attributed to windy conditions resulting in rapid loss of MITC. The annual bluegrass soil seed bank was reduced 46% in spring trials compared to 78% in fall trials. Increasing dazomet rates reduced the absolute number of viable annual bluegrass seeds remaining in the soil. However, significant quantities of viable seed remained, regardless of dazomet rate. Annual bluegrass infested the renovated turf in all trials to varying degrees. Dazomet rates of 420 or 504 kg·ha-1 yielded the lowest rates of annual bluegrass reestablishment. Trials conducted in the fall at these rates resulted in annual bluegrass cover of 1% to 20% in the resulting turf. Creeping bentgrass planted at 1 day after dazomet application had significantly less annual bluegrass than when seeded at 7 or 9 days after dazomet application. Dazomet is a tool that can help reestablish a new turf with lower levels of annual bluegrass. However, eradication of annual bluegrass with dazomet is not likely and environmental conditions will dramatically affect the success of the sterilization.
Depletion of the weed seed bank by stimulating germination during winter months and subsequently exposing the seedlings to adverse air temperatures is a possible means of controlling weeds in small-scale horticultural operations. Johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill], and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] were seeded in soil trays and maintained for 4 days at 4 or -12 °C, then heated to 32 °C for 4 days using electric heating pads. Germination percentages, after heating soils, were: 55% and 70% for hemp sesbania, 82% and 72% for barnyardgrass, and 45% and 55% for johnsongrass, respectively; for seeds kept at -12 and 4 °C, respectively. Subsequent exposure of seedlings to -12 °C for 7 days killed all seedlings, while exposure to 4 °C killed only 18% to 28%. The temperature regimes of -12 °C for 4 days, and 32 °C for 4 days followed by -12 °C killed 95%, 78%, and 68% of the johnsongrass, hemp sesbania, and barnyardgrass, respectively.
bank, likely due to the large number of weed seeds present in soil ( Hunter et al., 2016 ; Mashingaidze et al.,1996 ). For example, Rylander et al. (2020 ) determined that seed survival of the summer annual weeds powell amaranth ( Amaranthus powellii
at both locations in both years, indicating that there was a significant weed seedbank in the plots and the mulches indeed provided a barrier to weed emergence and/or growth. Other studies also have found that plastic BDMs controlled weeds equal to
The binational Southwest remains rich in native crop land races and crop wild relatives, despite numerous pressures favoring genetic erosion. Native Seeds/SEARCH is promoting in situ conservation in traditional Indian fields and nearby wild habitats, but also maintains a gene bank as a back-up, to allow future reintroductions. Seeds are distributed to Native American communities for free, and their value is reinforced through a variety of educational materials and presentations. Our regional focus allows us to serve as an effective bridge between in situ and ex situ conservationists, between Indian and international organizations, and between tribes. Methods, ethics and accomplishments to date will be highlighted.
The comparison of the electrophoretic patterns of seed polypeptides and basic proteins of 40 lentil germplasm accessions revealed a wide qualitative and quantitative variation that allowed the individual characterization of all the genotypes. The statistical analysis of the variation and the clustering of the samples by multivariate methods allowed the construction of five affinity groups that were consistent with the origin and genetic relationships among the accessions. These results indicate the reliability of this simple and inexpensive biochemical analysis in lentil germplasm bank management, cultivar identification and monitoring, and the construction of affinity groups that can help breeding programs.
Seldom are seeds harvested and immediately planted without undergoing at least a brief storage period. Exceptions would be certain seeds designated as “recalcitrant” (not readily storable) (45) which must be planted immediately, or viability is soon lost. Examples include many tropical plants as well as many of our temperate trees. The life span of these recalcitrant seeds may be of the order of a few days to several months (22). Another case where freshly harvested seeds may not undergo storage would be breeding materials where the object is to produce as many generations a year as possible. In this case, seeds are often harvested in an immature state and planted immediately. However, normally most seeds are stored several weeks or months before being planted. Longer storage periods, 1 to 5 years, are necessary for seeds which may be expensive or difficult to produce, or for those cultivars which are not produced every year due to lower demand by growers. Finally, germplasm banks, such as the USDA National Seed Storage Laboratory, may wish to preserve seeds for decades or even centuries (26).
Miscanthus sinensis was investigated where it has naturalized and invaded native plant communities in southeastern Pennsylvania, the Washington, D.C. area, western North Carolina, and Iowa. Plants were identified; inflorescences were collected; seed was cleaned and tested for viability; and soil was collected for seed bank analysis. Many individuals were interviewed at each location. Locations were mapped to show miscanthus. The species or “wild type” Miscanthus sinensis that has naturalized at the above locations is rarely sold in the nursery trade. The numerous, popular, ornamental cultivars derived from this species are vegetatively propagated clones that are common in the nursery trade. Miscanthus is self-incompatible and sets seed only when two or more genotypes are grown together. Individual isolated plants set little seed. Plants of the wild type which have naturalized each represent a unique individual or genotype and thus set heavy seed, quite different from ornamental cultivars. Further complicating this is the high variability of seed set due to environmental conditions. Management guidelines were developed along with recommendations which include: Do not plant the species Miscanthus sinensis. Cultivars of the species, especially when two are more are grown together, represent a high risk for self-seeding in the Mid Atlantic states. Cultivars should only be planted in areas where they can be watched and managed for self-seeding. No miscanthus should be planted where it can seed into native areas, such as highways, fields, meadows, or wooded areas. A comprehensive website with identification, pictures, management guidelines, and recommendations was developed: http://horticulture.coafes.umn.edu/miscanthus.
Much emphasis has been placed on the need to preserve plant genetic resources (13, 17, 18, 28, 31, 50). As a reuslt, the number of accessions added to gene banks around the world has risen dramatically over the past 10 to 12 years. The International Board for Plant Genetic Resources (IBPGR), during its first decade of work (1974–84), arranged for the collection of ≈ 121,000 samples of germplasm from more than 90 countries around the world (19). At the USDA National Seed Storage Laboratory, accessions in storage have increased from 91,000 in 1976 to more than 204,000 in 1986. These accessions represent ≈370 genera and 1960 species. The large influx of samples during recent years has placed greater responsibility on germplasm curators to ensure that samples are properly handled, including periodic germination testing and regrowing of samples when needed.
A question/answer discussion session was conducted at the conclusion of the workshop “Pest Management During Transition to Organic Farming Systems”. The following categories were used to summarize the discussion: 1) questions and answers related to cultural and biological practices and their effects under various climatic conditions, 2) recommendations for pest management, and 3) future research needs. While many tactics are available, selecting and adopting the most suitable approach depends on soil conditions of the land, location, and the availability of the resources at affordable prices. Definitely, more research studies are needed on 1) weed seed banks under various cultural practices at different regions, 2) relationships between soil nutrients, and pest control, and 3) approaches to increase profitability of organic production during the transition period.