The Control of White Root Rot of Apple Tree caused by Rosellinia Necatrix by Fluazinam and Prochloraz

AUTHORS

Research Article

Mery Dafny-Yelin 1*, Shlomit Dor 1,2, Orly Mairesse 1, and Jehudith Moy 1.

1 Migal Galilee Technology Center, Northern Agriculture Research and Development, Kiryat Shmona, Israel.

2 Migal Galilee Technology Center, Kiryat Shmona, Israel.

*Corresponding Author : Mery Dafny-Yelin, Migal Galilee Technology Center, Northern Agriculture Research and Development, Kiryat Shmona, Israel. E-mail: merydy@migal.org.il, merydy@gmail.com

White root rot Rosellinia necatrix (anamorph Dematophora necatrix, Ascomycotina) is an important soil borne disease of deciduous trees cultivated in northern Israel, with the fungus spreading to new trees and agricultural lands every year. About 60 plots of deciduous trees (most of them apple) in the Golan Heights and Galilee Mountains were found to be infested with R. necatrix (Mairesse et al. 2016). White root rot disease caused by the fungus R. necatrix infects 170 plant species from 63 genera and 30 families (Pliego et al. 2011). These include many fruit trees of commercially important crops and ornamental plants such as apple, sweet cherry, nectarine, peach, and avocado. The symptoms include rotting of the roots and yellowing of leaves, followed by wilting and death of the trees (Sztejnberg and Madar 1980; Teixeira de Sousa et al. 1995; Ten Hoopen and Krauss 2006). Currently, deciduous orchards cannot be replanted and infected orchards in Israel are abandoned (Dafny-Yelin et al. 2018). Apple trees (Malus domestica) grow in Israel at 600 to 1200 meters above sea level in the north of the country, as well as in the Jerusalem region. In Israel there are 3800 ha of apple orchards with an annual production of 115,000 tons. In 2005-2013, apple surpluses were exported to Syria, with a maximum of 18,000 tons in 2013 (Ministry of Agriculture and Rural Development, November 2013).

White root rot has been controlled using soil solarization in apple trees in Israel and avocado trees in Spain. Solarization is applied for 6-8 weeks in the summer and must be repeated every two-three years in order to guarantee that the fungal populations in the soil remain low (Freeman et al. 1990; López-Herrera et al. 1998). Use of fungicides can be effective for complementing the effect of soil solarization in order to increase the level of disease control. R. necatrix showed high sensitivity to various fungicides belonging to the following chemical groups: quinone outside inhibitors (Qoi), methyl benzimidazole carbamates (MBC), 2,6-dinitro-anilines, phenylpyrroles (PP), and demethylation inhibitors (DMI) (by the FRAC code list© 2018). An in vitro and greenhouse study on treatment of R. necatrix with benomyl, carbendazim, fluazinam and thiophanate methyl proved effective for controlling Rosellinia in avocado (López-Herrera and Zea-Bonilla, 2007).

In Japan, where there is no artificial irrigation, a soil drench with fluazinam was found to be effective and is widely used to control the disease in apple, Japanese pear, grapevine and fig (Eguchi et al. 2009; Kanadani et al. 1998; Morita and Kakogawa 2007; Nitta et al.1998). Fluazinam found to be effective also in Queenslend Australia when were applide post-planting of apple trees (Stephens 2003).

The research objective was to determine fungicide efficacy in controlling R. necatrix infection, of local isolates, in apple cultivars under Israeli weather conditions (dry summer apple orchard is irrigated). This study reports on in vitro inhibition of R. necatrix in PDA plates, in vivo by artificially-inoculated nursery grown apple plants, and in young apple trees planted in a naturally infested soil.

  1. Materials and methods
    1. In vitro study

Virulent R. necatrix isolates obtain from commercial apple orchards Rn-D (Netoa, coordinates: 35.371, 33.050), Rn-L (Mas`ada, coordinates: 35.780, 33.236) and Rn-E (Metulla, coordinates: 35.554, 33.257) were used in the in vitro tests. Potato dextrose agar (PDA) medium in 9 mm diameter plates were prepared with 1, 10, and 100 µg mL-1 a.i. of the following fungicides: (i) Rockstar (Rimi, Israel) containing 25% WP of azoxystrobin; (ii)  Bavistin  (Agan  Adama,  Israel) containing 50% WP  of carbendazim; (iii) Merpan (Makhteshim Adama, Israel) containing 80% WP captan; (iv) Mirage 450 (Makhteshim Adama,  Israel)  containing 45% WP prochloraz; (v) Ohayo (Luxembourg, Israel) containing 50%  WP fluazinam; (vii)  Topaz  (Makhteshim  Adama,  Israel) containing 70% WP thiophanate methyl; (viii) Scolar (Agrica CTS,  Israel)  containing 10% WP fludioxonil. Colonies were incubated at 250C and diameters were measured 8 days after inoculation when the control colony covered the entire Petri plate. Inhibition rate was calculated relative to the control plate. Each value is the mean of three replicates (each replicate was an average composed of two colonies on  one  plate).  This experiment was repeated twice, except for Ohayo and Captan that were repeated 3 times. The highest concentration of each fungicide was determined according to recommendations by the chemical companies.

    1. Nursery plants

On 28 May 2013, Hashabi13-4 bare rooted apple rootstocks (one year old plants from the "Tesler Nursery", Nov) were planted in eight liter pots of local heavy soil (the soil were taken near kibbutz Manara). Five grains of wheat colonized with R. necatrix isolate Rn-E were used for inoculating the pots 4 days after planting, according to the method described by Sztejnberg and Madar (1980). The plant pots were located at the Matityahu Research Station (ARO, The Volcani Center) under a shadow net blocking 60% of the sunlight. Fungicides were applied on the surface of the soil by two drenches with fungicide solution in volumes of 250 mL, after 8 and 14 days. Different concentrations of the following fungicides were applied: (i) fluazinam (50% WP un-registered, AGF-157, NUFARM, France) in 15.5 and 31 mg L-1 a.i., (ii) carbendazim in 15.5, 31.0 and 62.0 mg L-1 a.i. and

(iii) thiophanate methyl in 43.4, 86.8 and 173.6 mg L-1 a.i. Untreated plants used for control: plants that were not inoculated with R. necatrix in 4 repeats, and  inoculated  plants in 5 repeats  that received

250 mL of only water each time of application. Each treatment contained 5  replicates of one apple plant  except  thiophanate methyl

43.3 and 173.6 mg L-1 a.i in 6 and 4 repeats respectively. Symptoms of the inoculated plants were recorded every 10 days by evaluating the vitality of the plant on a scale of 0, 1, 2, 3, where 3 - is a healthy plants with new shots, 2 - healthy plants without new growth, 1 - weak plant started to wilt, and 0 - dead plant. This experiment was repeated with the highest dose of each fungicide that significantly improved the percentage of live plants compared with untreated plants. Roots from dead plants were observed for the typical R. necatrix mycelia in order to confirm the pathogen infection.

2.3 Orchards study

The experiments were carried out from May to October in 2013 and from June to November in 2014. Each year, new bare root tree grafted on Hashabi13-4 apple rootstocks (one year old) were planted in naturally infested soil in an apple orchard verity `Gala` in Netua and ver. `Star king` in Mas'ade. The treatments in 2014 were undertaken on the results of the treatments of 2013 (received the same Roman number in the following description and in Table 3). Netua treatment details in 2013: (i) 4.6 g L-1 thiophanate methyl and (ii) 3 g L-1 prochloraz applied three times on 11 March, 12 April, 11 November, (iii) 3 g L-1 prochloraz applied five times on 11 March, 29 March, 12 April, 26 April,  11  November.  Netua treatment details in 2014: (i) 4.6 g L-1 thiophanate methyl, (ii) since no significant benefit was seen in 2013 for five applications over three applications of prochloraz, only three applications were given in 2014 at a concentration of 3 g L-1. The application was on 8 April, 12 May, 24 October. Mas’ade treatment details in 2013: (i) 1.65 g L-1 carbendazim applied five times on 12 March, 4 April, 25 April, 16 May, 11 November, (ii) 1.65 g L-1 carbendazim applied three times on 12 March, 16 May, 11 November and (iii) 3.35 g L-1 fluazinam applied 3 times on  12 March, 16 May, 11 November.

Mas’ade treatment details in 2014: Since no significant benefit was seen in 2013 for 5 applications over 3 applications of carbendazim, the treatments were: (i) and (ii) 3 applications of 1.65 g L-1 carbendazim, (iii) 3.35 g L-1 fluazinam. All applications were on 9 April, 30 April and 18 September. The first applications in each experiment were conducted on the planting day. In 2014, new trees were planted again. The fungicides were applied  in 1.5 L of water on the soil surface before irrigation. The Netua plot was tested 7 times for vitality and viability in May to October 2013 or 8 times from June to November 2014. The Mas’ade plot was tested 10 times from May to September 2013 and from June to November 2014. Symptoms of the inoculated plants were evaluating the vitality of the plant on a scale of 0, 1, 2, 3, where 3 - is a healthy plants with new shots, 2 - healthy plants without new growth, 1 - weak plant started to wilt, and 0 – dead plant. Roots from dead trees were observed for R. necatrix typical mycelia in order to confirm the pathogen infection. The experiment design as random blocks with 5 repeats (3 and 4 tree in repeat in Netua and Mas’ade respectively), except thiophanate methyl that were given in only 4 repeats (in 2014 one of repeat were with 4 plants in 2013). One untreated tree were planted between each treatment. The distance between the trees were 0.5 m.

2.4 statistical analysis

ANOVA and Contingency Analysis (Pearson test) were carried out using JMP 13 SAS Institute, 2016. The significance of the treatments was determined using the Honestly Significant Difference (HSD, P≤0.05) test or each pair using student`s t (Least Significant Difference, P≤0.05) test. In the orchard study, Contingency analysis were done for each treatment in a plot against the control .A Bonferroni correction was applied to correct the critical alpha level, due to the multiple Chi-square tests which were conducted. Statistical effects of the blocks were evaluated for the studied parameters by a 4 treatments x 5 repeats ANOVA factorial desin .

  1. Results
    1. In vitro study

The active ingredients azoxystrobin, carbendazin, fludioxonil, prochloraz, and thiophanate methyl inhibited mycelial growth of isolates Rn-D, Rn-E and Rn-L by 100% at 1, 10, and 100 µg mL-1 a.i., without significant differences between the isolates or the tested concentrations. Total inhibition can be seen at 100 ppm a.i. of fluazinam for all isolates. At 10 ppm of fluazinam a.i., isolate Rn-D and Rn-E were totally inhibited. However, isolate Rn-L was significantly less influenced,  with  only 94.6% inhibition. At 1 ppm of fluazinam a.i., smaller effectiveness can be seen, with 82.5-91.9% inhibition. Captan was less effective than the other fungicides, with 21.7-35.8% inhibition at 100 ppm a.i. (Table1).

Fungicide                             Dosages

1 µg mL-1 a.i.

10 µg mL-1a.i.

100 µg mL-1 a.i.

A.i. name

Group name

Rn-D

Rn-E

Rn-L

Rn-D

Rn-E

Rn-L

Rn-D

Rn-E

Rn-L

Azoxystrobin 25%

QoI

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

Captan 80%

Phthalimides

10.4

b

-4.6

b

18.8

c

25

b

-2.5

b

18.8

c

35.8

b

21.7

b

34.2

b

Carbendazim 50%

MBC

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

Fluazinam 50%

2,6-Dinitro- Anilines

91.9

a

89.6

a

82.5

b

100

a

100

a

94.6

b

100

a

100

a

100

a

Fludioxonil 10%

PP

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

Prochloraz 45%

DMI

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

Thiophanate methyl 70%

MBC

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

100

a

Table 1: Fungicides % inhibition in vitro. Colony growth of R. necatrix isolates Rn-E, Rn-D and Rn-L in PDA medium amended with 1, 10, and 100 µg mL-1 a.i. of fungicides. Observations were made 7 days after inoculation when the control colony covered the Petri plate (0% inhibition). Each value is the mean of three replicates.

QoI – Quinone outside inhibitors, MBC – methyl benzimidazole carbamates. PP – phenylpyrroles. DMI– demethylation inhibitors. The fungicide group was named according to the FRAC code list© 2013. In each column, number followed by Different letters indicate significant differences according to Tukey-Kramer (Honestly Significant Difference, HSD) test.

Variations between isolates were seen in captan application in the 10 and 1 µg mL-1 a.i. Yet, the difference between isolates was not constant between 3 experimental repeats.

    1. Nursery plants

Apple plants inoculated with R. necatrix were treated twice with fungicides as presented in Table 2.

  A.i. name fungicide

Dosage

mg L-1 a.i.

n

Live plants (%) 98 DPI (LSD)

Average days of living 169 DPI (HSD)

Fluazinam

15.5

5

 100

  a

125.6

AB

31.0

5

 80

  ab

115.8

AB

Carbendazm

15.5

5

40

  bc

97.2

BC

31.0

5

40

  bc

80.6

BC

62.0

5

60

  ab

114.0

AB

Thiophanate methyl

43.4

6

33

  bc

99.2

AB

86.8

5

80

  ab

138.0

AB

173.6

4

50

  abc

109.3

ABC

Control (+)

(-)

4

0

  b

45.0

C

Control (-)

(-)

5

100

  a

162.0

A

Table 2: Chemical treatments in artificially infected nursery apple plants. Inoculations were performed on 28 May 2013 and were assessed 98 and 162 days post inoculation (DPI).

Untreated plants used for control"-" Control (+) - inoculated plants. Control (-): plants not inoculated with R. necatrix.

Different letters indicate significant differences (P≤0.05) according to the Each pair student`s t, (Least Significant Difference, LSD) and Tukey-Kramer, HSD test.

In the control plants without chemical treatments, all plants died within 45±2 days after inoculation. Treatment with 15.5 mg/L of fluazinam was the most effective, with 100% of the plants remaining alive in September, with 125.6 days on average. Interestingly, only 80% of the plants were alive in September in the 31.0 mg L-1a.i. treatment, were one, but with no significant differences in the number of living days. In November, more plants wilted, while those treated with 86.8 mg/L of thiophanate methyl remained viable for a longer period of time, for 138 days on average. However, an increase in the concentration to 173.6 mg/L did not contribute to longer viability. No phytotoxic symptoms were observed in all treatments.

    1. Field experiments

3.3.1 Netua orchard

Only 6.3% and 13.3% of the control plants survived by the fall of 2013 and 2014, respectively (Table 3). In 2013, prochloraz and thiophanate methyl treatments significantly improved plant viability between 19/6/13 to 7/10/13 (contingency analysis, after Bonferroni correction, p<0.05, Figure 1). Three application of prochloraz treatments resulted in 80% viability with an average of 240.1±14.4 survival days, significantly more than the control treatment with an average of 102.6±14.6 survival days. Three application of thiophanate methyl treatments resulted in 53.8% plant viability with an average of 225.3±13.4 survival days. Results did not improve with 5 compared to 3 applications of prochloraz in terms of viability of the plants and in average living days. As a result, only 3 applications of prochloraz were applied in 2014. In 2014, prochloraz and thiophanate methyl significantly improved plant viability until 7 July, whereas only prochloraz significantly improved plant viability until 1 August, (contingency analysis, after Bonferroni correction, P≤0.05, except in 6/8/14, p=0.0253 that did not emerge as significant following the application of the Bonferroni corrections, Figure 1). Only prochloraz yielded significant response compared to the control, with 49 more living days on average (HSD, P≤0.05, Table 3). Neither of the fungicides improved plant vitality by the end of November (Figure. 1). In general, the block is not a significant factor in all experiments in Netua in 2013 and 2014.

3.3.2 Mas'ade orchard:

The viability rate in the control plants was higher relatively to Netua, with 30% and 60% of the plants surviving during the fall of 2013 and 2014, respectively. Plants began to show symptoms of wilting later during the winter, when the average vitality start to decrease (Figure 1). In 2013, fluazinam application significantly improved plant viability compared to untreated trees from 17/8/13 to 5/9/13 (Figure 1) and improved plant survival to 70% (Contingency Analysis, p=0.0114) with significantly  more survival days.

In 2014, fluazinam application increased the number of survival days significantly, and the viability of the plants increased to 90% (p=0.0285). This value did not emerge as significant following the application of the Bonferroni corrections. In 2013 and 2014, the carbendazim treatment applied 3 or 5 times enhanced plant viability, but did not result in significant differences from the control (Table 3). The effect of carbendazim applied 3 or 4 times during 2013 was not significantly different, and it was therefore applied only three times in 2014. The block was a significant (p<0.05) factor on the experiments in 2013, perhaps due to an unequal inoculum of the fungus in the soil, and the statistical analysis takes this into account. 

Location

Treatment

Survival days ± SE

Viability (n)

Treatment

Survival days ± SE

Viability (n)

Date

3/12/13

20/11/14

 

Netua

i

Thiophanate methyl

225.3 ± 13.4 A

53.8 (13)

P=0.0043*

i

Thiophanate methyl

119.2 ± 10.7 AB

8.3% (12)

P=0.1953

ii

Prochloraz

240.1 ± 14.4 A

80.0% (15)

P<0.0001*

ii

Prochloraz

149.5 ± 15.5 A

33.3% (15)

P=0.6812

iii

Prochloraz (a)

223.6 ± 13.2 A

53.3 (15)

P=0.0039*

 

 

 

 

iv

Control

102.6 ± 14.6 B

6.3% (16)

iv

Control

100.5 ± 13.5 B

13.3% (15)

Date

13/9/13

 10/11/14

Mas’ade

i

Carbendazim

104.5 ± 10.0 B

30% (20)

P=1.000

i

Carbendazim

189.4 ± 12.1 AB

80% (20)

P=0.1645

ii

Carbendazim (a)

120.8 ± 10.0 AB

50%(20)

P=0.1098

ii

Carbendazim

194 ± 8.9 AB

70.0% (20)

P=0.5073

iii

Fluazinam

132.6 ± 9.7 A

70% (20)

P=0.0114**

iii

Fluazinam

203.3 ± 8.3 A

90.0% (20)

P=0.0285

iv

Control

102.3 ± 10.6 B

30% (20)

iv

Control

179.0 ± 12.5 B

60.0% (20)

Table 3: The effect of different fungicides on young apple trees in naturally infested soil in Netoa and Mas’ade.

The treatments in 2014 were given on the background of the treatments 2013 results. All treatments were given 3 times, except for prochloraz and carbendazim in 2013, that were given 5 times (a). Viability was calculated as the number of healthy plants out of all tested plants (n).

P-values indicate differences between the treatment and the control (Pearson test)

* Significant differences from the control (P≤0.01) using Contingency Analysis with Bonferroni correction.

** Significant differences from the control (P≤0.05) using Contingency Analysis with Bonferroni correction. Different capital letters indicate significant differences in the number of living days according to HSD, except in Mas’ade 2014, where different letters indicate significantly different LSD.

Fig 1: Vitality of apple trees during the year with or without fungicide treatments.

Symptoms of the inoculated plants were evaluated according to the plant’s vitality on a scale of 0-3, where  3  is  a  healthy  plant  and  0 is a dead plant.(a) and (b) Field  experience  in  Netua  2013  and  2014 respectively. (c)  and  (d)  Field  experience  in Masada 2013  and 2014 respectively.

α and β - prochloraz 3 and 5 applications (respectively) are significantly different from the control treatment, γ - thiophanate methyl is significantly different from the control, δ - fluazinam is significantly different from the control. α+ - p=0.0253, δ+ - p=0.0285, not significantly different after Bonferroni corrections. * -3 applications of carbendazim were given on the background of 5 applications in 2013.

  1. Discussion

In vitro inhibition tests were carried out in the lab, while in vitro experiments were carried out using artificial inoculation in nursery apple plants and on young trees growing in naturally infested soils. Here we show that the active ingredients carbendazin and thiophanate methyl that belong to the chemical group MBC and fluazinam that belongs to the  chemical  group  PP  inhibited  mycelial  growth  of two representative virulent isolates by more than 90% at a concentration of 1 µg mL-1. These results are in agreement with López Herrera and Zea-Bonilla (2007) who showed that these fungicides inhibit mycelial growth at a concentration of 0.5 µg mL-1. Azoxystrobin, fludioxonil and prochloraz that belong to the chemical groups Qoi, PP and DMI, respectively, which were to the best of our knowledge tested against R. necatrix for the first time, were also found to be effective at 1 µg mL-1 a.i. in culture. These fungicides are known to be effective for treatment against other soil-borne pathogens, such as Fusarium spp. (Gullino et al. 2002), Sclerotinia minor and S. sclerotiorum (Matheron and Porchas, 2004). Captan is a non-selective fungicide used for a broad spectrum of plant diseases (Chen et al, 2001). However, this fungicide has limit effect at 100 µg mL-1 a.i.

Although an application of carbendazim at 62 mg/L maintained plant health in nursery plants it did not improve plant viability relative to the control plants in the orchards. Gupta (1978) reported that treatment with carbendazim was effective in R. necatrix infected apple trees in India. Inoculated apple plants in pot and nursery beds recovered following a drench with 0.1% carbendazim and produced new healthy roots (Gupta 1978). Yarden et al., 1989 show that carbendazim can be rapidly degraded in the soil after re-application due to microbial activity in the soil. this can explain the low efficiency of carbendazim in our field experiments.

Thiophanate methyl inhibited R. necatrix isolates in vitro and significantly extended plant health in the nursery compared to untreated control plants. Interestingly, in the 2013 Netua orchards, thiophanate methyl treated young trees were viable, with 84% more surviving trees in the fall than to the control plants. However, these results were not repeated in 2014, where thiophanate methyl gave poor results and no benefit over the  control plants. Thiophanate methyl inhibited the R. necatrix on PDA plates and in the nursery plants at the lowest applied dose. López-Herrera and Zea-Bonilla (2007) tested thiophanate methyl and carbendazim on local R. necatrix isolates in Spain and showed high inhibition on PDA, but smaller efficiency in a greenhouse trial.

In nursery apple plants, 15.5 mg/L of fluazinam yielded the best results, where all plants survived ca. 100 days after inoculation. A double dose did not improve the efficiency. Young planted orchard trees treated with three and five applications of prochloraz yielded good results in 2013 with no significant differences between the number of applications. In 2014, prochloraz contributions were high until the mid of August, but survival of the plants at the end of the year was lower and not significantly different from the control plants. The results indicate that three applications in 2014 are not sufficient during the year and another applications of prochloraz during the summer might give better results. Fluazinam reduced plant mortality in Masada orchards in 2013 and 2014. Fluazinam afforded the best results in our study in apple orchards, similarly to other studies that showed long-term residues (Kanadani et al. 1998; López-Herrera and Zea- Bonilla 2007, Sthepens 2003). López-Herrera and Zea-Bonilla (2007) showed the efficiency of fluazinam in a greenhouse with 9-month avocado plants in bags. They showed that fluazinam persists in the soil and can provide good control for relatively long periods of time. In Japan, fluazinam is used solely to prevent the spread of the disease to grapevine and Japanese pear, and only when applied at low disease rates on the border of infested areas (Kandani et al. 1998; Nitta et al. 1998). Moreover, high humidity of the soil, due to summer rains, affords very good environmental conditions for R. necatrix infection. In Japan, irrigation systems are not used due to summer rains.

Therefore, the control method for R. necatrix involves drenching the soil around individual trees with 100-125 L of 0.05-0.1% fluazinam solution (Nitta et al. 1998). In Israel, the summer is dry and the orchards are irrigated. Therefore, R. necatrix can develop only under the drippers system where soil is irrigated, but cannot be detected in the nearby region where the soil is dry (Dafny Yelin, unpublished data). In Israel, the fungicides are applied through the dripping system directly to the point of infection. Most of the infected orchards in  Israel are located in the north of the country at 440-1100 meters above sea level (Dafny-Yelin et al. 2018), where the main crop is apples and other deciduous trees such as cherry and peaches that are also sensitive to R. necatrix. The efficiency of the tested fungicides needs to be tested on those crops as well.

Our study demonstrates, for the first time In Israel, that treatments with fluazinam and prochloraz in naturally infested apple orchard soils prolong young trees’ life in commercial plantations. Treatment with thiophanate methyl may control R. necatrix with limited efficiency and perhaps needs more applications or higher doses for better success. Although the treatment with fluazunam and prochloraze significant inhibit wilting of the trees, still in the end of each year 10- 30% mortality were seen. That results offer that application of the fungicide need to be applied in different interval, or alternatively to combine the treatment with other methods as using less sensitive rootstock or other crops on infested soil. Ruano-Rosa et al. (2017) have shown that a combination of low concentration of fluazinam and Trichoderma spp. can control white root rot in avocado. Moreover, The efficiency of fungicides in older apples and on other deciduous trees growing under Israeli weather conditions needs further study.

Acknowledgments

We thank Again Adama, Makhteshim Adama, Rimi, Luxembourg, and Agrica CTS for supplying the fungicides and for application in the field trial, the Daniel family from Netua and the Safadi family from Mas'ade for the experimental plots, Dr. Stanley Freeman for providing help during the research in writing assistance and to Dr. Dan Malkinson for statistic assistance.

 

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