Implementing biointensive pest management and evaluating hard cider manufacturing to increase sustainability of apple production

OBJECTIVE 1

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. In 2007, Treatments 1 (calendar-based spray timing), 2 (conventional IPM), and 3 (New IPM A) each required more pesticide sprays than Treatment 4 (New IPM B). 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 gap 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 2007, when few apples (and none of ‘Liberty’) were harvested due to a severe spring frost, marketable and cull apple weight and number did not differ significantly among treatments. In 2008, there was no difference among treatments in weight or number of marketable fruit weight, except in GoldRush, for which Treatment 2 had significantly less marketable weight than Treatments 1 or 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 2007, there were no significant differences among treatments for incidence of codling moth, SBFS, or plum curculio. However, incidence levels of codling moth and plum curculio were above commercially acceptable thresholds, possibly due to the anomalous nature of the greatly reduced crop (a result of springtime frost), which may have resulted in focusing pests on just a few apples per plot rather than a normal-size crop. In 2008, no SBFS or plum curculio was observed on Redfree, codling moth damage was minimal, and incidence of SBFS was less than 1 % in all treatments. 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 2008 and 2009 results are clear 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 10 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 2007, New IPM treatments has Field EIQ scores more than 40 % lower than calendar-based and more than 30 % lower than conventional IPM for cultivar ‘Redfree,’ while the New IPM treatments showed nearly 50 % less ecological risk than calendar-based spraying for cultivar ‘Goldrush.’ In 2008, in part because early-season spraying differed from 2007, Field EIQ values for New IPM B (Treatment 4) were less than one-third of the values for the calendar-based spray timing control (Treatment 1). Results from 2009 were similar, but some Field EIQ values were higher 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 each year (July and August 2007, May and July 2008, and 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 more effective in the same year in which a mulch layer was applied (2006, in a preceding study on the same site) or re-applied (2008), and somewhat less effective in years following application of fresh mulch (2007 and 2009).

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 2007 and 2008, average weekly soil temperatures beneath bare ground fluctuated considerably more than temperatures beneath mulched plots. Temperatures remained cooler under mulch, usually by at least 2° C, until late July, when the difference began to narrow. Volumetric water content beneath mulched plots at 15- and 30-cm depths was higher than under bare-ground plots throughout most of the season. The 2009 soil temperature and moisture content data were more equivocal due to problems with monitoring equipment.

The take-home message from these results is that, in well-drained soils such as at the ISU Hort Farm, the cooler and less variable soil temperatures and greater water availability resulting from mulching should help to minimize stress on root systems and maintain tree vigor during hot, dry periods. For the same reasons, however, mulching may not be as suitable for relatively poorly drained soils, where the mulch layer could potentially contribute to waterlogging, low-oxygen conditions, and resulting root injury during prolonged wet weather. Therefore, the suitability of composted hardwood bark mulching for apple orchards should be evaluated on a site-by-site basis.

Mean soil nutrient levels, organic matter, and pH varied widely among bare-ground and mulched plots in all three years. Total percent carbon, nitrogen, and organic matter were nearly identical between treatments in 2006, but in 2007 they all increased in mulched relative to bare-ground plots, and these differences were statistically significant in 2008. This finding suggests that decay of organic mulch can raise the organic matter content of soil and thereby yield benefits such as improved soil texture, structure, cation exchange capacity, and water-holding capacity. Again, however, this impact may be somewhat site-specific; the greatest benefit may accrue to soils that are relatively low in organic matter before mulching occurs; this would be true of many, but not all, agricultural soils in the North Central Region

In 2007 and 2008, means of foliar nutrients and foliar moisture content did not differ significantly between bare-ground and mulched plots. Trunk diameter, tree height, and limb spread did not differ significantly for trees in bare-ground and mulched plots in 2007, 2008, or 2009. In other words, there was no discernible impact of mulch in tree growth or nutrition. Two factors may explain this result. First, no droughts occurred during the entire period, and 2008 and 2009 growing seasons were 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

Results from the 2007 ISU Hort Farm trial on cv. Chieftain revealed no significant differences among treatments; the near-total crop loss in that year (due to spring frost damage) resulted in very high variability in number of apples rated per subplot, and thereby contributed to high variability within treatments. In 2008 and 2009, however, results were consistent: 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.

Pruning appeared to have less impact than spray volume. In 2008, for example, the non-pruned, non-sprayed control did not differ significantly from the pruned, sprayed control in SBFS incidence, whereas 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 2007, 2008, or 2009, presumably due to variability from year to year, comparison of different cultivars each year, and 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

Costs and revenue were not calculated for 2007, because a killing frost eliminated more than 95% of the fruit in the plot, including 100% of the Liberty apples. 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 both 2008 and 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.

Cost savings for Treatment 4 (New IPM using the SBFS warning system and two fewer springtime fungicide sprays against scab) compared to Treatment 1 (Traditional calendar-based pesticides spray timing) varied with cultivar and year. For an 8.1-hectare (20-acre) orchard, for example, annual per-orchard cost savings for fungicides and insecticides in Treatment 4, compared to Treatment 1, ranged from $300 (cv. Redfree in 2008) to $510 (cv. Liberty in 2008). When comparing Treatment 3 (Conventional IPM without SBFS warning system or reduced scab sprays) with Treatment 4, annual per-orchard savings ranges from $324 (cv. Goldrush in 2009) to $348 (cvs. Liberty and Goldrush in 2008). These cost savings from using Treatment 4 did not compromise yield or fruit quality compared to the controls (Treatments 1 or 2). 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 2007, results of on-farm demonstration trials were compromised by a spring frost that drastically reduced the apple crop in all cooperator orchards, as well as a miscommunication that resulted in the project scout’s failure to take data on incidence of SBFS on apples at harvest at the three cooperator orchards.

In 2008 and 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 Hort Farm trial, but needs to be validated over additional sites and years before it is sufficiently reliable for growers to use.

Also in 2008 and 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.