NAVEL ORANGEWORM IN SOUTHERN CENTRAL VALLEY WALNUTS: SOURCE

NAVEL ORANGEWORM IN SOUTHERN CENTRAL VALLEY WALNUTS: SOURCE, SEASONAL ABUNDANCE, AND IMPACT OF MATING DISRUPTION Charles Burks, Elizabeth Fichtner, Sara Goldman Smith, and Carolyn Pickel ABSTRACT The navel orangeworm is considered the principle insect pest of almonds and pistachios in California, but generally of secondary importance in walnuts. In the former nut crops, however, there is a gradient of navel orangeworm abundance and damage, with less damage in the north and more to the south. Efficacy of mating disruption for navel orangeworm has been demonstrated in almonds, but separate examination of mating disruption in walnuts is important due to a very different canopy structure compared to walnuts. In 2012 we examined abundance of navel orangeworm in walnuts the southern portion of the California growing area, and the impact of mating disruption on navel orangeworm in this crop. Traps with unmated females as a pheromone source found cohort structures of male abundance similar to those observed in almonds. Extensive arrays of egg traps captured many eggs during first flight, but few during subsequent flights. Comparison of males in pheromone traps with distance to other tree nut crops, and spatial analysis of egg trap captures in a walnut site adjacent to almonds suggest that this year-around navel orangeworm abundance at these sites is not due to principally to immigration from other crops. Biological impact of mating disruption was demonstrated; i.e., near-complete suppression of males captured in female-baited traps and significant reduction eggs captured in egg traps, demonstrating both disruption of sexual communication and impact on fertility. Insect damage at harvest was >10% in some cases. The impact of mating disruption on this harvest damage was less clear than the biological impact, although this was also true of grower standard insecticide treatments in the absence of mating disruption. Comparison of seasonal abundance of navel orangeworm and codling moth suggests that insecticides targeting codling moth flight 2A would also impact the second navel orangeworm flight, but that the first navel orangeworm flight would be less affected by insecticides timed against the 1B codling moth flight. OBJECTIVES

1. Characterize seasonal abundance of navel orangeworm in southern Central Valley walnuts, and compare these data with codling moth abundance and walnut infestation by these two pests.

2. Estimate the relative contribution of residents and immigrants to navel orangeworm

populations in orchards in this region.

California Walnut Board 271 Walnut Research Reports 2012

3. Examine the impact of mating disruption on reproduction and damage of navel orangeworm in the southern Central Valley.

SIGNIFICANT FINDINGS

• Pheromone trap data indicated that navel orangeworm is present throughout the growing season in mature orchards of early-season walnut varieties in the southern region (i.e., Fresno, Kings, and Tulare counties) (Figure 3).

• These navel orangeworm populations are probably not due principally to immigration from other crops. This finding is supported by comparison of males captured in pheromone traps with distance to the nearest other nut crop, and by examination of the spatial pattern of eggs in egg traps in an almond orchard bordering with Nonpareil almonds (figures 5 and 6).

• Navel orangeworm was responsible for the majority of the insect damage at harvest in

southern area study sites. This finding is supported by examination of harvest samples, and by a general trend of increasing harvest damage between husk split samples and harvest samples (tables 3 and 4).

• The abundance of navel orangeworm in pheromone traps, egg traps, and harvest samples

in the south is in contrast to companion data from the northern Central Valley (Butte County), where navel orangeworm was trapped more sporadically during the growing season (Figure 3) and harvest sample evaluation indicated that the majority of damage was due to codling moth rather than navel orangeworm (Table 5).

• There is potential for a pest management plan designed more specifically for

management blocks where navel orangeworm is an important pest. This includes investigation of timing of insecticide treatment for the first flight (Figure 4); and mating disruption, for which biological impact on male orientation and female were demonstrated (tables 6 and 8).

• Data on effect of trap height on suppression of males captured in female-baited pheromone traps suggest that further work is needed on horizontal and vertical movement of navel orangeworm pheromone in walnut canopies (Table 7).

INTRODUCTION The navel orangeworm is a key pest of California tree nut crops including almonds, pistachios, and walnuts, each worth >$1 billion annually (unprocessed) in recent years. In walnuts, unlike the other two nut crops, navel orangeworm entry is often tied to that of the codling moth (Light and Knight 2011). In the southern production areas, however, (e.g., Kings, Tulare, and Fresno counties) navel orangeworm abundance and damage is historically higher (Van Steenwyk et al. 1984).


Knowledge of factors contributing to abundance and damage of key pests is important in managing these pests while minimizing non-target impacts. Factors that possibly contribute to greater navel orangeworm abundance and damage in the southern area include sunburn (Shelton and Davis 1994), greater navel orangeworm degree-day accumulation, and proximity to other tree nut crops supporting higher abundance. Recent research found that pistachios support higher abundance of navel orangeworm compared to almonds given comparable maturity and sanitation effect (Burks et al. 2008), but few recent studies have made this comparison in walnuts, at least partially due to the difficulty of monitoring navel orangeworm (Sibbett and Stewart 1995). Over the last decade the bearing acreage has expanded by 14, 45, and 84% in walnuts, almonds, and pistachios, respectively, with much expansion of all these nut crops occurring in the southern walnut production area (USDA-NASS 2010). This trend suggests greater opportunity for movement of the navel orangeworm, a highly mobile pest species, between crop resources. Mating disruption for codling moth has become established in pome fruits (Welter et al. 2005), and demonstration of cost-effectiveness in walnuts has led to adoption in that crop (Steinman et al. 2008). Efficacy of mating disruption for management of navel orangeworm in almonds has been demonstrated (Higbee and Burks 2008), and mating disruption for navel orangeworm has been adopted in ca. 30,000 acres in that crop. The effectiveness of mating disruption depends on factors specific to individual combinations of crop, pest, and location; including abundance of the target pest, movement of mated females, and wind movement through the canopy (Cardé and Minks 1995, Gut et al. 2004), and relationship between abundance, host phenology, and damage. Detection of damaging levels of the target pest is also complicated by mating disruption. For the codling moth, high-strength lures placed high in the canopy allows detection of population growth (Charmillot 1990) and a plant attractant (kairomone) for codling moth lure provides detection in the presence of mating disruption (Light et al. 2001). Similar efforts for pheromone and kairomone lures for the navel orangeworm are in early stages of development (Beck et al. 2011). Traps baited with virgin navel orangeworm females usually capture similar number of males whether they are placed low or high in the canopy in almonds and pistachios, with both high and low traps shut down in the presence mating disruption (Burks et al. 2005). Recent studies have emphasized the importance of the number of traps used when using egg traps to monitor the abundance and fertility of navel orangeworm (Burks et al. 2011, Higbee and Burks 2011). The forgoing observations suggest that, to assess the potential utility of mating disruption for management of navel orangeworm in walnuts, it is necessary to examine: 1) the degree to which navel orangeworm damage is preceded by codling moth damage, 2) the impact of mating disruption on navel orangeworm mate-location in lower and upper canopy, and 3) whether navel orangeworm-specific and overall infestation are decreased by mating disruption. The fact of greater degree-day accumulation and historically higher navel orangeworm abundance in the southern growing area suggest that examining the potential for mating disruption in that area is particularly appropriate. In this report we describe experiments examining abundance and movement of navel orangeworm in southern San Joaquin valley orchards with a history of navel orangeworm damage. We also examine the impact of mating disruption on the ability of navel orangeworm males to locate females at various heights in the walnut canopy, and on fertility of females.


PROCEDURES Field sites. Initially, 10 cooperator sites were identified in Tulare County as potential sites for monitoring and/or mating disruption trials (Figure 1). Because of the nature of the study, sites with planted with susceptible varieties were sought, and particularly sites known to have had insect (Lepidoptera) damage in the past. The sites identified were predominantly planted in Serr, and were predominantly tall trees (Table 1). Two additional sites were monitored in Fresno County (Site 11, Table 1) and Kings County (Site 12, Table 1). The former site was small, but of interest for ease of access and because of known high Lepidoptera pressure. The latter sight was of interest because a long history was available for this site due to inclusion in previous studies of codling moth mating disruption. A companion study site in Butte County, planted in mature Vina trees, was selected based on previous work there (Deseret Farms) with monitoring and mating disruption for navel orangeworm. In 2012, sites 11 and the Butte County companion site were treated with mating disruption for codling moth but not for navel orangeworm. Plots and data concerning distance between walnut cooperator sites and the nearest plantings of almonds or pistachios were obtained with ArcGIS (ESRI, Redlands, CA). The distance measured was from the center of the walnut site to the nearest section for which pesticide use reports indicated the presence of almonds or pistachios. In some cases, the presence of pistachios was confirmed from other data sources. Insecticide treatments were left to grower discretion at all sites. Site 11 had no insecticide applications during the year. Site 12 had a reduced insecticide regime due to use of codling moth mating disruption, although chlorpyrifos with Nu-Lure was applied on August 17 and ethephon was applied on August 25. Ethephon was not used at other sites. Most of sites 1-10 applied a codling moth treatment targeted at flight 2A, sometime between June 12 and June 25. The flight 2A treatment at Site 3 was acetamiprid, and sites 7 and 8 were treated with chlorantraniliprole at this time; the remainder of sites 1-10 were treated with methyl parathion for flight 2A. Site 7 was also treated with methyl parathion for codling moth on August 5. Sites 1-10 were also treated with chlorpyrifos in late August, timed so that the 14-day pre-harvest interval would expire just before the anticipated date for the first harvest. Monitoring and trap phenology for navel orangeworm and codling moth. Navel orangeworm males and eggs were monitored using orange Suterra wing traps and Trécé egg traps (Van Steenwyk 1985), respectively. Wing traps were baited with three unmated females sealed in a plastic mesh cages (Curtis and Clark 1984), and were modified in a manner to facilitate this practice (Kuenen et al. 2005). Egg traps were baited with almond meal and 10% crude almond oil (Liberty Vegetable Company, Santa Fe Springs, CA). Large arrays of egg traps were used because highly aggregated frequency distributions require large sample sizes for inference (Higbee and Burks 2011), and because this distribution suggests a very small active area for such traps. In sites of 10-40 acres, traps were placed at ca. 30 ft intervals (depending on tree spacing) with two columns of 12 traps and a central column of 6 traps, covering a square area of approximately 10 acres. In larger blocks (sites 2, 3, and 5) 24 traps were placed in four arrays of 6, at 30 foot intervals. The four arrays were spaced evenly in the east and west halves of rectangular blocks of ca. 80 acres (Figure 2).


Prior to the beginning of mating disruption treatments and at the non-mating disruption sites, one navel orangeworm flight trap was used per site because data in almonds and pistachios demonstrate interference between female-baited traps over at least 440 yards (Burks and Higbee, in press). In the smaller sites, the pheromone trap was between and adjacent to the middle egg traps in the center column. At the larger non-mating disruption site, pheromone traps were placed near the far southwest and northeast traps, although only the former trap was maintained until after May 1. Pheromone traps in non-mating disruption treatment sites were hung from limbs approximately 6 feet above the ground. Modifications of pheromone trap arrange in mating disruption sites, as described below. Degree days associated with egg trap data were calculated using the UC IPM online Degree Day calculator at http://www.ipm.ucdavis.edu/WEATHER/index.html and the Hanford.C NCDC weather station. Single pheromone traps and a line of 6 pheromone traps at 30 foot intervals was used at sites 11 and 12. Egg trap monitoring at Site 12 was initated on the week of May 7; later than the other sites. At the Butte County location, flight traps baited with unmated females and egg traps were placed in the same location as previous years in the northern 40-acre Field 24, and the southern 165 acre Field 25. Trap positions are as shown in Figure F of the previous-year report (Pickel et al., 2011). Codling moth pheromone trap data in the southern regions was obtained from cooperators because cooperator pest control advisors (PCAs) did not wish to change the number or position of traps in the field, and wished to retain control over the interval at which the traps would be checked during key flight periods. Mating disruption for navel orangeworm. Mating disruption treatment was applied to the western half of Site 2, the northern half of Site 3, and to all of sites 4 and 6. Sites 2 and 3 offered the advantages of large blocks that were reported to have had moderate pressure in the past. While Site three contained varieties typically less susceptible two Lepidoptera (particularly Chandler), it had been organic in the past and was thought to have higher abundance than conventionally managed sites. Initial monitoring indicated greater navel orangeworm pressure at sites 4 and 6, while conversation with the cooperator indicated that navel orangeworm had historically been of less concern at Site 5 compare to other locations. The treated and untreated portions of Site 3 were divided north-south rather than east-west because that site contained different varieties in the east and west halves, which would have complicated damage comparisons if the treatment had been applied to the east (upwind) side as in Site 2. Mating disruption treatment was provided using CheckMate PufferNOW dispensers at the recommended density of two per acre. Treatment block sizes were 30 acres (Site 4) and 36 acres (sites 2, 3, and 6). Puffers were hung in trees with cords, using a contracted pruning tower that extended to a maximum height of 25 feet. Using a weighted throw line, Puffers were hung at a height of 30 to 35 feet. Cabinets were adjusted to start at 6PM local time and emit until 6AM. Puffers were activated on May 1 in order to collect initial monitoring data on male and egg abundance at the mating disruption sites prior to the start of mating disruption treatment.


Multiple pheromone traps were used in all mating disruption sites, with half of the traps hung 6 feet above the ground and the other half hung in the same manner and at the same height as the mating disruption dispensers. Pheromone traps in mating disruption treatment areas were placed as close as possible to midway between mating disruption dispensers. Husk-split and harvest sampling. Husk-split samples were taken at some cooperator sites, and samples at or near the time of harvest were taken at each of the sites 1-10. The husk-split sample was intended to help distinguish between navel orangeworm and codling moth as the primary agent of damage. If most navel orangeworm damage was to nuts previously attacked by codling moth, then damage should not have increased much with time. Conversely, increased damage after this time would likely be due to navel orangeworm. All commercial cooperators shook their blocks at least two times. For sites 1-10 in Tulare County, the first shake was between September 17 and October 1 (sites 2 and 10 were shaken on September 10 and September 12, respectively). The second shake at these sites was generally between October 3 and October 16. The first and second shake for the Chandler block at Site 3 was on October 17 and November 5, respectively. The first and second harvests at the Butte County site were September 19 and October 2-4, respectively. Husk-split samples were taken using poles with hooked wires on the end, aided in some cases by standing on the back platform of an all-terrain vehicle. Ten 50-nut samples were taken from each of the 24 to 30 egg trap postions. These samples were taken from above 10 feet from the ground (except when sampling replacement trees of <25 ft). These husk split samples were taken between September 4 and September 14. Harvest samples were taken after the trees had been shaken. Ten samples of 100 nuts each were taken. At the large mating disruption sites (2 and 3) these samples were taken from egg trap positions and adjacent trees. At other sites they were taken from 10 trees in a center row. Because of the small size of the mating disruption blocks, we wished to emphasize samples in the middle of the block. Because of difficulties in coordinating with cooperators, harvest samples for sites 7, 8 and 9 were taken in the same manner as husk-split samples. At sites 7 and 8 most of the canopy could be reached from the ground, but only part of the canopy at Site 9 could be reached in this manner. Samples were kept at -20°F until evaluation. Evaluation used guidelines from the UC IPM website (http://www.ipm.ucdavis.edu/PMG/C881/m881hppests.html). Insect infestation was assigned to one of three categories: codling moth, navel orangeworm, or unknown. Navel orangeworm infestation was often evident due to extensive frass formation and the presence of one or more larvae for identification. Nuts with little frass inside the nut and damage, typically toward the apical end of the nut, were attributed to codling moth. Nuts with webbing over much of the kernel but little frass were categorized as unknown. Damage is reported as total insect damage and damage attributed to navel orangeworm.


Data analysis. Data were analyzed using the SAS System (Cary, NC). The percent total insect infestation was compared between husk-split and harvest 1 samples in the southern region, and between harvest 1 and harvest 2 samples in Butte County, using 2 × 2 contingency table analysis with either the chi-square statistic or Fisher’s exact test. Navel orangeworm dispersal and residence in walnut orchards was examined by measuring the association of the mean weekly pheromone trap with the distance to the nearest almonds orchard, and by spatial analysis of eggs in egg traps in a walnut orchard adjacent to an almond orchard. The association between mean weekly pheromone trap count and distance from the nearest almond or pistachio orchard was tested with correlation analysis with Spearman rho statistic. This was used in place of the more statistically powerful Pearson r because the small size of the data set made the latter more vulnerable that the Spearman statistic to extreme values present at both ends of the distribution. The distribution of eggs in a walnut site adjacent to almonds were visualized using bubble plots, in which the area of the bubble was proportional to the number of eggs at the egg trap positions. Correlation was also used to determine if there was an association with egg trap captures between weeks, and Student’s t test to test the hypothesis that there were more eggs in the half of the field adjacent to almonds than in the far half. The folded F statistic was used to verify that the egg trap data met the assumption of homogeneity of variance. The number of males per trap per week was compared between plots in and adjacent to mating disruption treatments and the non-mating disruption plots by comparing the males per trap per week in the former to the lower 95% confidence interval of the latter. Impact was also described by trap suppression: %�� =100×A pheromone trap activity (figures 3 and 4). High insect damage— >10%—was observed in some of small and non-mating disruption southern regions sites (Table 3). Damage varied greatly among these sites, and most insect damage in this region was attributed to navel orangeworm. Moreover, overall insect damage increased numerically in all sites in Table 3, and the increase was statistically significant in three of these four sites. In contrast to other sites, damage was very light in both treated and untreated plots at the two larger mating disruption sites (sites 2 and 3, Table 4). Insect damage was moderate at the Butte County Site, where most of this damage was attributed to codling moth (Table 5). There was no significant difference in percent insect damage at this site between the first and second harvest for Field 24 (χ2 = 1.01, P = 0.31) or Field 25 (χ2 = 0.34, P = 0.56). Navel orangeworm dispersal. There was no significant association of males captured in pheromone traps with distance from the nearest section containing almond or pistachio orchards for any of the three periods involved (Figure 5). Although not significant, the figures and correlation coefficients suggest that, if there has been any correlation, it would be that walnut orchards farther away from other tree nut crops had more navel orangeworm. Spatial distribution of eggs on egg traps in a walnut site adjacent to almonds also failed to provide evidence for between-crop movement (Figure 6). For flight 1 (April 23 to May 28), there was no significant correlation (P > 0.05) of egg trap captures with captures at the same position in previous or subsequent weeks. The same was true of the period of June 3 to August 27, although that latter was trivial because many or most traps captures 0 eggs most weeks. Over


the 6-week period for flight 1, there were numerically more eggs per trap per week in the southern half of site 7 (57 ± 9.2)(mean ± SE) than in the northern half (48 ± 5.6), although this difference was not significant (t = 0.83, df = 28, P = 0.41). Over the subsequent 13 weeks there were also more eggs per trap per week in the southern half of site 7 (1.6 ± 0.62) than in the northern half (1.5 ± 0.35); this difference also was not significant (t = 0.11, df = 28, P = 0.91). Mating disruption for navel orangeworm. Near-complete suppression of males in female-baited traps was noted by the second week after initiation of mating disruption treatments (Table 6). Some males recovered during the week of April 30 were probably captured before the initiation of mating disruption treatments, whereas those recovered the week of May 7 represented trapping after mating disruption was activated. Starting the week of May 14, the mating disruption plots and the adjacent untreated area at site 3 had trap suppression of >99.9% with respect to traps in the plots not treated by mating disruption. In contrast, more males were captures in the adjacent untreated plot at site 2, and suppression there was 84% with respect to the untreated plots. There were clearly more males captured in high traps than low trap in the untreated portion of Site 2 (Table 7). In the week before mating disruption, 62% of males at that site were captured in the upper traps. From May 14 to September 17, after mating disruption, a significantly greater 90% of males at that site were captured in the other traps. In other locations, there were examples of both more and fewer males capture in high traps before mating disruption, and there were too few males captured following mating disruption to draw a conclusion (Table 7). There was a significantly smaller proportion of eggs laid after the beginning of mating disruption in mating disruption treatment plots compared to sites where mating disruption was not used (Table 8). However, at the two larger mating disruption sites, the differences between the proportions of eggs laid after the beginning of mating disruption was not significantly different between adjacent mating disruption and untreated plots (Table 9). DISCUSSION Navel orangeworm and codling moth damage. The damage characteristics, and the increase in damage between the husk-split and harvest 1 in southern region sites 1, 4, 5, and 6 (Table 3), indicate that most harvest damage this year at the study sites in this region came from navel orangeworm. The magnitude of difference in insect damage between the husk-split and harvest 1 samples is related to the interval between these samples; 11-12 days for sites 1 and 5, and 20-22 days for sites 4 and 6. Navel orangeworm abundance, trap phenology, and dispersal. The navel orangeworm pheromone trap phenology documented here for 6 walnut sites in the absence of mating disruption is generally similar to profiles previously documented in almonds in the San Joaquin Valley (Burks et al. 2008, Burks et al. 2011); i.e., greater trap counts during first and fourth flight, and lower counts during second flight and (Burks et al. 2008) and sometimes third flight (Burks 2011).


The relationship between navel orangeworm pheromone and egg trap phenology observed in this study is more similar to that previously seen in pistachios than in almonds. Previous studies have indicated a greater capacity for supporting navel orangeworm abundance in pistachios than almonds, and found generally higher pheromone trap counts in the latter crop (Burks et al. 2008). Egg trap counts, however, often drop in pistachios after the first flight (Burks, unpublished data). A similar pattern was observed in the data reported here (Figure 3A and 3B). The lack of association between distance between males in pheromone traps and distance from other tree nut crops (Figure 5) suggests that dispersal between crops is not an important aspect of maintaining navel orangeworm populations in the southern region orchards like those studied. These data are limited by a small number of sites and the limited information about the characteristics and precise location of the almond and pistachio orchards in the ArcGIS data base. The conclusion of limited importance of inter-crop dispersal is, however, supported by spatial analysis of egg trap data at Site 7, adjacent to almonds. Prior to the beginning of monitoring, infested mummies were found in both the almond and walnut orchards. The clustering of eggs away from the almond orchard during much of flight 1 indicates that the walnut trees themselves were a more important source of overwintered females than the adjacent almond orchard (Figure 6). The relatively even distribution of eggs during the period of June to September further suggested that the adjacent almond orchard was not an important source of ovipositing females. The interval observed between flights 1 and 2 in the egg trap data from Site 12 (Figure 3) further support the idea that inter-crop dispersal is not necessary to maintain navel orangeworm populations in walnut orchards like those in this study. The interval of 1110 degree days Fahrenheit is very similar to that documented for almond mummies and pistachios mummies (Seaman et al. 1984, Siegel and Kuenen 2011). Since Site 12 is 2.5 miles from the nearest section containing almonds or pistachios (Figure 1), this suggests that the second flight oviposition is from females that developed in the 250 acre contiguous block of walnuts which includes Site 12. Trends in the southern region v. Butte County. In a recent 5-year USDA-ARS navel orangeworm area-wide project, in collaboration with UC, the Walnut Board, the California Pistachio Research Board, and the Almond Board of California, multi-year data were presented indicating that mummy carry-over and infestation was least in the northern Sacramento Valley and increased with distance south, at least as far as San Joaquin County. Comparison of the data between the navel orangeworm trap and damage data for Tulare and Butte counties reveal a similar pattern. The data presented here from the southern region make a collective case that abundant navel orangeworm populations carry over from year to year, as previously described. In contrast, most harvest damage from the Butte County site was diagnosed as codling moth rather than navel orangeworm. Trap data from the Butte County site revealed fewer males and eggs captured. Moreover, pheromone trap captures did not increase in June and July as in the south, and they dropped off at the end of September instead of continuing to climb as in the south. These data suggest that at this Butte County Site, the navel orangeworm was less economically important, and the codling moth more so, compared to the southern regions study sites. The trap observations also suggest the possibility that inter-orchard movement between the walnuts at the Butte County site and the almonds to the east is more important for maintenance of navel orangeworm in those walnuts compared to the sites observed in the southern region.


The proportion of the crop collected in the various harvests also differed between the Butte County and Southern Region sites. At the Butte County Site harvests 1 and 2 yielded 49 and 51% of the crop, respectively. Field 25 was more back-loaded, with harvest 2 yielding 64% of the crop. In contrast the first, second and third harvests at Site 2 in Tulare County (the first two of which were sampled) yielded respectively 71, 19, and 11% of the overall crop. While similar statistics were not obtained for other southern regions sites, observations during harvest sampling suggested a similar distribution to that at Site 2. Mating disruption for navel orangeworm. Aerosol mating dispensers distinctly suppressed pheromone traps some distance from the treated area, and had a demonstrable but less dramatic effect on eggs in egg traps. Similar effects have been observed in almonds (Burks, unpublished data). When compared with distant untreated sites the proportions of eggs laid before mating disruption began compared to afterward was greater in three of the four mating disruption sites (Table 9). The fourth site, Site 3, contained Chandler and Tulare, generally considered less susceptible to lepidopteran pests than earlier varieties like Serr and Vina. That may be a factor in the lower overall number of eggs found at that site. The fact that pheromone traps were thoroughly suppressed in the adjacent untreated plot at Site 3, but less so at Site 2, calls into question the independence of the untreated area at Site 3. Site 2 and Site 3 were also very different in canopy structure. While both contained high, mature trees, those at Site 3 were planted more densely. Moreover, Site 2 was in an ongoing major reformation of the canopy. In 2011 one of two main trunks had been pruned on the west half of the orchard, and in winter 2012 (before the start of monitoring), the east half was pruned in a similar manner. During the 2012 growing season the orchard was generally more sparse than many walnut orchards of similar maturity, but the east half (treated with mating disruption) was more sparse than the west half. The males captured in the untreated portion of Site 2 offer insight into the effect of movement of pheromone from the navel orangeworm dispensers in the orchard. Before mating disruption treatments started, there were more males in the upper traps than the lower traps in the untreated portion of Site 2 (Table 7). However, data from the other plots (none under mating disruption at that point) did not reveal a consistent pattern of preference of high or low traps. In contrast, after mating disruption started, the preference for high traps in the untreated portion of Site 2 was significantly greater after mating disruption was applied in the adjacent plot (Table 7). Five of the 6 males captured over the season at other treated plots were in low traps; however, this number is too small to analyze. The data from Site 2 suggests that the pheromone traveled through the lower (under-) canopy at that site. Data from almonds and pistachios suggest that navel orangeworm pheromone rises from aerosol dispensers in those crops, but mature walnuts have a higher under-canopy and a thicker canopy which may result in less convective currents in the evening and night. Further work on the movement of pheromone from aerosol dispensers in walnut canopies is needed.


Pest management treatments and outcomes. Heavy damage to Serr walnuts was reported by many growers in 2012 in the southern regions. This may be due in part to injury and early husk break-down caused by six consecutive days with high temperatures of >100°F, starting August 9 (http://wwwcimis.water.ca.gov/cimis/, stations 86 and 169, Tulare County). While some sites had low damage despite this, such as Site 2 (and the less susceptible varieties at sites 3 and 8), others had high damage. At Site 6, late harvest (first harvest on September 29) may have been a factor. However, Site 10 was first harvested on September 14—as soon permitted by the post-harvest interval following a chlorpyrifos husk-split treatment—and still had heavy damage. It is conceivable that Site 7 was spared heavier damage by a methyl parathion treatment, in response to concern about codling moth stings, that fortuitously coincided with the beginning of the August heat wave. Given the range of damage, no conclusion can be made about the effect of mating disruption on harvest quality in 2012. Overall these data indicate a pattern of navel orangeworm abundance and carry-over in mature southern region walnut orchards planted in susceptible varieties. Under some circumstances, this high abundance can lead to high damage. The 2012 growing season brought such circumstances for many growers, and some growers in this regions have had chronic problems with insect damage which is likely attributable to navel orangeworm. Almond producers in areas with high navel orangeworm pressure often use a spring pesticide treatment with reduced-risk pesticides targeting flight 1 navel orangeworm (and/or peach twig borer). Comparisons of phenology of navel orangeworm and codling moth demonstrate that insecticide treatments targeting codling (e.g, the 1B flight) are unlikely to affect flight 1 navel orangeworm. For growers with chronic problems, it may be necessary to devise strategies to reduce navel orangeworm abundance instead of relying on protection nuts with insecticide applications at husk-split. REFERENCES Beck, J. J., B. S. Higbee, W. S. Gee, and K. Dragull. 2011. Ambient orchard volatiles from California almonds. Phytochemistry Letters 4: 199-202. Burks, C. S., B. S. Higbee, and D. G. Brandl. 2005. Mating disruption for suppression of navel orangeworm in almonds. Proceedings of the 33rd Almond Industry Conference: 1-10. Burks, C. S., B. S. Higbee, D. G. Brandl, and B. E. Mackey. 2008. Sampling and pheromone trapping for comparison of abundance of Amyelois transitella in almonds and pistachios. Entomologia Experimentalis et Applicata 129: 66-76. Burks, C. S., B. S. Higbee, J. P. Siegel, and D. G. Brandl. 2011. Comparison of trapping for eggs, females, and males of the naval orangeworm (Lepidoptera: Pyralidae) in almonds. Environmental Entomology 40: 706-713. Cardé, R. T., and A. K. Minks. 1995. Control of moth pests by mating disruption: successes and constraints. Annual Review of Entomology 40: 559-585. Charmillot, P. J. 1990. Mating disruption technique to control codling moth in Western Switzerland, pp. 165-182. In R. L. Ridgway, R. M. Silverstein and M. N. Inscoe (eds.), Behaviour-modifying chemicals for pest managment: Applications of pheromones and other attractants. Marcel Decker, New York.


Curtis, C. E., and J. D. Clark. 1984. Pheromone application and monitoring equipment used in field studies of the navel orangeworm (Lepidoptera: Pyralidae). J. Econ. Entomol. 77: 1057-1061. Gut, L. J., L. L. Stelinski, D. R. Thomson, and J. R. Miller. 2004. Behaviour-modifying chemicals: prospect and constraints in IPM, pp. 73-121. In O. Koul, G. S. Dhaliwal and G. W. Cuperus (eds.), Integrated Pest Management: Potential, Constraints and Challenges. CAB International, Wallingford, UK. Higbee, B. S., and C. S. Burks. 2008. Effects of mating disruption treatments on navel orangeworm (Lepidoptera: Pyralidae) sexual communication and damage in almonds and pistachios. Journal of Economic Entomology 101: 1633-1642. Higbee, B. S., and C. S. Burks. 2011. Effect of bait formulation and number of traps on detection of navel orangeworm oviposition using egg traps. Journal of Economic Entomology 104: 211-219. Kuenen, L. P. S., D. Brandl, and R. E. Rice. 2005. Modification of assembly of Pherocon® IC traps speeds trap liner changes and reduces in-field preparation time. Can. Entomol. 137: 117-119. Light, D. M., and A. L. Knight. 2011. Microencapsulated pear ester enhances insecticide efficacy in walnuts for codling moth (Lepidoptera: Tortricidae) and navel orangeworm (Lepidoptera: Pyralidae). Journal of Economic Entomology 104: 1309-1315. Light, D. M., A. L. Knight, C. A. Hendrick, C. A. Rajapaska, B. Lingren, J. C. Dickens, K. M. Reynolds, R. G. Buttery, G. Merrill, J. Toitman, and B. C. Campbell. 2001. A pear-derived kairomone with pheromonal potency that attracts male and female codling moth, Cydia pomonella (L.). Naturwissenschaften 88: 333-338. Sanderson, J. P., M. M. Barnes, and W. S. Seaman. 1989. Synthesis and validation of a degree-day model for navel orangeworm (Lepidoptera: Pyralidae) development in California almond orchards. Environ. Entomol. 18: 612-617. Shelton, M. D., and D. W. Davis. 1994. Navel orangeworm (Lepidoptera: Pyralidae) development in sunburned walnuts. Journal of Economic Entomology 87: 1062-1069. Sibbett, G. S., and J. Stewart. 1995. Efficacy of several trap types in monitoring navel orangeworm adults. Walnut Research Reports 1995: 187-189. Siegel, J. P., and L. P. S. B. Kuenen. 2011. Variable developmental rate and survival of navel orangeworm (Lepidoptera: Pyralidae) on pistachio. J. Econ. Entomol. 104: 532-539. Steinman, K. P., M. Zhang, J. A. Grant, C. PIckel, and R. E. Goodhue. 2008. Pheromone-based pest management can be cost-effective for walnut growers. California Agriculture 62: 105-110. USDA National Agricultural Statistics Service [USDA-NASS]. 2010. California Agricultural Statistics 2010 Crop Year, USDA National Agricultural Statistics Service, Sacramento, California. Van Steenwyk, R. A., L. W. Barclay, W. W. Barnett, K. M. Kelley, W. H. Olson, G. S. Sibbett, and C. V. Weakely. 1984. Investigations of navel orangeworm control in walnuts. Walnut Research Reports 1984: 135-158. Van Steenwyk, R. K., and W. W. Barnett. 1985. Improvements of navel orangeworm (Lepidoptera: Pyralidae) egg traps. J. Econ. Entomol. 78: 282-286.


Welter, S. C., C. Pickel, J. G. Millar, F. Cave, R. K. Van Steenwyk, and J. Dunley. 2005. Pheromone mating disruption offers selective management options for key pests. California Agriculture 59: 16-22.


Table 1. Summary of 2012 study sites

Site Number Variety Mating disruption?a

Canopy heightb

Size of block (acres)

Trees per acre

1 Serr No Tall 26 109

2 Serr Yes Tall 75 40

3 Chandler, Tulare Yes Tall 80 68

4 Vina Yes Tall 36 116


6 Serr Yes Tall 36 54

7 Serr No Medium 21 54

8 Tulare No Medium 37 52



11 Chandler, Vina, Hartley No Tall 0.2 48

12 Vina No Tall 56 54 aIndicates that part or all of the site was treated with mating disruption for navel orangeworm. Half of sites 2 and 3 were treated, and all of sites 4 and 6. bHeight categories: medium, canopy 30 to 40 feet high; tall, canopy 40 to 60 feet high.


Figure 1. Location of 2012 navel orangeworm study sites with respect to other nut tree nut crops. Numerals indicate the sites described in Table 1. Site 11 is 12.5 miles north (11 degrees) with respect to Site 12. Green and tan squares indicate 640-acre sections contain respectively almonds and pistachios, as surmised from pesticide use permits. Pink areas indicate confirmed pistachio locations.


Figure 2. Plot arrangement for sites >40 acres (sites 2, 3, and 5). Black dots represent egg traps, and red dots represent pheromone traps. In the absence of mating disruption (Site 5), only the farthest southwest and northeast pheromone traps were used in the large plots. Pheromone traps on the south ends of the arrays were 6 feet from the ground, and those on the north end were 25-30 feet high. At Site 2 mating disruption was applied to the east portion of the orchard, and at Site 3 mating disruption was applied to the north half of the block.

Feet west to east

0 660 1320 1980 2640

Fe

et s

ou

th to

no

rth

0

660

1320

150 ft


Figure 3. Phenology of (A) navel orangeworm males captured in pheromone traps and (B) eggs in egg traps at non-mating disruption sites. The solid black line provides mean and standard error (SE) of Tulare County sites 1, 5, and 7-10. The solid and dashed gray lines represent sites 11 and 12, respectively. The open red circles represent mean and SE for the Butte County Site. SE for eggs for the Tulare County sites is based on a mean of 6 site means of 24-30 egg traps each (i.e., the error is based on the number of sites and not the number of egg traps). SE for the Butte County traps is based on 8 traps.

B) Eggs

01-Apr 01-May 01-Jun 01-Jul 01-Aug 01-Sep 01-Oct

Eg

gs/tra

p/w

ee

k

0

20

40

60

80

100

A) Males

NO

W M

ale

s/w

ee

k

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150


Figure 4. Phenology of navel orangeworm and codling moth males (mean and SE) captured in pheromone traps traps at non-mating disruption sites. Closed black dots are navel orangeworm, and open red circles are codling moth. Flights 1A, 1B, 2A, and 2B are evident in the codling moth data. Most of the navel orangeworm first flight (April through May) is unaffected by treatments targeting codling moth flight 1B (cf. navel orangeworm egg data, Fig. 3).

01-Apr 01-May 01-Jun 01-Jul 01-Aug 01-Sep 01-Oct

NO

W M

ale

s/w

ee

k

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50

100

150

CM

Ma

les/w

ee

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4

8

12


Table 3. Percent navel orangeworm and total insect damage in harvest samples from non-mating disruption sites and smaller mating disruption sites Husk-splita Harvest 1b Harvest 2 Site Variety Total NOW Total NOW Total NOW

1 Serr 1.0 1.0 3.4ns 3.4 11.8 11.8 4c Vina 0 0 6.2*** 2.8 3.2 3.0 5 Serr 1.1 0.2 2.0 2.0 4.7 2.8d 6c Serr 4.6 1.1 34.5*** 18.0 20.0 12.0 7 Serr N/A N/A 7.0 5.8 1.7 1.5 8 Tulare N/A N/A 0 0 7.8 4.3 9 Serr N/A N/A 2.1 0 5.0 0

10 Serr N/A N/A 12.0 10.5 33.1 29.4 Reported damage based on evaluation of 200-700 nuts. aHusk-split samples were not collected at sites 7-10. bSuperscripts in the Total column indicate P for test of no difference in proportion of total infestation between husk-split and Harvest 1 samples: ns, P < 0.1; ***, P < 0.001. cSites 4 and 6 were treated with mating disruption for navel orangeworm. dDamage was 9.4%, all NOW, in samples from a third harvest at Site 5. Table 4. Percent navel orangeworm and total insect damage in harvest samples from large (>75 acre) mating disruption sites Harvest 1 Harvest 2

Site Variety Mating disruption? Total NOW Total NOW

2 Serr No 0.5 0 0 0 Yes 0 0 3.3 2.8

3 Tulare No 0.3 0.3 0.2 0.2 Yes 0 0 0.2 0.2

3 Chandler No 0 0 0 0 Yes 0 0 0 0

Reported damage based on evaluation of 200-700 nuts. No insect damage was found in husk-split samples from Site 3. At Site 2, total insect damage at husk-split was <0.4% each in the untreated and treated portion of the block.


Table 5. Percent navel orangeworm and total insect damage in harvest samples from orchards near Chico, California Harvest 1 Harvest 2 Site Variety Total NOW Total NOW Field 24 Vina 4.7 0.9 5.7 0.3 Field 25 Vina 4.2 1.0 4.5 0.1 Based on evaluations of 1,000 nuts (Field 24) and 3,500 nuts (Field 25). Differences in the total percent insect infestation were not different between harvests (P > 0.1) for either field.

Figure 5. Association of pheromone trap captures and tree nut crop proximity at non-mating disruption sites. The data for the seven sites examined do not support the hypothesis that navel orangeworm males are more abundant in sites closer to almond or pistachio orchards.

Flight 1

Miles

0 1 2 3

Ma

les/tra

p/w

ee

k

0

20

40

60

80

Flight 2

Miles

0 1 2 3

Flight 3

Miles

0 1 2 3

rs = 0.20, P = 0.67 rs = 0.43, P = 0.33 rs = 0.43, P = 0.33


Figure 6. Spatial distribution of navel orangeworm eggs on egg traps at Site 7. The northern upper edge of this site was adjacent to an almond orchard. Red x marks indicate individual egg trap positions. The area of the black dots is represents the proportion of eggs recovered from the indicated trap for the indicated time period. Sizes are proportional within figures, but not between them. There was no significant difference (Student’s t-test, P > 0.05) between the number of eggs captured in the northern and southern halves of this site, either in spring (23 April to 28 May) or in summer (3 June to 27 August).

23 Apr; mean = 72 eggs per trap

Ft s

outh

to n

orth

0

200

400

600

30 Apr; mean = 130 eggs per trap

Ft s

outh

to n

orth

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200

400

600

07 May; mean = 65 eggs per trap

Ft s

outh

to n

orth

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600


Ft west to east

0 200 400 600 800 1000 1200

Ft s

outh

to n

orth

0

200

400

600



Jun-Sep; mean = 1.5 eggs/trap/week

Ft west to east

0 200 400 600 800 1000 1200


Table 6. Mean navel orangeworm males per pheromone trap per week at sites treated with mating disruption for navel orangeworm. Site 2 Site 3 Site 4 Site 5 Week of Untreated

Mating Disruption Untreated

Mating Disruption

Mating Disruption

Mating Disruption

30 Apr 96.25* 46.75 41.25 24 53.5 65.5 07 May 47.75* 14.25 9.5 5 36.5 0 14 May 1.5 0 0 0.25 0 0 21 May 31 0 0 0.25 0 0 28 May 29.75 0 0 0 0 0 04 Jun 0 0 0 0 0 0 11 Jun to 16 Sep (20 weeks) 2.90 0.03 0.02 0 0.04 0

Sites 2 and 3 included treated and untreated areas; in sites 3 and 4 the entire area was treated. *Asterisks indicate values that exceeded the lower 95% confidence limit of the mean male captures for the 6 non-mating disruption sites during the equivalent time period (i.e., in all other cases there were significantly fewer males captured compared to the sites not treated with mating disruption).

Table 7. Distribution of navel orangeworm males between low and high traps in and near mating disruption plots before mating disruption (1 week, 30 Apr) and after mating (weeks of 14 May to 17 Sep)

30 Apr 14 May to 17 Sep

Site Mating Disruption

Total males from all traps

%Males from high trap

Total males from all traps

%Males from high trap

2 No 385 62*** 423 90***

Yes 187 47 2 0

3 No 165 53 1 0

Yes 96 68*** 2 50

4 Yes 107 32*** 1 0

5 Yes 131 56 0 0

Chi-square test for equal proportions, ***P < 0.001. The difference between the proportion of males in the high traps in the untreated portion of Site 2 before and during mating disruption is also significant (χ2 = 91.36, P < 0.001).


Table 8. Proportion of navel orangeworm eggs laid, in mating disruption and non-mating disruption sites, before (2 weeks) and after (8 weeks) the onset of mating disruption treatment.

MD Site Variety No. egg traps

Mean eggs/trap over the 10 weeks

No. egg traps with >0 eggs

Proportion of eggs laid during the first 2 weeks

Yes 2 Serr 12 214 ± 25 12 94 ± 1 Yes 4 Vina 30 25 ± 3 29 86 ± 5 Yes 6 Serr 30 86 ± 10 30 82 ± 4 No 7 Serr 30 103 ± 14 30 77 ± 4 No 8 Tulare 30 13 ± 3 28 70 ± 8 No 10 Serr 29 77 ± 13 29 68 ± 5 No 9 Serr 30 43 ± 7 30 64 ± 5 Yes 3 Chandler/Tulare 12 49 ± 12 12 63 ± 12 No 1 Serr 30 41 ± 7 29 46 ± 7 No 5 Serr 24 7 ± 2 14 32 ± 12 Data from sites 2 and 3 are from the treated area only. Traps with 0 eggs are included in calculation of the mean sum of eggs, but not in the calculation of the proportion of eggs laid during the pre-treatment period. The proportion of eggs laid during the pre-treatment period was significantly greater in the treated plots than the untreated plots (Mixed model ANOVA, P < 0.05). Table 9. Proportion of navel orangeworm eggs laid before (2 weeks) and after (8 weeks) the onset of mating disruption treatment at large sites that included treated and untreated areas.

Site Variety

Treated with mating disruption?

No. egg traps

Mean egg sum

Proportion of eggs laid during the first 2 weeks

2 Serr No 12 278 ± 39 91 ± 1.9 Yes 12 214 ± 25 94 ± 1.1

3 Chandler/Tulare No 12 41 ± 9 74 ± 8.0 Yes 12 49 ± 12 63 ± 12.2

The difference in the proportion of eggs laid during the pre-treatment period is not significant for either site (Student’s t, P > 0.05).


NAVEL ORANGEWORM IN SOUTHERN CENTRAL VALLEY WALNUTS: SOURCE

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