What Is Weed Seed

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Weed communities in agronomic fields are dominated by annual species. Summer annuals initiate growth each spring from seeds found in the upper soil profile (Figure 1). In most fields, a small percentage of the emerging plants survive and contribute new seeds to the soil seedbank. Historically, most research of the annual weed life cycle has focused on seed dormancy and emergence (A), effect of control tactics on weed survival (B), and weed seed production (C). The fate of seeds between the time of maturation on the plant and entering the seedbank (D) has largely been ignored. Now is the time to think about controlling summer annual weeds prior to seed set in cropping situations where possible. Preventing seed production is important for driving down the weed seed bank and reducing the need for weed control inputs (i.e. herbici Difference between marihuana vs cannabis vs weed seeds Cannabis vs Marihuana vs Weed Seeds Marihuana seeds (often spelt as marijuana seeds) are the main method of propagating the cannabis

Weed seed predation in agricultural fields

Weed communities in agronomic fields are dominated by annual species. Summer annuals initiate growth each spring from seeds found in the upper soil profile (Figure 1). In most fields, a small percentage of the emerging plants survive and contribute new seeds to the soil seedbank. Historically, most research of the annual weed life cycle has focused on seed dormancy and emergence (A), effect of control tactics on weed survival (B), and weed seed production (C). The fate of seeds between the time of maturation on the plant and entering the seedbank (D) has largely been ignored. However, current research at Iowa State University and other organizations has shown that significant seed losses routinely occur in agronomic fields, and these losses may influence the effectiveness of weed management programs. This article will provide a brief summary of some of the current research in this area and the potential importance of seed predation to weed management.

Prairie deer mouse – a common seed predator.

Plant seeds are storage organs for high energy compounds that supply plant embryos the resources needed to germinate and develop into seedlings. These energy reserves are an excellent food source for a variety of animals that live in or near agricultural fields, including ground beetles (carabid beetles), crickets, mice and others. Estimates of cumulative seed losses due to seed predators have ranged from 20% for barnyardgrass and lambsquarter in a chisel plow system (Cromar et al. 1999) to 88% for giant ragweed in no-tillage (Harrison et al. 2003).

A common method of measuring seed predation involves lightly attaching seeds to sandpaper or a similar material and placing the seed cards in the field. After a few days the card is retrieved and the percentage of seeds removed is determined (Westerman et al. 2005). Averaged over 12 sampling periods from May through November, seed losses ranged from 7 to 22% per day depending on the crop present in the field in a study conducted near Boone, IA (Figure 2). The higher predation rates in small grain and alfalfa compared to corn and soybean may be due to differences in crop canopy development. The rate of seed predation typically increases as a crop canopy develops within a field. Corn and soybean canopies provide little protection for predators early in the growing season compared to small grain or alfalfa, and thus predators may seek other habitats when little canopy is present. Later in the season, predator activity is typically similar in corn and soybeans as in other field crops.

Insect predators (field crickets, ground beetles, etc.) are active during the growing season when temperatures are favorable for cold-blooded species, whereas field mice are active year round. Seed predators have a remarkable ability to locate seeds on the soil surface; however, once seeds move into the soil profile the threat of predation is greatly reduced. The highest rates of seed predation likely occur in late summer and early fall when weed seeds are shed from plants onto the soil surface. Tillage buries the majority of seeds at depths where predation is minimal. Avoiding or delaying fall tillage following harvest should increase seed losses due to predation. Seeds can also enter the profile due to the impact of rain droplets, by falling into cracks, or due to freezing/thawing cycles during the winter. Ongoing research at ISU is evaluating the fate of seeds on the soil surface and how long they remain available to predators.

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Field crickets on seed card.

The preference of predators for different species of weed seeds in the field is poorly understood. When given a choice, seed predators often will feed preferentially on one species over another (van der Laat et al. 2006; Figure 3). A common question is whether seed predators pose a threat to crop seed. Seed size and depth of planting minimize risks of corn and soybean seed losses to predators. Small-seeded legumes and grasses are at greater risk for predation losses, but proper planting where the majority of seed are placed under the soil surface should minimize losses.

Significant numbers of weed seeds are consumed by predators in agronomic fields, but the full impact of seed predation on weed densities and weed management is poorly documented. Clearly, destruction of a significant percentage of the weed seeds produced in a field will impact the following year’s weed density. The impact of giant foxtail seed rain and seed predation on giant foxtail densities was evaluated near Boone, IA (Figure 4). Giant foxtail seed (750 / sq ft) were spread on the soil surface in standing corn in late September 2004. The field was planted to no-till soybean in 2005 and foxtail emergence monitored throughout the season. The experimental area had a history of good weed control, thus foxtail densities were very low (

Modeling efforts at ISU have shown that seed predation can significantly affect long-term weed population dynamics within agricultural fields. For example, in a 4-year crop rotation (corn/soybean/small grain+alfalfa/alfalfa) the seed bank of giant foxtail rapidly increased from 2000 seed/m 2 to 4.3 million seed / sq m over an 18 year simulation period in the absence of predation (Figure 5). However, allowing for 25% seed predation resulted in a static seed bank, whereas any seed predation in access of 25% resulted in a decline in the seed bank density. The diverse rotation required 80% less herbicide than a conventionally managed corn-soybean rotation.

The value of intercepting weed seed before they enter the seed bank is somewhat of a forgotten control tactic. In the 1930’s and 40’s, combines were commonly equipped with a weed seed collector that separated and collected weed seed from chaff as the crop was harvested. When modern herbicides were introduced in the 1950’s, it was considered less expensive and more convenient to control weeds with chemicals, and these accessories quickly disappeared from combines. In Australia, seed collectors are again being used on combines due to widespread herbicide resistance and the loss of effective herbicides. Rigid ryegrass infestations have been reduced by as much as 70% through use of weed seed collectors during harvest (Gill, 1995). The effectiveness of weed seed collectors varies among weed species depending on timing of seed shed. Weed species that drop the majority of their seed prior to crop harvest would not be impacted significantly by use of weed seed collectors.

Weed seeds are an important food source for a variety of organisms that live within or adjacent to agricultural fields. It is clear that seed predation is an important form of biological control that influences weed communities within agricultural fields. Yet to be defined is how cropping systems can be manipulated to enhance the activity of seed predators and maximize their benefit, therefore allowing reductions in other more disruptive control tactics.

ISU research cited in this article was partially funded by:

The Leopold Center for Sustainable Agriculture

USDA National Research Initiative

References

Cromar, H.E, S.D. Murphyand C.J. Swanton. 1999. Influence of tillage and crop residue on postdispersal predation of weed seeds . Weed Sci. 47:184-194

Gill, G.S. 1005. Development of herbicide resistance in annual ryegrass in the cropping belt of Western Australia. Aust. J. Exp. Agric. 35:67-72.

Harrison , S.K., E.E. Regnier and J.T. Schmoll. 2003. Postdispersal predation of giant ragweed seed in no-tillage corn. Weed Sci. 51:955-964.

van der Laat, R., M. D.K. Owen and M. Liebman. 2006. Quantification of post-dispersal weed seed predation and invertebrate activity-density in three tillage regimes. J. Agric. Ecosys. Envir. Under review.

Westerman, P.R., M. Liebman, F.D. Menalled, A.H. Heggenstaller, R.G. Hartzler and P.M. Dixon. 2005. Are many little hammers effective? – Velvetleaf population dynamics in two- and four-year crop rotation systems. Weed Sci. 53:382-392.

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Weed Seeds This Fall Means More Weeds Next Spring

Control annual weeds now in fallow areas to prevent seed set. Also, now is the time to start considering ways to manage perennials in small grain stubble.

Control weeds before seed set. Photo credit: Penn State Weed Science, D. Lingenfelter

Now is the time to think about controlling summer annual weeds prior to seed set in cropping situations where possible. Preventing seed production is important for driving down the weed seed bank and reducing the need for weed control inputs (i.e. herbicides). It is rather easy to prevent weed seed production following a cereal grain such as wheat, barley, or oats as well as some vegetable crops such as sweet corn or snap beans. Proper timing of the control practice is essential in preventing seed production. In general, below is a summary of estimated seed drop for various weed species:

  • Giant foxtail: late August and peak seed rain usually occurs from late September through the month of October
  • Yellow foxtail: early August and continues into late October
  • Pigweed species: begin to produce mature seed by mid-August
  • Lambsquarters and ragweed: generally, do not mature until the month of September
  • Palmer amaranth or waterhemp: make sure to monitor them routinely over the next couple months and control any regrowth or new seedlings before they set seed. Palmer amaranth plants notoriously retain their seeds late into the summer and fall and thus seeds don’t necessarily fall to the ground upon maturity but are usually spread via the combine.

To prevent seed production, fields can be sprayed with an effective herbicide or mowed once or twice. Glyphosate is particularly effective at stopping grass growth and reproduction. The plant growth regulators (2,4-D and dicamba) would probably be a better choice for broadleaf weeds. With giant foxtail, even treating the field by mid-September can greatly reduce seed production. If seed heads are present, check suspect fields to determine how advanced flowering and seed rain are and time control practices accordingly. In alfalfa or pastures, if weeds are taller than the forage, consider running a brush-hog at a high setting to clip off the immature weed seed heads above the forage canopy. Taking the time to prevent seed production this year can make a big difference next year. About 80% of weeds next season come from weed seed this fall. For more information on weed emergence, weed seed set, and seedbank dynamics, refer to “A Practical Guide for Integrated Weed Management in Mid-Atlantic Grain Crops.”

In addition, many perennial broadleaves are evident in these same small grain stubble fields. The challenge with perennial weeds at this time of year is the fact they are still in the vegetative and reproductive phases. Therefore, most of the plant sugars are not being significantly transported to the roots and a herbicide application now will mostly only impact the top-growth. One consideration would be to mow those fields soon to prevent seed production and allow regrowth to occur. Then apply an effective systemic herbicide (ie, glyphosate, 2,4-D, dicamba) in late September or early October so the herbicide will be transported to the roots for more effective control.

Difference between marihuana vs cannabis vs weed seeds

Cannabis vs Marihuana vs Weed Seeds

Marihuana seeds (often spelt as marijuana seeds) are the main method of propagating the cannabis plant, although many private growers often distribute cuttings of prized strains. However many growers claim that they achieve the best results when growing from seed.

Marihuana seeds are produced when pollen from the male plants fertilises the female plants initiating the female plant to produce seeds. Marihuana seeds can then be planted and will themselves grow into mature cannabis plants allowing the reproductive cycle to repeat itself. The seeds will remain viable for a few years, and when stored in cool/dry conditions (such as a refrigerator) marihuana seeds will remain viable for many years though the germination rates will decrease over time.

In the 1980’s the Dutch cannabis industry took cannabis breeding and seed supply to new levels of professionalism and excellence. Dutch Passion were one of the first companies to begin expert cannabis breeding programs using qualified biologists and geneticists.

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Only the best cannabis genetics from around the world were used in these specialised breeding programs. The result for companies such as Dutch Passion was the creation of marihuana seeds that gave new levels of quality and consistency in the final strains.

Marihuana seeds normally produce roughly equal numbers of male and female offspring. However Dutch Passion was able to stun the cannabis world in the 1990’s when they began selling feminised marihuana seed technology. These new feminised seeds gave rise to 95%+ female plants, this had been a dream of cannabis growers for many years but was widely believed to be technically impossible. Today, feminised marihuana seeds are now more popular than traditional seeds as they allow the grower to produce only the desired female plants.

The widespread availability of high quality marihuana seeds allowed an explosion of small- scale growing. Cannabis supply was no longer a battle between large foreign export gangs and government border control guards. Cannabis supply was domesticated and many small growers could produce their own personal supply simply by purchasing marihuana seeds of their favourite varieties which could be grown outside, in greenhouses or indoors under grow lights.

Growing your own cannabis had just become easy, convenient and highly satisfying. Just a small amount of knowledge was needed to get the best results. Cannabis is not difficult to grow, it has adapted to many different growing conditions and is not called ‘weed’ without reason. It can grow just about anywhere.

What Are Weed Seeds

Weed seeds is a street name for cannabis (or marijuana) seeds. They are natures method of allowing the cannabis plant to be spread around the environment and regrow.

Weeds seeds can be legally bought and sold in certain regions e.g. large sections of Europe but remain illegal in other areas. Over the last 2-3 decades many professional weed breeders have dedicated their expertise to breeding the best yielding and most potent weed varieties they can. The seeds from these prize strains can then be distributed to head shops and growers around the world.

One result of the trade in weed seeds has been the incredible enrichment in the genetic diversity of cannabis. Rare Cannabis indica genetics from in accessible Himalayan valleys have now found their way into back gardens and greenhouses all over the world.

Exceptional Cannabis sativa genetics from the deepest Thai jungles have made their way to growrooms and greenhouses in Canada and Scandinavia. Sometimes these strains retain their purebred characteristics, and other times the strains have been carefully and painstakingly crossbred with other varieties creating precious new weed strains.

Dutch Passion, as one of the very first companies to start selling weed seeds in the 1980’s, have played an important role in the preservation and diversification of cannabis.

Weed seeds of different varieties may have subtle differences in appearance, but they all perform the same job. The seeds will swell in moist conditions during germination and over the period of a few days a seedling will emerge complete with roots and a first pair of leaves. Weed seeds can be germinated and grown in soil or any number of modern alternatives such as coco fibre, clay pellets, glass wool etc. Growing great weed these days is not at all difficult. Good light levels are needed for respectable yields, along with a suitable growing medium with enough nutrients and water. But the first job for any potential grower is finding a seed supplier that has the experience and know-how to equip you with the best weed seeds that nature can provide. Dutch Passions advice is to get the best seeds you can, start with quality genetics from a trusted source.

Thanks to professional breeders, the choice of varieties has never been greater but the choice can sometimes seem confusing. The cheapest weed seed suppliers are rarely the best, but if you are looking for great quality at an affordable price then Dutch Passion recommend you take a look at their seed collection.

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