It’s All About the Weed Seedbank – Part 1: Where Has All the Marestail Gone?

Source: Mark Loux

For the second year in a row, we are scrounging to find enough marestail at the OARDC Western Ag Station to conduct the research we had planned on this weed.  After years of having plenty of marestail, we have had to look around for off-site fields where there is still a high enough population.  Which, since we are scientists after all, or at least make our best attempts, left us thinking about reasons for the lack of marestail, and our overall marestail situation, and seedbanks.

While the short game in weed management is about getting good enough control to prevent weeds from being a yield-limiting factor and interfering with harvest, the long game is about preventing seed production and managing the soil seedbank.  One of the characteristics shared by marestail, giant ragweed, and the nasty pigweeds, waterhemp and Palmer amaranth, is a rapid decline in seed viability in the soil within the first year, and an overall decline to 5% or less viable seed within 3 to 4 years.  Another characteristic of marestail and pigweed seed is a relative lack of dormancy, which results in the potential for an almost immediate increase in population the year following a year of substantial escapes and seed production.  How big that increase is depends upon how many plants go to seed and how many seeds are produced per plant, with the potential of up to about 200,000 seeds per marestail plant and one million per waterhemp or Palmer amaranth plant.  The net result of these two characteristics, though, is that these weeds can ramp up population fast following a year of poor control, but populations can also decline rapidly with good control that prevents seed.

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The LL-GT27 soybean – what’s legal?

Source: Dr. Mark Loux, OSU Extension

We are starting to see the availability of soybean varieties with more than two herbicide resistance traits, which can expand the herbicide options, improve control, and allow multiple site of action tank mixes that reduce the rate of selection for resistance.  One of these is the Enlist soybean, with resistance to glyphosate, glufosinate, and 2,4-D.  As of this writing, full approval for the Enlist soybean is still being held up by the Philippines (because they can apparently).  The other is the LL-GT27 soybean, which has resistance to glyphosate, glufosinate, and isoxaflutole (Balance).  There is no label for use of isoxaflutole on this soybean yet, but it is legal to apply both glyphosate and glufosinate.  In Ohio, as long as neither label prohibits applying a mixture of two herbicides labeled for a specific use, it’s legal to apply the mixture.  So, it’s also legal to apply a mixture of glyphosate and glufosinate to the LL-GT27 soybean.  There is no label that actually mentions or provides guidance for this mixture, which does not affect legality, but could affect who assumes liability for the recommendation to apply a mixture if that matters to you.  Some seed companies are making the recommendation for POST application of the mix of glyphosate and glufosinate to the LL-GT27 soybean in printed materials.  Our interpretation after discussion with ODA, is that these materials are essentially supplements to labels, and so the seed company would assume some liability for the recommendation.

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Changes Made to Ohio’s Prohibited Noxious Weeds List

Source: Peggy Kirk Hall, Associate Professor, Agricultural & Resource Law (edited)

Palmer Amaranth

New changes to Ohio’s prohibited noxious weeds list took effect Friday, September 14th.  The Ohio Department of Agriculture (ODA) added 13 new species to the list, and removed 3 species.

On this blog, throughout the spring and summer I posted information and identification tips on each of the 21 Ohio noxious weeds.  This information can be easily found by typing “noxious weeds” in the Search this blog… box found on any page within our blog.  In the upcoming weeks, I will add similar posts for each of the new weeds added to this list.

Added to the list of prohibited noxious weeds are:

  • Yellow Groove Bamboo (Phyllostachys aureasculata), when the plant has spread from its original premise of planting and is not being maintained.
  • Field bindweed (Convolvulus arvensis).
  • Heart-podded hoary cress (Lepidium draba sub. draba).
  • Hairy whitetop or ballcress (Lepidium appelianum).
  • Perennial sowthistle (Sonchus arvensis).
  • Russian knapweed (Acroptilon repens).
  • Leafy spurge (Euphorbia esula).
  • Hedge bindweed (Calystegia sepium).
  • Serrated tussock (Nassella trichotoma).
  • Columbus grass (Sorghum x almum).
  • Musk thistle (Carduus nutans).
  • Forage Kochia (Bassia prostrata).
  • Water Hemp (Amaranthus tuberculatus).

Removed from the list are:

  • Wild carrot (Queen Anne’s lace) (Daucus carota L.).
  • Oxeye daisy (Chrysanthermum leucanthemum var. pinnatifidum).
  • Wild mustard (Brassica kaber var. pinnatifida).

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Harvest Considerations to Reduce Weed Seed Movement

Source: Iowa State University Extension

Weed seed spread by a combine

Harvest is just around the corner for many Iowa farmers and now is a good time to consider options to reduce movement of weed seed between fields with harvest equipment. While we may not think of it during harvest time, combines are extremely effective at transporting seed from field to field. A few precautions leading up to harvest and during harvest can help manage any escaped problem weeds.

Prior to harvest, scout fields for escaped weeds since weeds are easier to see after crops have matured. This is important to identify problem fields or areas for next year. Your notes about weed problems are critical to choosing effective management tactics for next year, so make this a priority prior to harvest. In some situations scattered weeds could be removed from the fields prior to harvest. It is much easier to manage weed issues before they drop mature seed or before that mature seed goes through a combine.

… Click here to see full article

Palmer Amaranth – Remain Vigilant!

As weeds continue to rear their ugly heads above the soybean canopy, it is important to remain vigilant and continue scouting your corn and bean fields on a regular basis.  We are seeing many weeds, Palmer Amaranth, Marestail, Waterhemp, Pigweed, Ragweed (Giant & Common), and various grassed, just to name a few.

Marestail, Palmer Amaranth and 19 other weeds are on the Ohio Noxious weed list. This designation requires that the landowner Public or Private MUST control these evasive weeds.  See earlier posts in this blog for more information on each of the 21 noxious weeds in Ohio.

Need help to identify weeds? As you scout your fields and you come across a weed that you’re not sure about; Is it Pigweed, Is it Waterhemp, Or is it Palmer.  If you are not sure call me at 740-397-0401 and I will be happy to help you with the identification. Visit our Knox County Extension YouTube channel (Click Here) for locally produced videos an how to identify and control this devastating weed.  Additional resources for Palmer Amaranth can be found on the OSU Weed Management Blog (Click Here).

Palmer Amaranth may very well be the most devastating pest you have/will ever encounter. Soybean yield losses approaching 80% and corn yield losses exceeding 90% have been reported.  A single female plant can produce up to 1,000,000 seeds and these seeds can remain viable in the soil for many, many years.  As Dr. Mark Loux states “Waterhemp and Palmer Amaranth will have more impact on the profitability of your farm operation than probably any other weedPalmer Amaranth, in the south, essentially doubled the herbicide costs in beans.” Remember, weed seeds are easily spread within a field and from field to field during harvest.

It is Your Farm, Your Field, Your Operation, Your Future – Protect it by keeping a watchful eye on your fields!

No Pigweed Left Behind – Late-Season Scouting for Palmer Amaranth and Waterhemp

by: Mark Loux

If you don’t already have to deal with waterhemp or Palmer amaranth, you don’t want it.  Ask anyone who does.  Neither one of these weeds is easy to manage, and both can cause substantial increases in the cost of herbicide programs, which have to be constantly changed to account for the multiple resistance that will develop over time (not “can”, “will”).  The trend across the country is for them to develop resistance to any new herbicide sites of action that are used in POST treatments.  Preventing new infestations of these weeds should be of high priority for Ohio growers.  When not adequately controlled, Palmer amaranth can take over a field faster than any other annual weed we deal with, and waterhemp is a close second.  Taking the time to remove any Palmer and waterhemp plants from fields in late-season before they produce seed will go a long way toward maintaining the profitability of Ohio farm operations.  There is information on Palmer amaranth and waterhemp identification on most university websites, including ours –  u.osu.edu/osuweeds/ (go to “weeds” and then “Palmer amaranth”).  An excellent brief video on identification can be found there, along with a fact sheet.  The dead giveaway for Palmer amaranth as we move into late summer is the long seedhead, and those on female seed-bearing plants are extremely rough to the touch.

If you need help with identification, call John at 740-397-0401.

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Ohio Noxious Weed Identification – Week 21 Palmer Amaranth

Palmer Amaranth

FamilyPigweed, Amaranthaceae.

Habitat: Crop fields, pastures, and roadsides.

Life cycle: Summer annual.

Growth habit: Erect up to 6 ft. high.

Leaves: Prominent white veins on the undersurface unlike redroot pigweed, not pubescent, alternate, without hairs (glabrous), and lance or egg-shaped.  Leaves are 2 to 8 inches long and 1/2 to 2 1/2 inches wide with prominent white veins on the undersurface.  Leaves occur on relatively long petioles.

Flower: Small, green, inconspicuous flowers are produced in dense, compact, terminal panicles that are from 1/2 to 1 1/2 feet long. Smaller lateral flowers also occur between the stem and the leaf petioles (leaf axils).  Male and female flowers occur on separate plants. Each terminal panicle contains many densely packed branched spikes that have bracts that are 3 to 6 mm long; can produce 500 thousand to 1 million seeds per plant.

Roots: Taproot that is often, but not always, reddish in color

Stem: One central stem occurs from which several lateral branches arise.

Similar Plants: Loosely resembles many other pigweed species. Palmer’s petioles are as long or longer than the actual leaf. This plant is hairless and has elongated seed heads. Leaves are typically more diamond shaped than other pigweed species, and occasionally has one hair at the tip of the leaf.

The Problem is……..Palmer amaranth is one of the most difficult weeds to control in agricultural crops.  It developed a major glyphosate resistance problem in the southern US from 2006-2010, and has been spreading in the midwestern US since, causing crop loss and increases in weed management costs. Characteristics that make it a successful annual weed include: rapid growth rate; wide window of emergence (early May through late summer); prolific seed production (upwards of 500,000 seeds/plant); tendency to develop herbicide resistance; and tolerance to many post-emergence herbicides when more than 3 inches tall.

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Ohio Noxious Weed Identification – Week 20 Marestail

Marestail

FamilyComposite, Asteraceae.

Habitat: Thin turf, agronomic crops, pastures, orchards, fallow fields, waste areas, and roadsides.

Life cycle: Summer or winter annual.

Growth habit: Seedlings develop a basal rosette and mature plants erect are reaching 6 1/2 ft in height.

Leaves: The mature plant has leaves that are entirely without petioles (sessile). Leaves are 4 inches long, 10 mm wide, alternate, linear, entire or more often toothed, crowded along the stem, and hairy. Leaves become progressively smaller up the stem.

Stem: Erect, solid, hairy, reaching 6 1/2 ft in height.

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