AUGUST 2024 29 PESTICIDES as a pesticide if farmers have been using them for years? EPNs quickly perish when they are removed from the soil, either due to exposure to the sun’s ultraviolet rays or from dehydration. This inability to survive long above ground severely limits EPN application to the leaves of plants, which are the primary targets of most pests. One such pest is the fall armyworm caterpillar, a significant threat to corn crops in Africa and Asia. As noted above, researchers have found a solution within a solution— specifically one that involves the nematodes being kept alive within a gelatinous solution—acting like sunscreen, so when applied topically to a plant, the worms can feed on the above-ground pests. The nematodes are suspended— alive—within a gelatinous matrix of non-toxic biodegradable carboxymethyl cellulose. A team of scientists, led by Patrick Fallet from the University of Neuchâtel in Switzerland, began by genetically modifying a native Rwandan EPN (Steinernema carpocapsae) to specifically target the caterpillars. The researchers then developed a hydrogel, a non-toxic, biodegradable carboxymethyl cellulose matrix that contained live nematodes. In field trials conducted in Rwanda, volunteer farms applied the gel to the whorl of corn plants every two weeks throughout a growing season using caulking guns. Yes, we know that targeting individual plants with a caulking gun is not going to work on a typical Canadian corn field, but note that this is a test project. According to the study, four plant treatments were compared: 1) untreated control; 2) application of EPN in a commercially available liquid SPF (e-nema GmbH, Schwentinental, Germany); 3) application of EPN in a carboxymethyl cellulose (CMC) gel; and 4) a positive control with the application of the pyrethroid contact insecticide cypermethrin. “We had previously shown that the formulations by themselves (SPF and gel without EPN) did not affect FAW survival and that the application of EPN applied in just water was only marginally effective. We, therefore, excluded these treatments from the here-presented trials,” wrote the scientists in their final report. In their report, the research scientists noted that the “SPF and CMC were dissolved in sterile water to a final concentration of 0.11% (as recommended by the provider) and 3% (w/v), respectively. First, 42 grams of CMC or 1.54 grams of SPF were added to 1,300 mL of water and left to rest. The next day, solutions were vigorously mixed with a whisk until fully dissolved. Then, 2.1 million EPN concentrated in 100 mL of water were added to the formulations and gently mixed. Using a binocular magnifier, we confirmed that the formulations contained about 1,500 EPN/ mL (for an application of ~3,000 EPN per plant in a two-mL spot injection/ spray). The cypermethrin (Supra EC, ETG Inputs Ltd., India; 50 g a.i./L) was dissolved in water at 1.0 mL/L (~0.1 mg a.i. applied per plant in a two-mL spot-spray). The prepared formulations were kept in cool boxes and used within four hours.” The corn in the study, a Rwandan maize hybrid RHMN 1,601, was planted February 17–18, 2022, and sown every 30 centimetres in rows separated by 70 cm, representing about 47,000 plants per hectare. The fields were fertilized twice with NPK (nitrogen, phosphorus, and potassium) and urea at a rate of 300 and 100 kg/ha, respectively. They were fertilized once before sowing and a second time four weeks after sowing—which is what farmers usually do in Rwanda. The fields were then left untreated against insects until the beginning of the experimental applications, which were carried out between February and June 2022 in three locations that were a total of 30 kilometres apart and in different environmental conditions—altitude, exposure, and surrounding vegetation. While all fields treated with a pesticide showed some impact in killing the caterpillars, the hydrogel had greater success, reducing infestations by approximately 50 percent relative to the control plots. Better yet, the gel-treated plots were able to yield an additional ton of corn per hectare. The study’s report, published in the PNAS Nexus journal, stated that “the overall results imply that precisely formulated and easy-to-apply nematodes can be a highly effective, affordable, and sustainable alternative to insecticides for FAW [fall armyworm] control.” As for its application in Canadian crops, while there’s no research being performed yet, the principles of the gel should apply universally. The key for farmers would be to select local strains of nematodes that can target the specific pests affecting Canadian crops. Further research and field trials would be necessary to confirm its effectiveness in the Canadian context. Can the hydrogel be effective against different pests, different degrees of weather, and different crop types? Any takers? We are also not sure about a more automated form of delivery of the hydrogel to the crops, but this writer does suspect that as long as the gel doesn’t clog up the delivery system and the hydrogel contains the desired nematode species capable of consuming the pests you want to be consumed, then there is promise to this technology. Fallet suggests that a commercial version of the hydrogel should be less costly than traditional pesticides, pose no harm to humans or the environment, and prevent—as the team’s field research showed—armyworms from developing resistance.
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