Chemical Resistance Prevention

In order to keep control of the growth of vegetation in ponds and lakes, it is very important to avoid creating situations where weeds could become chemically resistant to herbicides.

Generally, weeds only develop resistance to chemicals if weeds are subjected to herbicides at a level that is below the ability of the chemical to kill the weed.  For example, Michigan lakes are developing fluridone resistance due to the law that limits the part per million (ppm) of fluridone to no more than 5 ppm to protect native vegetation while hoping it kills the Eurasian water milfoil located in the lake.  Unfortunately, there are resistant forms of milfoil beginning to show up and proliferate as the unresistant forms are being killed off.  This in effect is eliminating the competition and allowing a favorable environment for this resistant weed to thrive in.

Another way weeds can become resistant is by using systemic herbicides in the same manner as seen in the last paragraph.  Systemic herbicides, such as fluridone and glyphosate, can become ineffective over time as some weeds survive and reproduce and gradually out compete the weaker forms of weeds that have been treated.  Fortunately, resistance is less likely with products that simply burn back vegetation, such as diquat dibromide or endothal salts.  This is due to the fact that the burn-back simply damages the plant and does not completely kill it.  Therefore, nearly all of the plants are affected and there are no plants developing a resistance to the chemical and passing those genes on to a future generation without all of the plants passing on their genes at the same time.  This does not allow the resistant forms exclusive occupancy of the pond because the other un-resistant forms will still be there putting competitive pressure on the resistant forms.