Weed With A Lot Of Seeds

JSTOR is a digital library of academic journals, books, and primary sources. Small but mighty, weed seeds in manure can be problematic when they result in overgrown, weedy fields after manure application. Some manures can be a source of these troublesome weed seeds. But, luckily, there are some measures that can be taken to reduce the viability of those weed seeds. Virginia Law Creating a Report: Check the sections you’d like to appear in the report, then use the “Create Report” button at the bottom of the page to generate your report. Once the report is

Weed With A Lot Of Seeds

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Managing Weed Seeds in Manure

Small but mighty, weed seeds in manure can be problematic when they result in overgrown, weedy fields after manure application. A survey found that fresh manure on dairy farms had an average of 75,000 seeds per ton. But, luckily, there are some measures that can be taken to reduce the viability of those weed seeds.

First of all, don’t assume that animal digestion will take care of the problem. Though it will reduce weed seed viability, simply feeding the material to livestock will not eliminate all seeds. Grass and soft-coated broadleaf weed seeds are more easily destroyed in digestion than hard-coated seeds. In a study conducted on rumen animals, such as cattle, 27% of hard-coated seeds remained viable after digestion. The gizzard digestive system of poultry is highly effective at destroying weed seeds, and only 3.5% of hard-coated seeds fed to ducks were recovered and found viable in a similar study.

So what can you do to reduce weed seed viability beyond the gut? In general, heat is the enemy of weed seed survival. The benchmark for good seed mortality is 140⁰F (60⁰C) sustained for three days. Hot temperatures that fall below that mark or a shorter duration will still kill some weed seeds, but not as thoroughly. How you subject the weed seeds to heat is up to you, but below are a few suggestions.

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Minimize weed seeds in feed and forage by ensiling

What goes in, must come out; so killing seeds before they get to the animal is a good strategy. One way to do that is to ensile the feed (if appropriate for the feed type). The fermentation and heat generated during ensiling is quite effective for killing weed seeds. One study found that just one month after seed-contaminated alfalfa haylage was stored, viability of the toughest seeds dropped by 41%; and in corn silage, the drop was even greater at 60%. Logically, seed viability continues to decrease as silage storage time increases. Eight weeks of ensiling was shown to kill up to 87% of viable seeds; and when feed went through both ensiling and rumen digestion, the seed mortality increased to 89%.

Minimize weed seeds in manure by composting

What if ensiling isn’t feasible? What if your manure is already contaminated with weed seeds? In those cases, composting is a very effective method for killing weed seeds – more effective than ensiling.

Internal heat generated by properly composting manure will kill most weed seeds – even the hard-seeded weeds. The key word here is “properly.” Aged manure is not composted manure. I’ll say it again: aged manure is not composted manure. Proper composting requires active management and must be monitored and aerated for correct weed-killing conditions to develop.

Temperature and moisture are the two most crucial elements for seed mortality in compost. Studies have shown that sustaining the compost at that benchmark of 140⁰F for three days can reduce weed seed viability 90-98%, so long as a minimum of 35% moisture is maintained. Another study found that overall duration was important and that it took between 21 and 50 days of composting for best results.

Even under the most diligent composting program, there can be seeds that survive. It is theorized that since manure is not a uniform product, this mortality escape is due to cooler pockets that do not sustain high temperatures for long enough. Therefore, just because manure has been composted does not necessarily mean it is weed seed free.

Field application of contaminated manure

Remember, even if the feed was ensiled and the manure was composted before spreading, it’s still possible for weed seeds to remain viable. A 98% reduction in viability seems sufficient, but even low seed survival rates can be problematic. A 2% survival of 75,000 seeds would leave 1,500 viable seeds remaining per ton. Applied at 8 tons per acre, that would increase the weed seedbank by 12,000 seeds per acre! Therefore, it is crucial to scout fields that receive manure to head off any severe weed infestation.

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Watch for a second article on “Palmer amaranth Seeds in Manure – What Can You Do?” later in October.

Additional Reading

Cudney, D., Wright, S., Schultz, T., and Reints, J. 1992. Weed seed in dairy manure depends on collection site. California Agric. 46:31-32. http://calag.ucanr.edu/Archive/?article=ca.v046n03p31

Larney, F. and Blackshaw, R. 2003. Weed seed viability in composted beef cattle feedlot manure. J. Environ. Qual. 32:1105-1113. https://www.researchgate.net/publication/10706540_Weed_Seed_Viability_in_Composted_Beef_Cattle_Feedlot_Manure

This article was reviewed by Amit Jhala, University of Nebraska-Lincoln Extension Specialist and Ron Seymour, Nebraska Extension Educator

Virginia Law

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Virginia Administrative Code
Title 2. Agriculture
Agency 5. Department of Agriculture And Consumer Services
Chapter 390. Rules and Regulations for the Enforcement of the Virginia Seed Law

2VAC5-390-20. Noxious weed seeds.

Noxious weed seeds as defined in the Virginia Seed Law, Article 1 (§ 3.2-4000 et seq.) of Chapter 40 of Title 3.2 of the Code of Virginia are divided into two classes:

A. Prohibited noxious weed seeds are:

Balloonvine – Cardiospermum halicacabum

Canada thistle – Cirsium arvens

Field Bindweed – Convolvulus arvensis

Johnsongrass, Sorgrass and, Sorghum almum, and hybrids derived therefrom – Sorghum spp. – Perennial

Plumeless thistles, which includes Musk thistle, and Curled thistle – Carduus spp.

Quackgrass – Agropyron repens

Serrated tussock – Nassella trichotoma

Sicklepod – Cassia tora

B. Restricted noxious weed seeds are:

1. Restricted noxious weed seeds for agricultural and vegetable seed, except for lawn and turf seed and mixtures thereof, shall be prohibited from sale for seeding purposes if the number per ounce or per pound of such noxious weed seed found exceeds the limitations allowed for each. Such weed seeds and limitations shall be:

Wild onion bulblets and wild garlic bulblets – Allium spp.

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5 per ounce or 80 per pound for orchardgrass; 2 per ounce or 32 per pound for other kinds

Dodder – Cuscuta spp.

4 per ounce or 64 per pound

Wild mustard – Brassica spp. – includes species when incidentally occurring in agricultural seed, provided that species listed in 2VAC5-390-50 and 2VAC5-390-90 may be sold as such when labeled as required.

5 per ounce all or 80 per pound

Giant foxtail – Setaria faberi

4 per ounce or 64 per pound

Radish – Raphanus spp.

1 per ounce or 16 per pound

2. Restricted noxious weed seeds for lawn and turf seed and mixtures thereof. Those kinds listed below shall be restricted noxious weed seeds and shall be declared on the label under the heading “Noxious weed seeds” or “Undesirable grass seed” according to § 3.2-4008 J 5 when present in bentgrasses, Kentrucky bluegrass, chewings fescue, red fescue, hard fescue, varieties of perennial ryegrass, varieties of named turf type tall fescue, and/or mixtures containing these grasses. Such weed seeds are:

**Bentgrasses (creeping, colonial, velvet)

**Bermudagrass, Giant bermudagrass

**May be included as a labeled component of a mixture when in excess of 5.0% of the whole.

NOTE – EXEMPTIONS – This chapter does not apply to restricted noxious weed seeds in grasses or mixtures clearly labeled for pasture, forage, hay, or spoilbank reclamation usage.

§ 3.2-4001 of the Code of Virginia.

Derived from VR115-04-09 § 2, eff. November 13, 1985; amended, Virginia Register Volume 2, Issue 4, eff. December 24, 1985; Volume 2, Issue 17, eff. June 25, 1986; Volume 3, Issue 1, eff. November 12, 1986; Volume 7, Issue 7, eff. January 31, 1991; Volume 25, Issue 11, eff. March 4, 2009; Errata, 25:13 VA.R. 2566 March 2, 2009.

Website addresses provided in the Virginia Administrative Code to documents incorporated by reference are for the reader’s convenience only, may not necessarily be active or current, and should not be relied upon. To ensure the information incorporated by reference is accurate, the reader is encouraged to use the source document described in the regulation.

As a service to the public, the Virginia Administrative Code is provided online by the Virginia General Assembly. We are unable to answer legal questions or respond to requests for legal advice, including application of law to specific fact. To understand and protect your legal rights, you should consult an attorney.