Used for more than 150 years, copper fungicides and bactericides have become a staple against crop losses caused by bacterial and fungal diseases. While considered irreplaceable as a preventive disease management tool, not all copper fungicide products are created equal.
“Formulations and types of copper have significantly changed through the years. Product performance in disease control has improved with new entries like soluble coppers, which have helped growers move beyond ‘old school’ copper hydroxide inputs,” said Herb Young, Adama brand leader.
“Today’s copper fungicides are more active, which in the practical sense means less copper is actually applied to crops and soils. Beyond disease control, products are also evaluated based on whether they can alleviate some of the commonly-known negatives like residue, settling, nozzle clogging, equipment corrosion and problematic copper toxicity in soil. These issues can ultimately cost growers time and money” explained Young.
Young said there are two primary criteria for evaluating copper formulation efficacy with comparison being between suspension versus solution and copper particle size.
“Soluble solutions, like copper sulfate pentahydrate, have copper ions that are highly effective at fractional rates. Solutions that are insoluble, such the oxychlorides and hydroxides, have copper ions that are released over a period of time, and, therefore, not immediately available.
“When it comes to particle size, the smaller the particle, the more effective the copper. This comes down to the amount of surface area where the copper molecule comes into contact with the disease, or pathogen. Each time that particle size is cut in half, surface area gets increased by 8X. Versus large particles sizes, a very small particle of copper will do the same job with a fraction of the impact in copper loading to the environment,” according to Young.
Both soluble and insoluble solutions are proven as being effective, Young explained, but water-solubles are being favored based on characteristics that decrease obstacles in handling, mixing and re-suspension because water-soluble copper is a “true solution,” not a suspension. The active ingredient doesn’t settle or separates after mixing.
Insoluble solutions, on the other hand, can fall out of suspension in the jug, or if a spray tank sits idle. Agitation is required to keep the active ingredient from separating and settling. Young also contends that these large copper particles can be hard on equipment and cause more nozzle wear.
Young noted that the color blue is associated with copper coating of treated plants, but the blue coloring isn’t necessary. “In fact, beyond simple annoyance, research suggests that excessive residue on plants after a conventional copper application might cause some negative impact on crop quality and vigor. Equally important, today’s consumer is demanding fresh produce which has no visible evidence of any crop protection treatments,” he said.
He continued, “University researchers have reported that copper hydroxide coating can draw moisture out of plants following a traditional copper application. Copper residue on plants has also shown to slow down photosynthesis and temporarily halt growth. And although recovery occurs within one to two days, a growing number of experts agree the blue coating puts stress on plants. Copper without a visible residue maximizes photosynthesis and optimizes yield potential."
One other point that Young mentioned is that growers are quick to recognize that by eliminating copper residue, they protect the effectiveness of reflective mulch when used for insect control. Reflective mulch deters vectors like thrips and whiteflies from landing and feeding on plants, which prevents the spread of diseases like tomato spotted wilt virus (TSWS) and tomato yellow leaf curl virus (TYLCV).
Young said, “To maximize the quality and effectiveness with this type of highly-expensive insect control, growers should be vigilant in using a copper fungicide that won’t leave excess residue on plastic mulch during the season.”
Young and Adama contend that growers can “lose the blue” and gain benefits that Young noted without sacrificing disease control by using the company’s MasterCop fungicide/ bactericide as an alternative to other copper products. The product is a copper complex formulation of copper sulfate pentahydrate.
More information is available at adama.com.