Asian soybean rust control in response to rainfall simulation after fungicide application

Chechi, Amanda; Deuner, Carolina Cardoso; Forcelini, Carlos Albeto; Boller, Walter

doi:10.4025/actasciagron.v43i1.45689

ABSTRACT.

Asian soybean rust (Phakopsora pachyrhizi) is the main disease that affects soybean in Brazil. Fungicide applications are the main control method, but they can be influenced by the occurrence of rain. We aimed to study the control of Asian soybean rust in response to the occurrence of simulated rainfall at different times after fungicide application. The penetrant fungicides trifloxystrobin + prothioconazole (60 + 70 g a.i. ha^-1) and azoxystrobin + benzovindiflupyr (60 + 30 g a.i. ha^-1) and the nonpenetrant fungicides mancozeb (1,500 g a.i. ha^-1), chlorothalonil (1,440 g a.i. ha^-1), and copper oxychloride (672 g a.i. ha^-1) were tested using two spray volumes: 70 and 150 L ha^-1. Rain was simulated from 30 to 240 minutes after fungicide application. Soybean leaflets were collected and inoculated with a spore suspension of P. pachyrhizi (5.0 x 10⁴ mL^-1) and incubated in plastic boxes for 20 days. The trials were repeated twice. Nonpenetrant fungicides were more susceptible to rain washing, mainly when the 70 L ha^-1 spray volume was used. For the penetrative fungicides, the best control percentages were obtained when the rainfall occurred between 120 and 180 minutes after application, while the protective fungicides had the best control percentages when the rainfall occurred approximately 240 minutes after application. The Asian rust control is affected by the characteristics of the fungicide applied, by the time interval between fungicide application and rain occurrence and by the spray volume.

Keywords:
application technology; chemical control; Phakopsora pachyrhizi; spray volume

[1] *Author for correspondence. E-mail: amandachechi@hotmai.com

Time interval (minutes)	Trifloxystrobin + prothioconazole
	----- number of uredinia per leaflet-----
	2017		2018
	70 L ha^-1	150 L ha^-1	70 L ha^-1	150 L ha^-1
30	74.0 a A^*	55.3 a B	77.3 a A	63.7 a B
60	57.3 b A	40.0 b B	65.0 b A	56.0 b B
90	35.3 c A	25.7 c B	48.7 c A	35.3 c B
120	28.3 c A	15.0 d B	37.7 d A	28.3 d B
180	15.3 d A	8.0 e B	34.3 d A	24.3 d B
240	14.7 d A	7.3 e B	30.7 e A	23.0 d B
No rain	12.7 d A	7.4 e B	30.0 e A	23.3 d B
CV (%)	18.1	15.4	10.4	13.4
Time interval (minutes)	Azoxystrobin + benzovindiflupyr
	2017		2018
	70 L ha^-1	150 L ha^-1	70 L ha^-1	150 L ha^-1
30	85.7 a A	71.0 a B	93.7 a A	78.7 a B
60	67.7 b A	60.0 b B	83.7 b A	65.7 b B
90	56.7 c A	46.0 c B	60.3 c A	48.7 c B
120	48.0 d A	38.7 d B	50.7 d A	42.0 d B
180	38.0 e A	29.7 e B	41.3 e A	31.0 e B
240	33.3 e A	26.7 e B	39.0 e A	29.0 e B
No rain	31.3 e A	25.9 e B	37.0 e A	27.7 e B
CV (%)	11.9	9.8	11.1	11.9
Time interval (minutes)	Mancozeb
	2017		2018
	70 L ha^-1	150 L ha^-1	70 L ha^-1	150 L ha^-1
30	97.7 a A	93.7 a A	113.3 a A	110.0 a A
60	87.3 b A	80.0 b A	104.7 b A	97.3 b A
90	75.8 c A	60.7 c B	84.7 c A	74.3 c B
120	56.0 d A	47.3 d B	68.3 d A	50.7 d B
180	47.0 e A	38.7 e B	52.0 e A	42.0 e B
240	37.3 f A	28.0 f B	42.7 f A	30.0 f B
No rain	35.3 f A	28.6 f B	42.3 f A	26.0 f B
CV (%)	10.2	11.0	7.9	8.9
Time interval (minutes)	Chlorothalonil
	2017		2018
	70 L ha^-1	150 L ha^-1	70 L ha^-1	150 L ha^-1
30	96.8 a A	94.3 a A	111.8 a A	108.6 a A
60	85.3 b A	78.0 b A	100.3 b A	96.3 b A
90	71.5 c A	64.3 c B	81.1 c A	71.0 c A
120	52.6 d A	45.0 d B	61.6 d A	53.3 d B
180	44.6 d A	35.6 e B	48.3 e A	36.6 e B
240	34.0 e A	25.0 f B	37.3 f A	26.7 f B
No rain	35.2 e A	23.8 f B	36.3 f A	24.6 f B
CV (%)	14.1	11.0	9.4	9.4
Time interval (minutes)	Cooper oxychloride
	2017		2018
	70 L ha^-1	150 L ha^-1	70 L ha^-1	150 L ha^-1
30	97.1 a A	94.6 a A	116.3 a A	111.3 a A
60	89.0 b A	80.7 b B	107.6 b A	99.3 b B
90	79.3 c A	69.0 c B	100.3 b A	91.3 c B
120	60.0 d A	51.6 d B	79.3 c A	69.0 d B
180	48.0 e A	38.7 e B	66.7 d A	56.7 e B
240	38.0 f A	32.0 f B	56.3 e A	48.6 f B
No rain	36.6 f A	30.5 f B	56.8 e A	46.9 f B
CV (%)	7.0	7,1	7.5	8.2

A 2017 - Trifloxystrobin + prothioconazole	A 2018 - Trifloxystrobin + prothioconazole
70 L ha^-1	70 L ha^-1
$y = - 0.002 x^{2} + 0.8363 x + 1.285$	$y = - 0.0014 x^{2} + 0.556 x + 18.153$
R² = 0.991	R² = 0.980
150 L ha^-1	150 L ha^-1
$y = - 0.0017 x^{2} + 0.7009 x + 24.325$	$y = - 0.0014 x^{2} + 0.5361 x + 29.39$
R² = 0.996	R² = 0.961
B 2017 - Azoxystrobin + benzovindiflupyr	B 2018 - Azoxystrobin + benzovindiflupyr
70 L ha^-1	70 L ha^-1
$y = - 0.0014 x^{2} + 0.6166 x - 2.7135$	$y = - 0.0015 x^{2} + 0.6417 x + 0.2896$
R² = 0.994	R² = 0.979
150 L ha^-1	150 L ha^-1
$y = - 0.0012 x^{2} + 0.5187 x + 13.545$	$y = - 0.0013 x^{2} + 0.5473 x + 17.26$
R² = 0.985	R² = 0.993
C 2017 - Mancozeb	C 2018 - Mancozeb
70 L ha^-1	70 L ha^-1
$y = - 0.0011 x^{2} + 0.5955 x - 18.172$	$y = - 0.0011 x^{2} + 0.5897 x - 16.392$
R² = 0.981	R² = 0.988
150 L ha^-1	150 L ha^-1
$y = - 0.0015 x^{2} + 0.7172 x - 16.007$	$y = - 0.0016 x^{2} + 0.7549 x - 17.77$
R² = 0.987	R² = 0.977
D 2017 - Chlorothalonil	D 2018 - Chlorothalonil
70 L ha^-1	70 L ha^-1
$y = - 0.0012 x^{2} + 0.6395 x - 18.109$	$y = - 0.0012 x^{2} + 0.6369 x - 15.83$
R² = 0.983	R² = 0.988
150 L ha^-1	150 L ha^-1
$y = - 0.0015 x^{2} + 0.7258 x - 16.777$	$y = - 0.0015 x^{2} + 0.7443 x - 16.477$
R² = 0.989	R² = 0.989
E 2017 - Cooper oxychloride	E 2018 - Cooper oxychloride
70 L ha^-1	70 L ha^-1
$y = - 0.0008 x^{2} + 0.5129 x - 16.011$	$y = - 0.0006 x^{2} + 0.415 x - 13.445$
R² = 0.981	R² = 0.976
150 L ha^-1	150 L ha^-1
$y = - 0.0013 x^{2} + 0.6604 x - 16.115$	$y = - 0.0009 x^{2} + 0.5083 x - 11.378$
R² = 0.993	R² = 0.978

Treatment	Coverage (%)				Impacts density (impacts cm^-2)
	70		150		70		150
	------------ L ha^-1 ------------				------------ L ha^-1 ------------
Trifloxystrobin + prothioconazole	15.2	cB	39.4	aA	260.4	bA	396.1	aA
Azoxystrobin + benzovindiflupyr	8.0	cB	31.3	bA	188.6	bB	371,7	aA
Mancozeb	22.0	bA	29.2	bA	261.9	bA	468,5	aA
Chlorothalonil	29.3	aA	31.6	aA	312.5	aB	552.9	aA
Cooper oxychloride	21.9	bB	43.7	aA	296.4	bA	322.1	aA
	CV (%)		17.45		CV (%)		>24.52

Brasil

Brasil

Asian soybean rust control in response to rainfall simulation after fungicide application

ABSTRACT.