Plantpro 45 as a Control of Soil-Borne Pathogens,
Weeds, Nematodes, and Seed-Borne Pathogens

Plantpro 45, a low-risk iodine-based compound, was studied by Nancy Kokalis-Burelle to ascertain its usefulness for soil-borne pathogen and weed control. The results are somewhat mixed. Two years of greenhouse and field trials have shown that Plantpro 45 has some potential for control of root-knot and sting nematodes, some soil-borne fungal and bacterial pathogens, seed-borne fungal pathogens, and economically important weed species.

"Plantpro 45 works by disrupting membranes in organisms. When compounds are in contact with nematodes and eggs in the lab you get good toxicity, but in the soil the effect is lessened," says Burelle. "Soil is a very complex medium and water doesn't move through the soil as expected, and results vary from trial to trial."

Nematode Control

Plantpro 45 showed some reduction of root-knot nematode damage on tomato at multiple field locations in Florida. However, Burelle found it didn't perform as well as methyl bromide.

In field trials conducted in cooperation with the IR-4 methyl bromide alternatives research program on strawberries in Florida, Plantpro 45 seemed to control soil populations of sting nematode. In two locations, nematodes were reduced from about 175 nematodes per 250 cc of soil in the untreated plots to approximately 50 in the Plantpro 45 (plus Devrinol) plot and about 25 nematodes per 250 cc of soil in the methyl bromide treated plot. In another IR-4 trial at Duke Farm, Dover, Florida, a combination of Plantpro 45 + Fosthiazate + Devrinol brought sting nematode levels to 0.8 per 100 cc of soil compared to 29.3 per 100 cc of soil in the untreated control plot. When a combination of only Plantpro 45 + Devrinol was used, the sting nematode population was reduced to 6.8 per 100 cc soil.

Efficacy for nematode control was not tested in the IR-4 California strawberry trials, since plant parasitic nematodes are not widely prevalent in California soils cropped to strawberries due to a lack of sandy soil, the nematode's preferred environment, explained Mike Nelson of Plant Sciences, Inc. (Watsonville, California). In addition, Nelson found that Plantpro 45 seems to confer some fungicidal benefits; for instance, it controls Rhizoctonia at upper soil depths and meets industry standards.

Fungal and Bacterial Control

In several locations in Florida, Plantpro 45 demonstrated fungicidal and bactericidal effects by providing significant control of Fusarium crown rot and bacterial wilt of tomato in naturally infested fields. Under greenhouse conditions, a soil drenching with Plantpro 45 of 80 ppm followed by a planting 21 days later and a foliar application at 80 ppm 1 week after planting increased root and shoot weight and improved root condition of tomato when grown in field soil naturally infested with Fusarium crown rot.

In an IR-4 tomato trial carried out in southern California (Tustin, Orange County), by Nelson, a preplant application of Plantpro 45 (1X rate of 142 gallons per treated acre, applied in 1.5 inches of water), gave control of Rhizoctonia solani comparable to that of the methyl bromide/chloropicrin standard at the 6-inch soil depth. However, a postplant application at a reduced rate of (63 gallons per treated acre, also applied in 1.5 inches of water), did not provide similar control of this soil-borne pathogen.

Crop Performance

In IR-4 tomato trials conducted over a 2-year period in California, Plantpro 45 treatments produced marketable fruit yields comparable to the industry standard, according to Nelson. "Plantpro 45 produced the best looking fruit and best yield in tomatoes." At the Oceanside, California, site during 2001 trials, Plantpro 45 (3/4X) + metam (applied as a bed-top broadcast spray strictly for weed control) outperformed all alternatives in yield, producing 5,069 25-pound cartons/acre compared to 5,059 25-pound cartons/acre produced by a combination of methyl bromide and chloropicrin (50/50) and 4,518 25-pound cartons/acre in the untreated control.

Strawberry trials in Oxnard and Salinas, California, produced mixed results. During first-year trials (2000 fall planting/2001 harvesting), plants were substantially less vigorous in Plantpro 45 treated plots, relative to the methyl bromide/chloropicrin treated plots. However, Nelson notes that the compound was applied both as preplant treatment and as postplant treatment applications and that the postplant applications in particular appeared to inhibit growth of the strawberry plants. In the second-year trials (2001 fall planting/2002 harvesting), the postplant application was eliminated and vigor improved. Plants will continue fruiting until June 2002 in the southern California (Oxnard) trial and until late October 2002 in the northern California (Salinas) trial, at which times the season-total fruit yields will be assessed.

Burelle notes that Plantpro 45 can negatively impact crop growth. "Postplant applications should not be attempted on peppers or strawberries since they are especially sensitive to the chemical and should be closely monitored on all other crops."

Weed Control

Plantpro 45 does provide some weed control, according to Burelle's study. Multiple greenhouse experiments on weed infestation levels in naturally weed-infested soil showed that Plantpro 45 has potential to control one of Florida's major herbaceous weed species in vegetable crops: purslane (Portulaca oleracea). Further studies on the herbicidal effects of Plantpro 45 confirm significant reductions in populations of nightshade, purple and yellow nutsedge, and crabgrass. High-foliar applications of Plantpro 45 on emerged weeds, followed by rototilling prior to planting, provided effective control of weed species without phytotoxic effects on tomato when an interval of 21 days was allowed before planting and adequate soil moisture was maintained between application and planting.

In contrast, in Nelson's 2001 California tomato trials mortality of annual bluegrass and common purslane buried 6 inches deep prior to application of Plantpro 45 was significantly lower, relative to the methyl bromide/chloropicrin standard, and not statistically different from that of the untreated control. Further, mixed results were observed in the 2000 Florida tomato trials. At the Lake Jem trial site, the combinations of Plantpro 45 + metam (applied as a bed-top broadcast spray strictly for weed control) did not significantly control yellow nutsedge. However, at the Live Oak trial site, the Plantpro 45 (1X) + metam (metam again used strictly for weed control) combinations reduced the incidence of this weed species to a level comparable to that of the methyl bromide/chloropicrin standard.

Seed Treatment

In a different application, Plantpro 45 seems to also provide some efficacy as a seed treatment. Burelle worked with an oriental-vegetable grower who had a problem with Fusarium. "Plantpro 45 has good potential as a seed treatment," says Burelle. Further studies are needed.

Last Updated: July 17, 2002