Toward Sustainability in Northeastern Apple Production: Orchard Ecosystem Architecture, Key Pests, and Cultivar Selection

Toward Sustainability in Northeastern Apple Production: Orchard Ecosystem Architecture, Key Pests, and Cultivar Selection

Summary

2003 was the third and final year of a 3-year study of the influence of 2 major components of orchard architecture (cultivar composition and border habitats) on bio-based approaches to managing 4 key apple pests: plum curculio, apple maggot, mites, and flyspeck disease. For plum curculio, a new approach to pattern of spray application together with a new approach to monitoring adult activity (using odor-baited trap trees on perimeter rows) led to a 74% reduction in insecticide use (across a variety of cultivars and border habitat types) compared with a conventional approach to control. For apple maggot, a new approach to determining distance between odor-baited sphere traps on perimeter trees for direct control (using a formula incorporating cultivar, border habitat, tree size, and extent of pruning) led to a 100% reduction in insecticide use compared with a conventional approach to control and a 37% reduction in number of spheres needed. Beneficial mite predators released in 2000 continued to provide excellent suppression of pest mites in most cases, regardless of tree cultivar and nature of border habitat. For flyspeck, further application of our prediction model to orchard border surveys resulted in 57% less summer fungicide use in orchard blocks adjacent to low or moderately-infected border habitats as compared to heavily-infected borders. Many new disease-resistant cultivars, such as Goldrush, Pristine, and Scarlet O’Hara, show promise for growers seeking further fungicide reductions.

Objectives/Performance Targets

This was the third year of a 3 year study of the influence of orchard architecture (specifically the nature of cultivar composition of perimeter-row apple trees and the nature of the border area habitat) on bio-based approaches to managing 4 key apple pests: plum curculio (PC), apple maggot flies (AMF), flyspeck (FS), and mites. The primary objective was to reduce pesticide reliance in regional apple production through refinement of biologically-based management of key apple pests. The secondary objective was to enhance sustainability of northeastern apple production through evaluation of new cultivars.

Accomplishments/Milestones

Good progress was made in the advancement of bio-based management of the 4 key pests. In particular, a new odor-baited “trap tree” for localizing and monitoring fresh injury to fruit caused by plum curculio led to a 74% reduction in insecticide use against this key pest in plots where spray applications were driven by a pre-set threshold of 1 freshly injured fruit out of 50 fruit sampled on a trap tree. The trap tree approach performed well across various apple cultivars and border habitats. A new approach to determining distance between odor-baited sphere traps that incorporated type of apple cultivar and nature of border habitat as distance-determining factors led to a 100% reduction in insecticide use against apple maggot and a 37% reduction in number of traps needed to achieve direct control. Typhlodromus pyri mite predators released in 2000 continued to provide excellent suppression of pest mites in most orchards, regardless of tree cultivar and nature of border habitat. Further refinement of our flyspeck prediction model resulted in summer fungicide reductions of 57% in plots adjacent to “low-risk” border habitats as compared to “high-risk” border habitats. The environmentally benign Flint fungicide performed well and can be used with confidence for summer disease and scab control. Continued favorable evaluations of new scab-resistant cultivars, like Pristine, Goldrush, and Scarlet O’Hara (Coop 25), give growers another opportunity to reduce pesticidal inputs. Unlike many scab-resistant apples, Goldrush stores well and will therefore have an advantage. Among the non-resistant new cultivars, Cameo and Honeycrisp (from the 1995 planting) are showing consistent promise.

Impacts and Contributions/Outcomes

Background:

Most of our studies were conducted in 3 plots of apple trees in each of 12 commercial orchards (36 plots in all). Each plot measured 60 meters in perimeter-row length and ran 7 rows deep. In 6 of the 12 orchards, perimeter rows were comprised of the cultivars Gala, Jonagold or Fuji. Perimeter-row trees in the other 6 orchards were comprised of McIntosh or Empire cultivars. Habitat adjacent to perimeter rows consisted of woods, hedgerows or open field.

For plum curculios (PCs) immigrating from overwintering sites in border area habitats:

A trap tree baited with benzaldehyde (=a component of attractive host fruit odor) plus grandisoic acid ( PC pheromone) was established as the central tree of the perimeter row of each of the 3 plots. Each plot was pre-assigned at random a threshold of either 1, 2, or 4% freshly injured fruit on the trap tree. Each trap tree was sampled for freshly injured fruit 3 times per week.(M, W, F) beginning 7 days after a petal fall spray of insecticide to the entire plot. An entire plot insecticide application was made at petal fall to control PCs that had immigrated into interior rows before petal fall, but thereafter, insecticide against PC was applied only to perimeter and second rows and only when the proportion of trap-tree sampled fruit showing fresh injury had reached the pre-established threshold of 1, 2, or 4% for that plot.

Results showed that the mean number of insecticide applications to rows 1 and 2 declined successively from 1.56 to 1.44 to 0.89 sprays per plot and the mean percent whole-plot injury increased successively from 0.77 to 1.17 to 1.27% of sampled fruit as the pre-assigned threshold calling for spray application increased from 1 to 2 to 4%.

Our findings lead us to conclude that after a whole-orchard insecticide application against PC at petal fall, subsequent applications can be confined to peripheral-row trees and be driven by a provisional threshold of 1 freshly injured fruit out of 50 fruit sampled on a perimeter-row odor-baited trap tree. In 2003, this approach led to 74% reduction in insecticide use against PC compared with a conventional approach of 3 whole-orchard sprays. Further study is necessary to determine precisely how cultivar composition of peripheral-row trees and nature of border area habitat affect this new approach to monitoring and reducing insecticide use against PC.

For apple maggot flies (AMF) immigrating from overwintering sites in border area habitats:

Sticky red sphere traps baited with a 5-component blend of synthetic attractive fruit odor were deployed varying distances apart on perimeter trees on all 4 sides of plots measuring 120 meters long X 7 rows deep (two 60 meter plots of the PC study were combined into one plot having baited spheres for our AMF study). Distances between spheres (range 5-15 meters) on perimeter trees were based on a newly-developed formula that incorporated tree size, extent of pruning, tree cultivar and nature of adjacent habitat as distance-determining factors. Performance was assessed on the basis of captures of AMF on unbaited monitoring spheres at interiors of plots and percent fruit injured by AMF.

Results showed that in 10 of the 12 orchards, performance of sphere traps equaled that of 2-3 sprays of organophosphate insecticide (applied to each remaining 60 meter plot) in preventing immigration and damage by AMF. In 2 of the 12 orchards, each characterized by large trees that were not well-pruned, performance of sphere traps was inferior to that of insecticide sprays. Distances between spheres averaged 11 meters apart in 2003 as driven by our new formula compared to 7 meters apart in 2001 and 2002 when driven by a fixed-distance approach. The greater the distance between spheres, the fewer needed per acre and the lower the cost (25 needed per test plot in 2003 compared with 40 per test plot in 2001 and 2002).

Our findings lead us to conclude that assigning distance between odor-baited spheres on perimeter trees of an orchard according to a formula that incorporates tree size, pruning, cultivar, and adjacent habitat as variables will minimize need and cost of spheres for AMF control. In 2003, this approach led to a 100% reduction in insecticide use against AMF compared with a conventional approach of 2-3 whole-orchard sprays and required the equivalent of only 73 spheres per 10-acre block of orchard trees.

For Mites, which can be controlled biologically by predators:

European red mites (ERM) exceeded acceptable threshold levels in 2 of the 12 orchards in 2003 and required rescue treatment with miticide. Typhlodromus pyri (TP) mite predators that were released in 2000 were not detectable in these orchards in 2003. TP were detectable in almost all of the other 10 orchards in 2003 and apparently were a primary factor in keeping ERM below damaging levels.

There were no detectable differences in abundance of ERM or TP on perimeter-row trees vs. trees in the 4th and 7th interior rows in 2003, indicating a rather even distribution of pest and predator mites.

Overall, TP were far more abundant than Amblyseius fallacis (AF) mite predators in 2003 in 11 of the 12 orchards, suggesting that AF is less likely than introduced TP to be an effective and widespread biocontrol agent of ERM in Massachusetts.

As in 2001 and 2002, few or no AF predators were found in 2003 on American hazel trees planted in 2000 in habitats adjacent to perimeter-row trees, again calling into question the value of planting or encouraging hazel trees in orchard border areas.

For flyspeck (FS), dispersed by wind from overwintering sites in border area habitats:

All apple tree plots were evaluated for flyspeck risk in June by conducting surveys of several orchard factors, such as amount of flyspeck on alternate hosts in border areas up to 100 m from each apple block. Measurements or samples were also taken of host-plant density, height and depth of borders, slope and altitude of site, size of apple trees, planting density of apple trees, and canopy density of apple trees. Risk for unacceptable levels of flyspeck at harvest was calculated for each block using survey results and parameters form our flyspeck predictive model. The five blocks with the greatest FS risk were at 5 different orchards. Each of these blocks was paired with another block, at the same orchard, that had moderate-to-low FS risk. Growers sprayed high risk blocks three times after the mid-June spray and sprayed lower-risk blocks only twice after mid-June. Flint, an environmentally benign and relatively new fungicide was used with an occasional Captan spray to comply with label restrictions and resistance management practices. One end of each plot was an untreated control area and received no fungicide after the last scab spray in mid-June. Disease progression was tracked with bi-monthly counts of symptoms on apples in marked trees at known distances from each significant border. Flyspeck spores were trapped from early July to early September with rotational air samplers at the interface of the apple plots with border habitats at 3 high-risk plots and 3 low-risk plots. Weather data was collected with Campbell Scientific dataloggers installed next to each air sampler.

In this extremely wet year inoculum levels were very high. At all except for one orchard, far more conidia were trapped next to the high-risk border than next to the lower-risk border (up to 800 conidia per trap per day versus 300 at one orchard). The exception was a low-risk border that scored higher in risk than the other low-risk borders. Although it was steeply-sloped and relatively high in the orchard, factors which usually correlate with lack of flyspeck in the apples, it was bordered by dense woods and a stream and had more flyspeck inoculum than the other low-risk borders. At harvest, there were an average of 84% infected fruit in unsprayed control plots, eleven % infected fruit in high-risk blocks that received 3 or 4 summer sprays, and 5% infected fruit in low-risk blocks that received 2 summer fungicide sprays. Summer fungicide use was reduced by 57% in low-to-moderate risk plots as compared to high-risk plots.

Our findings lead us to conclude that great summer fungicide reductions are possible, even in very wet years, if accurate risk assessments can be done for plots of apple trees. Further study is necessary to simplify and integrate border surveys and weather monitoring and to transfer the strategies to growers and independent consultants. Flint performed well and can be an important tool for the grower, if used wisely.

Evaluation of new cultivars:

2003 was the third year of fruit evaluation in the 1999 NE183 horticulture and disease plantings. Differences in bloom, fruit set, fruit quality, and disease susceptibility (or resistance) exist, but these are young trees, and part of this can be attributed to differences in precocity and fruit set. A more accurate picture of tree performance and disease susceptibility/resistance will develop when trees fruit for several seasons and biennial cycles manifest themselves. However, even now we are getting a sense of which will be the most precocious, high yielding, best tasting, and most disease-resistant cultivars. As it becomes possible to identify promising cultivars, we will make preliminary recommendations at grower meetings and through UMASS extension publications for planting these cultivars in New England. One cultivar, Scarlet O’Hara (Coop 25), from the 1999 planting, seems especially good. Goldrush and Pristine are stand-outs in the 1995 planting. These are all scab-resistant. Goldrush also gets high scores for maintaining fruit quality in storage. Among the non-resistant new cultivars, Cameo and Honeycrisp (from the 1995 planting) are showing consistent promise.

Collaborators: