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  Effectiveness of Citric Acid

Citric acid was identified by the Hawaii Dept. of Agriculture and the USDA Wildlife Service as an effective, legal pesticide for coqui frogs. The U.S. Environmental Protection Agency (EPA) considers citric acid to be a minimum risk pesticide, and it is, therefore, not regulated. The efficacy of citric acid was tested on coqui frog eggs. Egg clusters or clutches (at least 4 days old) were cleared of dead or infertile eggs and dissected into two masses; one half was treated and the other half served as untreated control. Treatments were 16% citric acid (1 ml applied by aerosol) with no rinsing or rinsing one hour after treatment.

Egg clutches were observed until all viable eggs hatched. Both treatments greatly reduced hatch rate compared to the untreated controls. Two of the 7 clutches that were not rinsed had some degree of hatching, while 6 of the 10 clutches that were rinsed had some degree of hatching. A solution of 16% citric acid was 97% effective in decreasing coqui frog egg viability, especially if the solution is not rinsed off.

Phytotoxicity studies using 25% citric acid were conducted on a variety of ornamental plants. Palms and dracaena varieties were the most tolerant of the citric acid.


Frequently Asked Questions:

Does citric acid kill only adult male coqui frogs?

Tests conducted by USDA APHIS Wildlife Services, National Wildlife Research Center and Hawaii Department of Agriculture in Hilo showed that 16% citric acid solution killed nearly 100% of coqui frogs - including males, females with eggs (gravid), juveniles, and eggs- upon direct contact  Mortality is based on contact with the solution, not the sex, age or reproductive state of the frog.


Are pregnant female coqui frogs or eggs not affected by citric acid?  

The female coqui frog lays eggs within hours of fertilization by the male. Female frogs are therefore not considered "pregnant". Females are no less susceptible to citric acid than males; the most important factor is direct contact with the spray.

Coqui frogs are unusual among frogs in that it is the male that sits on the fertilized eggs until they hatch into fully formed froglets approximately two weeks later. This extraordinary amount of parental care helps to protect the eggs from predators, disease, and dehydration, as well as chemical sprays. Eggs are also laid in protected spots easily overlooked when spraying. When eggs are not directly contacted with citric acid, they can continue to develop and hatch. 


I sprayed with citric acid, but a few days later, I heard the frogs again. Citric acid doesn't work. 

Occasionally people find frogs that remained alive in treated areas and may conclude that treatment was ineffective, but it is more likely that those survivors managed to avoid direct contact with the chemical solution. Adult coqui frogs are about the size of a quarter, and are capable of hiding in very small cracks, under vegetation, and in crevices along rock walls. If the citric acid solution is mixed or used improperly, is washed away by rain or watering, or if frogs do not come into direct contact with it, then effectiveness is reduced.

We sprayed once and haven't heard anything for several weeks.  We got them all, right?

If you sprayed as soon as you heard a single male coqui frog calling, you may actually be coqui-free after one application of citric acid.  If you waited until a chorus of many calling coquis developed, then you most likely have a breeding population of males as well as silent females, juveniles and eggs. Since the egg hatching cycle is about 14 days, we advise respraying every 2 weeks for several months in conjunction with clearing vegetation and other debris in which the frogs might take refuge and escape from the spray. Also, prevent infestations by determining how the coqui frogs got to your site in the first place - on plants from another site? on a vehicle that went to a site with coqui frogs?  on lumber, tile or gravel? Get plants from coqui-free sources or "quarantine" them in an enclosed area, inspect them for eggs, juveniles and adults, and listen at night for calling males before planting or placing the plants in your yard.



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