Pick up know-how for tackling diseases, pests and weeds.
Farm bill, farm marketing, agribusiness webinars, & farm policy.
Find tactics for healthy livestock and sound forages.
Scheduling and methods of irrigation.
Explore our Extension locations around the state.
Commercial row crop production in Arkansas.
Agriculture weed management resources.
Use virtual and real tools to improve critical calculations for farms and ranches.
Learn to ID forages and more.
Explore our research locations around the state.
Get the latest research results from our county agents.
Our programs include aquaculture, diagnostics, and energy conservation.
Keep our food, fiber and fuel supplies safe from disaster.
Private, Commercial & Non-commercial training and education.
Specialty crops including turfgrass, vegetables, fruits, and ornamentals.
Find educational resources and get youth engaged in agriculture.
Gaining garden smarts and sharing skills.
Creating beauty in and around the home.
Maintenance calendar, and best practices.
Coaxing the best produce from asparagus to zucchini.
What’s wrong with my plants? The clinic can help.
Featured trees, vines, shrubs and flowers.
Ask our experts plant, animal, or insect questions.
Enjoying the sweet fruits of your labor.
Herbs, native plants, & reference desk QA.
Growing together from youth to maturity.
Crapemyrtles, hydrangeas, hort glossary, and weed ID databases.
Get beekeeping, honey production, and class information.
Grow a pollinator-friendly garden.
Schedule these timely events on your gardening calendar.
Equipping individuals to lead organizations, communities, and regions.
Guiding communities and regions toward vibrant and sustainable futures.
Guiding entrepreneurs from concept to profit.
Position your business to compete for government contracts.
Find trends, opportunities and impacts.
Providing unbiased information to enable educated votes on critical issues.
Increase your knowledge of public issues & get involved.
Research-based connection to government and policy issues.
Support Arkansas local food initiatives.
Read about our efforts.
Preparing for and recovering from disasters.
Licensing for forestry and wildlife professionals.
Preserving water quality and quantity.
Cleaner air for healthier living.
Firewood & bioenergy resources.
Managing a complex forest ecosystem.
Read about nature across Arkansas and the U.S.
Learn to manage wildlife on your land.
Soil quality and its use here in Arkansas.
Learn to ID unwanted plant and animal visitors.
Timely updates from our specialists.
Eating right and staying healthy.
Ensuring safe meals.
Take charge of your well-being.
Cooking with Arkansas foods.
Making the most of your money.
Making sound choices for families and ourselves.
Nurturing our future.
Get tips for food, fitness, finance, and more!
Understanding aging and its effects.
Giving back to the community.
Managing safely when disaster strikes.
Listen to our latest episode!
Two residuals PRE better than one for soybean!
By: Tom Barber, Jason Norsworthy, and Tommy Butts
There were lots of conversations last week about soybean herbicide programs and specifically
which herbicides to use at planting before the weeds and crop emerge. Since the
2015 discovery of PPO-resistant Palmer amaranth in Arkansas, our herbicide options
for pigweed control have been drastically reduced. By 2017 our recommendations for
herbicide selection at planting changed from a Valor- (flumioxazin) or Authority-
(sulfentrazone) based system to a metribuzin plus Group 15 (Dual Magnum) system.
Ten site-years of data (Figure 1) in fields heavily infested with PPO-resistant pigweed
suggested that this mixture was the best approach. Although at the time we didn’t
know, now we are confident that pigweed populations at these locations were also resistant
to POST HPPD (Group 27)-containing herbicides such as mesotrione (Callisto) and tembotrione
(Capreno) and some PRE applied Group 15 herbicides, specifically metolachlor (Dual
Magnum) and acetochlor (Warrant).
Figure 1: Multiple-resistant Palmer pigweed control with various herbicide programs
applied at planting. All product rates represented are in ounces within parenthesis
following the names. Average pigweed control for each treatment is listed on the
right side of the figure. These data are presented in a box and whisker plot, where
the smaller the box the less variability in control across site-years. Yellow dots
The last 2 years of research at these locations in Crittenden County indicate that
herbicides containing dimethenamid (Outlook) and pyroxasulfone (Anthem Maxx, Zidua)
work much better on these multiple-resistant pigweed populations that exhibit resistance
to metolachlor. These are all Group 15 herbicides but because of the difference in
herbicide metabolism in resistant pigweed populations, Anthem Maxx /Zidua and Outlook
have consistently worked better from a residual standpoint (Figure 2).
It is also important to point out the appropriate rate of these herbicides. Notice
the Outlook rate of 12.8 fluid ounces per acre and Zidua SC rate of 3.25 fluid ounces
per acre (Figure 2). This should be the lower end of rates for each of these products
for effective pigweed control. In addition, although Dual Magnum did not perform
well at 1 pint per acre, when rates were increased on this pigweed population, improved
control was observed (Figure 3 below). Keep in mind these pictures are from last
year and data can vary based on environmental conditions and rainfall for activation
Looking back at Figure 1, all herbicide combinations that provided 85% control or
greater of multiple-resistant pigweed 28 days after planting contain metribuzin, a
Group 5 herbicide. Additionally, all but one combination contained Zidua, a Group
Talking with producers and consultants across Arkansas, most soybean fields will likely
see a mixture of metribuzin and Group 15 at planting this year. This will be especially
important from central up through Northeast, Arkansas, especially east of Crowley’s
ridge because this area has the most wide-spread PPO-resistant pigweed. Make sure
varieties selected are tolerant to metribuzin, otherwise injury may occur especially
in high soil pH areas. A list of the metribuzin tolerance of soybean varieties in
Arkansas can be found here. We are not sure how widespread the Group 15 (metolachlor) resistance is, but at
this time we have only confirmed it in Crittenden County. Regardless of which population
you have, as long as you are mixing a Group 15 with at least 6 oz/A (dry) metribuzin
(ex., Tricor), approximately 80% or more control can be expected for approximately
3 weeks following activation. It is very important to make a timely POST application
once pigweed emerges. In south Arkansas, PPO resistance is not as widespread, but
we know that it’s never a bad idea to rotate our chemistry and move away from flumioxazin
(Valor) combinations at least on a rotational basis, especially if you are relying
on Flexstar (fomesafen) for POST control.
According to preliminary estimates, soybean growers in Arkansas will plant most of
their acres in an Xtend soybean. The cutoff date for dicamba applications in Arkansas
is May 25th. If you farm east of the ridge in Northeast Arkansas, down to Phillips county, it
is doubtful that Flexstar will work POST for pigweed control when they emerge in Xtend
soybean. As we get closer to the second week of May, producers with fields containing
PPO-resistant pigweed should switch to either an Enlist, LLGT27, or LibertyLink variety
that allows POST alternatives for pigweed control such as Enlist One or Liberty.
It is also important to start CLEAN! I have had several calls this week wondering
if I have seen pigweed emerge. Be prepared, they are up in some areas! From this
point forward, unless the field has been tilled immediately prior to planting, Gramoxone,
approved dicamba in Xtend (Engenia, Fexapan, Xtendimax, Tavium) or Enlist One in Enlist
soybean should be applied with the PRE herbicide residual mixture. Be sure to check
individual herbicide product websites for approved tank-mix options. Wishing everyone
a safe and healthy planting season. Call us with questions.
If you would like to read journal article publications from this research click here for management of PPO-resistant pigweed and here for discovery of Group 15 resistance in Arkansas.