Optimizing Pesticide Performance

Allen D. Owings, Hollier, Clayton A., Pollet, Dale K.  |  4/17/2005 7:30:38 PM

Many factors are often overlooked when using pesticides on our landscape plants. Poor performance of pesticides is a concern, but the pesticide usually is not the problem.
Factors that influence pesticide performance include water quality, coverage, agitation, mixing, watering practices, water temperature, rotation, application time, pesticide incompatibility, residual activity and surfactant use. Here is some information on these topics, and others, that will improve pest management success in landscape plantings.

The most important first step to pest management success is the proper identification of the insect, disease or weed pest. Many times a beneficial insect will be sprayed and problems explode. Without identification of the pest, controls may be misused or improperly timed.

Water Quality
The primary factors important in water quality are pH and alkalinity (bicarbonates). Many water sources in Louisiana have alkaline pHs (>7.0). High pH levels are responsible for alkaline hydrolysis, a process that breaks down the active ingredient in many insecticides, fungicides and herbicides. Add a buffer agent to lower spray solution to a pH of 5.5-6.5. This will give better initial knockdown and longer residual action.

Watering Practices
Longevity and effectiveness of pesticides are influenced by irrigation practices. Limit overhead irrigation­; its washes off pesticide residue of contact chemicals. Soil-applied pesticides are less effective when over-irrigation and leaching occur from the root zone.

Spray Coverage
Uniform coverage is essential. Direct spray applications toward the target pests. Avoid spraying during the heat of the day. Early morning or late afternoon are the best times to spray. Know the location on plants where different insects commonly occur. Also know what insect growth stage is most easily controlled.

Be sure to agitate pesticides before applying. Pesticides, especially wettable powders, can settle out in the bottom of a sprayer. Wettable powders should be mixed in a small container to get into solution and then added to the tank. Remember that the concentration of spray solution is weakest when you first start spraying and gradually increases as you have less solution in the sprayer.

Pesticide Compatibility
Are the pesticides being mixed together compatibly? Incompatibility results in phytotoxicity and reduced effectiveness. Settling out indicates incompatibility. Follow label directions on tank mixing pesticides.

Time of Application
Apply pesticides early in the morning or late afternoon, when insects are most active. Applying on hot, sunny days leads to more rapid drying and reduced pest control. If the pesticide has an oil base, applying during hot, sunny portions of the day can burn tender foliage.

Residual Activity
Most of the newer pesticides on the market have shorter residuals than older pesticides. This means additional or more frequent applications may be necessary. Ultraviolet light tends to degrade newer pesticides faster than older pesticides. Using buffers and spreader stickers will enhance residual activity and initial knockdown.

Water Temperature
Most pesticides, including biological control agents and neem oil products, should be applied at water temperatures of 60EF or higher. Water temperature also influences dissolving of water-soluble bags. The pH also plays a role here unless it is properly buffered.

Pesticide Rotation
Rotate pesticides that have different modes of action. Applying the same chemical continuously increases the likelihood of resistance/tolerance buildup. Rotate common chemical names, not trade names.

Label Rates
Follow label recommendations. More than the label rate leads to phytotoxicity. Less than the label rate results in reduced pest control and increased potential for tolerance and resistance buildup.

Target Pest Stage
It is important to know the most controllable stage in the life cycle of each insect pest. Scout regularly to monitor insect, disease and weed problems.

Pesticide Shelf Life
Most pesticides have a shelf life of two to three years (many fungicides only one year). They are broken down by temperature extremes, high humidity and light exposure. Sometimes liquid formulations will settle out and not go back into solution or become murky or milky.Once these products begin a degradation process, the effectiveness of the pesticide is proportionally reduced.

Improper Product for Pest
Know the target species, and be sure the pesticide is labeled for control of that species. Many insecticides do not have spider mite activity.

Does the product call for the use of a surfactant? It makes a significant difference! This is especially true for some herbicides. Surfactants improve pesticide coverage and increase effectiveness. Some materials have surfactants in the mix, so read the label.

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