Innovation in Natural Insect Control for Citrus

Tacy Callies Organic, Pesticides

A microscopic view of diatoms shows the sharp parts that harm insects.

By Chip Henry

When I chose to produce citrus organically nearly five years ago, I accepted the responsibility of implementing a nature-based protocol of production for my grove. Subsequently, I searched for products that were available to address the aspects of nutrition, soil health, undesirable vegetation suppression and insect control. The process of “turning over every rock” was imperative, with insect control being of the highest priority based on the necessity to effectively manage Asian citrus psyllids(ACP).

I was rewarded in the summer of 2015 upon discovery of a natural material known as diatomaceous earth (DE) that utilizes mechanical control as the method to subdue insects. According to the Diatomaceous Earth General Fact Sheet provided by researchers from Oregon State University and published in 2013, DE is primarily composed of the silica skeletons of fossilized ancient marine life, known as diatoms. Silica is 26 percent of the earth’s crust by weight, and silicon is the second most abundant element in soils and found in great quantity in plants as well.

When combined with oxygen and water, DE forms into silicon dioxide, which is a desiccant. Therefore, insects succumb via contact with silicon dioxide as it absorbs oils and fats from the exoskeleton cuticle. In addition, the diatoms have sharp edges, needles and spines which accelerate the desiccation with abrasion as the insect moves its body. DE is not poisonous, and ingestion is not necessary for efficacy. Biologically, DE is not degraded by microbes or sunlight, which are major benefits in the citrus grove environment.

DE was first registered for use in 1960 to control insects, primarily in its mined form as a dust or flour (commonly called shell flour). Since DE is easily airborne and can cause lung inflammation and eye and skin irritation in humans, it is advantageous to apply the material in soluble paste form. However, DE does not easily dissolve in water and requires the addition of a reagent to facilitate solubility. According to scientific principles described in “Remington: The Science and Practice of Pharmacy,” colloidal silicon dioxide (DE) will form a hydrophobic (water repellent) gel when combined with a sulfate. The product I am applying has potassium sulfate as the gelforming catalyst, which enables the DE to blend uniformly with water, flow freely through sprayer nozzles and coat target insects with a desiccating, abrasive waterrepellent gel.

From the first spray application to my grove in August 2015, I observed a trend of declining ACP populations. This was verified by a second-party agency conducting routine monitoring every three weeks to collect and count psyllids. No double-digit counts were recorded when I began applying DE. Within six months, the counts were very low single digits. Soon thereafter, zero psyllids were documented in nearly every sampling. Reports also noted that no psyllid nymphs or eggs were discovered. This pattern of ACP decline remained constant through the conclusion of the second-party monitoring program.

Due to the mode of action (desiccation and abrasion) of DE, I have witnessed the decline of other soft-bodied insects and mites as well. Scale insects, whiteflies, thrips, aphids, fire ants, rust and spider mites, and other damaging pests, including snails, have been adequately controlled by using DE.

Adult instars of grasshopper species appear to be somewhat unaffected, presumably due to the thickness and durability of their exoskeletons, as are some beetles. Fortunately, these insects are transient, cause relatively insignificant damage to foliage, and are not known to transmit disease to citrus trees.

A young tree treated with diatomaceous earth has a burst of healthy new shoots.

DE is not harmful to honeybees, foraging wasps, lady bugs and other beneficial insects. My apiarist friend has been overwintering his brood hives in my grove for four years and believes his bees are benefitting from the DE because the hives have not been affected by the devastating varroa mite infestations.

DE has nutritive benefits to plants in addition to effective mechanical insect control. Silicon, calcium, magnesium, iron and many other nutrients are present in shell flour. These nutrients, along with the gel-forming catalyst potassium sulfate, boost plant health and supplement existing fertilization practices.

Another remarkable feature about DE is the synergy created when combined with liquid-form beneficial microbial products. The product I have been using has a proprietary blend of stabilized microbes that augment DE. As insects and mites are scorched and lacerated by mechanical action, bacteria feed on the wounded insects as well. Additionally, the microbes enter the plant’s stomata by the potassium sulfate facilitator and begin removing pathogens from the vascular network via consumption or competitive exclusion.

Blemish-free fruit were sprayed with diatomaceous earth.

To summarize, innovation in natural insect control has been rediscovered in the form of DE. DE combined with a hydrophobic gelpromoting substance such as potassium sulfate and a proprietary beneficial microbial liquid creates a powerful three-in-one product suitable for citrus and virtually any other crop application. It is effective, practical to apply and very affordable. Dosage rates place the cost of DE at less than $10.00 per acre per application.

Whether utilized in organic or conventional insect control, DE has proven to be worthy of consideration as a valuable tool in integrated pest management for citrus.

Chip Henry ( grows citrus at McGuire Groves in Apopka, Florida.