Dykstra refers to this picture of Kauai, Hawaii, as proof that “something is going on.” The insects aren’t decimating the island because they only go after unhealthy plants, “no exceptions.” 

Insects as Indicators for Plant Health

Entomologist Thomas Dykstra’s Leaf Brix chart provides a way to identify unhealthy crops.

Throughout his 25-plus years studying insects, Thomas Dykstra has found one thing to be unequivocally true: Insects only feed upon food that is considered unfit, nutritionally poor, dead or dying.

“No exceptions,” Dykstra says. “If you have insects attacking your crop, your crop is suffering in some fashion or another. No insect will attack a healthy plant.”

The founder of Dykstra Laboratories in Florida, the Ph.D and entomologist took center stage at the 2022 National No-Tillage Conference in Louisville, Ky., detailing how to use insects as indicators for plant health. The first step, he says, is identifying what a healthy plant looks like. 

“The quickest way to determine plant health is with a refractometer,” Dykstra says. “A refractometer is going to give you an answer on the spot within minutes.” 

Measuring Brix

A refractometer is a tool that essentially shows how well the plant is photosynthesizing. It does this by testing the plant sap and ultimately revealing a Brix measurement, which represents how much sugar is in the plant. Dykstra says the best time to test leaves is between 1 p.m. and 5 p.m., when maximum photosynthesis is occurring.


MEASURING BRIX. A digital refractometer (pictured left) will reveal a Brix reading within a matter of seconds. Dykstra says the best time to test leaf Brix is in the afternoon, when there’s maximum photosynthesis.

“There is nothing more important for a plant than to photosynthesize,” he says. “There is a direct correlation between photosynthesis and plant health.” 

Digital refractometers cost about…

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Noah Newman

Noah Newman started at Lessiter Media in March 2022 as Associate Editor for No-Till FarmerStrip-Till Farmer and Cover Crop Strategies. He previously worked in broadcast journalism as a sports anchor/reporter for television stations in central Illinois and most recently Jackson, Mississippi, where he was named the state’s sportscaster of the year by the National Sports Media Association. The Cleveland, Ohio, native looks forward to engaging with growers, learning extensively about their operations, and sharing impactful stories with the audience.

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