التداخلات الكيميائية والطبيعية بين منظمات النمو النباتية وبعض مبيدات الاّفات في مزارع العنب

CHEMICAL AND PHYSICAL INTERACTIONS BETWEEN PLANT GROWTH REGULATOR AND SOME PESTICIDES IN VINEYARDS RANIA MOHAMED ABD-EL-HAMID

Senior Researcher of Pesticides, Pesticide Residue and Environmental Pollution, Dept., Central Agricultural Pesticides Laboratory, Agriculture Research Center""Grape crop is mainly subjected to infestation with mealy bugs, powdery mildew and berry rot. The insecticide fenitrothion (Sumithion) is recommended for controlling mealy bugs; thrips while the triazole fungicide diniconazole (Sumi-eight) is recommended for controlling powdery mildew and berry rot. On the other hand, GA3 applications are currently used to increase the berry size of Thompson Seedless grapes.

The present study aimed to investigate four principal points as follows:

1-            The compatibility of formulated pesticides Sumi-eight 5% E.C. (diniconazole) and Sumithion 50% E.C. (fenitrothion) with the plant growth regulator namely berlex 10% TB [gibberellic acid (GA3)].

2-            The persistence of diniconazole, fenitrothion, gibberellic acid and their mixtures in and on grape fruits.

3-            Photo and thermal decomposition of diniconazole, fenitrothion, gibberellic acid and their mixtures in laboratory.

4-            The interaction between the used pesticides (diniconazole and fenitrothion) and the plant growth regulator (gibberellic acid) applications on thinning, yield, berry shape and berry composition of Thompson seedless table grapes.

The obtained results could be summarized in the followings:

1.            Physical properties of tested agrochemicals

Results indicated that there were a physical compatibility between used agrochemicals Sumithion, Sumi-eight and the plant growth regulator GA3 at their field dilution rates in both soft and hard water. They passed successfully emulsion stability without creamy separation or precipitation.GA3 addition to the used pesticides decreased the foam layer in comparison with that formed from pesticide alone.

The physico-chemical properties of spray solution of the tested pesticides alone, GA3 alone and their mixtures revealed that GA3 had the highest value of surface tension therefore; it slightly increased the surface tension of pesticide spray solution.

There were no differences in viscosity between the spray solutions under study. On the other hand, the mixture of GA3 and the two pesticides under study was slightly increased the pH values of spray solutions than each one alone. This increase in pH value caused decreasing effect on initial deposits of the mixtures with increasing degradation rate.

2: Persistence behaviour of the tested agrochemicals on/in grape fruits.

2.1. Diniconazole when used alone showed higher residue level than its mixtures within most intervals during the two seasons. The initial deposits found after one hour from the fourth treatment in 2006 was 0.49 ppm for diniconazole alone and 0.30 ppm for its mixtures. The loss difference was 38.77 % at the same interval. On the other, hand the initial deposits at 2007 were found to be 0.50 ppm for diniconazole alone and 0.29 for its mixture with loss difference 42.0 % at the same interval. The corresponding recommended pre-harvest intervals (PHI) were 7.0 and 5.0 days in the two seasons after application for diniconazole alone (D) and the mixture of diniconazole with (M-D), respectively. The estimated half-life (t1/2) values for diniconazole alone was 22.49 hrs and 25.32 hrs for its mixture on/in grape fruits at 2006.At 2007 the (t1/2) values for diniconazole alone was 23.03 and 24.78 for its mixture.

2.2. Fenitrothion alone showed higher persistence than its mixtures with at all intervals during the two seasons. The initial deposits found after one hour from the fourth treatment at 2006 was 11.35 ppm for fenitrothion alone and 6.46 ppm for its mixture. The loss was 43.08 % at the same interval. On the other hand, the initial deposits at 2007 reached 11.19 for fenitrothion alone and 5.80 ppm for its mixture with loss 48.16 %. The corresponding recommended pre-harvest intervals (PHI) were 9.0 and 7.0 days at the two seasons after application for fenitrothion alone (F) and the mixture of fenitrothion with (M-F), respectively. The estimated half-life (t1/2) values for fenitrothion alone were 28.23 hrs and 20.15 hrs for its mixture on/in grape fruits at 2006.At 2007 the (t1/2) values reached 26.72 and 19.21, respectively.

2.3. Gibberellic acid alone showed more persistence than its mixtures within all intervals during the two seasons. The initial deposits found after one hour from the fourth treatment at 2006 was 30.52 ppm for gibberellic acid alone and 28.42 ppm for its mixture. The loss difference was 6.88 % at the same interval. On the other hand, the initial deposits at 2007 were 30.42 and 28.29 ppm, with loss difference 7 % at the same interval, respectively. The corresponding recommended pre-harvest intervals (PHI) were 4.0 and 2.0 days in the two seasons after application for GA3 alone (G) and the mixture of GA3 with (M-G), respectively. The estimated half-life (t1/2) values for gibberellic acid alone 17.15 hrs and 13.69 hrs for its mixture on/in grape fruits at 2006.while at 2007 the (t1/2) values reached 17.11 and 13.68, respectively.

3: Effect of some environmental factors on the degradation of the tested agrochemicals and their mixtures.

Effect of different temperature on the degradation of tested agrochemicals and their mixtures.

The obtained data indicated the great role of exposure to different temperatures on the degradation rate of the two pesticides and the plant growth regulator. In this respect, the mixtures of the two pesticides with the plant growth regulator were more degraded than each one alone or when mixed with the plant growth regulator.

Effect of UV-Rays and direct sunlight on the degradation of tested agrochemicals and their mixtures.

Data clearly showed that the mixture of diniconazole + fenitrothion + GA3 had the highest degradation rate than its contents when exposed separately to UV-rays and direct sunlight. GA3 alone, revealed slight degradation rate.

4: Effect of GA3 treatments on yield and quality of Thompson seedless grapes.

Results showed that GA3 alone or in combination with the pesticides delayed ripening by increasing T.S.S and reducing acidity for both seasons. The GA3 treatments in combination with the pesticides or alone significantly increased the total yield, cluster weight, berry weight, size, length, width, bunch compactness and rachis weight, berry shape become global at both seasons of 2006 and 2007."