Kaolin for pest control and improved fruit

quality of apples

Gordon Brown, et al Scientific Horticulture P/L

Project Number: AP00036

AP00036

This report is published by Horticulture Australia Ltd to pass on information concerning horticultural research and development undertaken for Apple and Pear industry.

The research contained in this report was funded by Horticulture Australia Ltd with the financial support of the Engelhard Corporation; Scientific Horticulture Pty Ltd and USDA.

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Final Report

Horticulture Australia

Project: AP00036 (completion date 30 June 2001)

Kaolin for pest control and improved fruit quality of apples

Gordon Brown, Lisa Schimanski, David Jennings

Scientific Horticulture Pty Ltd August 2001

Final Report

Horticulture Australia Project: AP00036

Kaolin for pest control and improved fruit quality of apples

Gordon Brown, Lisa Schimanski, David Jennings

Scientific Horticulture Pty Ltd 3 Kadina Close, Aliens Rivulet, Tasmania 7150 BrownGS@Tassie.net.au phone 03 6239 6411

August 2001

Summary During the 2000 / 2001 season a sprayable formulation of Kaolin (3% solution) was applied at 10 to 14 day intervals throughout the growing season to apple trees growing in the Huon Valley of Tasmania. Two cultivars of apple, 'Gala' and 'Fuji' were tested and insect populations and foliar and fruit properties were measured. The season was mild with an average temperature of 14°C and an average relative humidity of 77%. Temperatures rarely exceeded 28°C and relative humidity rarely dropped below 40%.

On the 'Fuji' trees the Kaolin treatment reduced the number of aphids on the young growing tips from 26 to 9 colonies per tree. The size of the colonies was also reduced. Despite the lack of insecticide applications no other pest insects or mites were noted in the experimental orchards.

While overseas the Kaolin treatment has been reported to improve fruit yields and colour due to reduced tree temperatures and resultant increased photosynthesis no effect on these parameters were recorded in these trials. In addition leaf size, colour and chlorophyll content was not affected by the treatment and fruit size, red area, russet, firmness, TSS, starch or internal disorders were not affected. The treatment also had no effect on foliar and fruit total polyphenolics.

It is concluded that under the low stress conditions experienced in these apple orchards the Kaolin material had no impact on tree health or fruit quality. This may not be the same where apples are grown in a hotter or drier environment or in regions where other stresses may be present.

Acknowledgements The author wishes to acknowledge the Engelhard Corporation, the USDA and Horticulture Australia

for their financial support of this project.

Disclaimer Any recommendations contained in this publication do not necessarily represent current HAL policy. No person should act on the basis of the contents of this publication, whether as to matters of fact or

opinion or other content, without first obtaining specific, independent professional advice in respect of the matters set out in this publication.

Scientific Horticulture Pty Ltd August 2001 2

Introduction

Kaolin is a naturally occurring, safe, relatively inert, white mineral particle with many uses including porcelain production, as a whitener in paper and as a filler in medicines. While Kaolin in its natural form is detrimental to plant leaves, a new method of processing the material has been developed that makes it safe to apply to plant foliage.

Kaolin sprays have been found to reduce leaf transpiration and hence water use in some experiments, and to decrease leaf temperature by increasing leaf reflectance. This has lead to an increase in photosynthesis and hence net carbon gain particularly in plant species which are light saturated at low irradiances. This effect on leaf temperature and net carbon gain appears to be particularly evident under conditions of mild water or heat stress.

Glenn et al. (1999) demonstrated that a dusted particle film such as Kaolin, did not reduce carbon assimilation in potted apple, peach or pear growing under controlled conditions. They also applied this dust film to peach trees in the field and observed no reduction in fruit yield or quality although leaf temperature was reduced. More detailed studies on the effects of Kaolin on apples were published by Glenn et al. (2001). In this study fruit yield and quality for Kaolin sprayed trees were studied in Chile, at Santiago, and in the United States at Yakima, Kearneysville, York Springs and Wenatchee (several trials at some sites). While the results for fruit size are mixed overall there was an increase in fruit yield partially due to increased fruit numbers per tree. At three sites the date of application was studied and it was found that the early applications, in May and June, had the most impact on yield and interestingly on fruit red colouration. Of interest is that the treatment did not have any effect on fruit colour in the Washington orchards. In all these trials, contrary to earlier reports, it appeared as though the Kaolin treatment increased water use of the trees.

This trial was established to determine the effect of the Kaolin particle film technology on Tasmanian grown 'Gala' and 'Fuji' apple trees and their fruit.

Materials and Methods

For these trials two cultivars of apple, 'Gala' and 'Fuji' from one apple orchard were sprayed with Kaolin and the insect populations, leaf characteristics and fruit quality measured. The test orchards were located on Hansen's orchards in the Huon Valley of Tasmania. The 'Gala' trees were approximately 6 years old while the 'Fuji' trees were approximately 10 years old. Both cultivars were grown on mm 106 rootstocks. The 'Gala' trees were trained to an upright 4 wire trellis with 3.5m between rows and 1.5m between trees (1900 trees / Ha) while the 'Fuji' trees were free standing with 5m between rows and 2.5m between trees (800 trees / Ha). At both sites irrigation was via a drip irrigation system. Experimental units consisted of 4 trees for 'Gala' and 3 trees for 'Fuji' with the outside 2 trees of the experimental units acting as buffers. At both sites all treatments were replicated 6 times. There was a data logger located in the 'Gala' site to record hourly temperatures and humidity. A frost occurred on October 16, however, this appeared to have minimal impact on the fruit.

Scientific Horticulture Pry Ltd August 2001 3

At both sites there were 4 common treatments, an untreated control, a treatment with insecticides as applied by the grower in the adjoining orchard, Kaolin only and Kaolin plus insecticide. At the 'Gala' site 2 additional treatments, Kaolin for the first half of the growing season and Kaolin for the second half of the growing season were also included.

Kaolin was applied in a 6% solution at lOOOL/Ha using hand spray lances on October 6 and 20 at both sites. After these initial sprays the material was applied as a 3% solution on November 3, 17, 27, December 8, 20 January 5, 22, February 5, 19 and March 5. All sprays applied after November 25 were applied using a special airblast sprayer applying 1200 L / Ha of material. For the treatments where Kaolin was applied in the first half of the season compared to the last half of the season the change over date was 30 December 2001. Although the orchard was surrounded by native forest and pheromones were not in use by the grower the season proved to be of low insect pressure. Only a few light brown apple moth were caught in pherhormone traps and the grower only applied 2 mimic sprays as a precaution. Mimic was applied to the appropriate treatments on November 18 and December 8.

The trees were regularly inspected for presence of insects and or insect damage. On December 4 the number of young growing shoots on the 'Fuji' trees were assessed for presence of aphids and the number of colonies counted. At this date 12 leaves per plot were collected and inspected with a hand dissecting microscope for the presence of mites or thrips however, none were found. Apart from odd isolated insect observations no other insects were noted at any other date in sufficient numbers to warrant an assessment on either cultivar of apple.

Leaves (minimum 6 per plot) were collected from both the cultivars on December 4 and 20, January 5 and 22, February 5 and 19 and April 6. These were then pooled by treatment and frozen prior to analysis by the State analytical laboratories for total polyphenolics using a spectroscopic method adopted from Spanos (1990). The April 6 harvest of leaves consisted of 20 leaves per plot. Fruit (minimum 6 per plot) were also collected on January 5, February 5 and March 19 ('Gala') or January 5, February 5, March 5 and April 6 ('Fuji'). The April 6 fruit sample was of sprayed and untreated fruit only. These fruit had their peel removed within 48 hours of harvest. The peel was frozen prior to analysis of total polyphenolics by the same method as the leaves.

On March 19 a sample of 100 fruit per plot were harvested from the 'Gala' trees and the number of fruit remaining on the trees counted. The grower accidentally harvested the 'Fuji' trial on April 5, one day prior to the planned sampling date and 1 week prior to the advised commercial harvest. Despite this, the bulk bins were located in the cool rooms and due to the spray residue on the fruit it was possible to locate 19 clusters of Kaolin treated fruit in the 400 kg bulk bins. 20 fruit were sampled from each cluster along with 20 clean fruit from a nearby location within the bin.

Sixteen leaves from the last leaf harvest date were washed in water to reduce the spray residue and a 3 mm diameter leaf disk from near the midrib was removed and added to lml of ethanol. The chlorophyll was then allowed to passively extract for 24 hours

Scientific Horticulture Pty Ltd August 2001 4

prior to quantification by measuring light transmission at 666nm using a spectrophotometer. Ten of the leaves were then scanned and a digital image recorded for image analysis using Optimas 6.1 to determine the average leaf area, length, breadth and brightness.

The fruit from the last harvest were stored at 0.5°C and then visually assessed for Russet on either the stem bowl or the side of the fruit. The fruit was also inspected for sunburn damage. For a sub sample of 20 'Gala' fruit per plot and all the 'Fuji' fruit a equatorial peel about 10mm wide was taken and a digital image recorded. This image was analysed to determine the percent area of the skin that was red (hue angle between 20° and 300°). The fruit were then weighed and placed on a machine developed by the author to electronically determine fruit firmness (11mm probe, skin removed), diameter and to remove a sample of juice for fruit sugars (TSS) determination. The fruit were then cut in two and dipped in iodine solution to identify the level of starch breakdown. All fruit (including the 80 fruit not used for quality assessment in the 'Gala' sample were cut in half and inspected for internal damage.

Data for total leaf and fruit polyphenolics was plotted to study the influence of harvest date on total polyphenols concentration. Data for the final leaf and fruit harvest was analysed by the analysis of variance. Data for Fuji fruit was analysed by the 'T' test (2 treatments). Where appropriate mean separation was by the LSD method with/? = 0.05.

Results and Discussion

Climatic Records The temperature records from the data logger reveal that the test orchard was neither temperature or humidity stressed. The average temperature during the growing season was 14.4°C with only 187 degree hours above 28°C. There were several nights during the growing season where the temperature dropped below 5°C. The humidity during the growing season was high and averaged 77%. There was only one day when the humidity dropped below 20% with most days the minimum humidity being above 40%. After this trial the temperature and humidity sensors calibration was verified in a controlled humidity cabinet operating at 60% RH and 25°C.

Temperature

T—i—i—i—i—i—i—i—i—i—i—i—i—i—r 20/1010:233/11 17/11 1/12 15/12 29/12 12/1 26/1 9/2 23/2

Time (starting 20/10/20001

T—r 9/3

T—r 23/3

T—r 6/4

T—i—r 20/4

Scientific Horticulture Pty Ltd August 2001

Humidity

1 — i — i — i — i — i — i — i — i — i — i — r — r 20/1010:23 3/11 17/11 1/12 15/12 29/12 12/1

T — I — i — i — i — i — r 26/1 9/2 23/2 9/3

T—i—i—i—r 6/4 20/4

Time (starting 20/10/2000)

Insect Control From the grower pherhormone trapping activities the insect pressure in the test orchard was very low during the 2000 / 2001 season. This was reflected in the low numbers of insect pests found on the leaves and fruit of the trees despite no insecticide application in the untreated control trees. It was found, however, that on the 'Fuji' trees the Kaolin treatment significantly reduced the number of aphid colonies on the young shoot tips from 25.5 colonies per tree to 8.7. Although the grower advised that he was not concerned with these insects their presence is a risk in terms of their potential to spread viral diseases. The Mimic insecticide applications had no impact on this pest species.

Total Polyphenolics Both apple cultivars revealed a similar pattern of total polyphenols concentration in their leaves and fruit (figures 1 and 2). For leaves the initial measurement, on December 4, was higher than the following date, on December 20. However, after December 20 the levels steadily increased till a maximum on the fifth harvest date (February 5) where approximately 15000 mg/kg of polyphenolics was present in the foliage of both cultivars. After this maximum the concentration decreased slightly with each successive leaf harvest.

The concentration of total polyphenolics in the fruit skin was lower than those found in the leaves for both cultivars and the concentration decreased between the first and final harvest of fruit. For Gala the final concentration of total polyphenolics in the skin of the fruit at commercial harvest was close to 6000 mg/kg while the level in the Fuji fruit skin was lower at 3000 mg/kg.

No pattern appeared in the data to indicate that either the Kaolin or Insecticide treatments had an impact on the concentration of total polyphenolics in either the skins or leaves of the fruit.

Scientific Horticulture Pty Ltd August 2001

Untreated

Insecticide

Kaolin+ Insecticide

Kaolin

Average

•—Fruit untreated

-t—Fruit Insecticide

— Fruit Kaolin + Insecticide

— Fruit Kaolin

• " F r u i t Average

09/01/01 28/02/01 19/04/01

Date

Figure 1. The development of total phenolics in leaves and stems of 'Gala' apples sprayed with mixtures of Kaolin and insecticide.

—*— Untreated

—a—Insecticide

Kaolin + Insecticide

-**~ Kaolin

" ^ • " A v e r a g e

—•—Frui t Untreated

—I—Fru i t Insecticide

Fruit Kaolin + Insecticide

Fruit Kaolin

^ • • • F r u i t Average

20/11/00 19/04/01

Date

Figure 2. The development of total phenolics in leaves and stems of 'Fuji' apples sprayed with mixtures of Kaolin and insecticide.

Leaf characteristics There was no observable effects of either the Kaolin or insecticide on any of the leaf parameters measured for 'Fuji' apples (Table 1). For 'Gala' there was no effect of either treatment on foliar size or chlorophyll content although the Kaolin treatment appeared to increase the reflectance of light from the leaf surface in some of the treatments (Table 2). This was probably an artefact, however, as it was found that the Kaolin was very difficult to physically remove from the leaves prior to the brightness assessment. This conclusion is supported by the finding that the treatment had no effect on chlorophyll content of the leaves.

Table 1. The influence of Kaolin on foliar characteristics of 'Fuji'. Area (cm2)

Length (cm)

Breadth (cm)

Brightness (% reflection)

Chlorophyll (% trans)

UTC Mimic Kaolin Kaolin + Mimic

52.6 51.3 52.5 55.9

9.6 9.6 9.7 10.1

5.8 5.7 5.8 5.9

34.7 33.9 36.7 36.3

78.2 79 75

77.7 F3.15 0.794 1.231 0.250 2.322 0.426

Determined as % transmission of light at 666nm

Scientific Horticulture Pry Ltd August 2001 7

Table 2. The influence of Kaolin on foliar characteristics of 'Gala'. Area (cm2)

Length (cm)

Breadth (cm)

Brightness (% reflection)

Chlorophyll" (% trans)

UTC Mimic Kaolin Kaolin + Mimic Kaolin first half Kaolin second Half

52.3 52.9 51.7 51.9 49.6 49.6

10.7 10.6 10.8 10.8 10.2 10.5

5.2 5.3 5.1 5.1 5.2 5.0

40.8 a 40.5 a 41.9 a 45.5 c 44.7 be 42.6 ab

54.5 54.2 52.0 50.3 52.0 52.5

F5.25 5% LSD

7F

0.136 0.387 0.251 5.567 2.4

1.299

Determined as % transmission of light at 666nm

Fruit Yield Fruit yield was only measured on the 'Gala' trial site. At this site it was found that the Kaolin had no effect on fruit yield .

Fruit appearance As for the leaves neither the Kaolin or the insecticide appeared to have any impact on the appearance of the fruit for either cultivar (Tables 3 and 4). It is interesting to note, however, that the Kaolin treated trees tended to produce fruit that had a higher percentage of red fruit for both cultivars although this was not statistically significant.

Table 3. Appearance of 'Fuji' fruit.

UTC Kaolin % change t36

Russet Free (%) 6.5 5.0

23.0 0.766

Russet Side (%) 37.1 34.2 7.7

0.608

Russet Top (%) 56.3 60.7 -7.8

-0.980

Russet Area (%) 4.3 4.5 -4.2

-0.406

Red Area Red Bright red (%) (%) 54.9 20.9 57.8 22.7 -5.3 -8.7

-0.716 -0.700

Table 4. Appearance of 'Gala' fruit.

UTC Mimic Kaolin Kaolin + Mimic Kaolin first half Kaolin second Half F5.25

Yield

(T/Ha) 38.8 39.3 32.7 43.5 47.1 48.8 1.297

Russet Side (%) 2.3 1.8 2.0 2.8 2.3 2.3

0.187

Russet Stem bowl

(%) 36.8 41.3 44.7 45.3 43.7 37.3 0.822

Sunburn

(%) 0.2 0 0 0 0 0

NA

Red Area (%) 49

55.8 62.3 63.0 59.4 61.9 1.456

NA data not analysed due to lack of variation

Scientific Horticulture Pry Ltd August 2001

Fruit Quality As for the preceding factors the Kaolin treatment failed to produce any effect on the internal quality of the fruit (tables 5 and 6).

Table 5. The effect of Kaolin on fruit quality of 'Fuji' apples.

UTC Kaolin % change t36

Weight (g/frt) 146 143 2.3

0.779

Diameter (mm) 66.8 65.9 1.4

1.022

Firmness (N)

95.0 94.6 0.4

-0.001

TSS (%) 15.5 15.1 2.6

0.519

Starch (% black)

6.4 6.5 -1.7

-0.017

Internal Problems (%) 2.5 0.6 76.0

2.034

Table 6. Effect of Kaolin on fruit quality of 'Gala' apples. Weight Diameter Firmness TSS Starch Internal Problems (g/frt) (mm) (N) (%) (% black) (%)

UTC 143.7 65.7 84 12.4 21.7 0.2 Mimic 153.7 67.5 80 12.2 10.3 0.2 Kaolin 131.2 65.5 81 12.2 13.7 0 Kaolin + Mimic 132.6 63.3 82 11.9 5.7 0 Kaolin first half 122.6 63.5 80 12.0 12.0 0.2 Kaolin second Half 138.5 64.5 84 1Z0 8J3 0 F5.25 1.388 1.228 1.394 0.188 0.902 NA NA data not analysed due to lack of variation

Conclusions

While the Kaolin provided useful control of aphids in these trials the material failed to affect other aspects of tree health or fruit quality on either of the two apple cultivars tested in the Huon Valley of Tasmania. Inspection of the climatic data revealed that the growing conditions in the Huon Valley were extremely conducive to apple production with a season long average temperature close to 14°C with few days above 28°C. These temperatures were associated with humidities within the orchard above 40%RH. As a result the test trees were rarely, if ever, stressed and hence the Kaolin had very little impact on the productivity of the trees. Results in hotter, drier climates, or in a different season may prove to be different to the ones reported here.

Scientific Horticulture Pty Ltd August 2001 9

References

Glenn D. M., Puterka G. J., vanderZwet T., Byers R. E., and Feldhake C. (1999). Hydrophobic particle films: A new paradigm for suppression of athropod pests and plant disease. Journal of Economic Entomology. 92:759-771

Glenn D. M., Puterka G. J., Drake S. R, Thomas R. U., Knight A. L., Baherle P., Prado E. Baugher T. A. (2001). Particle film application influences apple leaf physiology, fruit yield, and fruit quality. Journal of the American Society of Horticultural Science. 126(2): 175-181.

Spanos (1990). Journal of Agriculture Food Chemistry. 38:1565 - 1571

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