New Developments In Direct Seeding Weed Management

K. J. Kirkland

Agriculture and Agri-Food Canada

Scott, Saskatchewan

There are numerous new developments and approaches emerging for weed management in direct seeding systems. In the time frame allotted today I will present a brief research update on the following areas:

• non-incorporated granular herbicide.
• herbicide tolerant canola and weed management.
• nitrogen fertilizer placement and the weed/crop interaction.
• changing seeding dates and weed management.
• dandelion management in the absence of tillage?
• new chemistry introductions.

Non-incorporated granular herbicides

Granular herbicides, particularly Treflan, Avadex, Fortress and Edge have been evaluated by Agriculture and Agri-Food Canada at Scott for many years and more recently Treflan and Edge by Agriculture and Agri-Food Canada at Indian Head and Dow Elanco at several locations in the prairies. At Scott, non-incorporated granular Treflan, Fortress and Avadex were evaluated in a 3-year study from 1989-1991. Granules were applied to stubble in mid-October with no incorporation and direct seeded the following spring to three separate crops; barley, canola, and wheat. Comparisons were made to treatments that had been incorporated following application followed by a second incorporation in the spring. Over the 3 years and 3 crops (9 site years) wild oat biomass reductions from non-incorporated Treflan, Fortress and Avadex were equivalent to incorporated treatments (Table 1). Light infestations of green foxtail in the Treflan and Fortress studies were virtually eliminated with control >95% (data not shown).

Table 1. Non-incorporated* vs incorporated fall applied granular herbicide effects on wild oat biomass and crop yield on stubble summarized over crops and years, Scott, 1989-1991.

* contrasts comparing non-incorporated to incorporated. non-incorporated (no incorporation fall

or spring-direct seeded), incorporated (one incorporation fall with a second incorporation in spring).

Averaged over the 3 years, barley and wheat yields for the three herbicides were higher from the non-incorporated treatments (Table 2). These yield gains are not the result of better weed control, but are largely attributed to the moisture conserved in the non-incorporated direct seeded treatment. In canola, slightly lower yields with the non-incorporated direct seeding treatment were largely the result of improper seed placement on our part in the direct seeding treatment, particularly in the first two years of the study.

Table 2. Effect of incorporation* for annual grass weed control on crop yields from fall applied granular Treflan, Avadex and Fortress on stubble. Scott, 1989-1991.

* non-incorporated (no incorporation fall or spring-direct seeded).

incorporated (one incorporation in fall with a second incorporation in spring).

In 1994 and 1995, Dow Elanco initiated an extensive research program across the prairies to evaluate non-incorporated Treflan and Edge. Overall results indicate good control of the nine weed species listed in Table 3. Fall applied Edge with no incorporation and direct seeded the following spring averaged 91% over all species. A single pass with a rotary tine harrow produced a marginal improvement in control. By comparison, Treflan applied at the same time and direct seeded the following spring averaged 85% over all species and declined marginally when harrowed. The same treatments applied in early spring (data not shown) were less effective (decline of 7-8% control), and harrowing made no difference.

Table 3. Broad spectrum weed control with fall applied non-incorporated and harrow incorporated granular Edge and Treflan, 1994-1995. Dow-Elanco Data.

* applied in mid-October at 22 kg product/hectare (20 lb/acre) in Brown Soil Zone and 28 kg product/hectare (25 lb/acre) in Black Soil Zone.

** non-incorporated = no incorporation fall or spring, direct seeded. Harrow = rotary or tine harrow with single shallow incorporation in fall.

Herbicide tolerant canola

Argentine canola lines tolerant to Roundup, Liberty and Pursuit have recently been licensed or approved for licence. These types of canola offer the grower broad spectrum weed control in a single pass and will be particularly useful in direct seeding systems.

A trial to compare the effectiveness of Roundup, Liberty and Pursuit on various weeds was conducted at Scott, Sask. and Lethbridge, Alta. in 1995. At Scott, Roundup at 440 g ai/ha (0.5 litre/on acre) on RT canola gave excellent control of wild oat, wild mustard, cow cockle and cleavers. Liberty applied to Innovator canola (500 g ai/ha) gave excellent control of wild mustard and cow cockle, good suppression of cleavers, but control was not acceptable on wild oat. Pursuit applied to Pursuit Smart canola (45A71) gave excellent control of wild mustard and cleavers, but control was not acceptable on wild oat and cow cockle (Table 4). The drought conditions experienced through most of the growing season are probably responsible for the unacceptable control of wild oat recorded with Liberty, Pursuit and Poast.

At Lethbridge the identical treatments were applied to the tolerant canola. Control of wild oat, wild mustard, red root pigweed and shepherd's-purse was good with Roundup, Liberty and the Pursuit analogue. Control of wild oat with Pursuit was not acceptable. The only treatment providing acceptable control of stork's-bill was Roundup at 78%. Both Liberty and Pursuit suppressed storks-bill (Table 5).

Table 4. Broad spectrum weed control in herbicide tolerant canola with Roundup,

Liberty and Pursuit, Scott, 1995 (Kirkland).

* All treatments applied when weeds in 3 to 4 ­ leaf stage.

** Roundup, Liberty and Pursuit applied to Roundup tolerant RU3, Innovator and

Pursuit tolerant 45A71 canola, respectively.

Table 5. Broad spectrum weed control in herbicide tolerant canola with Roundup,

Liberty and Pursuit, Lethbridge, 1995 (Blackshaw)

* All treatments applied when weeds in 3 to 4 ­ leaf stage.

** Roundup, Liberty and Pursuit applied to Roundup tolerant RU3, Innovator and

Pursuit tolerant 45A71 canola, respectively.

Nitrogen fertilizer placement and the weed/crop interaction

Both weeds and crop species respond to available nitrogen. In general, the greater the access to available nitrogen the more competitive weeds are with crop. A study was initiated at Scott in 1994 and repeated in 1995 to determine the effect of nitrogen placement on a multi-weed infestation in zero tillage wheat. The major weed species present were; wild oats, green foxtail, wild mustard, volunteer canola, cow cockle and lamb's-quarters. No in-crop herbicides were applied, and all treatments received phosphate fertilizer applied with the seed. Urea nitrogen fertilizer (46-0-0) was applied in four treatments: (1) none,

(2) broadcast in early spring (3) band in early spring (4) side-band at seeding. Treatments 2, 3 and 4 were applied to soil test recommendation levels. Wheat was direct seeded with a narrow opener hoe drill.

Preliminary results indicate the greatest weed biomass occurred in the broadcast treatment where weed and crop had equal access to nitrogen (Table 6). Banding tended to give the crop some advantage as weed biomass declined and wheat biomass increased. Side banding disadvantaged the weeds significantly and produced the lowest amount of weed biomass among the nitrogen treatments. However, it was also evident visually and from the wheat biomass and yield data that nitrogen fertilizer in close proximity to the wheat seed caused some suppression (injury). Further research in this area is required to quantify some of the weed/crop relationships regarding nutrient utilization. However, it is evident that the method used to supply nitrogen will have a significant impact on weed management decisions in direct seeding.

Table 6. Effect of nitrogen fertilizer placement on total weed and wheat biomass and wheat yield in a zero tillage system Scott, 1994-95.

a All treatments received seed placed 12-51-0.

b Total annual grass and broadleaf weeds.

c Some crop suppression from side banded N.

Changing seeding dates and weed management

This topic has probably been addressed by Doug Derksen and perhaps others in earlier sessions so I will only touch on it briefly. There are three important considerations that relate to weed management and seeding date. First is the sequence of seeding from field to field. For example, if seeding is conducted over a two week period and fields are always seeded in the same order then certain weed species will be favoured and trend to dominate. By alternating the seeding pattern on a regular basis the environment favoured by these weed species will be disrupted putting them at a disadvantage and making burn-down and in-crop treatments more effective.

Secondly, a rotation of crops with similar maturity requirements can lead to a consistent, well adapted weed spectrum from year to year. For example; a rotation of wheat/peas/wheat/argentine canola means a maturity requirement of approximately 100 days on a continuous basis. By substituting a shorter season crop in the rotation such as, polish canola or barley existing weed spectrums and populations can be significantly disrupted making weed management treatments more effective.

Third, a shift to a fall seeding date or very early spring would have a major impact on weed management. The competitive nature of winter wheat and fall rye with weeds has been well documented and utilization of these crops in rotation is encouraged. Another opportunity for fall seeding is planting seed of a spring crop in late fall when risk of germination is low. Although this concept is in the experimental phase at present, the potential benefits as a technology for crop maturity and weed management appear large. Two years of fall seeding (late October) research at Scott, Sask. with argentine canola indicate maturity gains of 14 to 21 days over mid-May seeding dates. Fall seeded canola emerged in late April and was extremely competitive with weeds as ground cover was established early. Similarly, a late April seeding date for argentine canola resulted in maturity gains of approximately 7 to 10 days and a crop that was highly competitive with weeds. The introduction of herbicide tolerant canola (ie. Roundup) will fit well with October or late April seeding dates for improved weed management in direct seeding systems.

Dandelion management in the absence of tillage?

In most areas of the prairies, particularly northern regions, dandelion has become a major weed problem in direct seeding systems. The move to less tillage combined with good moisture conditions and, a lack of highly effective herbicide treatments have contributed to increased dandelion populations.

Monsanto recently registered Roundup as a preharvest treatment for dandelion. At

1 litre/acre control has averaged 87% 10 to 12 months following application and had a control range of 75 to 95%. Monsanto also reports that pre-seed and post-harvest Roundup at 1 litre/acre provided 84% control of dandelions less than 15 cm in diameter. For dandelion larger than 15 cm in diameter 1.5 to 2.0 litre/acre of Roundup was required (Table 7).

Table 7. Pre-seed* dandelion control with Roundup, 1995 Monsanto data.

* not a registered treatment Dec/95.

** included all sizes of dandelions.

New chemistry introductions

Horizon (Ciba-Geigy) - controls wild oat and green and yellow foxtail in wheat. Has proven highly effect over a wide range of weed leaf stages and environmental conditions. Tank mixable with nine separate broadleaf herbicide treatments (registered treatment).

BAS 514 - quinclorac (BASF) - control green foxtail and some broadleaf weeds in wheat. Effective over a wide range of environmental conditions. Tank mix potential with several herbicides to increase weed spectrum. New chemistry with regard to herbicide resistance (not registered, Dec/95).

Fluroxypyr (Dow Elanco) - controls cleavers in wheat and barley. Expected to be an important technology for reducing cleaver populations during the cereal years of the rotation. Can be tank-mixed with other herbicides to increase the weed spectrum. (not registered, Dec./95).