Fish extracts for integrated disease, insect and fertility management in organic blueberries

Fish extracts for integrated disease, insect and fertility management in organic blueberries

Summary

An on-farm trial was conducted in an organically managed planting of ‘Star’ southern highbush blueberry in southern Georgia to evaluate an integrated system for improved disease, insect, and nutrient management based on foliar applications of fish byproducts. Four spray applications of four different fish formulations (Omega Grow, Organic Gem, Organocide, and SeaCide) were made between late August and early October 2010 at each site and compared with an untreated check, an organic standard fungicide (Serenade), a plant oil-based biofungicide (Sporan), and a micronutrient-based host resistance inducer (KeyPlex). High levels of Septoria leaf spot and of leaf beetle damage developed during the trial. Applications of the fish-sesame oil product Organocide reduced Septoria leaf spot severity markedly, despite the high disease pressure and the fact that applications started after the disease had already been established in the planting. All treatments (fish products as well as the other biofungicides) reduced the number of leaf beetles within 1 week after treatment, indicating that the insects avoided the treated plots. However, the overall amount of beetle damage to leaves was not reduced, presumably because a large part of the damage had already been done by the time the treatments commenced in late August. In conditions of relatively good plant growth, none of the treatments improved plant vigor, leaf retention, or flower bud set. KeyPlex applications markedly increased Fe, Zn, and Mn levels in treated plants, whereas increased concentrations of P were observed following application of Organic Gem and Omega Grow. Plants treated with Organic Gem had considerably higher foliar Na levels, but no adverse effects on plant growth or development were noted.

Objectives/Performance Targets

Overall aim: develop an integrated approach for disease, insect, and nutrient management in organic blueberries centered around foliar applications of fish byproducts.

Specific objectives:
(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.

Accomplishments/Milestones

An on-farm trial was conducted during summer and fall 2010 in an organic planting of mature ‘Star’ southern highbush blueberry (Vaccinium corymbosum interspecific hybrid) in Clinch County, GA. Four foliar spray applications of four fish product formulations were made between late August and early October: (1) Omega Grow, 2% (Omega Protein, Houston, TX); (2) Organic Gem, 2% (Advanced Marine Technologies, New Bedford, MA); (3) SeaCide, 1% (Omega Protein); and (4) Organocide, 2% (Organic Laboratories, Stuart, FL). The latter product contains sesame oil in addition to fish oil. Furthermore, (5) Sporan at 2.5 pt/acre (EcoSMART Technologies, Franklin, TN), a plant-derived biofungicide containing rosemary and wintergreen oils; (6) KeyPlex 350 OR at 0.5% (KeyPlex, Winter Park, FL), a micronutrient-based host resistance inducer; (7) an organic standard treatment of the biofungicide Serenade Max at 1.5 lb/acre (AgraQuest, Davis, CA); and (8) an untreated check were included. Applications were made with backpack sprayers calibrated to deliver the equivalent of 75 gal/acre. Treatment plots were arranged in a randomized complete block design with four replicates. Individual plots were five bushes long with the outer two bushes serving as buffers.

DISEASE SUPPRESSION
Septoria leaf spot (caused by the fungus Septoria albopunctata) was the dominant foliar disease at this location. The disease 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 (Table 1). Disease severity was evaluated in mid-October by visually estimating percent leaf area covered with spots on a sample of 40 leaves per plot. The assessor had been trained with DiseasePro (Nutter 1997), a computerized disease assessment training program, prior to making the assessments. At a P-level of 0.0689, Organocide (15.6% severity) reduced disease significantly compared with the untreated check (23.1% severity). None of the other treatments resulted in disease reductions compared with untreated. Significant suppression of Septoria leaf spot with Organocide was also observed in our 2009 trial on rabbiteye blueberry.

LEAF BEETLE SUPPRESSION
High levels of beetle-induced leaf damage developed in the experimental plots by early October, with the untreated check averaging 3.92 on a 0 (no damage) to 4 (severe damage) scale (Table 1). None of the treatments reduced leaf damage significantly (P = 0.2369), presumably because a large part of the damage had already been done by the time the treatments commenced in late August. When detailed counts of leaf beetles (Colaspis pseudofavosa) 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.

PLANT VIGOR, FLOWER BUD SET, AND LEAF NUTRIENT LEVELS
A visual plant vigor rating was conducted in mid-October using a whole-plant scale from 1 (poor) to 5 (excellent). At the same time, defoliation was determined by counting the number of missing leaves from nodes on a sample of ten shoots per plot. A random sample of still attached spring leaves from each plot was submitted for tissue nutrient analysis. In early February of the following year (2011), flower bud set was determined on 20 shoots per plot to assess treatment effects on return yield potential.

There was no treatment effect on plant vigor (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, 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).

Significant treatment effects on foliar nutrient levels were observed (Table 4), the most pronounced of which were >5-fold and >4-fold increases in Fe and Zn levels, respectively, associated with KeyPlex application; and an almost 3-fold increase in Na concentrations associated with Omega Grow treatment. This latter effect was also observed in our 2009 trial. Less pronounced but significant were the increases in Mn following KeyPlex application and in P following application of Organic Gem and Omega Grow. Similar beneficial increases in P concentrations associated with application of fish products were observed in our 2009 trial. All treatments reduced foliar Ca and Mg levels compared with the untreated check.

Impacts and Contributions/Outcomes

• Applications of the fish-sesame oil product Organocide reduced Septoria leaf spot severity, despite the very high disease pressure and the fact that applications started after the disease had already been established in the planting. This confirms the favorable results obtained with Organocide in our 2009 trial.
  All treatments (fish products as well as the other biofungicides) reduced the number of leaf beetles within 1 week after treatment, indicating that the insects avoided the treated plots. However, the overall amount of beetle damage to leaves was not reduced significantly, presumably because a large part of the damage had already been done by the time the treatments commenced in late August. Applications will need to be initiated earlier in future trials.
  In conditions of relatively good plant growth, none of the treatments improved plant vigor, leaf retention, or flower bud set. Improvements in vegetative and generative plant growth seem to be limited to conditions with weaker growth potential, as occurred in our 2009 trials on rabbiteye blueberry.
  The micronutrient-based host resistance inducer KeyPlex markedly increased Fe, Zn, and Mn levels in treated plants, whereas the fish product Organic Gem resulted in considerably higher Na concentrations. These high Na levels did not appear to impact plant growth negatively. Increased concentrations of P were observed following application of Organic Gem and Omega Grow. Similar beneficial increases in P concentrations associated with application of fish products were noted in our 2009 trial.

• Tables 1 through 4

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