When you need to control unwanted plants using herbicide, your major concern is going to be making sure that the herbicide works properly.
If the herbicide is to be effective, the unwanted plants need to be appropriately wet.
Therefore, you most likely are going to include a wetting agent in your herbicide spray mixture.
What is a wetting agent?
A wetting agent is an activator adjuvant that is classified as a surfactant. It is designed to improve the coverage of a plant’s surface when you spray herbicide, commonly referred to as ‘wetting’.
A wetting agent is added into a spray mixture to reduce the surface tension of spray droplets which prevents droplets from beading up on the leaf surface.
Therefore, the wetting agent lowers spray droplet surface tension which enables the spray to increase the leaf area covered by each droplet. A good wetting leads to improved coverage of plant surface and potentially good herbicide activity and plant death.
Why do you need to use a wetting agent?
First, most herbicides are formulated to use water as a carrier. Each water molecule is bipolar, meaning it has a negative and positive charge.
Thus, the molecules on the surface of a water droplet are held together by cohesive forces which are so strong that water tends to form beads on a surface due to the surface tension of the droplet. The surface tension of droplets can prevent many substances from going into the solution or getting wet.
Second, the waxy leaf surface of plants makes it difficult for water-based spray solutions to penetrate their target. Epicuticular wax on the surface of leaves repels water, resulting in the beading of spray droplets as they land on leaves. When this happens, the herbicide spray droplets will roll off leaves and fall harmlessly to the ground.
How does a wetting agent overcome surface tension to improve the wetting of leaf surfaces?
Most herbicides are applied using water as a carrier. As such the initial challenge is ensuring that the herbicide you are applying mixes well with water. The next challenge is dealing with the surface tension of the spray droplet.
The droplet is held together by the strong cohesive forces of the water molecule, which make the droplets develop into beads when they come into contact with the waxy cuticles of leaf surfaces.
The molecules of a wetting agent have two distinct components: a hydrophilic (water-soluble) component, and a lipophilic (oil-soluble) component.
The components of the wetting agent help reduce the surface tension of spray droplets by weakening the cohesive forces which hold droplets together.
The weakening of cohesive forces of a droplet allows adhesive forces, or the forces between the liquid molecules and a surface, to be stronger which helps a liquid spread on a surface.
The result of a wetting agent is improved wetting of a leaf’s surface.
Where else can wetting agents be used?
You may have localized dry spots on lawns or golf courses that usually occur on sandy soil and become much worse during the hot summer months or when drought is in progress.
The dry spots resist wetting, typically, and the result is a barren or dry spot in a lawn as seen in the photograph. Really ugly!
No matter how much water you apply, these dry spots never seem to change. To remedy the situation, you will need to use a soil surfactant, lawn surfactant, or wetting agent.
What causes localized dry spots?
During times of hot and dry weather that is typical in summer, a waxy coating can form around soil particles. When this happens, water reacts with the soil in the same manner it does on the surfaces of leaves that have a waxy cuticle. The water droplet beads up and does not penetrate the soil.
Having localized dry spots in your lawn can be unsightly. Although, if present on golf greens or putting greens they can be very costly if not properly addressed.
So, what are the major causes of localized dry spots on golf courses.
- Soil type – Sandy soils are commonly used on the construction of putting greens and tees of most golf courses. Compared to other soil types, sandy soils are most likely going to develop localized dry spots when the weather is hot and dry.
- Irrigation management – Golf course superintendents seek to provide firm playing conditions for their patrons. Consequently, golf course greens and tees need to be relatively dry at the time of play, increasing the likelihood of the development of localized dry spots.
- Thatch – golf course greens and tees sometimes develop an excess amount of organic matter (thatch) which creates the conditions for the development of localized dry spots.
Other causes of localized dry spots.
- Steep sloping grade – causes water runoff leading to the development of dry spots.
- High soil salinity – reduces the ability of plants to absorb soil moisture resulting in dry spots.
- Improper chemical usage – which can change soil properties leading to water repellent soils and the occurrence of dry spots.
- Pests – the occurrence of insect pests or diseases can affect grass on golf course greens and tees and the occurrence of dry spots.
What are some ideal characteristics of a wetting agent?
Now that you have become familiar with the reasons why you need to use a wetting agent, here is a list of ideal characteristics of a wetting agent.
- Nonionic properties – Having a neutral charge allows the wetting agent to be mixed with a variety of herbicides.
- Penetrant – Capable of dissolving or penetrating waxy layers on leaves and allow the herbicide to interact with plant tissue.
- Thickener – Reduce spray drift.
- Emulsifier – Allows petroleum-based pesticides and water to blend.
- Spreaders – Help pesticides to cover plants evenly,
- Stickers – Improve the adhesion of herbicide to foliage.
Can you use an adjuvant that combines some of the ideal characteristics to improve plant wetting?
Yes, that would be a good idea. However, you will need to do so with some caution…
- First – Make sure you read the herbicide label and follow all recommendations.
- Second – Some types of adjuvants that improve wetting can cause unwanted injury to desired plants under certain conditions, for example…
- When using a thickener to reduce spray drift to enhance wetting, be aware that some thickeners may contain… polyacrylamide, polyethylene polymers, polysaccharides, or vegetable oils. When applied at too high a strength, these products can burn plants, or block spray nozzles.
- The stickers are comprised of a diverse group of chemicals that may contain fatty acids, latex, alcohols, plant oils, or inorganic oils. As such, some stickers may be harmful to rough-leaved and hairy-leaved plants, annuals, and herbs.
Brewer International has been a leader in land and water chemistry since the 1980s. For over 40 years we have proudly served our national and regional distributors.
The Brewer International products are used widely across the United States in agriculture, aquatics, forestry, rights of way, and land management.
Our customers trust our dedication to quality ingredients, tried and true formulas, and positive outcomes.