available citric acid on infested plants to kill coqui frog
eggs, juveniles, and adult males and females. Citric acid is a common food
additive and is considered safe for environmental use by the
EPA. Citric acid (anhydrous, or dry powder) can be obtained
in 50 lb bags or in repackaged 5 and 10 lb bags from chemical
or garden supply stores. It must be first mixed with water
to make a 16% (w/v) solution (1.3 lb citric acid per 1 gallon
of water). (Note: 16% citric acid is now available ready-to-use
as a premixed solution at most garden shops - check product
Frogs are killed by direct contact with the spray and not by its residue. For maxiumum effectiveness, spraying should be done following removal of dense shrubs and dead foliage to increase contact with the frog. In landscaped or vegetated areas, spray in the early evening after a drizzle or
heavy rain, when frogs start to call, rather than during a
dry period or drought when frogs remain hidden and call less
frequently. Moderate to heavy rain will dilute and wash away sprayed citric acid, so consult the weather forecast prior to spraying. Thorough coverage of plants with the citric acid
solution (including undersides of leaves where frogs may be hiding) is important. Spray
or hand-capture frogs agitated by the citric acid that may jump out of the plants before
they can find another hiding place.
Frogs that are not directly contacted during spraying may retreat and males may refrain from calling for a few days before re-emerging. Spray again after two-weeks (time it takes for eggs to hatch) and monitor for calling males up to one year (time it takes for hatchlings to mature).
Citric acid may damage some sensitive plants, plants that
are stressed, or young, growing plant parts, causing leaf
spotting or yellowing. To avoid damage to delicate plants
or flowers, thoroughly rinse the treated plants with fresh
water to completely remove citric acid residue about an hour
after spraying. Phytotoxicity (chemical damage) varies depending on exposure
conditions. Pre-testing on a small section of a plant is always
recommended. After spraying and/or rinsing, observe the section
for a few days for discoloration before spraying a large number
of plants or valuable plants.
(see Research section for a
list of tested plants and photos of damage symptoms.
Follow all precautions on the Hawaii Department of Agriculture citric acid label. Click here to view or
download the HDOA
citric acid label.