Weeds

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 Late-Season Waterhemp – The Goal is Stopping Seed →

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 Distribution of Waterhemp and Palmer Amaranth in Ohio →

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

Fall Herbicide Treatments and Cover Crops

By Mark Loux OSU Extension

There is still time to apply herbicides yet this fall. The frosts that are starting to occur have little effect on the weeds of concern – marestail, purple deadnettle, chickweed, etc. We have applied well into December with acceptable results. Fall treatments are a key component of marestail management programs, and it’s not necessary to spend a lot of money to get the desired result.
• This pertains to marestail infestations in grass cover crops also. Cereal rye can integrate well with herbicides to improve control of marestail, but the help the rye provides is variable. In our studies, the rye has at some sites provided enough additional control that fall herbicides are unnecessary, but there have also been sites where the rye contributed almost no control.
• So in fields with grass covers and a history of marestail, our recommendation would be to either treat the fields this fall yet, or scout thoroughly for the presence of marestail before making a decision. Keep in mind also when making this decision, an early-planted cover that is well-established, uniform, and relatively tall at this time of the year is likely to provide more control of marestail and other weeds than a later-planted cover that is variable in stand and still small. Continue reading Fall Herbicide Treatments and Cover Crops →

Fall weed control reminders on late and prevent plant acres

By Erin Burns Michigan State University Extension

Horseweed shown in a soybean field. Photo by Erin Burns, MSU

In general, 2019 was a difficult year for weed control with the large number of acres that were planted late or not at all leading to higher weed populations and extensive weed seed production in some fields. Below are reminders for fall weed control that will set the stage for successful spring 2020 weed control given the drastic increase in weed seedbank populations from 2019.

Fall herbicide applications

Seeds of many winter annual weeds for example horseweed (marestail) lack dormancy and can germinate immediately after dropping from the plant this fall. Given the above average horseweed populations across the state, this will lead to an immediate increase in fall emerging weeds. During optimal years, fall burndown herbicide applications should be made by mid-October before the first hard freeze and daytime air temperatures are at least 50 degrees Fahrenheit. Actively growing weeds are the key to consistent control.

Due to spring conditions, many corn and soybean harvests are late this year. Herbicides can be applied at daytime temperatures ranging from 40-60 F, but weeds may be killed slower at these cooler temperatures. For example at cooler temperatures absorption and translocation of herbicides such as glyphosate and 2,4-D are lower compared with applications at warmer temperatures therefore these applications take longer to kill the plant. When temperatures are below 40 F for a prolonged period after herbicide application, weed control will be reduced. If a hard freeze has occurred, evaluate the condition of the weeds in your field prior to herbicide application. Frost may cause leaf damage (water-soaked leaves that turn black and die) and reduced herbicide absorption. Some winter annual weeds may tolerate a frost and herbicide applications can be made after active weed growth has resumed (appearance of new green leaves), usually after multiple days with nighttime temperatures above 35°F followed by 50 F or above daytime temperatures.

Results from Michigan State University Extension weed scientist Christy Sprague’s research in no-till soybeans found that fall applications of 2,4-D, dicamba, or Sharpen will control fall emerged horseweed and are cost-effective. Tank-mixtures with glyphosate are needed to control other winter annual and perennial weeds outside of horseweed (many populations throughout the state are resistant to glyphosate). For detailed information on controlling horseweed season long see the fact sheet “Herbicide-resistant horseweed (marestail) in Michigan: keys to management in no-till soybean” by Sprague.

Continue reading Fall weed control reminders on late and prevent plant acres →

Allen County Weed Survey

By Clint Schroeder OSU Extension

Each fall Ohio State University Extension conducts a survey of the different types of weeds present in soybean fields, as well as, the level of infestation. Weed Science State Specialist Dr. Mark Loux leads this study and uses the information gained to help develop future weed management programs. This study is conducted in each county where there is an Ag and Natural Resources Educator. The educator selects a route 80-100 miles long through the county and takes notes on one soybean field in each mile.

Allen County 2019 Weed Survey Results

Continue reading Allen County Weed Survey →