control of walnut husk fly using reduced risk...

CONTROL OF WALNUT HUSK FLY USING REDUCED RISK PRODUCTS R. A. Van Steenwyk, A. Verhaeghe, C. A. Leslie, W. W. Coates, J. A. Grant, J. K. Hasey, and C. J. DeBuse ABSTRACT Studies were conducted to examine various parameters to improve WHF trap efficacy. The Trécé trap/lure combination was about ½ as efficacious as the Alpha Scent trap/lure combination or the Trécé trap/standard vial super charger lure combination. The increase in efficacy is related to the lure efficacy and not the trap efficacy. Host plant volatiles did not improve efficacy, but this could be the result of the release rate. Control of WHF was demonstrated with low volume (10 gal/ac) applications of a high rate of Malathion 57% and Nu-Lure (3 pt/ac each) at 10 mph. The low volume technique was as efficacious as conventional applications with a high volume (100 gal/ac) and a high rate of Malathion 57% and Nu-Lure (3pt/ac each) at 2 mph in control of WHF and was superior to a treated check. However, low volume (10 gal/ac) applications of a low rate of Malathion 57% and Nu-Lure (0.3 pt/ac each) at 10 mph were not as efficacious as conventional applications with a high volume (100 gal/ac) and a high rate of Malathion 57% and Nu-Lure (3 pt/ac each) at 2 mph in control of WHF. Six nut characteristics in 12 cultivars were examined:. The most promising characteristic that could confer resistance or susceptibility to WHF infestation is the pressure to penetrate the husk. However, this will need to be confirmed next season when the various cultivars can be exposed to gravid female WHF. OBJECTIVES The walnut husk fly (WHF), Rhagoletis completa, is a serious pest of walnuts. Control of WHF populations has relied on the combination of a neonicotinoid (NEONIC) or organophosphate (OP) insecticide and feeding stimulant (Nu-Lure Insect Bait, Monterey Insect Bait, molasses). However applications are costly and time consuming. Past research has demonstrated that effective control of WHF can be achieved with repeated low volume applications of GF-120. However, GF-120 needs to be applied more frequently and earlier in the season than conventional insecticides and control in tall trees or high WHF population is problematic. Low volume applications of a NEONIC or OP pesticide with feeding stimulant can provide comparable control to the conventional application of NEONIC or OP with feeding stimulant. Low volume applications are more cost effective because they can be applied more quickly than conventional treatments. Control may be achieved at lower rates of application, further reducing the cost of the a low volume technique. Studies were conducted to determine whether WHF control can be achieved with a low volume of final spray solution and low volume and reduced rate of insecticide. Treatment initiation and evaluation of a treatment has relied on commercial WHF traps. These traps are yellow sticky panels with an attractant of an ammonium-releasing chemical such as ammonium carbonate. Growers and PCAs have not been satisfied with these traps in that they find WHF infestation with few WHF captured in the traps. Thus they are not able to determine the best time to initiate treatment or how often to reapply the treatment. Without this basic

California Walnut Board 193 Walnut Research Reports 2012

population data it is difficult to provide the best pest management decisions for the control of WHF. Studies were conducted to determine the most efficacious commercial trap/lure and possible trap improvements. Seasonal and cultivar susceptibility is known to occur with WHF infestation in walnuts. However, the factors responsible for varied susceptibility are not well understood. Mid-season or late-season leafing cultivars such as Hartley and Franquette are highly susceptible while Chandler is much less susceptible. However, Chandler can become highly infested if there is not a more susceptible cultivar in the same orchard. Thus simple phenological asynchrony does not appear to be a primary case of the resistance. If the traits such as husk firmness, thickness, surface texture, chemical composition, etc. that infer resistance or susceptibility can be identified and quantified, then these traits can be used to more accurately initiate and terminate control programs and can be incorporated as desirable characteristics into the breeding program. Studies were conducted to quantify nut characteristics. SIGNIFICANT FINDINGS

• Alpha Scents back-folded yellow traps/lures captured significantly more WHF than Trécé yellow panel AM traps/lures.

• Low volume (10 gal/ac) applied at 10 mph control of WHF was as efficacious as standard volume (100 gal/ac) applied at 2 mph.

• Pressure to penetrate the husk may be the key characteristic to WHF nut resistance. PROCEDURES A. Trap and Bait Efficacy Comparisons

Trials were conducted in three commercial orchards and cultivars in Hollister (Payne), Rio Oso (Hartley), and Linden (Vina), CA. Ten treatments were replicated four times, each at two different trap heights in a randomized complete block (RCB) design in each orchard. There were two to five trees in between each replicate, however high and low traps of the same treatment were in adjacent trees. Low traps were placed about 6 ft above the ground. High traps were placed in the top 5 ft of the tree canopy. There was a minimum of 5 rows between blocks. All traps were checked weekly and trap positions were rotated within the block weekly to correct for position effects. All treatments contained a standard supercharger vial (except where noted) that was 2 1/8” long, 5/8” in diameter with a 3/8” hole to release 3.9 g of either ammonium carbonate or ammonium bicarbonate. The ten treatments were: Trécé trap with ammonium carbonate, Trécé trap with ammonium bicarbonate, Trécé trap with 3.9 g ammonia carbonate in a high-output mesh bag, Trécé trap with ammonium carbonate and time-released green leaf (GL) alcohol blend, Trécé trap with time-released GL alcohol blend, Trécé trap with ammonium carbonate and time-released caryophyllene, Trécé trap with time-released caryophyllene, Trécé trap with Trécé brand lure, Alpha Scents trap with Alpha Scents brand lure, Alpha Scents trap with ammonium carbonate (Table 1). Traps were placed in trees 12-14 June depending on location and were monitored with trap position rotated weekly until 4-7 September.


B. Control of WHF with Reduced Amounts of Pesticide and Application Time

A trial was conducted in three commercial orchards in Linden (Vina), Modesto (Vina) and Hollister (Chandler). Four treatments were replicated once in each orchard. Each replicate was a minimum of 5 acres. All treatments were applied to every other row (skip row). The four treatments were: Malathion 57% and NuLure at 3.0 pt/ac each applied at 10 gal/ac, Malathion 57% and NuLure at 0.3 pt/ac each applied at 10 gal/ac, Malathion 57% and NuLure at 3.0 pt/ac each applied at 100 gal/ac (grower standard) and a treated check. The check was treated with NuLure at 3.0 pt/ac applied at 10 gal/ac. When infestation in the treated check reached 6% damaged nuts then the treated check was converted to the grower standard to prevent unacceptable damage. The Modesto orchard reached 6% on 15 August and the Linden orchard reached 6% on 4 September. The Hollister orchard never reached 6%. Treatments applied at 10 gal/ac were applied using two handheld orchard sprayers operating at 450 psi at approximately 10 mph. The grower standard was applied using a grower operated speed sprayer at 2-3 mph. The low concentration treatment was applied the week following the first fly captures in the adult traps for each orchard and at approximately two week intervals for the remainder of the season (Table 2). The high concentration treatment was applied at the same time as the grower standard, two or three times during the season. Grower standard and high concentration treatments were applied after consultation with PCAs and were about a week after “substantial” fly captures in the adult traps. Adult WHF populations were monitored using one ammonium carbonate “supercharged” yellow apple maggot panel trap placed high in a centrally located tree in each replicate. These traps were inspected, and the ammonia carbonate bait replaced weekly from 26 June to 12 September. WHF nut infestation was monitored weekly by visually inspecting 100 nuts per replicate for stings, larval feeding and exits from 29 July through 18 September. The final nut infestation on 18 September was based on 500 nuts per replicate.

C. Identification and Quantification of Nut Characteristics by Cultivar

Ten nuts from twelve cultivars were collected every two weeks from 18 July to 9 September. Cultivars were located in the New Stuke block at UC Davis. Nuts were collected from the lower 1/3 of the tree (≤12 ft.) and placed in egg cartons to preserve the integrity of trichomes during transport to UC Berkeley for processing. Each nut was assessed for trichome density, weight, volume, length, husk thickness, husk penetration pressure and husk water content. Trichome density was determined by cutting a circular piece of the mesocarp with a cork borer with a diameter of 0.7cm and then removing the periderm from mesocarp with a scalpel and counting the trichomes on the periderm under magnification (80X) using a 22 mm grid reticule from Microscope World (6122 Innovation Way, Carlsbad, CA 92009). Nut volume was determined by the water displacement method. Nut length and width were determined using calipers at the longest/widest point. Husk thickness was measured using calipers at pistillate, at mid-nut and stem end. Husk penetration pressure was determined using a penetrometer (Fruit Pressure Tester, Model No. FT 444, Facchini, Via Reale, 63 48011 Alfonsine, Italy) fitted with an extra small tip (standard tip milled to 3.2 mm diameter) to record maximum pressure before penetration of the husk. Water content of the husk was determined by measuring the initial wet weight of the husk and then drying the husks for two weeks


prior to taking the final dry weights. The difference in weights was then divided by the wet weight. Selected cultivars included: C. Mayette, Carmello, Chandler, Earliest, Hartley, Payne, S. Franquette, Serr, Sinensis #5, Tulare, 91-90-41, and 91-96-3. Nut metrics obtained for each of the ten individual nuts from each cultivar were averaged by collection date and for the entire observation period.

RESULTS AND DISCUSSION

A. Trap and Bait Efficacy Comparisons Trap data from the three orchards at both high and low placement were analyzed both on an individual orchard basis and as combined orchards. Only the combined orchard analysis is presented here. In traps placed high in the tree canopy, T-carb, AS-alpha and AS-carb traps captured significantly more female, male, and total WHF than all other treatments except T-bicarb. T-bicarb was not significantly different compared to T-hi carb or T-carb+GL in female WHF catches, but captured significantly more male and total WHF than T-hi carb (Table 3). There were no significant differences among T-hi carb, T-carb+GL, T-trece and T-carb+cary in female, male or total WHF catches, but these were significantly higher than T-cary and T-GL, in female WHF catches. T-trece, T-carb+cary and T-cary were not significantly different compared to each other in male WHF catches but were significantly higher than T-GL. T-GL was not significantly different compared to either T-carb+cary or T-cary in male WHF catches. In total WHF catches, T-cary and T-GL were not significantly different compared to T-carb+cary. In traps placed low in the tree canopy, AS-alpha traps captured significantly more female WHF than all other treatments except AS-carb and AS-carb but were not significantly different compared to any other treatment (Table 4). There was no significant difference among any of the remaining treatments. There was significantly more male WHF captured in T-carb, AS-alpha and AS-carb than T-GL, T-carb+cary, T-cary and T-trece but not in the T-bicarb, T-hi carb or T-carb+GL treatments. T-bicarb and T-carb+GL captured significantly more male WHF compared to T-GL and T-cary, but not T-hi carb, T-carb+cary and T-trece. T-hi carb captured significantly more males compared to T-GL, but not compared to T-carb+cary, T-cary or T-trece. AS-alpha, AS-carb, T-carb+GL and T-carb captured significantly more total WHF compared to all other treatments except T-bicarb and T-hi carb. T-bicarb captured significantly more total WHF compared to all other treatments except T-carb+cary. T-hi carb captured significantly more total WHF compared to T-GL. Since there was no significant difference in the number of total flies in high or low traps between AS-carb and T-carb treatments, there is no difference in efficacy between trap types. The AS traps have hot melt pressure sensitive (HMPS) adhesive while the T traps have Tangle-trap Sticky Coating (TSC) (Tanglefoot Co.) adhesive. The HMPS adhesive is less messy than the TSC. However, it is very difficult to remove flies or debris from the HMPS adhesive, which cannot be reapplied, and is thus a single-use trap. Additionally the AS traps were observed to have large amounts of by catch, potentially causing trap saturation and reducing WHF flies captured under very high population densities. The TSC adhesive can be reapplied to the T traps and the traps reused for a number of times for significant savings.


There was no significant difference in the number of total flies in high or low traps between T-carb and T-bicarb treatments, thus no difference in the efficacy of the two lures. However, as the carb lure captured numerically more flies than the bicarb lures, the carb lures are preferred over the bicarb. Since the AS lure captured numerically more flies than the carb or bicarb lures, although not significantly more, and PCA and growers have a difficulty in purchasing ammonium carbonate or ammonium bicarbonate, the commercial AS lures would be the preferred lure. AS lures also had significantly greater catch than the Trécé lures. This is probably due to the increased load rate of the ammonium carbonate in the AS lures. AS lures contain ca.11.7 g of ammonium carbonate, while Trécé lures contain only ca. 2.2 g. The GL and cary lures were not as attractive to WHF as all other lures, and they decreased in attractiveness when combined with ammonium carbonate. The GL and cary lures appeared to be seeping attractant and the lures appeared moist. Thus, additional research is needed to determine the proper release substrate for these lures. Traps placed high in the tree canopy that contained ammonium carbonate or ammonium bicarbonate lures captured more female and total WHF than traps placed low in the tree. This was not the case with male WHF, with slightly more males captured low in the tree than high in the tree. Previous research had found that traps with ammonium carbonate or ammonium bicarbonate lures and placed high in the tree canopy always captured more total WHF than traps placed low in the canopy but the sex of the flies was not determined in the previous studies. Traps placed low in the tree canopy that contained caryophyllene and green leaf alcohol blend lures captured more female, male and total WHF than traps placed high in the tree. It is difficult to know why more flies are captured in the low traps with caryophyllene and green leaf alcohol blend than high traps, but it could be related to sexual maturity of the flies. As flies emerge from the soil they are sexually immature while flies at the top of the canopy are more sexually mature. Thus, the differential capture betweem low and high traps with caryophyllene and green leaf alcohol blend could be the response of immature flies to the plant odors rather than a nitrogen source.

B. Control of WHF with Reduced Amounts of Pesticide and Application Time

There were very high WHF populations in the orchards, with a season mean total adult catch of over 33 flies per week and with a peak weekly catch of 124 flies. However, there were no significant differences in trap catch among the treatments (Table 5). This was to be expected, since flies are constantly emerging from late June through mid-September and insecticide treatments only suppress the population that is present at the time of application. Also, the plots were not square but rectangular in design to accommodate the individual orchards and the growers’ spray equipment. Thus the plots were not as wide as desired. This allowed for movement of the flies between plots. Additionally, there were only three replicates (orchards) in the study and there was considerable variation in WHF populations among orchards. Only three orchards were selected for the study to limit the growers’ exposure to a new and untried control technique. Nut infestation was highest in the treated (Nu-Lure) check followed by the low volume/low concentration, then the low volume/high concentration and then the grower standard (Fig. 1). There was, however, no significant difference among the treatments. The nut infestation in the grower standard and low volume/high


concentration treatments were similar all season and total infestation remained below 6% infested nuts in both treatments. Thus, it appears that the low volume/high concentration treatment (3 pt/ac of Malathion 57% and Nu-Lure each in 10 gal/ac applied at 10 mph) is just as efficacious as the grower standard (3 pt/ac Malathion 57% and Nu-Lure each in 100 gal/ac applied at 2 mph). This allows for the orchard to be treated in about 1/5 the time and would result in considerable savings to the growers. The low volume/low concentration treatment (0.3 pt/ac of Malathion 57% and Nu-Lure each in 10 gal/ac applied at 10 mph) was not as efficacious as hoped. It appears that 0.3 pt/ac of Malathion 57% and Nu-Lure each in 10 gal/ac applied at 10 mph was just not enough insecticide despite more applications. Despite this disappointment, these results are very encouraging. It appears that control of WHF can be accomplished with this new technique at considerable savings to the growers over conventional control practices.

C. Identification and Quantification of Nut Characteristics by Cultivar Trichome Density: The average trichome density from 18 July to 6 September was between 102.1 and 360.4 trichomes/cm2 (Table 6 and Fig. 2). This trichome density is very similar to density by cultivar observed by Christofferson et al. (2000). However, the number of trichomes among sample dates within the same cultivar was often highly variable. The trichome density was not uniformly distributed on the nut surface and the sampling technique did not adequately sample the nut surface. Carmello and Sinensis #5 had the lowest number of trichomes followed by Serr and Tulare, with nearly double the trichomes/cm2 as Carmello. Earliest and Payne had comparable trichome densities at roughly 250/cm2, but the standard error for Earliest was much larger then Payne. Hartley, Chandler, 91-90-41 and S. Franquette had similar numbers, about 300 trichomes/cm2, however the standard error for Hartley was relatively large and relatively small for Chandler. 91-96-3 and C. Mayette had the densest trichomes at approximately 360/cm2. Trichomes have been shown to offer some degree of resistance to many lepidopteran pests including codling moth. However, trichomes do not appear to be an important factor in WHF resistance. Using information from Integrated Pest Management for Walnuts - Third Edition (ANR Pub. # 3270) Hartley, Tulare and Franquette are more susceptible to WHF infestation than Serr or Chandler with Payne having intermediate susceptibility. Since both Franquette and Chandler have high trichome levels while both Serr and Tulare have low trichome levels, it appears that trichome levels do not play a significant role in WHF susceptibility. However, this will need to be confirmed next season when the various cultivars will be exposed to gravid female WHF. Husk thickness: The mean husk thickness at the middle of the nut ranged from between 4.5 and 8.1 mm (Table 7 and Fig. 3). All cultivars had thinner husk and more highly variable husk thickness at the pistillate end of the nut as compared to the middle of the nut while husk thickness at the stem end of the nut was similar to the middle of the nut (data not shown). There was not a great deal of variation among the cultivars with the exception of Sinensis #5. Sinensis #5 had much thicker husk than all other cultivars. The thinner husk cultivars were Tulare, Chandler and Payne and the thicker husk cultivars were Serr, Hartley and Carmello. Again, husk thickness does not appear to be a characteristic that confers resistance. However, this will need to be confirmed next season when the various cultivars can be exposed to gravid female WHF.


Nut length, width, volume and weight: The mean nut length ranged from 4.4 (Payne) to 5.6 cm (Carmello) (Table 8, Fig. 4). The mean nut length nor standard error of the mean varied greatly for most cultivars. The shortest nuts were Payne and 91-90-41 and the longest nuts were Sinesis #5 and Serr. The mean nut width ranged from 4.0 (Payne) to 5.2 cm (Carmello) (Table 9, Fig. 5). The mean nut width nor standard error of the mean varied greatly for most cultivars. The narrow nuts were Payne, Tulare and Franquette and the widest nuts were Carmello and Sinensis #5. The mean nut volume ranged from 37.8 (Tulare) to 87.9 ml (Carmello) (Table 10, Fig. 6). Carmello was twice as large as the Tulare nuts. The smallest nuts were Payne and Tulare and the largest nuts were Carmello and Sinensis #5. The mean nut weight ranged from 37.4 (Tulare) to 92.6 g (Carmello) (Table 11, Fig. 7). Nut weight correlated closely with nut volume with similarly low standard error for the mean. The lightest nuts were Tulare, Payne and A. Franquette and the heaviest nuts were Carmello, Sinensis #5. Since WHF attraction to spherical traps has been shown to increase with an increase in size of the sphere, then it is speculated that Carmello or Sinensis #5 will become more infested than Tulare or Payne. However, this will need to be confirmed next season when the various cultivars will be exposed to gravid female WHF. Husk penetration pressure: The mean husk penetration pressure ranged from 26.6 (S. Franquette) to 39.6 kg/cm2 (Sinensis #5) (Table 12, Fig. 8). C. Mayette, Carmello and Sinensis # 5 produce nuts with the highest pressure required for penetration and were about 45% higher than S. Franquette. This maybe the most important characteristic in conferring resistance in that S. Franquette and Tulare have the lowest pressure while Chandler, Payne and Serr have higher pressure. Again this will need to be confirmed next season when the various cultivars will be exposed to gravid female WHF but this is a promising lead. Husk percent water content: The mean husk water content ranged from 75.8 (C. Mayette) to 88.3%. (Serr) (Table 13, Fig. 9). Serr, Sinensis # 5 and 91-90-41 produce nuts with the highest water content as compared to C. Mayette and Chandler and C. Mayette had a decrease of 14.2% compared to Serr. The standard error for mean percent water content was small for all cultivars. It does not appear the water content of the husk provides an important characteristic in conferring resistance in that Serr has very high water content while Chandler has a very low water content.

CONCLUSIONS Trapping study: Trécé trap/lure combination was about ½ as efficacious as the Alpha Scent trap/lure combination or the Trécé trap/standard vial super charger lure combination. The increase in efficacy is related to the lure efficacy and not the trap efficacy. The Alpha Scent lures contain about 4 times the amount of ammonium carbonate as compared to the Trécé lures, which is the probable cause of the increased efficacy. Control of WHF with reduced amounts of pesticide and application time: Low volume (10 gal/ac) applications of a high rate of Malathion 57% and Nu-Lure (3 pt/ac each) at 10 mph were as efficacious as conventional applications with a high volume (100 gal/ac) and a high rate of


Malathion 57% and Nu-Lure (3pt/ac each) at 2 mph in control of WHF and superior to a treated check. However, low volume (10 gal/ac) applications of a low rate of Malathion 57% and Nu-Lure (0.3 pt/ac each) at 10 mph were not as efficacious as conventional applications with a high volume (100 gal/ac) and a high rate of Malathion 57% and Nu-Lure (3 pt/ac each) at 2 mph in control of WHF. Identification and quantification of nut characteristics by cultivar: There was considerable variation in the six characteristics examined in the 12 cultivars. The most promising characteristic that could confer resistance or susceptibility to WHF infestation is the pressure needed to penetrate the husk (husk hardness). However, this will need to be confirmed next season when the various cultivars will be exposed to gravid female WHF. ACKNOWLEDGEMENTS We gratefully acknowledge the following growers and PCAs whose assistance and cooperation made the above studies possible: Bryan DeRosa, Bob & Bill Molloy, Manual Kafkares, Jake Onstott, Andy Dugo, Mark Gibson, Darren Ventura and Cheryl Gartner. Further, we gratefully recognize the invaluable contributions of Lesley Thayer, Lauren Novotny, and Caroline Wise without whose tireless hard work and dedication resulted in the successful completion of this research.


Table 1. Trap and lure combination evaluated for WHF capture efficacy – 2012 Trap Lure Abbreviation 1. Trécé Pherocon® AM/NB Standard vial super chargera (SVSC) T-carb

2. Trécé Pherocon® AM/NB SVSC b T-bicarb 3. Trécé Pherocon® AM/NB High output super chargerc T-hi carb 4. Trécé Pherocon® AM/NB SVSCa + green leaf (GL) alcohol blend T-carb+GL 5. Trécé Pherocon® AM/NB GL-alcohol blend T-GL 6. Trécé Pherocon® AM/NB SVSCa + caryophyllene T-carb+cary 7. Trécé Pherocon® AM/NB Caryophyllene T-cary 8. Trécé Pherocon® AM/NB Trécé lure T-Trece

9. Alpha Scents back folding Alpha Scents lure AS-alpha 10. Alpha Scents back folding SVSCa AS-carb aStandard vial super charger: 6 ml vial with 4 mm opening containing 3.9 g of ammonium carbonate. bStandard vial super charger: 6 ml vial with 4 mm opening containing 3.9 g of ammonium bicarbonate. cHigh output super charger: small gauze bag containing 3.9 g of ammonium carbonate


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21

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Table 3. Seasonal mean total female and male WHF captured in high traps at three locations, CA – 2012

Meana number flies per trap Treatment Females Males Total WHF

1. T-carb 38.7 A 23.8 a 62.4 a 2. T-bicarb 34.3 ab 23.2 ab 57.5 ab 3. T-hi carb 25.3 bc 14.3 c 39.5 c 4. T-carb+GL 25.1 bc 15.9 bc 41.0 bc 5. T-GL 5.3 D 3.2 e 8.5 d 6. T-carb+cary 16.6 C 9.3 cde 25.8 cd 7. T-cary 5.6 D 5.1 de 10.7 d 8. T-trece 18.4 C 10.8 cde 29.1 c 9. AS-alpha 44.1 A 26.4 a 70.5 a 10. AS-carb 38.0 A 23.8 a 61.8 a aMeans followed by the same letter in a column are not significantly different (Fisher’s protected LSD, P ≤ 0.05) Table 4. Seasonal mean total female and male WHF captured in low traps at three locations, CA – 2012

Meana number flies per trap Treatment Females Males Total WHF

1. T-carb 25.0 B 26.9 a 51.9 a 2. T-bicarb 24.3 B 24.3 ab 48.6 ab 3. T-hi carb 19.5 B 22.0 abc 41.5 abc 4. T-carb+GL 25.8 B 24.6 ab 50.3 a 5. T-GL 11.1 B 10.8 d 21.9 d 6. T-carb+cary 16.7 B 17.5 bcd 34.2 bcd 7. T-cary 12.5 B 15.2 cd 27.7 cd 8. T-trece 14.5 B 16.0 bcd 30.5 cd 9. AS-alpha 27.6 A 29.7 a 57.3 a 10. AS-carb 27.1 ab 27.1 a 54.2 a aMeans followed by the same letter in a column are not significantly different (Fisher’s protected LSD, P ≤ 0.05)


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Table 6. Mean (± std. error) number of trichomes per cm2 by cultivar over the growing season, Davis, CA – 2012

Cultivar 18 Jul 1 Aug 17 Aug 29 Aug 6 Sep Average

91-90-41 344.3 ± 42.5 208.1 ± 35.1 391.3 ± 39.1 296.2 ± 42.3 340.1 ± 15.7 316.0 ± 30.9 91-96-3 496.6 ± 38.3 369.0 ± 57.6 354.9 ± 36.1 325.6 ± 48.2 245.0 ± 25.0 358.2 ± 40.7 C. Mayette 389.5 ± 37.0 323.2 ± 41.7 291.3 ± 38.6 359.4 ± 24.4 438.4 ± 23.2 360.4 ± 25.6 Carmello 107.8 ± 28.0 61.1 ± 12.8 68.9 ± 11.4 109.4 ± 29.1 163.2 ± 17.5 102.1 ± 18.2 Chandler 231.5 ± 22.6 315.5 ± 44.2 296.5 ± 24.9 332.1 ± 73.5 304.3 ± 38.4 296.0 ± 17.2 Earliest 363.8 ± 28.2 142.4 ± 29.5 95.1 ± 15.6 158.2 ± 29.0 460.7 ± 39.2 244.0 ± 71.1 Hartley 264.5 ± 35.2 189.7 ± 31.1 490.8 ± 55.9 306.4 ± 12.0 203.5 ± 21.5 291.0 ± 54.2 Payne 252.6 ± 23.2 158.8 ± 30.7 298.8 ± 40.7 264.5 ± 33.9 272.3 ± 32.3 249.4 ± 23.9 S. Franquette 281.9 ± 30.9 303.2 ± 37.9 265.8 ± 17.9 323.8 ± 30.7 423.8 ± 31.2 319.7 ± 27.8 Serr 92.2 ± 15.7 154.6 ± 21.5 192.3 ± 21.3 276.7 ± 36.9 135.1 ± 19.3 170.2 ± 31.1 Sinensis #5 77.7 ± 10.4 74.8 ± 21.2 79.0 ± 22.2 40.3 ± 13.7 278.8 ± 32.8 110.1 ± 42.8 Tulare 133.8 ± 22.2 192.3 ± 22.4 191.0 ± 35.5 310.3 ± 34.5 148.1 ± 29.8 195.1 ± 31.0 Table 7. Mean (± std. error) thickness (mm) of nut husk at mid-nut length by cultivar over the growing season, Davis, CA – 2012

Cultivar 18 Jul 1 Aug 17 Aug 29 Aug 6 Sep Average 91-90-41 5.0 ± 0.4 4.6 ± 0.2 5.8 ± 0.3 4.7 ± 0.4 6.0 ± 0.4 5.2 ± 0.3 91-96-3 5.7 ± 0.3 5.6 ± 0.3 5.0 ± 0.4 5.9 ± 0.3 5.2 ± 0.3 5.5 ± 0.2 C. Mayette 3.9 ± 0.3 4.5 ± 0.4 5.7 ± 0.4 4.9 ± 0.3 4.9 ± 0.6 4.8 ± 0.3 Carmello 5.5 ± 0.5 5.6 ± 0.4 6.5 ± 0.5 6.3 ± 0.4 6.8 ± 0.2 6.1 ± 0.3 Chandler 4.8 ± 0.2 4.5 ± 0.2 4.6 ± 0.3 4.4 ± 0.4 4.9 ± 0.2 4.6 ± 0.1 Earliest 5.3 ± 0.4 4.6 ± 0.4 4.8 ± 0.1 5.0 ± 0.5 6.1 ± 0.3 5.2 ± 0.3 Hartley 4.8 ± 0.5 5.6 ± 0.6 6.4 ± 0.4 7.0 ± 0.3 6.8 ± 0.4 6.1 ± 0.4 Payne 4.2 ± 0.4 5.7 ± 0.3 5.7 ± 0.4 4.5 ± 0.3 4.6 ± 0.3 4.9 ± 0.3 S. Franquette 5.6 ± 0.5 5.2 ± 0.3 7.2 ± 0.5 6.6 ± 0.2 8.1 ± 0.6 6.5 ± 0.5 Serr 7.3 ± 0.6 6.5 ± 0.6 6.9 ± 0.3 7.0 ± 0.3 6.4 ± 0.3 6.8 ± 0.2 Sinensis #5 6.4 ± 0.7 8.9 ± 0.5 7.2 ± 0.5 8.9 ± 0.3 9.5 ± 0.4 8.1 ± 0.6 Tulare 4.2 ± 0.3 4.4 ± 0.4 4.3 ± 0.3 5.1 ± 0.2 4.3 ± 0.2 4.5 ± 0.2


Table 8. Mean (± std. error) nut length (cm) by cultivar over the growing season, Davis, CA – 2012

Cultivar 18 Jul 1 Aug 17 Aug 29 Aug 6 Sep Average 91-90-41 4.1 ± 0.4 4.5 ± 0.1 4.6 ± 0.1 4.7 ± 0.2 4.6 ± 0.1 4.5 ± 0.1 91-96-3 4.8 ± 0.0 4.6 ± 0.1 4.6 ± 0.1 4.7 ± 0.1 4.6 ± 0.1 4.6 ± 0.1 C. Mayette 4.6 ± 0.1 4.8 ± 0.1 4.9 ± 0.1 4.9 ± 0.1 4.4 ± 0.2 4.7 ± 0.1 Carmello 5.5 ± 0.1 5.5 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 5.8 ± 0.1 5.6 ± 0.1 Chandler 4.8 ± 0.0 4.6 ± 0.1 4.6 ± 0.1 4.5 ± 0.1 4.9 ± 0.1 4.7 ± 0.1 Earliest 4.7 ± 0.1 4.6 ± 0.1 4.5 ± 0.1 4.7 ± 0.1 4.7 ± 0.1 4.6 ± 0.0 Hartley 4.8 ± 0.1 5.0 ± 0.1 5.1 ± 0.1 5.2 ± 0.1 5.4 ± 0.0 5.1 ± 0.1 Payne 4.0 ± 0.1 4.7 ± 0.1 4.4 ± 0.1 4.6 ± 0.1 4.4 ± 0.1 4.4 ± 0.1 S. Franquette 4.7 ± 0.1 4.7 ± 0.1 4.9 ± 0.1 4.9 ± 0.1 4.8 ± 0.2 4.8 ± 0.0 Serr 5.2 ± 0.1 4.9 ± 0.1 5.1 ± 0.1 5.1 ± 0.1 5.1 ± 0.2 5.1 ± 0.0 Sinensis #5 5.6 ± 0.1 5.6 ± 0.1 5.5 ± 0.1 5.7 ± 0.1 5.6 ± 0.1 5.6 ± 0.0 Tulare 4.6 ± 0.1 4.5 ± 0.1 4.4 ± 0.1 4.5 ± 0.1 4.7 ± 0.1 4.5 ± 0.0 Table 9. Mean (± std. error) nut width (cm) by cultivar over the growing season, Davis, CA – 2012



Table 10. Mean (± std. error) nut volume (ml) by cultivar over the growing season, Davis, CA – 2012

Cultivar 18 Jul 1 Aug 17 Aug 29 Aug 6 Sep Average 91-90-41 43.9 ± 2.7 40.5 ± 2.3 46.9 ± 2.1 42.5 ± 3.3 47.0 ± 1.9 44.2 ± 1.3 91-96-3 47.1 ± 1.1 42.5 ± 2.0 39.2 ± 2.6 45.0 ± 3.8 37.9 ± 2.6 42.3 ± 1.7 C. Mayette 40.0 ± 2.3 46.7 ± 1.9 47.4 ± 2.6 49.8 ± 3.5 33.3 ± 4.8 43.4 ± 3.0 Carmello 87.9 ± 4.3 83.0 ± 4.6 87.0 ± 5.2 94.0 ± 4.8 87.7 ± 4.2 87.9 ± 1.8 Chandler 48.5 ± 1.5 44.5 ± 2.7 42.9 ± 2.6 41.7 ± 3.1 53.2 ± 2.4 46.2 ± 2.1 Earliest 51.5 ± 2.4 45.5 ± 2.5 48.5 ± 3.0 48.7 ± 1.8 46.5 ± 1.8 48.1 ± 1.0 Hartley 45.6 ± 1.9 52.0 ± 1.3 47.3 ± 3.7 53.4 ± 3.5 59.6 ± 3.0 51.6 ± 2.5 Payne 29.4 ± 2.4 46.0 ± 3.4 42.7 ± 2.4 44.2 ± 2.5 41.3 ± 2.6 40.7 ± 2.9 S. Franquette 40.5 ± 2.0 39.7 ± 2.7 43.3 ± 1.8 43.5 ± 1.3 45.8 ± 5.0 42.6 ± 1.1 Serr 62.5 ± 2.5 52.0 ± 1.7 59.3 ± 2.7 59.1 ± 1.3 57.6 ± 4.2 58.1 ± 1.7 Sinensis #5 86.7 ± 3.4 83.8 ± 4.9 70.2 ± 4.6 91.3 ± 4.7 75.8 ± 3.1 81.6 ± 3.8 Tulare 41.6 ± 1.0 41.1 ± 2.2 32.8 ± 4.3 33.4 ± 3.3 40.1 ± 2.0 37.8 ± 1.9 Table 11. Mean (± std. error) nut weight (g) by cultivar over the growing season, Davis, CA – 2012



Table 12. Mean (± std. error) pressure to penetrate husk (kg/cm2) by cultivar over the growing season, Davis, CA – 2012

Cultivar 18 Jul 1 Aug 17 Aug 29 Aug 6 Sep Average 91-90-41 26.9 ± 1.6 25.6 ± 1.6 47.1 ± 5.0 27.2 ± 2.4 23.4 ± 1.9 30.0 ± 4.3 91-96-3 24.7 ± 1.6 25.2 ± 1.0 37.4 ± 5.3 33.2 ± 3.8 21.6 ± 1.2 28.4 ± 2.9 C. Mayette 34.8 ± 2.2 31.1 ± 1.2 36.9 ± 4.6 35.1 ± 3.4 34.2 ± 2.3 34.4 ± 0.9 Carmello 24.0 ± 1.4 26.2 ± 2.2 43.0 ± 2.9 57.7 ± 6.6 32.6 ± 1.7 36.7 ± 6.2 Chandler 28.2 ± 2.7 27.2 ± 2.8 40.5 ± 4.2 21.9 ± 1.7 31.7 ± 1.4 29.9 ± 3.1 Earliest 34.7 ± 0.7 25.7 ± 1.6 39.2 ± 4.6 24.1 ± 1.7 22.5 ± 1.3 29.2 ± 3.3 Hartley 24.4 ± 1.5 25.0 ± 2.0 44.5 ± 3.3 26.7 ± 1.3 22.4 ± 1.2 28.6 ± 4.0 Payne 34.2 ± 1.6 24.6 ± 1.4 44.4 ± 3.9 20.0 ± 1.8 25.9 ± 2.6 29.8 ± 4.3 S. Franquette 24.6 ± 2.1 25.6 ± 1.6 36.9 ± 3.7 18.3 ± 1.3 27.5 ± 5.1 26.6 ± 3.0 Serr 26.0 ± 1.8 25.1 ± 2.6 43.1 ± 3.4 29.0 ± 1.4 20.3 ± 2.1 28.7 ± 3.9 Sinensis #5 21.1 ± 1.1 50.6 ± 34.5 60.6 ± 4.9 36.1 ± 4.1 29.8 ± 3.5 39.6 ± 7.1 Tulare 23.7 ± 1.5 28.1 ± 1.8 31.7 ± 3.4 31.3 ± 2.2 24.5 ± 1.5 27.9 ± 1.7 Table 13. Mean (± std. error) percent water content of husk by cultivar over the growing season, Davis, CA – 2012



Figure 1. Mean percent WHF infestation per week in Modesto, Linden and Hollister, CA – 2012.

Figure 2. Mean (± std. error) number of trichomes per cm2 by cultivar, Davis, CA – 2012.


Figure 3. Mean (± std. error) thickness (mm) of nut husk at mid-nut length by cultivar, Davis, CA – 2012.

Figure 4. Mean (± std. error) nut length (cm) by cultivar, Davis, CA – 2012.


Figure 5. Mean (± std. error) nut width (cm) by cultivar, Davis, CA – 2012.

Figure 6. Mean (± std. error) nut volume (cm2) by cultivar, CA – 2012.


Figure 7. Mean (± std. error) nut weight (g) by cultivar, CA – 2012.

8. Mean (± std. error) pressure to penetrate husk (kg/cm2) by cultivar, Davis, CA – 2012.


Figure 9. Mean (± std. error) percent water content of husk by cultivar, Davis, CA – 2012.


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