Do you read the label of each pesticide you apply before you buy, before you apply, and before you dispose? Many people read a label once and assume that the next time they purchase the chemical it will be the same. Labels change. Chemicals change. Names change. The product you thought you were purchasing may be quite different than the last time you purchased it.

Did you know that there are more than 62 different Roundup formulations? Check it out on pages 6–7 of http://msucares.com/pubs/publications/p1532intro.pdf. Each one is a little different, may or may not be labeled for your crop, and may give you drastically different results. Roundup might be the brand name, but the active ingredient list will tell you what is actually in the product. Some formulations have other ingredients, like surfactants or even other herbicides, to give a residual or longer-term effect. You may think you have genetically resistant weeds when it is really a question of the formulation used. It is important to know exactly what you are applying, and you need to read the label for that.

Damage Control

Herbicide damage to ornamental shrubs can be costly.

The Commercial Diagnostic Plant Clinic at the Mid-Florida Research and Education Center has received several samples that can only be caused by herbicide damage, even though the landscapers claimed never to have applied herbicide to the ornamental beds. We cannot tell what herbicide caused these symptoms; only that it was something with a growth-regulator effect. Distorted growth on one plant species may be explained by many things, but the same type of distorted growth on several species in one landscape (and no evidence of chilli thrips or broad mites!) can only be explained by misapplication of a chemical. If you find yourself in this kind of situation, check your records, check your labels, and read them.

Good records should indicate what was applied, when, how much, what the weather conditions were like, where exactly it was applied, and who applied the pesticide. What was applied includes EPA registration number, active ingredients, and brand name. This kind of detail, and more, is required for restricted-use pesticides, but it also is very useful for any pesticide if you find that you have problems later on.

Watching Weather
With your records of the weather, you may find that the herbicide drifted onto the plants because of windy conditions during application nearby. It may have gotten onto the ornamental non-target plants instead of nearby turf through improper application or faulty equipment. If environmental conditions were humid (but not raining) and warm enough for good plant growth, the misapplied herbicide may have been more active than expected. Under these conditions, the chemical is active on the plant for a longer period than if it were too dry, too wet, too hot, or too cold. On the other hand, high temperature with low humidity may allow the pesticide to form a vapor that drifts to other sites. Sometimes systemic herbicides will be active on exposed roots or root suckers even though it looks like you are applying herbicide to mulch or unwanted seedlings. A systemic herbicide will be translocated, move through the plant’s vascular system, back to the mother plant, which may be affected as if it had been sprayed directly.

The Right Chemistry
The chemical applied may have been a different formulation than the one the applicator thought he or she was applying. Your records would tell you active ingredients for comparison to previous successful treatments. The same brand name may be used, but the formulation may have changed since the last time you purchased the chemical. Perhaps the formulation was more concentrated with a higher percentage of active ingredients and less was needed, or added adjuvants or surfactants made the chemical more effective. Adjuvants are any chemicals added to make pesticide formulations more effective or more safe. Surfactants are chemicals that allow the pesticide to spread out on the target surface to result in better coverage.

Watch the weather. Herbicides can drift to non-target plants if applied during windy conditions.

Buffering agents or pH-adjusting agents can be important to the effectiveness of the pesticide when the water you are using is much above or below pH 7. However, these agents may not always be needed, even with high or low pH levels. Read the label to find out if they are recommended or not. Mixing with other chemicals also may affect your results. Some pesticides may be inactivated by mixing with other chemicals; other pesticides may become more effective than expected. The pesticide label will tell what you may mix with.

Dirt Diligence
The soil type also could affect the application
rate required if the chemical is applied to the
soil. Roundup is not active on soil, only on plant material, but pre-emergent herbicides are used
on soil, and the type of soil may affect results. Sandy soil allows the chemical to move quickly through the soil and possibly off site and off target with irrigation or rain, and may reduce results on the target while increasing chances of non-target effects. Soil with more clay in it will hold onto the chemical, not allowing the chemical to leach or run off, and perhaps requiring a different application rate. High organic matter in the soil will have an effect similar to clay because organic matter tends to bind chemicals to it, preventing them from moving off site. Soils with higher organic matter may degrade the pesticide more quickly if degradation of the pesticide is a biological process carried out by soil microbes because there are more microbes in this type of soil. A soil analysis can be useful in more ways than fertility management.

Follow Instructions
Attention to labels will help you prevent plant damage. Good recordkeeping will help you find out what caused the problem if you ever run into a situation with these kinds of results. Agricultural chemicals are not something you should handle carelessly, no matter how common the chemical or how small an area to be treated. Know what you are applying, what you are applying it for, how much to apply, and whether the environmental conditions are right for application, and you can avoid costly mistakes.

Juanita Popenoe is a commercial horticulture agent at the University of Florida/Institute of Food and Agricultural Sciences Lake County Extension Office in Tavares, FL.