Aquatic Pest Control Unit 4. Test Your Knowledge

What aspects of water chemistry and diluent chemistry can affect a herbicide treatment?

pH, turbidity, and water hardness.

Some herbicides work by interrupting one or more plant processes. Name four plant processes that herbicides sometimes target.

1. Cell division. 2. Tissue development. 3. Photosynthesis. 4. Respiration.

Name three things that can increase the contact time when applying herbicides to submersed plants in moving water.

1. Invert emulsions, polymers, and trailing hoses can help herbicides sink and persist near the plants. 2. Herbicides that rapidly absorb into the plant. 3. Sequential applications or injection equipment.

Treating underwater plants requires you to do what three things?

1. Sink the herbicide. 2. Keep the herbicide near the plants. 3. Prevent the herbicide from being diluted by the surrounding water.

What type of adjuvant would you use if the pH of your diluent was excessively low? Why?

A buffering agent. Water with extreme pHs can cause a herbicide to precipitate out of solution. Buffering agents can "buffer" the herbicide and prevent these reactions.

What is a surfactant? Describe how it improves the effectiveness of a herbicide?

A surfactant is a type of activator. It improves the effectiveness of a herbicide in two ways. 1. Surfactants increase the spreading and wetting properties of a herbicide. They do this by decreasing the surface tension of the herbicide spray droplets. As the surface tension decreases, the droplets begin to flatten and spread over a larger area of the plant. The more area the herbicide covers, the more chemical the plant can absorb. 2. Surfactants also help liquid herbicides penetrate plant leaves. Surfactants do this by dissolving leaf cuticle.

Name the three main groups of adjuvants. Describe the function of each one.

Activators - increase the activity of the herbicide Spray modifiers - influence the delivery and distribution of the spray solution Utility modifiers - improve conditions in which you mix a herbicide

What is an adjuvant?

An adjuvant is a material that aids or changes the action of a herbicide. Adjuvants work by affecting the way a herbicide flows, wets a surface, disperses, suspends in solution, foams, and how easy it is to store.

What type of adjuvant would you use if your diluent water was too soft? Why?

An antifoaming agent. Soft water produces the most unwanted foam in the spray tank. Excess foam makes it difficult to discharge all of a solution from a spray tank. An antifoaming agent can prevent foam buildup.

What is an inverting oil?

An inverting oil is a type of spray modifier. When blended with water, it forms droplets of water surrounded by oil. This viscous blend is called an "invert emulsion." It resembles mayonnaise.

Describe what happens to a plant when a herbicide interrupts tissue development. What name is given to these types of chemicals?

As a plant grows, it develops different tissues. These tissues form leaves, stems, flowers, roots, and other plants structures. Some herbicides cause abnormal tissue development. For example, stems may twist or leaves may curl. If sufficient abnormalities occur, plants can die. Herbicides that work in this manner are called "plant growth regulators."

What source(s) of water should you try to avoid when obtaining a diluent?

Avoid mixing chemicals with water from wells or springs, especially in limestone areas. Water from these sources often has a high mineral content.

Explain how the shape and angle of plant leaves can affect the entrance of herbicide into a plant.

Broad, horizontally oriented leaves will intercept and retain more herbicide than narrow, upright leaves such as those of grasses and cattails. Liquid herbicide tends to run off grass blades, while it may sit on top of a palm shaped leaf for hours. The longer a chemical contacts a leaf, the more the plant will absorb.

How do inverting oils help herbicides reach underwater plants?

By wrapping around a droplet of herbicide, oil allows a chemical to reach submersed vegetation without being diluted on the way. In addition, the increased weight of the droplet helps the solution sink quickly.

What is the difference between a contact herbicide and a systemic herbicide?

Contact Herbicide: A contact herbicide kills or injures most plant parts that it touches. It does not affect areas of the plant that it does not touch. In general, contact herbicides work faster than systemic herbicides. Systemic Herbicide: Systemic herbicides are absorbed into the plant through its leaves, stems, or roots. Once inside, the chemical moves throughout the plant, usually killing it completely.

Are contact herbicides more effective on annual plants or perennial plants? Why?

Contact herbicides are most effective on annual plants. Annuals have small root systems. They usually do not store enough energy in their roots to regrow after the above ground growth has been killed. On the other hand, perennial plants can be defoliated by contact herbicides, but these plants will generally grow back. Large perennial root systems store enough energy to support regrowth. Woody stems and bark covered areas are usually not affected by contact herbicides.

Why is it important to control drift during a herbicide application?

Controlling drift is important for two reasons. First, herbicide drift can injure desirable plants and other organisms. This not only may upset your client. You may also risk legal penalty and public disapproval. Second, if a breeze carries herbicide away from the target plants, the plants may not receive enough chemical to provide control. Efficacy could decrease and you may have to re-treat.

In aquatic environments, where is drift a problem: above the water, in the water, or both? Explain.

Drift occurs when wind or a light breeze carries pesticides away from the target plant. In aquatic systems, this can occur above the water or in the water. Above the water, heavy or even light wind can cause pesticides to drift into nontarget areas or onto nontarget plants. In the water, wind can cause water movement to carry chemicals away from submersed weeds.

Name several factors that can affect herbicide applications on land and in water.

Drift, evaporation, treating plants in the rain, and the chemistry of your diluent.

At what point in the growing season is it best to apply "soil-active" herbicides to perennial plants? Why?

Early in the growing season. At this time, plant roots are rapidly moving water and nutrients from the soil up into plant. If herbicides are present, they will be readily absorbed.

Name three adjuvants that increase the size of a herbicide droplet.

Foaming agents, inverting oils, and polymers.

Name two types of systemic herbicides. Which one do plants tend to absorb faster?

Foliar-active and soil-active. In general, plants absorb foliar-active herbicides faster than soil-active herbicides.

How can you avoid turbidity in your diluent water?

If you use lake water as your diluent, keep the suction end of your filler hose far enough from the lake bottom to avoid drawing in sediments.

How does increased droplet size improve the performance of a herbicide?

Large particles are heavier and can reduce drift during application. Larger droplets also evaporate more slowly.

At what point in the growing season is it best to apply "foliar-active" herbicides to perennial plants? Why?

Late in the season. After perennials flower and produce seed, they begin to translocate materials from the leaves down to the roots. Herbicide applied to the leaves will also be transported downward.

Why is it difficult to treat submersed plants in moving water?

Moving water may carry herbicide away from the plant before absorption has time to occur. This can decrease the contact time and render a treatment ineffective.

How do oils improve the effectiveness of a herbicide? In what conditions might you choose to use an oil adjuvant?

Oils help prevent spray solutions from evaporating. This increases the contact time and the amount of herbicide a plant absorbs. Oils are most helpful during hot, dry weather when evaporation rates are high.

Are adjuvants added by the manufacturer or the applicator?

Over 80 percent of the herbicides for sale in the United States contain adjuvants. These are added by the manufacturer. However, if a herbicide does not contain an adjuvant, you may need to add one. You may also add a second adjuvant to a herbicide that already contains one.

Describe the difference between photosynthesis and respiration.

Photosynthesis is the process by which plants make food. Respiration is the process by which plants use the food made during photosynthesis.

Name the physical and biological factors that affect whether a herbicide is selective.

Physical factors - Placement, chemical formulation, and application rate of the chemical you are applying. Biological factors - Anatomy, physiology, and stage of growth of the plant to which you are applying the chemical.

What is the difference between a selective and a non-selective herbicide?

Selective herbicide - A pesticide that controls certain plants but does not affect others. Non-selective herbicide - A pesticide that controls all or most types of plants.

Which is the better diluent: hard water or soft water? Why?

Soft water is the preferred diluent. Water hardness is the measure of certain minerals in the water. Soft water contains few minerals. Hard water has a high mineral content. Some herbicides "react" with or "bind" to the minerals in hard water. This can cause the herbicide to become inactive or precipitate.

How does the formulation of a herbicide affect its selectivity?

Some chemical formulations can easily pass through a leaf cuticle (the waxy coating on leaves). Others stick to vertical plant leaves instead of running off of them. By selecting a specific formulation for your situation, you may be able to control troublesome weeds, without harming other plants.

Describe the process of translocation.

Translocation is the process by which plants absorb and transport water and nutrients throughout their structure - to their leaves, stems, and roots.

Name three challenges unique to aquatic herbicide applications.

Treating underwater plants, treating underwater plants in moving water, and working with the chemistry of the water in which the plants are growing.

What is turbidity? How does it affect a herbicide

Turbidity occurs when many small particles become suspended in water. These tiny particles can inactivate herbicides by binding to them.

In what ways might the pH of a water body and the pH of a diluent affect a herbicide application?

Water pH can affect the rate at which plants absorb some herbicides. Some herbicides are more active at different pH levels. Water pH can also dictate how much herbicide you need in order to obtain successful control.

In what ways can you and others create turbidity in a body of water?

You can cause turbidity by walking in the water, driving a motor boat in shallow areas, or collecting samples of plants rooted to the bottom. Recreation activities such as swimming, boating, and even fishing can also cause turbitiy.