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OBJECTIVE

The aim of this study was to evaluate the efficacy and selectivity of Bullet (P2O5 7%, K2O 14%, SL) for the control of the fruit set on orange trees.

 

MATERIALS and METHODS

Trial was established on a commercial orange grove, variety Navel, placed in a typical commercial area in Canals (Valencia).

The experimental design was RCB (randomized complete blocks), with a total of 4 reps of 60m2/plot (12x5 m) and 3 trees/plot per thesis. In addition giberellic acid (16g/L SL) was used as standard product and untreated thesis was left for comparison. 

Two application timing were defined to increase the fruit set: majority of petals fallen (April 27th, corresponding to the phenological stage BBCH 67), and beginning of fruitlets abscission (May 18th, corresponding to the phenological stage BBCH 71).

These applications were performed using a portable motorized pump sprayer with a gun sprayer with a single 1.5 mm Æ cone nozzle. The application pressure was 15 bars and the spray volume was 1500 l/Ha in both applications according to GAP and protocol.

 

Table 1. Application Description

Trt

Nr.

Type

Treatment Name

Formulation

Conc. Unit. Type

Active Ingredient

F.P.

Rate Unit

A.I.

Rate Unit

Appl Code

1

PGR

Bullet

500         G/L         SL

P2O5 -7%,

K2O -14%

70 mL/HL

525 g ai/ha

AB

2

PGR

Giberellic acid

   16        G/L          SL

AG3

40  mL/HL

9.6 g ai/ha

AB

3

CHK

Untreated

-

Not treated

-

-

-

 

The study was carried out following an adaptation of the EPPO guideline number PP 1/184(2) “Regulation of growth in citrus”. The product effect on the fruit set was evaluated counting the number of flowers on four marked branches per plot at first application and the number of fruitlets on the same four marked branches at 49 DAB, at BBCH crop stage 74 according to the protocol. The percentage of fruit set was calculated.

To determine the possible effect on the yield the central tree of each plot was harvested in order to determine the weight of the fruit. A sample of 200 fruits from the central tree was separately weighted and the weight per fruit was calculated to determine the fruit size. The number of fruits per tree was also calculated. Thus the studied variables were the yield (Kg/tree), the average per fruit (g/fruit) and the number of fruits per tree. 

Phytotoxicity and selectivity was assessed following EPPO guide line PP1/135(3) “Phytotoxicity assessment”. General Phytotoxicity symptoms were evaluated at each assessment, using the EWRC scale (1= no symptoms, 9= total destruction).

 

Table 2. Sequence of events

Momento

Fecha

Descripción

Experimental start date (DAA 0)

27/4/11

Flowers assessment

0 Days after 1st application (DAA 0)

27/4/11

Application A

0 Days after 2nd application (DAB 0)

18/5/11

Application B

49 Days after 2nd application (DAB 49)

6/7/11

Fruit set assessment

210 Days after 2nd application (DAB 210)

14/12/11

Harvest

 

 

 

RESULTS

The most relevant studied variables in this trial to evaluate the possible effects on the crop of Bullet were the percentage of fruit set calculated at 49 DAB and the harvest data such as the yield (Kg/tree), the average weight per fruit (g/fruit) and the number of fruits per tree.

 

         Tabla 3. Porcentaje de frutos cuajados

Trt

Nr.

Tipo

Nombre del

tratamiento

% Cuajado

1

PGR

Bullet

16,34    (113%)

2

PGR

Ácido Giberélico

11,58     (80,3%)

3

Testigo

Sin tratar

14,41      (100%)

                                  

 

The natural fruit set in the field was moderate, showing 14,41% in untreated plots. The fruit set in plots treated with Bullet at 70ml/hl was slightly higher than in untreated plots (13,4% of increment). The fruit set in plots treated with giberellic acid at 40ml/hl was 11,58%, lower than untreated plots.

 

A clear increase of the yield (Kg/tree) and the number of fruits per tree were found in treated plots, as shown in table n4. The yield in plots treated with Bullet was 142,4 Kg/tree (48,43 Kg/tree higher than untreated plots). Besides, the yield in plots treated with Bullet was 12,67 Kg/tree higher than in plots treated with the reference product Giberellic acid (129,7 Kg/tree).

 

Table 4. Harvest data results

Trt

Nr.

Type

Treatment Name

Yield

(Kg/tree)

Weight/fruit

(g/fruit)

Number of fruits/ tree

1

PGR

Bullet

142,4   (151%)

188,7   (95%)

754,5    (132%)

2

PGR

Giberellic acid

129,7   (138%)

160,5   (81%)

796,2    (139%)

3

Control

Untreated

94,0    (100%)

197,1   (100%)

571,2   (100%)

 

 

 

 

 

 

The number of fruits/tree in plots treated with standard product was approximately 796,2 fruits, slightly higher than plants treated with Bullet (with 754,5 fruits/tree), while in untreated plots fruits counted were 571,2 per tree.

Regarding the weight per fruits, a slight reduction was observed on the treated plots without significant differences between treatments. The weight of fruits ranged from 160,53 and 197,13 g.

 

  CONCLUSIONS

 

 

Regarding the percentage of fruit set on marked branches an slight response (13% of increment) was observed in plots treated with Bullet respect to untreated control and acid Giberellic treatment.

Bullet increased the yield (Kg/tree) and the number of fruits per tree. The yield using experimental product was 48,43 Kg/tree higher than in untreated plots and 12,67 Kg/tree higher than plots treated with reference product (10% of increment).

Despite the increase in number of fruits/tree, that could decrease significantly the size of the fruits, no significant differences neither between treated and untreated nor among treatments were found.

The little differences detected in fruit size were lower than 5%, and they were offset by the increment in yield (51,5% in plots treated with Bullet).

With an average price of the variety Navel of 0,30 €/Kg the increment of the yield in plot treated with Bullet represents 7264,5 €/Ha, which justify the application of the product to improve the fruit set.

Bullet used at 70ml/hl applied at BBCHs 67 and 71 resulted completely selective to crop and there were not any phytotoxicity symptom present. Spots or other alterations on the leaves and fruits skin were not observed. Other effects, positive or negative, on the incidence of other pests were not observed.

 

 

José Morera, S.L.

Dep. Investigación y Desarrollo



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