Implementing biointensive pest management and evaluating hard cider manufacturing to increase sustainability of apple production
Results in the third year of this 3-year systems-level project continued to show that scab resistant varieties, a disease-warning system, and mulching can enhance sustainability of Iowa apple orchards. Combining scab-resistant varieties with a warning system for sooty blotch and flyspeck disease resulted in fewer pesticide sprays and spray trips, lower pest management costs, and sharply reduced environmental impact compared to either calendar-based spray timing or a standard integrated pest management (IPM) program, with equivalent yield and fruit quality. As in previous years of the study, mulching with composted hardwood bark mulch reduced reliance on chemical herbicides and resulted in soil that was cooler, moister, and higher in organic matter than in bare-ground plots. Year 3 results also showed that high-quality hard cider can be produced from Iowa apples, including scab-resistant varieties, as a value-added product for apple growers. Results were shared with Iowa growers through field days and annual research reports.
Objective 1: Compare innovative practices to conventional IPM and traditional practices for disease, insect, and weed management in annual field trials.
Objective 2: Develop methods for producing hard apple cider of consistently high quality that Midwest consumers are willing to buy.
Objective 3: a) Calculate the costs, benefits, and risks of the alternative apple management systems in Objective 1; b) Estimate the costs, benefits, and risks associated with local-scale manufacturing and marketing of hard cider in Iowa.
Objective 4: Communicate project findings to North Central Region apple growers through on-farm demonstration trials, field days, meeting presentations, statewide and regional newsletter and trade-journal articles, a project website, press releases, and an on-line Extension bulletin. Performance targets for research, stated in the project proposal: field validation of best management practices that integrate current disease, insect pest, and weed management innovations with disease-resistant apple varieties; cost-benefit and environmental impact analyses of each strategy; hard cider production methods that produce a superior product; and refereed publications in technical journals. Outreach targets included: three field days; nine presentations at regional grower meetings; articles in Fruit Growers News; a project website; and an on-line extension bulletin.
Trial 1 – IPM systems for disease, insect pest, and weed management.
For each treatment, pesticide spray trips were often fewer in number than individual pesticide sprays because fungicide and insecticide sprays that were required at nearly the same time on the same treatment blocks were tank mixed where feasible in order to conserve energy, fuel, and time. Averaged over all three cultivars and 3 years, Treatment 4 required the fewest pesticide sprays (14.3) and spray trips (10.6) of any treatment. In each year, cv. Redfree had the fewest insecticide and fungicide sprays, since it matured 5 and 9 weeks earlier than Liberty and GoldRush, respectively. Redfree was the least pesticide-intensive of the three cultivars, which suggests that it would also be the least expensive to grow (see Objective 3).
The period between first- and second-cover fungicide sprays varied from 14 days (calendar-based control and conventional IPM) to 34-60 days (Treatments 3 and 4), depending on year and the version of the SBFS warning system that was used. This increased time between fungicide sprays translated to a savings of 2 to 4 sprays per year. Interestingly, thresholds for timing of the second-cover fungicide spray were quite similar (2 to 10 days different, depending on year) for two alternative versions of the SBFS warning system – 175 hours of leaf wetness duration (Treatment 3), or 192 hours of relative humidity of 97% or more (Treatment 4).
In 2009, there were no treatment differences in marketable fruit weight; for GoldRush, however, number of marketable fruit for Treatment 4 was significantly higher than for Treatments 1 or 3.
No scab damage on fruit was evident during the study; this was expected due to each cultivar’s high level of genetic resistance to scab. Furthermore, no SBFS was ever observed on ‘Redfree’ apples; the reason was not inherent genetic resistance of ‘Redfree,’ but rather that its early maturity date enabled it to escape this disease. Even in unsprayed and organic orchards, cultivars that mature in early August, such as Redfree, exhibit little or no SBFS. For this reason, the most suitable apple cultivars for minimal-fungicide orchards or organic disease management in the North Central Region may be scab-resistant, early-maturing ones. On the other hand, early-maturing cultivars typically do not store well, so they must be marketed within 4 to 6 weeks after harvest. In addition, a local or regional market must be established for any cultivar that is new to consumers. Redfree has sold well for Iowa growers who have tried it, however, and could be a good addition to the cultivar mix in other NC Region orchards due to its minimal fungicide needs.
In 2009, incidence of SBFS, codling moth injury, and injury by other insects was less than 1% in all treatments, with one exception: injury by other insects was 1.6% on cv. Liberty in Treatment 4. These injury levels are all within commercially acceptable thresholds. The 2009 results are additional evidence that the New IPM treatments (3 and 4) suppressed the targeted summertime diseases and pests (SBFS and codling moth) and non-target insect pests as effectively as either a traditional, calendar-timed pesticide spray schedule (Treatment 1) or a conventional IPM spray schedule (Treatment 2).
Using the Field Environmental Impact Quotient (EIQ) as a measure, the New IPM Treatments (3 and 4) had far less environmental risk than calendar-based spraying (Treatment 1) or conventional IPM (Treatment 2). In 2009, some Field EIQ values were higher than in 2007 or 2008 due to more pesticide applications in a wetter year. Overall, comparison of the Field EIQ and pest management results show convincingly that combining scab-resistant cultivars with new IPM strategies such as warning systems can dramatically reduce the environmental impact of pesticide spraying in the North Central Region without compromising effectiveness of pest and disease control.
Mulched plots required spot treatments of herbicide throughout the season to manage localized outbreaks of weeds, but bare-ground plots required herbicide applications over the entire ground surface. Across the 3 years, mulched plots required an average of 23.9% less herbicide than bare ground plots. In the early to mid-season, which are the most important time for weed competition with apple trees, weed coverage was significantly greater on bare ground than on mulch in July 2009, whereas weed coverage on bare ground was never less than on mulch. In midsummer, common purslane (Portulaca oleracea) covered nearly 50% of sampling points in bare-ground plots, whereas it was nearly absent from mulched plots. In contrast, barnyard grass (Echinochloa crus-galli) and large crabgrass (Digitaria sanguinalis) occasionally covered significantly more of the mulched than bare-ground plots. Weed suppression was somewhat less effective in 2009 than in 2008, because mulch was then more than one year old (applied in May 2008).
A key take-home message for growers is that composted hardwood bark mulch effectively suppressed weed growth on the orchard floor during the critical period of the growing season for competition with apple tree growth (May through July). This suppression would likely mean that apple trees that are mulched within the tree row would experience less weed competition for water and nutrients during dry growing seasons than under the bare-ground cultivation that is common in many North Central Region orchards. This advantage could be particularly important during orchard establishment, when it is critically important economically for young trees to reach full bearing size and fill the rows in as few years as possible.
In 2009, trunk diameter, tree height, and limb spread did not differ significantly for trees in bare-ground and mulched plots. In other words, there was no discernible impact of mulch in tree growth or nutrition. Two factors may explain this result. First, the 2009 growing season was exceptionally rainy. As a result, water for growth was not as relatively limiting on bare ground as it could have been during prolonged dry conditions. Second, the mulching treatments were applied across all three cultivars; the resulting variability may have obscured cultivar-specific growth differences between bare ground and mulched treatments.
Trial 2 – Impact of pruning and spray volume on performance of a SBFS warning system. In 2009, when using the SBFS warning system, a high volume (200 gallons per acre) in the first- and second-cover fungicide sprays resulted in significantly lower incidence of SBFS at harvest than low-volume (48 gallons per acre) sprays. Using 100 gallons per acre for these two sprays resulted in an intermediate incidence of SBFS. These differences occurred for both pruned and non-pruned trees. The spray-volume results were similar to those in the on-farm demonstration trials (see below), in which average SBFS incidence when using the warning system was lower when spray volume was 80 to 100 gallons rather than 40 to 50 gallons.
In 2009, the non-pruned, non-sprayed control had significantly lower SBFS incidence than the pruned, non-sprayed control. The take-home message for North Central Region growers is that it is more reliable to use the SBFS warning system with spray volume of at least 100 gallons per acre than at lower volumes (e.g., 40 to 50 gallons per acre). The results have practical value for growers by clarifying a basic rule of thumb (minimum spray volume for first- and second-cover fungicide sprays) necessary for reliable use of the SBFS warning system. Although annual dormant-season pruning may have less impact on warning-system performance than spray volume, pruning is still strongly recommended to insure adequate light penetration, remove dead wood than can contribute to certain diseases, and provide needed shaping of developing trees.
OBJECTIVE 2 – Hard cider trials. No statistical differences in hard cider quality characteristics were noted in 2009, presumably due to the fact that only two replications were completed for all cultivars. Golden Delicious was the only cultivar evaluated in each year, and had three replications per evaluation. Although no statistical differences were noted, hard cider made from Jonathan, Fireside, Chieftan, MacIntosh, and Golden Delicious apples tended to be rated higher in aroma, sweetness, and apple flavor and lower in sourness than cider from Gold Rush and Liberty apples. It should be noted, however, that fermented aroma, effervescence and cloudiness can be altered in processing. Sweetness and sourness can be adjusted with addition of sugar or by blending with other juices, and coloring agents could be added. In comparing our ciders with commercial brands, ISU hard ciders were most similar to the commercial brand “K”, made by Matthew Clark Brands, Bristol, England. Commercial hard ciders made in the U.S. were darker yellow-amber in color and more effervescent, with less apple flavor, than ISU ciders. Blends were made with traditional, widely grown cultivars (Jonathan, Golden Delicious, MacIntosh) and Fireside. Fireside was similar to other cultivars in several attributes and may be a suitable apple for cider; however, hard cider made from Fireside apples tended to be lower in apple flavor than other apple cultivars.
OBJECTIVE 3 – Economic analysis. In 2009, pest management costs were somewhat higher than in 2008 across all cultivars because wetter weather required several more pesticide sprays.
For all treatments in 2009, per-hectare costs were lower and revenue was higher as orchard size increased from 0.4 hectare (1 acre) 16.2 hectares (40 acres). Cost of pest management was highest for Treatment 3 at all orchard sizes because weekly sprays of Cyd-X (codling moth granulosis virus) required substantially more spray trips than the other treatments. Cost for Treatment 4 was the lowest of all treatments at orchard sizes of 2 hectares (5 acres) and larger.
While the cost savings from Treatment 4 are not massive, they can strengthen a farm’s balance sheet. At the same time, reducing the pesticide load and substituting lower-toxicity products can substantially reduce the environmental impact of spraying (see Field EIQ results), thereby enhancing populations of beneficial arthropods and reducing pesticide contamination of the orchard soil community, groundwater, and nearby surface waters.
OBJECTIVE 4 – Outreach. In 2009, on-farm, non-replicated trials included three cooperators in each year, for a total of six site years. In the trials evaluating the SBFS warning system with a threshold of 175 hours of cumulative leaf wetness duration, use of the warning system resulted in a 10% average incidence (% apples infected) of SBFS compared to 3% in the control (calendar-based spraying). Although the results were highly variable among cooperators, the higher level of SBFS with the warning system suggests that the leaf-wetness-based warning system may need to be re-evaluated. In fact, a new warning system, based on cumulative hours of relative humidity greater than 97%, was field-validated in Objective 1. This new system performed well in the ISU Hort Farm trial, but needs to be validated over additional sites and years before it is sufficiently reliable for growers to use.
Also in 2009, the impact of spray volume on performance of the warning system (with the 175-hour cumulative leaf wetness threshold) was tested in three commercial orchards. Incidence of SBFS at harvest varied widely among the six site years, so differences among orchards and across site years were not statistically significant, but several trends emerged. The highest average SBFS incidence (8.8%) occurred when the warning system was used in conjunction with low-volume gallonage (i.e., 40 to 50 gallons per acre) for the first- and second-cover fungicide sprays. In contrast, SBFS incidence was lower (6.3%) when the warning system was applied using higher spray volume (80 to 100 gallons per acre). The lowest average incidence of SBFS, 3.7%, occurred when low-volume fungicide sprays were applied on a calendar basis. These results suggest that spray volume does make a difference in controlling SBFS when using the warning system; 80 to 100 gallons outperformed 40 to 50 gallons. At 80 to 100 gallons per acre, however, a sprayer would need to be refilled twice as often as at 40 to 50 gallons per acre, so labor, fuel costs, and overall spray time required would be somewhat greater for the higher volume. However, data presented in this report and elsewhere indicate that the SBFS warning system can cut the number of fungicide sprays for North Central Regions growers by at least two per season, resulting in cost and time savings that are considerably greater than the added costs of refilling a spray tank a few more times. However, the fact that the calendar-timed fungicide spray schedule resulted in an even lower incidence of SBFS than the warning system with higher spray volume suggests that the warning system needs to be further refined in additional field trials, and also that it would be valuable to try applying the warning system with spray volumes exceeding 80 to 100 gallons.
Impacts and Contributions/Outcomes
Our Iowa State University (ISU) Horticulture Farm study was the first systems-level assessment of the impact of scab-resistant cultivars on apple orchard sustainability in the North Central Region. By eliminating several springtime sprays for scab and implementing weather-based spray timing for the primary summer pest problems (sooty blotch/flyspeck and codling moth), we demonstrated that apple growers can dramatically reduce the environmental impact of pest and weed management, save money, and safeguard the quality and yield of their apples. We also showed that using composted hardwood bark mulch in the tree-row strip can suppress weeds, reduce the need for herbicide sprays, create a cooler and moister rooting environment, and enhance the organic matter content of the soil. The pruning and spray volume experiment and on-farm trials pointed to adequate spray volume
The greatest impact of our field experiment and on-farm trials is likely to be as a source of ideas for Midwest apple growers who are looking to cut production costs while reducing their orchard’s environmental footprint.
The project’s progress has been shared mostly with Iowa apple growers so far, via three field days and publication of annual summaries in the Iowa State University Fruit and Vegetable Progress Report. Publications summarizing the project are also in preparation for submission to the Iowa Fruit and Vegetable Growers newsletter, Midwest grower journal Fruit Growers News and the national research journal Agriculture, Ecosystems, and Environment by the end of 2010.