There are several biopesticides labeled for application to soil and/or foliage to manage Phytophthora, some specifically for the blight pathogen, P. capsici. Most have a microbial organism (bacterium or fungus) as the active ingredient. They are approved for organic production. Biopesticides are recommended applied at low rate frequently rather than high rate once. They are also suggested used in combination based on the organism: Bacillus (AVIV, Companion, Double Nickel, Serenade, Stargus, Taegro 2), Gliocladium (Prestop, PVent, SoilGard), Streptomyces (Actinovate, Mycostop), and Trichoderma (Bio-Tam, RootShield Plus). Many are also labeled for managing Fusarium, Pythium and Rhizoctonia. Other labeled biopesticides are Regalia, OxiDate 2, and TerraClean 5. Their active ingredient is a natural substance, extract of giant knotweed, hydrogen dioxide and peroxyacetic acid.
Products listed by labeled use pattern:
- soil treatment before planting: Bio-Tam (broadcast apply to soil up to 7 days before planting; immediately incorporate with irrigation (best) or light cultivation), TerraClean 5.
- seed treatment as a spray or dry coating: Actinovate, Mycostop.
- drench to seedlings before transplanting: Bio-Tam, RootShield Plus (in greenhouse), Serenade ASO (pepper), SoilGard, Taegro 2.
- foliar spray in greenhouse: Companion.
- soil drench during or soon after planting: AVIV, Mycostop, Prestop, PVent, Regalia, Stargus, TerraClean 5.
- in-furrow during seeding: Actinovate, AVIV, Bio-Tam, Double Nickel, Regalia, RootShield Plus, Serenade ASO, Taegro 2.
- plant dip before transplanting: AVIV, Mycostop, Regalia.
- in transplant water: RootShield Plus, SoilGard.
- banded over the row: Bio-Tam, Companion, Taegro 2.
- basal directed spray: Bio-Tam, SoilGard, Taegro 2.
- through drip irrigation: Actinovate, AVIV, Bio-Tam, Companion, Double Nickel, Mycostop, Prestop, PVent, RootShield Plus, SoilGard, Taegro 2, TerraClean 5.
- foliar spray: Actinovate, AVIV, Companion, Double Nickel, OxiDate 2, Regalia, Serenade, Stargus.
Evaluations of Biopesticides and other Organic Fungicides
Efficacy has not been documented with the products and programs tested so far, but experiments were not conducted in the context of an integrated management program or in an organically-managed field, and Phytophthora blight is notoriously variable in occurrence spatially and temporally (year to year) making it challenging to detect treatment effects. Also, an evaluation can be unsuccessful because conditions are too favorable or not sufficiently favorable. The field used at LIHREC is dedicated to research on Phytophthora blight. Below is information about the experiments followed by a list of the publications with download links to obtain the reports which have more information plus results tables. Names of products tested are in bold.
Experiments conducted in 2017 and 2018
Four replicated experiments were conducted to evaluate programs with a combination of biopesticide products labeled for Phytophthora blight in two different crop types, pepper and pumpkin. Biopesticides were selected to have a full range of available active ingredients:
- Actinovate AG 12 oz/A (AI is Streptomyces lydicus)
- Bio-Tam 2 4 lb/A (Trichoderma asperellum and T. gamsii)
- Double Nickel 1.5 lb/A (Bacillus amyloliquefacinens)
- Regalia 3 qt/A (extract of Reynoutria sachalinensis)
- SoilGard 12G 10 lb/A (Gliocladium virens)
- Stargus 4 qt/A (B. amyloliquefacinens)
- Taegro 2 4 oz/A (B. subtilis)
Methods: Bio-Tam plus Taegro were applied in alternation with SoilGard in 2017 and with Stargus in 2018, starting with an application to soil before direct-seeding pumpkin and to seedling trays before transplanting pepper, followed by three soil-directed applications while plants were small. Foliar applications were started one week after the last soil application. Actinovate plus Regalia were applied in alternation with Double Nickel plus the copper fungicide Cueva (2 qt/A) plus Regalia for a total of five applications in 2017. Actinovate plus Cueva were applied in alternation with Stargus for a total of four applications in 2018. In addition to a nontreated control, there was a treatment with conventional fungicides applied on the same dates as the foliar biopesticides: Revus plus K-Phite alternated with Presidio plus K-Phite. Having a conventional fungicide treatment provides a measure of ability to suppress a pathogen. There was a fourth treatment in the pumpkin experiments consisting of the soil-directed biopesticide applications followed by the conventional fungicide foliar program. Soil-directed and foliar applications were made using a tractor sprayer. All applications were made on a weekly schedule. The field used has a history of Phytophthora blight. Phytophthora capsici proliferation was encouraged in 2016 by growing squash and pumpkin throughout the field with no management practices for Phytophthora blight.
Results: Phytophthora blight became severe in at least the nontreated control plots in all experiments. In 2017 conditions were generally dry and thus unfavorable for development of Phytophthora blight until an intensive rainstorm on 18 Aug (3.28 in. rain) whereas more frequent rain events in 2018 created favorable conditions throughout the growing season. Symptoms were first observed on 24 Aug 2017 and 3 Aug 2018. The biopesticide program was not effective in any of the four experiments; however, the conventional fungicide program was ineffective in the pepper experiment in 2017 and the pumpkin experiment in 2018 reflecting high disease pressure. There were significantly fewer affected pumpkin fruit in plots receiving the conventional fungicide program in 2017: 1.6 versus 31.5 for nontreated control plots. Control was not improved by applying biopesticides to soil before starting the conventional fungicide program. In 2018 this treatment with biopesticides and conventional fungicides had numerically fewest affected plants, but not significantly less than the nontreated control. In the experiments there was variation in Phytophthora blight development among replications that did not appear to be associated with treatments.
Experiment conducted in 2014 with pepper
Three organic biopesticides (Actinovate, Double Nickel, and Serenade Soil) were tested in combination and/or with an organic copper fungicide (Cueva) that was also tested alone for a total of six treatments. Some treatments included up to four soil drenches starting before transplanting followed by weekly foliar applications for a total of 12 applications. Three treatments included oomycete-targeted fungicides for conventional production applied alone or combined with the biopesticides. Applications were made with a backpack sprayer.
Serenade Soil has been replaced by Serenade ASO (AI is Bacillus subtilis), which is labeled for use only as a soil drench for managing Phytophthora blight. It and Serenade Opti (another formulation with this active ingredient) are labeled for foliar applications to manage other diseases.
Results: Conditions were not favorable for Phytophthora blight during most of the growing season due to limited rainfall, with less than 2.5 inches of rain per month falling in July, Aug and Sep. Rainfall was at least 1 inch on only two days in July and Aug: 1 inch on 15 July and 1.8 inches on 13 Aug. Symptoms were first observed on 29 July. Disease development was slow initially. Symptoms were found in only ten plots on 12 Aug. Due to very limited disease development through early Aug, a piece of infected zucchini fruit was placed in the center of each plot on 11 Aug before predicted rain. Many plants died due to blight following this inoculation and an intense rainstorm on 13 Aug. Control was achieved with two of the three treatments that included an alternation of the conventional fungicides, Revus and Presidio. No dead plants were observed in these treatments on 19 Aug. While effective, 35 and 42% of plants were dead at the last assessment (9 Sep, 5 days after the last application) versus 88% of nontreated control plants. Control obtained with these conventional fungicides was not improved by adding soil drench or foliar applications of biopesticides.
Experiment conducted in 2014 with acorn squash
Treatments applied to pepper described above were also applied at the same time to squash in an adjacent experiment (except pepper received 1 more soil drench to seedlings before transplanting). Similar results were obtained.
Experiment conducted in 2012 with pepper
Four organic biopesticides (Actinovate, Double Nickel, Regalia, Serenade Soil, and SoilGard) were tested alone, in combination, and/or with an organic copper fungicide (Badge X2) that was also tested alone for a total of six treatments. Some treatments included up to four soil drenches starting before transplanting followed by weekly foliar applications for a total of 12 applications. Three treatments included oomycete-targeted fungicides for conventional production applied alone or combined with the biopesticides. Applications were made with a backpack sprayer.
Results: Symptoms were not seen in this experiment until 23 Aug whereas blight was observed on 30 July in pumpkin in another research field at this facility. Disease development was slow. Incidence of affected fruit remained low. For some plots, it appeared that the treatment applied to the plot had less of an effect on occurrence of Phytophthora blight than the location of the plot being in a section of the field where conditions appeared to be more favorable that elsewhere for this disease. No symptoms were seen in some plots. Symptoms were not observed until 1 Oct for three treatments: Badge X2 alone, Serenade Soil + Badge X2, and the conventional fungicide program. At the last assessment on 12 Oct, while there were no significant differences among any treatments, incidence of affected plants was numerically greatest for non-treated peppers (42%) and lowest for peppers treated with the program of SoilGard + Badge X2 (5%). Incidence was 10% or less for the Actinovate treatment (10%), Serenade Soil applied as soil drench plus Badge X2 treatment (8%), and the conventional fungicide program (7%). Incidence was 18% for a program with Regalia, Serenade Soil, plus Badge X2, 37% for Regalia plus Badge X2, and 22% for Badge X2 alone.
Experiment conducted in 2012 with acorn squash
Treatments applied to pepper described above were also applied at the same time to squash in an adjacent experiment (except pepper received 1 more soil drench to seedlings before transplanting). Phytophthora blight also developed slowly in the squash experiment, and similarly, disease occurrence in some plots appeared to be influenced more by their location in the field rather than the treatment applied. For example, no foliar symptoms were seen in plots treated with Badge X2 alone or with three Serenade Soil drenches followed by Badge X2 applied to foliage; however, symptoms were observed in plots treated with Badge X2 plus Regalia or plus Regalia and Serenade Soil or plus SoilGard. Incidence of fruit rot was similarly variable in occurrence and no significant differences were detected among treatments. Similar to the experiment with pepper, best control appeared to be provided by applying SoilGard or Serenade Soil as soil drenches early in season followed by weekly applications of Badge X2 to foliage; however, in contrast with pepper, as good control was achieved by just applying Badge X2 to foliage.
Experiment conducted in 2007 with acorn squash
Two products with thyme oil as the active ingredient were tested together:
- Promax (formulation for soil application) was applied through the drip and
- Proud-3 was applied to the foliage.
These products are exempt from EPA registration and have general labels. While not specifically labeled for Phytophthora blight, they can be used for this disease. There were five other treatments in the experiment with conventional fungicides plus a nontreated control. Conditions were dry and unfavorable for Phytophthora blight during most of the growing season. Symptoms were first observed in mid-September. The treatment with the organic-type biopesticides was ineffective for suppressing Phytophthora fruit rot while three treatments with conventional fungicides were very effective.
Experiment conducted in 2006 with pumpkin
A goal of this study was to evaluate eight treatments with both foliar and drip applications of organic or conventional (phosphorous acid) biopesticides. All these treatments were a weekly alternation of applications to foliage and through drip irrigation. Actinovate is the only organic product tested that is now registered and labeled for Phytophthora. Other organic-type products tested were Kodiak (Bacillus subtilis GB03), Yield Shield (Bacillus pumilis GB34), and Proud-3 plus Promax. Kodiak and Yield Shield are no longer available. Conditions were dry and unfavorable for Phytophthora blight during most of the growing season. Phytophthora fruit rot was not found until 9 Sep. Treatment efficacy was evaluated on 11 Oct when fruit rot was more widespread but percent affected fruit was still low. The only treatments providing significant control were two with conventional fungicides. None of the treatments consisting of organic or conventional biopesticides applied alone suppressed Phytophthora fruit rot relative to the nontreated control. Results from this experiment are not considered definitive because disease began to develop very late in the growing season and was at a low level at the end of the trial.
Experiment conducted in 2005 with pumpkin
Companion (Bacillus subtilis GB03) was the only organic product tested. It is registered and labeled for aerial phase of Phytophthora blight in cucurbits but not pepper and other fruiting vegetables.
Several alternative products not approved for organic were also tested. Conditions were dry during most of the 2005 growing season and thus not conducive for Phytophthora blight. Foliar symptoms were not assessed. Phytophthora fruit rot was assessed on 24 Oct when 28% of fruit in nontreated plots were affected. Only the treatment with conventional fungicides had significantly higher percent marketable fruit than the nontreated control.
Reports with results listed above
(Note publication year listed after author names is a year after study was conducted, which is in the report title):
- McGrath, M. T., and Davey, J. F. 2006. Efficacy of alternative products for Phytophthora capsici in pumpkin, 2005. Fungicide and Nematicide Tests 61:V025.
- McGrath, M. T., and Davey, J. F. 2007. Evaluation of foliar and drip applications of biopesticides for management of Phytophthora blight on pumpkin, 2006. Plant Disease Management Reports 1:V126.
- McGrath, M. T., and Fox, G. M. 2008. Foliar and drip applications of biopesticides evaluated for managing Phytophthora blight in cucurbits, 2007. Plant Disease Management Reports 2:V075.
- McGrath, M. T. and LaMarsh, K. A. 2013. Evaluation of biopesticides for managing Phytophthora blight in cucurbits, 2012. Plant Disease Management Reports 7:V012.
- McGrath, M. T. and LaMarsh, K. A. 2013. Evaluation of biopesticides for managing Phytophthora blight in pepper, 2012. Plant Disease Management Reports 7:V017.
- McGrath, M. T. and LaMarsh, K. A. 2015. Evaluation of biopesticides for managing Phytophthora blight in cucurbits, 2014. Plant Disease Management Reports 9:V028.
- McGrath, M. T. and LaMarsh, K. A. 2015. Evaluation of biopesticides for managing Phytophthora blight in pepper, 2014. Plant Disease Management Reports 9:V029.
- McGrath, M. T. and Sexton, Z. F. 2018. Efficacy of biopesticides for managing Phytophthora blight in cucurbits, 2017. Plant Disease Management Reports 12:V071.
- McGrath, M. T. and Sexton, Z. F. 2018. Efficacy of biopesticides for managing Phytophthora blight in pepper, 2017. Plant Disease Management Reports 12:V005.
- McGrath, M. T. and Sexton, Z. F. 2019. Efficacy of biopesticides for managing Phytophthora blight in cucurbits, 2018. Plant Disease Management Reports 13:V117.
- McGrath, M. T. and Sexton, Z. F. 2019.Efficacy of biopesticides for managing Phytophthora blight in pepper, 2018. Plant Disease Management Reports 13:V116.
Acknowledgment: this research was mostly funded by the IR-4 Project, Biopesticide and Organic Support Program