WHEN PESTICIDES FAIL

Adapted from “Turf West”, August 2000

As much as one tries to keep ahead of weeds by pulling and hoeing, herbicides are needed to achieve optimum control. This is due to the fact that “...it is quite common for each cubic foot of soil to contain between 10 and 50,000 weed seeds.”  If we are to use herbicides, it is best to use them prudently, so we spend less money and protect the environment. The following guidelines will help reduce the amount of herbicides applied and obtain better results when they are used.

INCORRECT IDENTIFICATION OF THE TARGET WEED-

You need to know what kind of weed you are trying to kill. There are different herbicides for different weeds. Bring in your weeds for a positive I.D. and we will help you get the right herbicide.

CHOICE OF HERBICIDE-

Going back to point #1 At Gardener’s Supply we want you to ask questions. We want you to purchase the correct product for the target weed. It is very easy to choose the wrong herbicide. Pay attention to your label and don’t be afraid to ask us questions.

PHOTODECOMPOSITION-

Mainly happens to pre-emergent. This is where, when a product is not watered in appropriately, the sunlight breaks down the chemical and render it inactive or reduces its effectiveness. Remember: all pre-emergents must be watered in so be sure you can get water to the area either by irrigation systems or by rain.

VOLATILIZATION-

This basically involves evaporation of the applied herbicide, lowering the percentage of active ingredient. This can be avoided by not spraying on hot, windy days and using as low pressure as practical.

LEACHING-

This occurs when the active ingredient is moved downward through the soil moving the herbicide past the weeds seeds. This typically happens in in sandy soils. Leaching can be avoided by using composts and avoiding excessive watering.

ADSORPTION-

Is where the herbicide becomes tightly bound to organic materials. This usually occurs when spraying liquid pre-emergent in a flowerbed over bark or mulch of some sort.  

MICROBIAL DEGRADATION-

Instead of the herbicide and the microbial population of the soil co-existing, the microbes feed on the herbicide making it less effective.

Temperature-

Most post-emergent herbicides are designed to be most effective when sprayed during temperatures 60º-85º F. Always check the label of herbicides before use.  

TIMING OF APPLICATION-

Timing is vital. Applications of pre-emergents should be made at least 2-3 weeks before the target weed germinates while post-emergents should be applied when the weeds are newly germinated.  

DRIFT-

An herbicide can fail because of drift. Drift can also cause injury or death to neighboring vegetation. To avoid this do not  spray during windy days or use too fine of a spray tip.

APPLICATION ERROR-

This is simply the case of spraying the wrong thing in the wrong place, usually due to lack of communication.  

RESIDUAL OF PRODUCT-

Some products last longer than others do especially with pre-emergents.  Pay attention to labeled rates and residual and know when to re-apply necessary. Our calendar and newsletter can help with this.

THICKNESS OF CUTICLE-

In summer and fall, most weeds develop a thicker cuticle to deal with excessive moisture loss, making it harder for some herbicides to penetrate. Use a surfactant to help lower surface tension of the herbicide and allow more material into the plant.

EQUIPMENT CALIBRATION-

Whether it be spray or granular application calibration is very important. In sprayers, you need to know that your sprayer is delivering 1 gallon per 1,000 sq.ft.  If you do not know how to calibrate your sprayer or spreader, ask us and we will show you how.

IMPROPER CULTURAL PRACTICES-

Things like constant use of improper fertilizer, incorrect mowing height, and incorrect watering can reduce the effectiveness of an herbicide.  

READING THE LABEL-

When reading the label pay attention to things like:

A. Amount of water to mix with product

B. Agitation requirements, if necessary.

C. Restrictions on mixing with other products, which may reduce effectiveness.

D.Directions for most appropriate timing.

E. Possible use of spray pattern indicators

  1. Indications of enhancement with the addition of spreader-stickers or crop oils.

SOIL PENETRATION-

Some soils do not allow water to penetrate and flow evenly and freely.   When this happens, a pre-emergent herbicide will not be distributed evenly throughout the target area resulting in uneven or “spotty” weed control.