Xylosandrus germanus (Blandford) has caused increasing damage in high-density New York apple orchards since 2013, resulting in tree decline and death. We documented their occurrence and timing in > 50 orchards using ethanol-baited traps from 2014 to 2016. First captures ranged from 48 to 83 degree days (base 10 °C) from 1 January. Captures were numerically higher at the orchard–woods interface than within the orchard interior, but differences were not significant in locations with lower populations. Control using insecticide trunk sprays was tested in potted, waterlogged apple trees placed in orchards and nurseries, and inside wooded areas adjacent to orchards. A verbenone repellent was used in combination with trunk sprays to improve control. Overall, insecticide sprays were inconsistent and marginal in preventing new infestations. Chlorpyrifos significantly reduced infestations versus lambda-cyhalothrin and untreated trees at one location in the 2015 orchard trials, and versus untreated trees at one location in the 2016 nursery trials, but otherwise performed no better than other treatments. The addition of verbenone to either the check or permethrin treatments resulted in significantly fewer attack sites containing brood at one orchard site in 2016. Chlorpyrifos, lambda-cyhalothrin, and permethrin significantly reduced the number of attack sites containing adults compared with untreated trees at one nursery trial location in 2016, but were otherwise ineffective in reducing numbers of trees in other locations and infestation categories. We found several fungal and bacterial species associated with X. germanus and its infestation of apples. These microbes likely play a minimal role in apple decline.

Fire blight, a bacterial disease of rosaceous plants caused by Erwinia amylovora, is one of the most important diseases affecting commercial apple production worldwide. Antibiotics, applied at bloom to protect against blossom infection, are the most effective means of management but raise concern due to the potential for antibiotic resistance in both the pathogen population and nontarget organisms. In addition, most fire blight outbreaks in New York State often emerge in late June to July as shoot blight, calling into question the role of blossom infections and the antibiotic applications made to manage them. Prohexadione-calcium (PhCa) is a gibberellic acid inhibitor used post-bloom to control shoot vigor and to manage shoot blight. However, the magnitude of shoot blight management is directly related to the suppression of shoot growth, which is undesirable, especially in young orchards during establishment years. PhCa is believed to control shoot blight by thickening cell walls in cortical parenchyma, preventing invasion of host tissues by E. amylovora. We hypothesize that PhCa applied pre-bloom could similarly prevent invasion of blossom pedicels following infection, leading to reduced disease incidence. We evaluated novel pre-bloom PhCa programs for their effects on disease management (blossom and shoot blight) as well as their impact on shoot growth for three years in a mature ‘Gala’ orchard in New York. In all three years of the study, all PhCa programs resulted in less than 27% incidence (71% control) of blossom blight and less than 13% incidence (77% control) of shoot blight with minimal effect on tree growth. Inclusion of a biopesticide during bloom further reduced the incidence of blossom blight in one year of three. Using light microscopy, we found that cell walls in the cortical parenchyma of fruitlet pedicels on trees receiving pre-bloom PhCa applications were significantly thicker than those of untreated trees 40 days after full bloom and inoculation. Overall, we found that pre-bloom applications of PhCa had utility in reducing blossom blight and shoot blight with minimal impacts on tree growth. These pre-bloom programs would fit with standard production practices and may contribute toward the development of fire blight management programs without the use of antibiotics.

Fire blight, caused by pathogen Erwinia amylovora, is a major disease in Malus. Biological, chemical and cultural controls are efficient to manage fire blight, while rootstocks, and host resistance can limit damages. During the 2020 season a naturally occurring fire blight outbreak occurred in the United States Department of Agriculture (USDA) Malus collection, providing a unique opportunity to evaluate the diverse collection for fire blight susceptibility. The E. amylovora strain in the collection was identified as streptomycin resistant and characterized as CRISPR (clustered regularly interspaced short palindromic repeats) spacer array profile, 41:23:38. Fire blight severity was assessed using two approaches: (1) Average severity percentage, where the number of infected shoots was divided by the total number of shoots for the east and west facing sides of the tree; and (2) cut severity rating, where the trees were visually assessed after fire blight removal for amount of tree removed. Overall, 1142 trees of 41 Malus species were assessed for average severity and 2525 trees of 48 species were assessed for cut severity. A subset of 667 trees were for average severity in June and July to understand the disease progression. The species and trees presented here, can provide insight for future genetic fire blight resistance studies.

Precision crop load management of apple requires counting fruiting structures at various times during the year to guide management decisions. The objective of the current study was to evaluate the accuracy of and compare different commercial computer vision systems and computer applications to estimate trunk cross-sectional area (TCSA), flower cluster number, thinning efficacy, and yield estimation. These studies evaluated two companies that offer different vision systems in a series of trials across 23 orchards in four states. Orchard Robotics uses a proprietary camera system, and Pometa (previously Farm Vision) uses a cell phone camera system. The cultivars used in the trials were ‘NY1’, ‘NY2’, ‘Empire’, ‘Granny Smith’, ‘Gala’, ‘Fuji’, and ‘Honeycrisp’. TCSA and flowering were evaluated with the Orchard Robotics camera in full rows. Flowering, fruit set, and yield estimation were evaluated with Pometa. Both systems were compared with manual measurements. Our results showed a positive linear correlation between the TCSA with the Orchard Robotics vision system and manual measurements, but the vision system underestimated the TCSA in comparison with the manual measurements (R²s between 0.5 and 0.79). Both vision systems showed a positive linear correlation between nubers of flowers and manual counts (R²s between 0.5 and 0.95). Thinning efficacy predictions (in June) were evaluated using the fruit growth rate model, by comparing manual measurements and the MaluSim computer app with the computer vision system of Pometa. Both systems showed accurate predictions when the numbers of fruits at harvest were lower than 200 fruit/tree, but our results suggest that, when the numbers of fruits at harvest were higher than 200 fruit/tree, both methods overestimated final fruit numbers per tree when compared with final fruit numbers at harvest (R²s 0.67 with both systems). Yield estimation was evaluated just before harvest (August) with the Pometa system. Yield estimation was accurate when fruit numbers were fewer than 75 fruit per tree, but, when the numbers of fruit at harvest were higher than 75 fruit per tree, the Pometa vision system underestimated the final yield (R² = 0.67). Our results concluded that the Pometa system using a smartphone offered advantages such as low cost, quick access, simple operation, and accurate precision. The Orchard Robotics vision system with an advanced camera system provided more detailed and accurate information in terms of geo-referenced information for individual trees. Both vision systems evaluated are still in early development and have the potential to provide important information for orchard managers to improve crop load management decisions.

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most important diseases of apple. The antibiotic streptomycin is routinely used in the commercial apple industries of New York (NY) and New England to manage the disease. In 2002 and again, from 2011 to 2014, outbreaks of streptomycin resistance (SmR) were reported and investigated in NY. Motivated by new grower reports of control failures, we conducted a follow-up investigation of the distribution of SmR and E. amylovora strains for major apple production regions of NY over the last 6 years (2015 to 2020). Characterization of clustered regularly interspaced short palindromic repeat (CRISPR) profiles revealed that a few “cosmopolitan” strains were widely prevalent across regions, whereas many other “resident” strains were confined to one location. In addition, we uncovered novel CRISPR profile diversity in all investigated regions. SmR E. amylovora was detected only in a small area spanning two counties from 2017 to 2020 and was always associated with one CRISPR profile (41:23:38), which matched the profile of SmR E. amylovora, discovered in 2002. This suggests the original SmR E. amylovora was never fully eradicated and went undetected because of several seasons of low disease pressure in this region. Investigation of several representative isolates under controlled greenhouse conditions indicated significant differences in aggressiveness on ‘Gala’ apples. Potential implications of strain differences include the propensity of strains to become distributed across wide geographic regions and associated resistance management practices. Results from this work will directly influence sustainable fire blight management recommendations for commercial apple industries in NY state and other regions.

The adoption of mechanical thinning and pruning in commercial apple orchards has been limited largely by the risk of development and spread of fire blight. This devastating disease, caused by the bacterial pathogen Erwinia amylovora, may be transmitted by mechanical injury such as pruning, especially under warm, moist conditions conducive to bacterial growth, infection, and disease development. However, risk may be mitigated by avoiding highest-risk times and applying a bactericide, such as streptomycin, after mechanical thinning or pruning. In ‘Gala’ and ‘Idared’ orchards, we evaluated the risk of fire blight development and spread after mechanical thinning early in bloom (20% bloom), when seasonal temperatures are cooler and there are few open flowers available for infection. In both orchards, we also evaluated the spread and development of fire blight by mechanical pruning in July and in August, before and after terminal bud set, when shoot growth is slowed and the tree is less susceptible to infection. We also assessed the potential efficacy of a streptomycin or Bacillus subtilis biopesticide application after mechanical thinning and pruning to mitigate the spread of fire blight. In the ‘Gala’ orchard, disease never developed beyond the inoculated tree after thinning or pruning, which was unexpected for this highly susceptible cultivar. In the ‘Idared’ orchard, incidence of blossom or shoot blight from the point source, represented as relative area under the disease progress curve, was rarely different for trees that underwent mechanical thinning or mechanical pruning compared with untreated trees, and it was often reduced or eliminated when the antibiotic streptomycin or the B. subtilis biopesticide was applied within 24 h of mechanical thinning or pruning. For both thinning and pruning, incidence of fire blight dropped off quickly beyond the inoculated tree in the ‘Idared’ orchard and generally was not observed in trees beyond 10 to 15 m from the inoculated point source or predicted beyond 10 m by exponential and power law models fit to the disease progress curves. The results of this work demonstrate the low risk for fire blight development and spread by mechanical thinning and pruning when practiced under low-risk conditions—early in bloom for mechanical thinning and after terminal bud set (in August) for mechanical pruning—especially when paired with a subsequent bactericide application. This study demonstrates the safe use of mechanical thinning and pruning in commercial apple production, corroborated by anecdotal evidence from apple growers in western New York State.