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.
Timely tips for the Arkansas home gardener.
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!
The Confusing World of Adjuvants
By: Tommy Butts, Extension Weed Scientist
Adjuvants perform numerous roles within a spray application and there are a wide variety of different options available. Some adjuvants work by reducing surface tension of the spray solution resulting in fewer droplets that bounce and shatter (spreaders/stickers; surfactants) and some help improve spray water quality by tying up cations associated with hard water (water conditioners). Others break down the leaf cuticle to enhance absorption (oils) and some increase droplet size to reduce drift potential (drift reduction adjuvants). As a result, there are no “one size, fits all” type adjuvants that can be or should be used for every application.
Research results have shown that a herbicide solution with methylated seed oil (MSO) had the greatest retention on a plant surface compared with other tested adjuvants (Figure 1) (Creech 2015). Nonionic surfactant (NIS), silicone, and crop oil concentrate (COC) adjuvants also increased retention of a herbicide solution on a plant surface compared to a drift reduction adjuvant (DRA) and no adjuvant; however, it was to a lesser extent than the MSO. This may help explain increased weed control observed when MSO, NIS, silicone, and COC adjuvants are used, but it can also explain the added crop injury potential especially with certain MSO products. Recommendations on herbicide labels should be followed to maximize the effectiveness of the herbicide while not substantially increasing crop injury.
Other research has shown the effect of adding a water conditioning adjuvant like AMS to herbicide solutions for increased weed control, especially in hard water environments. In a greenhouse study conducted recently here in Arkansas (Figure 2), Roundup PowerMax alone at 11 fl oz/acre provided approximately 65% control and Roundup PowerMax plus added NIS (0.25% v/v) provided approximately 75% control of a barnyardgrass population. When AMS (2 lb/acre) was used, nearly 100% control was achieved with the same rate of Roundup PowerMax.
Adjuvant labels should also be carefully read prior to use to identify the actual type of adjuvant it is and to follow the manufacturer recommended rates. I have received reports of high surfactant oil products (HSOC) such as Superb HC being recommended at standard COC rates (1% v/v). This will lead to much greater crop injury potential. An HSOC and COC are not equivalent adjuvant types as an HSOC contains a much greater load of surfactant. The recommended rate for an HSOC like Superb HC is half a normal COC rate (0.5% v/v).
Anytime a new herbicide solution or adjuvant combination is to be used, consultants or applicators should perform a jar test to test for compatibility and applicators should carefully observe the application for drift potential and efficacy. Figure 3 and Figure 4 illustrate a couple of examples of severe incompatibility when adjuvant or micronutrient products were added to herbicide solutions. In Figure 3, the addition of a DRA caused some WDG formulated herbicides to precipitate out and never fully go into solution. Not only could this lead to plugged sprayer equipment, a majority of the herbicide activity has been lost. In Figure 4, when the micronutrient boron was added to herbicide solution A (left panel), you can see a drastic change in the chemical solution. When those spray solutions were evaluated for droplet size, the solution with boron had a decreased droplet size and almost four percentage points more driftable fines when sprayed through a TTI nozzle. In contrast, when boron was added to herbicide B (right panel), no observable effect to the herbicide solution occurred and droplet size remained relatively unchanged.
Care should be taken to read each herbicide label and follow the recommendations provided on adjuvant selection. If tank-mixing herbicides, the first option would be to select an adjuvant that is recommended on both labels. If no overlap of recommended adjuvants occurs, typically a NIS or COC are the most viable options to use to increase activity while limiting crop response. Use best judgment as well with certain herbicides on whether an additional adjuvant is even needed. Often, a tank-mixture with heavy surfactant loaded products (such as Roundup PowerMax II) does not require the addition of another adjuvant.
If any questions arise or if I can help at all, please don’t hesitate to get a hold of me at tbutts@uada.edu or (501) 804-7314. Good luck out there.
References:
Creech CF (2015) Herbicide Application Technology Impacts on Herbicide Spray Characteristics and Performance. Lincoln, NE: University of Nebraska-Lincoln. 205 p