By: Jackie Carroll
Shepherd’s purse weeds are among the most plentiful prolific weeds in the world. No matter where you live, you won’t have to travel far from your door to find this plant. Find out about controlling shepherd’s purse in this article.
Shepherd’s purse gets its name from the resemblance of its seed pods to purses once carried by shepherds in Europe and Asia Minor. When the heart-shaped pods burst open, they release seeds that are carried by the elements and on the coats and feathers of animals to far-flung areas. The seeds remain viable for a long time, and they germinate easily once they come in contact with soil. One of the challenges of shepherd’s purse control is dealing with a new crop that germinates from seeds each fall.
A member of the mustard family, shepherd’s purse is an edible plant that adds a peppery flavor to salads and stir-fries, and it is an important part of Chinese cuisine. Even so, it’s not a good idea to plant or cultivate shepherd’s purse. It is very difficult to eliminate from an area, and it will infest surrounding areas as well.
Shepherd’s purse weeds have an unusual way of obtaining nutrients when they live in nutrient-poor areas. Moistened seeds release a substance that entraps and digests insects. As the insect breaks down, it provides nutrients that feed the seedling. So is it a carnivorous plant? Although it’s hard to see the difference, scientists prefer to call it a protocarnivore.
When shepherd’s purse seeds germinate in fall, the plant forms a little rosette of leaves that remains flat on the ground. In late winter or spring, the plant sends up a flower stem that will hold several small, pale pink flowers. They can bloom again later in the year when conditions are favorable.
When you find shepherd’s purse in your garden, the best way to control it is to pull it up. The herbicides and cultivation techniques used to control it can also kill desirable garden plants. Frequent mowing doesn’t help with the control of this weed because it grows so close to the ground.
In lawns or open areas, you can use post-emergent herbicides. These herbicides kill weeds after the seeds germinate and the plant begins to grow. Look for a post-emergent labeled for use against shepherd’s purse. You’ll get good results from an herbicide that contains 2, 4-D and MCCP. Follow the package instructions carefully. Success depends on paying close attention to the conditions favorable for spraying.
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No one likes to talk about weeds, but some plants compete with your garden for nutrients, water, and light, as well as harbor diseases and pests. Here are 13 of the most common weeds found in gardens and lawns—with weed identification pictures and tips on how to manage their growth.
There are different types of weeds. Here are definitions from the Weed Science Society of America:
Keep in mind: Of approximately 250,000 species of plants worldwide, only about 3% behave as weeds that we don’t want in cultivated areas. “Weeds” aren’t inherently bad. Many weeds stabilize the soil and add organic matter. Some are edible to humans and provide habitat and food for wildlife, too. See “ Eating Weeds: Why Not? ”
The best control strategy for weeds is always prevention. Before resorting to herbicides, look first to nonchemical weed control methods. Why? Herbicides may be a quick fix this year but will not keep your weed problem from recurring year after year. Only taking preventitive controls will reduce the weed problem in the future.
Never let ‘em seed! This is the #1 rule with weeds. Some varieties produce tens of thousands of seeds from a single plant, multiplying your weed control problems for years to come. So make certain you remove weeds around your home before they flower and produce seeds.
Pay special attention to perennial weeds. Perennial weeds (versus annuals) are more difficult to control. You need dig up any roots, underground tubers and rhizomes without leaving fragments behind. New weeds can grow from any pieces that break off and remain in the soil.
With these techniques, you’ll soon find that you won’t spend much time weeding the following years!
This European native occurs in waste places, roadsides, pastures, gardens, lawns, and almost any open or disturbed habitat. Like the common dandelion, this plant traveled with European explorers and settlers throughout the world. Because of its small size and shallow root system, it is not as troublesome a weed as some others. This is the only species in its genus, worldwide.
The young leaves and fruits are rich in vitamin C and are esteemed in salads. Poultry relish this plant, too! Many medicinal uses have been recorded for shepherd's purse, as well, and some herbalists value it today.
Today, you would have to look hard to find a sheep herder who uses a triangular bag shaped like the fruit of this plant, but the name goes back to such medieval fashions.
Shepherd’s purse has many adaptations that make it a successful "weed," a quick colonizer of disturbed soils: The flowers can self-fertilize, and the plant keeps blooming all year. A single plant can produce 90,000 seeds in its year of life. The seeds are tiny and sticky, which aids in their dispersal.
Our data have demonstrated that primary dormancy was marginal and did not differ between the TTF in-field genotypes of shepherd's purse (Fig. 2). On the other hand, secondary dormancy was obtained easily and was much stronger than primary dormancy (Fig. 3). There was weaker secondary dormancy in seeds from early TTF genotypes (Fig. 4). Thus, time to germination and time to flowering seem to have co-adapted. The long-lived character of the shepherd's purse seeds in the soil suggests that genotypic differences in secondary dormancy are more relevant than primary dormancy for the life-history characteristics of this species ( Darlington and Steinbauer, 1961). Our principal findings are that the depth of secondary dormancy (and the response to nitrate) localizes the seeds of the early reproducing genotypes to a single, weak dormancy, functional group (FG-III) that is distinct from seeds of the later (intermediate and late) reproducing forms (Fig. 6). Two other categories of non-myxospermous (FG-II) and myxospermous (FG-I) seeds are functionally distinct, so that both intermediate- and late-reproducing genotypes possess seeds with weaker (non-myxospermous) and stronger (myxospermous) secondary dormancy. The production of FG-I seeds that express a stronger secondary dormancy could partially mitigate the risks associated with the less structured behaviour of seeds associated with later flowering types. However, the later flowering plant types also produce FG-II, i.e. weaker dormant, seeds. Although these seeds are at risk of not reproducing, as the seedlings produced are potentially all exposed to a single catastrophic event, their presence reduces the negative aspect of dormancy, which is a reduction in mean fitness for the genotype, and provides an opportunity to form a biennial life cycle. Although our results confirm a role for nitrate in induction of germination upon seed dormancy release in shepherd's purse ( Popay and Roberts, 1970), we highlight the importance of intraspecific assessments of functional variation the depth of dormancy differs between and within TTF genotypes of the species. Secondary dormancy in genotypes of FG-III (the early TTF group) is sufficiently weak to result in germination with light (and water) alone, reflecting a high level of nitrate-independence and making these genotypes physiologically distinct from the later TTF genotypes.
The studied UK genotypes seem to behave differently from those from Sweden, where considerable primary dormancy was observed ( Baskin et al., 2004). They also behave differently from a UK accession described by Popay and Roberts (1970), which displayed strong primary dormancy. This difference possibly reflects an adaptation to the different climatic conditions or, alternatively, the reduced primary dormancy in the studied UK genotypes is an adaptation to arable fields. Furthermore, the predominance of the early-flowering genotypes that produce FG-III seeds within arable fields across the UK ( Iannetta et al., 2007) suggests that reduced secondary dormancy combined with rapid reproduction is the preferred strategy in this environment. Like time to flowering, dormancy is an important adaptive strategy in weeds faced with environmental stochasticity, allowing populations to spread the risk of future disturbance and avoid annihilation as a consequence of a single, pre-reproduction, field-wide disturbance event ( Childs et al., 2010). In genotypes producing the FG-III seeds, the combination of rapid germination prior to the application of nitrogen fertilizer and crop establishment and subsequent early flowering is likely to increase the probability of successful reproduction. Success of this strategy is consistent with a diminished requirement for dormancy. The ‘weediness’ ( Baker, 1974) of early-flowering genotypes that combine high fecundity ( Iannetta et al., 2007) and weak secondary dormancy with early flowering is consistent with an r-selected life-history strategy that is well adapted to frequent disturbance ( Begon et al., 1986). Such r-strategists direct resources to reproduction as opposed to somatic output and this improves the likelihood of persistence in environments that are time limited by major events such as ploughing, herbicide application or harvest. Genetic evidence for the association of seed dormancy, seed fecundity and TTF was provided by Huang et al. (2010) in A. thaliana, a species that is phylogenetically closely related to shepherd's purse, and was further associated with plant lifetime fitness.
Myxospermy appears to form a component of the dormancy bet-hedging strategy ( Rees et al., 2006 Childs et al., 2010). Seed heteromorphism has been described for species in a limited number of families, including the Brassicaceae ( Sorensen, 1978). The production of heteromorphic seeds was thought to broaden the range of conditions required for germination and subsequent plant growth, increasing the chances of reproduction ( Fenner and Thompson, 2005). Seed heteromorphism was described to coincide with different germination and soil persistence strategies in Atriplex species ( Carter and Ungar, 2003). Heteromorphic shepherd's purse seeds in this study reflect seed classes whose dormancy behaviour is underpinned by particular physiological and biochemical states ( Bewley and Black, 1994). A similar colour heteromorphism in Sisymbrium officinale also revealed a non-myxospermous and myxospermous fraction. However, the latter fraction was associated with high quality while the former fraction displayed low viability ( Iglesias-Fernandez et al., 2007), which contrasts with the high viability of the non-myxospermopus shepherd's purse seeds.
Within-field arable weed populations are typically presented with narrow windows for growth that result from competition with crop plants for light and nutrients, and by herbicide and tillage regimes. The difference in 100-seed weight of the myxospermous and non-myxospermous seeds appeared to reflect differences in seed filling, with a lower mass for non-myxospermous seeds. However, the carbon content did not differ between TTF categories or myxospermy types, indicating similar seed filling and maturity. Early-flowering genotypes demonstrated the capacity to partition nitrogen resources to their seeds with greater efficiency than the later flowering forms and non-myxospermous seeds partitioned more nitrogen than myxospermous seeds (Table 1). The trend of increased seed resources being linked to weaker dormancy is also a characteristic of domesticated species and is probably the result of faster seed filling combined with unperturbed development we may therefore postulate that such attributes are pleiotropic. The counterintuitive higher nitrogen content in seeds with a lower mass is probably due to selectively stronger nitrogen partitioning.
The results reported here provide evidence that flowering time and seed secondary dormancy are synergistic traits in shepherd's purse. Primary dormancy and flowering time traits have also been linked at the molecular level in the related species A. thaliana ( Colucci et al., 2002 Chiang et al., 2009), and Flowering Locus C (FLC) was proposed as a key gene in the control of seed dormancy ( Chiang et al., 2009). Flowering time variation in shepherd's purse has also been attributed to differences in FLC ( Slotte et al., 2009). In addition, H2B deubiquitination is involved in the control of seed dormancy ( Liu et al., 2007) and flowering through the same gene FLC ( Cao et al., 2008 Schmitz et al., 2009). Thus, it seems reasonable to presume that the observed concurrence of variation in flowering time and seed dormancy in shepherd's purse genotypes is the result of a genetic or epigenetic event. Three functionally distinct clusters were also identified for shepherds purse on the basis of flowering time and other (non-seed) traits which further supports the hypothesis that the genetic control of key life-history traits differs significantly among the intraspecific forms ( Iannetta et al., 2007). More work is required to unravel the molecular mechanisms that underlie the link between flowering time, seed dormancy and other life-history traits in shepherd's purse.
In conclusion, the correlation between seed secondary dormancy and flowering time in the seeds of shepherd's purse indicates the pivotal role of the earliest life-history stage in the determination of time to reproduction. Weaker dormancy in the seeds of early-flowering forms confers a selective advantage in the extreme selection pressures of the arable environment, and determines plant persistence and coexistence.