This study sought to develop an integrated system for disease, insect, and nutrient management in organic blueberries centered around foliar applications of fish-derived products. Three on-farm trials (two in 2009 and one in 2010) were conducted on rabbiteye and southern highbush blueberries in southern Georgia. Four to six foliar sprays of four fish product formulations (Omega Grow, Organic Gem, Organocide, and SeaCide) were made during summer and early fall at each site and compared with an untreated check, an organic standard fungicide (Serenade Max), and one or two additional biofungicides. Two different foliar diseases, Septoria leaf spot and leaf rust, were suppressed successfully with fish products across the three trials. There was no clear “winner” among the four formulations, with Omega Grow, Organocide, and SeaCide being most effective in different trials. Effects on leaf beetle damage were inconsistent across trials, with one trial showing damage reduction by SeaCide and another showing no such effects. This inconsistency could be due to the higher amount of leaf damage already present at the onset of the latter trial. The effects of fish products on plant vigor and leaf retention also were variable, with Organocide and SeaCide improving both parameters at a low-vigor site (rabbiteye trial in 2009) but not a higher-vigor site (southern highbush trial in 2010). Thus, improvements in plant growth seem to be limited to conditions with weaker growth potential. None of the treatments translated into a higher flower bud set for the next growing season. Consistently across the three trials, application of Organic Gem resulted in considerably higher Na concentrations in leaf tissue of treated plants. Although these high Na levels did not appear to impact plant growth negatively, it would be advisable to apply this product only in rotations to preclude potential negative effects. In two of the three trials, increased concentrations of P were observed following application of some fish products, providing a potential nutritional benefit of these products. Overall, although fish products are no “silver bullets” for managing blueberries organically, they contribute consistently to leaf disease suppression and foliar nutrition.
Overall aim: develop an integrated approach for disease, insect, and nutrient management in organic blueberries centered around foliar applications of fish byproducts.
(1) compare and demonstrate the efficacy of several fish products against foliar diseases of blueberry;
(2) evaluate leaf beetle suppression in fish product-treated plots; and
(3) determine the nutritional benefits of fish product applications by measuring foliar nutrient status as well as plant growth and yield parameters in treated plots.
The organic blueberry acreage is expanding rapidly in Georgia and in Florida (Scherm & Krewer 2008), but pest management options for organic blueberries are limited. For example, yields can be reduced by several leaf diseases that cause premature defoliation in the summer, reduced flower bud set during the fall, and lower return yields the following year (Ojiambo et al. 2007, Scherm et al. 2007). A field trial in 2007 with four organic fungicides (Scherm et al. 2008) showed that two OMRI-listed fish byproducts provided substantial control of Septoria leaf spot (Septoria albopunctata), the most common foliar disease on blueberry in Georgia. Based on these preliminary results, our main objective in 2009 and 2010 was to compare and demonstrate the efficacy of several such products against the leaf disease complex on organic blueberries.
Insect and nutrient management are major challenges in organic blueberry production. The blueberry leaf beetle (Colaspis pseudofavosa) can destroy the tender new vegetative growth produced after berry harvest during the summer. Fields containing extensive weed growth in the aisles, such as most organic blueberry farms, can have a serious problem with this pest, and several months of young growth can be destroyed in a short period when beetles are numerous. Furthermore, nutrient supply is often suboptimal in organic production in sandy blueberry soils, leading to reduced shoot growth and flower bud formation, hence providing a poor foundation for next year’s yield. Previous studies on other perennial crops have shown that fish product applications can have marked repellent, antifeedant, and/or insecticidal activity against a range of insects and mites (Beattie et al. 1999, Sams and Deyton 2002), and most of these products are also marketed as fertilizers to supplement both macro- and micronutrients. Thus, the added value of fish extracts as foliar fertilizers and/or insecticides or insect repellents would provide a powerful incentive for their use as summer sprays in organic blueberries. Based on these considerations, additional objectives were to evaluate leaf beetle suppression, foliar nutrient status, and plant growth in organic blueberries treated with fish extracts.
A total of three on-farm trials were conducted during summer and fall of 2009 and 2010 in collaboration with grower and county agent cooperators in south Georgia’s blueberry belt. Site 1 in 2009 was a certified organic farm near Baxley (Appling County), where several cultivars of rabbiteye blueberry (Vaccinium virgatum) are grown. The trial was conducted in mature bushes (>10 years old) of Brightwell, a commonly grown cultivar in both conventional and organic production systems. Site 2 in 2009 was a higher-fertility farm near Alma (Bacon County), where the trial was carried out in mature bushes of Bluecrisp southern highbush blueberry (Vaccinium corymbosum interspecific hybrid). This planting was not certified organic, but remained untreated with fungicides and insecticides during the experimental period. The 2010 trial was conducted in a certified organic planting of mature Star southern highbush blueberry in Clinch County. Southern highbush cultivars are generally more susceptible to disease and insect pest damage than rabbiteye cultivars (Scherm & Krewer 2008, Scherm et al. 2007), but both species are grown organically in the southeastern U.S.
Foliar applications of four different fish products and two or three other biofungicides were evaluated in the three trials (Table 1). All products are OMRI-listed. In 2009, six spray applications were made between late July and early October (site 1) or mid-July and late September (site 2); whereas in 2010, four sprays were applied between late August and early October. Applications were made with backpack sprayers at a rate of 60 to 75 gal/A, and treatment plots were arranged in a randomized complete block design with four replicates. Individual plots were four (site 1, 2009), between two and four (site 2, 2009), or five (2010) bushes long and separated by untreated buffers.
Periodic disease, leaf beetle damage, and plant growth assessments were made during the experimental period. Final severity of Septoria leaf spot was determined on a sample of 40 leaves per plot in mid- to late October, either by counting the number of spots per leaf (in 2009) or – due to higher disease severity in 2010 – by visually estimating percent leaf area covered with spots. In the latter case, the assessor had been trained with DiseasePro (Nutter 1997), a computerized disease assessment training program, prior to making the assessments. At site 2 in 2009, leaf rust, caused by Thekopsora minima, appeared in late fall, and final disease severity was estimated as the percentage of leaf area covered with rust pustules on a sample of 25 leaves per plot in early December.
Leaf beetle damage assessments were also made in October of 2009 and 2010 using a whole-plant rating scale from 0 (no damage on new growth) to 4 (severe damage on new growth). In addition, in 2010, detailed counts of the number of leaf beetles per bush were made 1 and 7 days after the third spray application in late September.
A plant vigor rating (considering leaf coloration, leaf retention, and overall shoot growth) was conducted for each plot in mid- to late October using a scale from 1 (poor) to 5 (excellent). At the same time, a random sample of spring leaves from each plot was submitted for tissue nutrient analysis (both macro- and micronutrients) to the UGA Soil, Plant, and Water Laboratory. Also in mid-October (2010) or early December (2009) defoliation was assessed by counting the leaves missing on a sample of ten spring shoots per plot. Finally, between early December and early February of the following year, flower bud set was determined on 20 shoots per plot to assess treatment effects on return yield potential. Data were summarized for each plot and subjected to analysis of variance followed by means separation (Fisher’s protected LSD test) where appropriate.
At site 1 in 2009 (Brightwell rabbiteye blueberry), Septoria leaf spot was the dominant foliar disease. Disease severity remained low until late August, increasing to moderate levels during the fall and reaching an average of ~10 spots per leaf in the untreated plots during the late-October assessment (Fig. 1A). Biofungicide treatments differed at a significance level of P = 0.0647 (slightly more liberal than the customary P = 0.05 level), with all fish products (Omega Grow, Organic Gem, Organocide, SeaCide) as well as Sporan having less severe disease than the untreated check. Leaf spot severity was lowest for Omega Grow (less than one-third of untreated).
Septoria leaf spot was all but absent at site 2 in 2009 (Bluecrisp southern highbush blueberry), with <0.2 spots per leaf in the untreated plots during the late-October assessment. However, late-season leaf rust developed at this site, as evident in the early-December assessment (Fig. 1B). Due to high variation among replicates, no significant treatment effects on rust severity were observed; however, Omega Grow and SeaCide-treated plots consistently had very low rust severities.
In the 2010 trial on Star southern highbush blueberry, Septoria leaf spot was already present in the planting at moderate levels when the treatments commenced in late August, attaining very high levels by the end of the trial (Fig. 1C). At a P-level of 0.0689, Organocide (15.6% severity) reduced disease compared with the untreated check (23.1% severity). None of the other treatments resulted in disease reductions compared with untreated.
No leaf beetle populations built up at site 1, hence only results from site 2 are shown for 2009. On average, about 20% of the leaves inspected during the late-October assessment showed symptoms of leaf beetle damage. Beetle damage differed among biofungicide treatments at a level of P = 0.0641, with SeaCide, Serenade Max, and Sporan having lower damage scores than the untreated plots (Fig. 2).
In the 2010 trial, high levels of beetle-induced leaf damage developed in the experimental plots by early October, with the untreated check averaging 3.92 on the 0 (no damage) to 4 (severe damage) scale (Table 2). None of the treatments reduced leaf damage significantly (P = 0.2369), presumably because a large part of the damage had been done by the time the treatments commenced in late August. When detailed counts of leaf beetles per bush were made after the third spray application in late September, none of the treatments affected the number of live or dead beetles 1 day after application (Table 2); however, beetle numbers were reduced significantly (P < 0.0001) and by more than 50% in all treated plots 7 days after application, indicating that the insects avoided the treated plots.
When plant vigor was assessed at site 1 in late October 2009, biofungicide treatment effects were highly significant (P = 0.0011). Vigor was increased by all treatments relative to untreated, except by Organic Gem (Table 3). Ratings were highest for Serenade Max, Organocide, and SeaCide. The latter two fish products also reduced defoliation (assessed separately in early December) significantly compared with the untreated plots (Table 3). For example, the SeaCide-treated plants retained three times more leaves than their untreated counterparts. Flower bud set (also assessed in early December) was very low overall and was not significantly affected by treatment (Table 3).
No vigor or leaf retention assessments were made at site 2 in 2009 due to confounding effects of infections with the bacterial leaf scorch bacterium Xylella fastidiosa, which causes a novel systemic disease of blueberry resulting in dieback and plant death (Chang et al. 2008).
There was no treatment effect on plant vigor in the 2010 trial (P = 0.3748; Table 3), most likely because overall plant growth was relatively vigorous at this site (mean score = 3.00). In contrast, in our 2009 trial at site 1, in which untreated check plants were consistently less vigorous (mean score = 2.13), showed significant increases in vigor for all treatments. Thus, it appears that the ability of the treatments to increase plant vigor is dependent on overall plant growth potential, with greater increases likely in conditions with weaker growth potential. The mean defoliation level in the untreated check in mid-October was 59.2% (Table 3). Although several of the treatments (Sporan, Omega Grow, Serenade Max, and KeyPlex) had defoliation levels below 40%, these reductions were not statistically significant (P = 0.1280) due to experimental variability among plots. Treatment effects on flower bud numbers in late winter were similarly not significant (P = 0.1077; Table 3).
At site 1 in 2009, a highly significant (P < 0.0001) increase in leaf Na concentrations following application of Omega Grow and, to a lesser degree, Serenade Max was observed (Table 4). A less pronounced (P = 0.0643) increase in leaf Na concentrations following the application of Omega Grow was also observed at site 2 in 2009. At the latter site, applications of Organic Gem and Organocide had the beneficial effect of increasing leaf P levels compared with the untreated check (P = 0.0510; Table 4).
In the 2010 trial (Table 5), Omega Grow again increased Na concentrations significantly (by almost 3-fold). In addition, KeyPlex, which was not tested in the previous year, resulted in >5-fold and >4-fold increases in Fe and Zn levels, respectively. Less pronounced but significant were the increases in Mn following KeyPlex application and in P following application of Organic Gem and Omega Grow. All treatments reduced foliar Ca and Mg levels compared with the untreated check.
Educational & Outreach Activities
The most important outreach activity was the close collaboration and interaction with our grower collaborators and their county extension agents while the three trials were conducted in 2009 and 2010. They were active participants in the trials, received regular updates, and provided critical feedback. In terms of reaching a large audience of organic growers and those interested in converting to organic production, our most important activity has been the participation in the organic blueberry educational sessions at the Southeast Fruit and Vegetable Conference and Trade Show in Savannah, GA, in January 2010 and 2011, where more than 100 growers specifically attended our sessions each year. A major venue for outreach to extension personnel was a presentation at the North American Blueberry Research and Extension Workers Conference (NABREW) in Kalamazoo, MI, in July 2010; this biannual conference has been a key educational forum for blueberry researchers, Extension educators and industry leaders since the 1960s.
Scherm, H., Savelle, A.T., Tertuliano, M., and Krewer, G. 2011. Fish product trials for leaf disease management in organic blueberries in Georgia, 2009-2010. Dixie Blueberry News 11(4):10-23.
Tertuliano, M., Krewer, G., Smith, J.E., Plattner, K., Clark, J., Jacobs, J., Andrews, E., Stanaland, D., Andersen, P., Liburd, O., Fonsah, E.G., and Scherm, H. 2011. Growing organic rabbiteye blueberries in Georgia, USA: Results of two multi-year field studies. Journal of Tree Fruit Production (in press).
Scherm, H., Savelle, A.T., Krewer, G., Tertuliano, M., and Clark, J.R. 2008. Control of Septoria leaf spot of blueberry with biofungicides, 2007. Plant Disease Management Reports 2:STF037.
Although cultivars, cultural practices, and disease and pest pressures differed among the three trials, the following can be concluded about the impacts and outcomes of this 2-year project:
- Two different foliar diseases, Septoria leaf spot and leaf rust, were suppressed successfully with fish products across the three trials. There was no clear “winner” among the four tested formulations, with Omega Grow, Organocide, and SeaCide being most effective in different trials.
Effects on leaf beetle damage were inconsistent, with one trial showing damage reduction by SeaCide applications and another trial showing no such effects. This inconsistency could be due to the higher amount of leaf damage already present at the onset of the latter trial. Regardless, it appears that any leaf beetle suppression associated with fish products is mostly incidental, with the greater impact being on leaf disease management.
The effects of fish products on plant vigor and leaf retention also were variable, with Organocide and SeaCide improving both parameters at a low-vigor site (rabbiteye in 2009) but not a higher-vigor site (southern highbush in 2010). Thus, improvements in vegetative plant growth seem to be limited to conditions with weaker growth potential. Regardless, none of the treatments translated into a higher flower bud set for the next growing season.
Consistently across the three trials, application of the fish product Omega Grow resulted in considerably higher Na concentrations in leaf tissue of treated plants. Although these high Na levels did not appear to impact plant growth negatively, it would be advisable to apply this product only in rotations to preclude potential negative effects. In two of the three trials, significantly increased concentrations of P were observed following application of some fish products, providing a potential nutritional benefit of these products. The organic host resistance inducer KeyPlex, which was tested only in one of the trials, markedly increased Fe, Zn, and Mn levels in treated plants, providing a potential benefit in terms of micronutrient supply.
Overall, although fish products are no “silver bullets” for managing blueberries organically, they do contribute consistently to leaf disease suppression and foliar nutrition and can have added, more incidental benefits on leaf beetle suppression.
As with many specialty crops, a full economic cost-benefit analysis for organic blueberries is challenging due to major price fluctuations depending on marketing channel, harvest date, and overall quality and supply. Input costs can be compared more readily and indicate favorable economics for fish byproduct application. For example, the fixed cost of a typical fish product application is <$10 per acre, assuming a 2% rate (corresponding to ca. 1 gal/acre). This compares favorably with a fixed cost of ca. $60 per acre for one of the leading biofungicides.
Based on informal surveys we estimate that about half of the organic blueberry growers in GA, FL, and SC have adopted summer and/or fall applications of fish byproducts, primarily for managing foliar diseases. Other growers apply compost teas or use weekly applications of a hydrogen dioxide-based biofungicide during this period.
Areas needing additional study
The area most in need of additional study is optimization of application timing for fish product applications. In the present study, applications were made more or less on a calendar schedule for four to six applications during the summer and fall, but the optimal timing likely varies based on disease pressure and cultivar resistance. It may also be possible to define a disease severity treatment threshold for one or more of the most prevalent diseases, such as Septoria leaf spot.
Beattie, G.A.C., Rae, D.J., Watson, D.M., Liu, Z.M., Jiang, L., Ahmad, N., and Manadarakas, P. 1999. Comparison of fish emulsion, fish oil and petroleum spray oil for control of citrus leafminer, Phyllocnistis citrella Station (Lepidoptera: Gracillariidae). J. Austr. Entomol. Soc. 34:335-342.
Chang, C.-J., Donaldson, R.,, Branne, P., Krewer, G., and Boland, R. 2009. Bacterial leaf scorch, a new blueberry disease caused by Xylella fastidiosa. HortScience 44:413-417.
Nutter, F. W., Jr. 1997. Disease severity assessment training. Pages 1-7 in: Exercises in Plant Disease Epidemiology. L. J. Francl and D. A. Neher, eds. American Phytopathological Society, St. Paul, MN.
Ojiambo, P.S., Scherm, H. and Brannen, P.M. 2007. Temporal dynamics of Septoria leaf spot of blueberry and its relationship to defoliation and yield. Plant Health Progress doi:10.1094/PHP-2007-0726-05-RS.
Sams, C.E., and Deyton, D.E. 2002. Botanical and fish oils: History, chemistry, refining, formulation and current uses. Pages 19-28 in: Spray Oils Beyond 2000: Sustainable Pest and Disease Management. G.A.C. Beattie, D.M. Watson, M.L. Stevens, D.J. Rae, and R.N. Spooner-Hart, eds. Univ. of Western Sydney, Sydney.
Scherm, H., and Krewer, G. 2008. Disease management in organic rabbiteye blueberries. International Journal of Fruit Science 8:69-80.
Scherm, H., Savelle, A. T., Brannen, P. M., and Krewer, G. 2007. Occurrence and prevalence of foliar diseases on blueberry in Georgia. Plant Health Progress doi:10.1094/PHP-2008-0421-01-RS.
Scherm, H., Savelle, A. T., Krewer, G., Tertuliano, M., and Clark, J. R. 2008. Control of Septoria leaf spot of blueberry with biofungicides, 2007. Plant Disease Management Reports 2:STF037.
- Table 1. Treatments evaluated in three on-farm trials to determine the effects of foliar applications of fish products and other biofungicides on leaf disease development, leaf beetle suppression, and plant growth in blueberries in Georgia
- Fig. 2. Effects of fish products and other biofungicides on leaf beetle damage on ‘Bluecrisp’ southern highbush blueberry in Bacon County, GA, 2009. Values are means and standard errors of four replicate plots. Letters signify means separation results by Fisher’s protected LSD test at the P-level indicated.
- Table 4. Effects of fish products and other biofungicides on select foliar nutrient concentrations in on-farm trials in blueberries in Georgia, 2009
- Table 2. Effects of fish products and other biofungicides on leaf beetle damage and the number of beetles per bush on ‘Star’ southern highbush blueberry in Clinch County, GA, 2010
- Table 5. Effect of fish products and other biofungicides on the concentrations of select foliar nutrient concentrations on ‘Star’ southern highbush blueberry in Clinch County, GA, 2010
- Fig. 1. Effects of fish products and other biofungicides on the severity of Septoria leaf spot (A and C) and leaf rust (B) in on-farm trials in blueberries in Georgia, 2009 and 2010. Values are means and standard errors of four replicate plots. Letters signify means separation results by Fisher’s protected LSD test at the P-levels indicated.
- Table 3. Effects of fish products and other biofungicides on plant vigor, defoliation, and flower bud set in on-farm trials in blueberries in Georgia, 2009 and 2010