K.J. Kirkland

Agriculture Canada, Experimental Farm

Scott, Saskatchewan

Most of the herbicides used in the prairie provinces of Canada are applied to field crops with conventional spray equipment applying 100-110 I/ha of water. As water is merely a carrier for the active ingredient there has been substantial interest in reducing the spray volume per hectare. Availability of clean, abundant surface water is a major problem in many communities forcing producers to haul long distances and line-up to fill supply tanks. Access to supply and the requirement for large volumes per hectare make optimum application timing difficult and often impossible.

Provincial weed control publications generally recommend water volumes of 100-110 I/ha. These recommendations are largely based on the fact that high water volumes, with large droplets are less prone to wind drift than small water volumes with finer droplet size. There has been little or no research conducted to indicate that herbicide efficacy is greater with higher water volumes. The introduction of shrouded sprayers make it possible to apply reduced water volumes with much lower risk of drift to non-target areas.

These same shrouded sprayers also make it possible to apply herbicides in very low water volumes, at high pressure (fine droplet size). This allows research to evaluate the effect of increased active ingredient contacting the plant, leading to greater herbicide efficacy and the potential for reducing herbicide rates.

In 1985, preliminary research was initiated at the Scott Experimental Farm to determine:

(a) if herbicides could be applied in reduced water volumes without loss of efficacy.

(b) if the rate of active ingredient could be reduced when herbicides are applied in reduced water volumes at higher pressures (fine droplets).

WATER VOLUME

Commonly used wild oat and annual grassy weed herbicides were applied in water volumes of 100 and 50 I/ha (Table 1). Over the course of the study reductions in efficacy were noted for Hoegrass and Assert in 1987 at lower water volumes.

Table 1 EFFECT OF WATER VOLUME ON THE EFFICACY OF WILD OAT HERBICIDES - SCOTT, 1987-88
	Water volume	Wild oat - % injury
Treatment	(l/ha)	1986	1987	1988
Hoegrass	100	78	67	71
Hoegrass	50	78	61	71
Mataven	100	93	89	81
Mataven	50	94	89	84
Avenge	100	-	78	90
Avenge	50	-	78	90
Assert	100	96	59	91
Assert	50	96	48	93
Poast	100	88	-	-
Poast	50	96	48	93
Excle	100	93	45	81
Excel	50	90	45	78
PP-604	100	92	96	81
PP-604	50	93	96	85
LSD (0.05)		N.S.	3.0	N.S.

Similar results were obtained with seven broadleaved herbicides or herbicide combinations applied to a volunteer canola-wild mustard infestation (Table 2). With the exception of.MCPA in 1987 there was a trend toward greater herbicide efficacy with the lower water volume (50 l/ha).

Table 2.. EFFECT OF WATER VOLUME ON ThE EFFICACY OF BROADLEAVED HERBICIDES - SOOTT, 1987-88.
	Water volume	Volunteer Canola-Wild mustard - % injury
Treatment	(1/ha)	1987	1988
Buctril M	100	93	92
Buctril M	50	92	93
Torch	100	48	61
Torch	50	48	64
2,4-D + Banvel	100	95	56
2,4-D + Banvel	50	98	78
2,4-D amine	100	89	70
2,4-D amine	50	96	72
HCPA amine	100	94	69
HCPA amine	50	87	70
Glenn	100	95	92
Clean	50	100	96
Ally	100	70	89
Ally	50	100	92

WATER VOLUME AND REDUCED RATE

Seven herbicides or herbicide combinations were evaluated at four rates in four water volumes. Herbicide rates were; recommended rate (100%), 75, 50 and 25% of recommended respectively. The above rates were applied in water volumes of 100, 50, 30 and 10 litres per hectare using a shrouded sprayer.

At all rates Roundup (glyphosate) activity was greater with lower water volumes. Maximum activity on wild oat (chemical fallow burnoff) was achieved with water volumes of 10 litre/hectare. (Figure 1). Combined over years and rates, % wild oat injury for water volumes of 100, 50, 30 and 10 litres/hectare was 72, 80, 80 and 86% respectively.Figure 1

Similar trends were noted with Poast, Rustler (glyphosate portion), 2,4-D amine/Banvel. A small trend toward increased activity with lower water volumes occurred with Fusilade while the activity of Hoegrass and Buctril M showed limited effect from changing water volumes.