Get your Waterhemp Populations Screened for Herbicide Resistance

By Mark Loux OSU Extension

We have been screening a random sample of waterhemp populations for herbicide resistance over the past two years.  Herbicides used in the screen include mesotrione, atrazine, 2,4-D, fomesafen, and metolachlor.  Results of our research show that it’s possible for Ohio waterhemp populations to have some level of resistance to one, several, or all of these herbicides.  Glyphosate is not included because we assume almost all populations are already resistant to this.  We are also part of a regional project that has been screening for dicamba and glufosinate resistance with populations that we supply, although none has been identified to date.  Our sample size has been small so far, so at this point we are looking to expand our screening to include waterhemp populations submitted by anyone in Ohio looking for more information about their response to herbicides.  It’s preferable to have seed from waterhemp plants that have survived POST herbicide treatments, or where it appears that preemergence herbicides were fairly ineffective, if possible.  But we will screen any populations provided within the constraints of time and greenhouse space.  For a quick reminder about how to tell when seed from waterhemp is mature, check out this video.  When seed is mature, you can cut off seedheads and place in an open paper bag until ready to get them to us.  Or just shake heads into some type of container to collect seed.  Send us an email and we will figure out the best way to get seed to us, or if you need more information.  loux.1@osu.edu

Also – a reminder that while we would like to have seed from surviving waterhemp plants, the most effective method of preventing future problems with this weed is to not let any go to seed.  Not only because plants that survive may have resistance, but because they produce gobs of seed that will result in misery the following year.  Removal of these plants should have high priority right now.  However, where it’s apparent that this is not going to happen for whatever reason, make a note of the infested fields, and check on them starting in a couple weeks for seed.  This should help us to get a better handle on how resistance in waterhemp is evolving.

Poison Hemlock is in Full Flower

By Joe Boggs – OSU Extension

Poison Hemlock is in Full Flower and Towering over Fields and Landscapes in Ohio.

Poison hemlock is one of the most lethal plants found in North America.  This biennial weed is now in full flower throughout much of Ohio.  So, the clock is ticking on preventing seed production by this non-native invasive plant.

As a biennial weed, poison hemlock spends the first year as a basal rosette and the second year as an erect, towering flowering plant that can measure 6-10′ tall.

Poison hemlock belongs to the carrot family, Apiaceae (formerly Umbelliferae).  It shares many characteristics with other notable non-native members of the carrot family found growing in Ohio such as Queen Anne’s Lace (Daucus carota) and Wild Parsnip (Pastinaca sativa).  Indeed, some of the accidental poisonings in the U.S. have occurred with people mistaking poison hemlock for Queen Anne’s Lace.

Poison hemlock contains highly toxic piperidine alkaloid compounds, including coniine and gamma-coniceine, which cause respiratory failure and death when ingested by mammals.  The roots are more toxic than the leaves and stems; however, all parts of the plant including the seeds should be considered dangerous.  It is a common misconception that poison hemlock sap will cause skin rashes and blisters.  In fact, poison hemlock toxins must be ingested or enter through the eyes, cuts, or other openings to cause poisoning.

All stages of the poison hemlock plant have bluish-green leaves that are 3-4 times pinnately compound, and the deeply cut parsley-like leaflets have sharp points.  Flowering plants have hairless, light-green to bluish-green stems that are covered with obvious purplish blotches.  Clusters of tiny white flowers are borne on structures called umbels that look like upside-down umbrellas.

While poison hemlock can be partially managed by mowing and tilling, the most effective control approach involves properly timed applications of selective or non-selective post-emergent herbicides including glyphosate (e.g. Roundup).  However, applications of herbicides must be made now to have any chance of reducing seed production this year.

Fall-Applied Herbicides: Odds and Ends

A commonly asked question about fall herbicides – how late in the fall can herbicides be applied and at what point is it too cold to apply?  We have applied well into December under some very cold conditions and still obtained effective control of winter annuals.  We suggest applying before Thanksgiving and aiming for a stretch of warmer weather if possible, but the effective treatments should work regardless.  Extended periods of freezing weather will cause the perennials to shut down – dandelion, thistle, dock.

We received a lot of questions about annual bluegrass this year, especially regarding difficulty in controlling it in the spring.  Fall is a good time to control this weed.  This will require the addition of glyphosate to whatever herbicide mix is being used. Continue reading

Scout now for cressleaf groundsel in hayfields, or pay the price in May

By Mark Loux OSU Extension

Some hay producers have been unpleasantly surprised in the past when cressleaf groundsel infestations became evident in their hay fields in May prior to first cutting.  Cressleaf groundsel in hay or silage is toxic to animals, and infested areas of the field should not be harvested and fed.  Groundsel is a winter annual, emerging in late summer into fall, when it develops into a rosette that overwinters.  Growth restarts in spring, with stem elongation and an eventual height of up to several feet tall.  The weed becomes evident in hay fields when in becomes taller than the alfalfa/grass and develops bright yellow flowers in May.  The problem with passively waiting until this point to discover that the hay is infested with groundsel is that: 1) it’s too late to control it with herbicides; and 2) hay from infested areas has to be discarded instead of sold or fed, and large plant skeletons are still toxic even if herbicides were effective on them.  Groundsel plants finish their life cycle in late spring, once they flower and go to seed, so it should not be problem in subsequent cuttings.

Cressleaf Groundsel

The solution to this is scouting of hay fields in fall and early spring to determine the presence of cressleaf groundsel, when it is small and still susceptible to the few herbicides that can be used.  We expect groundsel to be more of a problem in new August seedings, since it would be emerging with the new stand of alfalfa/grass.  A well-managed established and uniform hay crop should be dense enough to largely prevent problems with winter annuals although there have been exceptions.  Groundsel will be most easily controlled in the fall while in the rosette stage.  Controlling plants in the spring is more difficult, because of cold conditions in early spring when plants are still small, and increased tolerance to herbicides as stems elongate.  Continue reading

Soil Residual Herbicides And Establishment Of Cover Crops In The Fall

By Marcelo Zimmer and Bill Johnson, Purdue Extension

Indiana growers have shown increased interest in utilizing cover crops in our corn and soybean production systems over the last decade.  Concurrently, there has also been increased utilization of soil residual herbicides to help manage herbicide-resistant weeds such as marestail (horseweed), waterhemp, and giant ragweed in our corn and soybean production systems.  Soil residual herbicides can remain active in the soil for a period of weeks to months after application.  The length of time a residual herbicide remains biologically active in the soil is influenced by soil texture, soil pH, organic matter, rainfall, and temperature.  Since these factors will vary from field to field, definitive time intervals of residual herbicide activity can be difficult to predict. Continue reading

Late-Season Waterhemp – The Goal is Stopping Seed

By Mark Loux OSU Extension

In our windshield scouting of soybeans this year we have seen a lot of weedfree fields.  This makes sense given the shift toward Xtend, LibertyLink, LLGT27, and Enlist soybeans over the past several years, which provides us with effective POST options for our major weed problems – common and giant ragweed, marestail, and waterhemp (now if we could just get rid of the baggage some of these traits carry).  We are however getting manyreports of late-season waterhemp as it grows through the soybeans and becomes evident.  This also makes sense given that statewide we are in the midst of an overall increase in waterhemp, and continue to move up the curve in terms of number of fields infested and the size of the infestations.  Prevention and management of waterhemp and Palmer amaranth has been one of the primary goals of our state and county educational programs for half a decade or more.  And one of the most important points about waterhemp and Palmer that we try to get across is their capacity for prodigious seed production – 500,000 to upwards of a million seeds per plant – and what this means for their ability to rapidly ramp up populations, infest equipment, etc.

Flowering Waterhemp

The bottom line here is that it’s essential to scout fields this time of the season and kill or remove plants that could produce seed.  Allowing even a few plants to produce seed means an increased population for the next year or two at least.  Running harvest equipment through planst loaded with seed is a primary mechanism of spread from field to field.  Plants can survive into late season because they emerged after herbicide treatments, or survived an improperly timed and less than effective POST treatment.  These plants should produce less seed than plants allowed to grow full season without interruption.  It’s also possible given waterhemp’s propensity to become resistant to any herbicide used against it, that the survivors are resistant to whatever POST herbicide was used.  Resistance to glyphosate, ALS, and PPO inhibitors is widespread in Ohio, and we expect the development of resistance to dicamba, 2,4-D, and glufosinate will occur given their intensity of use (which is why the current period of clean fields makes us nervous).  The only way to ensure that resistance does not develop is to follow herbicide programs with later season scouting and removal of plants to prevent seed. Continue reading

Looking for soybean fields with late season waterhemp

By Mark Loux OSU Extension

OSU weed scientists and ag engineers are looking for soybean fields that have populations of waterhemp or Palmer amaranth surviving into July and August (after all control with herbicides has been attempted).  We have a project involving the use of a drone to identify these weeds in mid to late season when they are evident above the soybean canopy.  We need fields with more than just a few surviving plants.  Populations consisting of a few good patches up though a disaster are fine.  Contact Mark Loux – loux.1@osu.edu, 614-395-2440.  Thanks in advance for your help.

Distribution of Waterhemp and Palmer Amaranth in Ohio

By: Mark Loux and Bruce Ackley, OSU Extension

The maps that accompany this article show our current knowledge of waterhemp and Palmer amaranth distribution in Ohio.  These are based on information from a survey of OSU Extension County Educators, along with information we had from samples submitted, direct contacts, etc. We still consider any new introductions of Palmer amaranth to be from an external source (brought in from outside Ohio) – hay or feed, infested equipment, CRP/cover/wildlife seedings.  Palmer is not really spreading around the state, and as the map shows, we have had a number of introductions that were immediately remediated.  The number of counties where an infestation(s) is being managed is still low, and within those counties, the outbreak occurs in only a few fields still.  Waterhemp is much more widespread in Ohio and is spreading rapidly within the state from existing infestations to new areas via equipment, water, animals, etc.  We do not have Ag Educators in all counties, and even where we do, infestations can occur without us knowing about them.  Feel free to contact us with new information to update the maps. Continue reading

Omitting residual herbicides in soybeans – really – we have to have this argument again?

By Dr. Mark Loux OSU Weed Science

According to our network of sources, the effectiveness of new soybean trait systems has some growers once again thinking about omitting preemergence residual herbicides from their weed management programs.  Some people apparently need to learn the same lessons over and over again.  Having gone through this once in the early 2000’s when Roundup Ready soybeans had taken over and we all sprayed only glyphosate all day every day, we think we’re pretty sure where it leads.  We’re sensitive to concerns about the cost of production, but the cost-benefit analysis for residual herbicides is way in the positive column.  We’re not the ones who ultimately have to convince growers to keep using residual herbicides, and we respect those of you who do have to fight this battle.  Back in the first round of this when we were advocating for use of residuals, while the developers of RR soybeans were undermining us and telling everyone that residuals would reduce yield etc, we used to have people tell us “My agronomist/salesman is recommending that I use residuals, but I think he/she is just trying to get more money out of me”.  Our response at that time of course was “no pretty sure he/she is just trying save your **** and make sure you control your weeds so that your whole farm isn’t one big infestation of glyphosate-resistant marestail.”  And that answer probably works today too – maybe substituting waterhemp for marestail.

Continue reading