Dr. Al Black was one of the first to start the work on use of incorporated herbicides in zero till systems. Dr. Black used a wide blade cultivator to incorporate granules into the soil while maintaining upright stubble.

Since Al Black's initial thrust and success, many farmers and researchers have been examining the efficacy of soil applied herbicides as affected by rate, timing, type of (or lack of) incorporation, number of years in zero till, soil disturbance at seeding and influence of crop competition (crop type).

As a result of the early work, the manufacturers of these compounds are now vigorously pursuing registration.

RESEARCH RESULTS & OBSERVATIONS

There can be some loss of weed control with the soil applied herbicides when surface application is compared to incorporation. In some trials, there was no reduction in weed control, but in others, there has been as much as a 20% reduction. Often the number of weeds in the zero till system is lower than in conventional tilled fields thus yield loss due to weeds escapes should be about the same. The average loss of wild oat control in 8 trials conducted in 1994 using ethalfluralin at 1.1 kg ai/ha in spring or 1.4 kg ai/ha in fall was about 12%. Weed control can often be boosted by increasing rates 10-20%, however crop injury could also become a problem. Figures 1, 2 and 3 illustrates the effects of incorporation on herbicide performance from trials conducted at Minto in 1992 and 1993. In these trials herbicide performance was better or equal with no incorporation.

Table 2. Wild Oat Control, surface application, 1994*
Timing	Rate	Trifluralin	Ethalfluralin	# of trials
	kg ai/ha	% control
Fall	1.1	67	73	8
Fall	1.4	83	88	8
Spring	1.1	84	89	8

Table 3. % Weed control, fall application 1994*
Product	Rate	Wild Oats	Chickweed	Hemp Nettle	Wild Buckwheat
	kg ai/ha	% control
Trifluralin	1.1	60	76	36	81
Trifluralin	1.4	66	74	46	84
Trifluralin	1.7	76	77	73	89
Ethalfluralin	1.1	74	62	66	90
Ethalfluralin	1.4	80	68	83	90
Ethalfluralin	1.7	91	90	93	91
*Whitefas, Saskatchewan Dow Elanco data.

PRODUCT CHOICE

Between trifluralin and ethalfluralin, there appears to be a trend toward superior performance with ethalfluralin. The advantage in wild oat control appears to be 4-5% in favor of ethalfluralin (Table 2). While recrop studies are just being carried out, the authors personal experience is ethalfluralin causes a lot less injury to a succeeding wheat crop than trifluralin. It is not currently known if carryover of these products will be greater or less than when they are conventionally incorporated.

It should be noted that in some situations some broadleaf crops are more sensitive to ethalfluralin than trifluralin, in the year of application.

Table 1. % Weed control, Ethalfluralin 1994*
Surface Application	Conventional Application
% control
98	100
87	100
74	94
80	90
80	94
80	100
89	95
Average = 84%	Average = 96%
*Manitoba, Saskatchewan and Alberta trials Ag-Quest, Inc and Dow Elanco data.

RANGE OF WEEDS

An example of the range of weed control achievable with surface applied dinitronalines is shown in Table 3. Surface applied ethalfluralin gives slightly better control of weeds at a given rate of application than trifluralin. Ethalfluralin was effective in the control of wild oats, chickweed, hempnettle and wild buckwheat in this 1994 trial. Boosting the rates above the recommended 1.4 kg ai/ha fall rate improved weed control particularly of chickweed, however caution should be used as higher rate of ethalfluralin can cause injury on some sensitive crops.Table 1. % Weed control, Ethalfluralin 1994*

RAPIDITY OF WEED CONTROL

In many of our trials we have noticed that there is initially some escapes of the weeds the surface applied treatments. Table 4 illustrates how weed control improved over time. Wild buckwheat in particular appears to be missed initially, but often is well controlled by the end of the season. Obviously the escaped plants grow with weakened root systems and eventually succumb to competition during the season. In extremely favorable weather conditions and/or with a very non competitive crop the weakened plants may outgrow initial injury.

Table 4. Weed control, surface applied ethalfluralin 1994.
Weed	56 DAT	84 DAT
	% control
Wild Oats	83	98
Green Foxtail	90	98
Wild Buckwheat	50	100
*DAT dats after treatment.

LENGTH OF TIME IN ZERO TILL

While many of the studies conducted at Minto, Mb. have been placed on land only zero tilled for short time with good success, results compiled by DowElanco over a wider range of conditions suggest the best results come after land has been zero tilled for 3 or more years. Part of the reason may have to do with density of weeds as an equally important factor affecting perceived performance in some annual weeds such as green foxtail and wild oats as length of time in zero till increases. 90% control of 15 weeds/m2 of course looks a lot better than 90% of 1000 wild oats/m2.

SOIL DISTURBANCE AT SEEDING

While the data for this question is somewhat limited, there does not seem to be a direct correlation between good and bad performance tied in with high or low disturbance direct seeding drills. Work conducted at Minto suggests the difference between hoe drills and disc drills in a one pass direct seeding system in terms of weed stimulation is small. Often, however, hoe drills give more consistent soil seed contact and can be in warming the seed zone faster. The seed zone in a zero till field. can have the same soil temperature as on a conventionally tilled field if a paired row system is used for seeding, whereas a field seeded with a lower disturbance will be colder resulting in slower emergence. Dinitroline products tend to cause greater crop injury when the crop is seeded deep or has slow emergence due to cold seedbeds.

Hoe drills equipped with paired row seeded and precision fertilizing capabilities can also offer the advance of being able to selectively feed the crop while largely excluding the weeds from the rich nutrient zones, thus further aiding in weed control.

OTHER WEED CONTROL CONSIDERATIONS

While surface applications of incorporated herbicides is not yet even registered, newer alternatives for weed control particularly in canola and peas are emerging. The use of new herbicide resistant canola varieties, such as glyfosinate tolerant, glyphosate tolerant of imazethapyr (Pursuit) tolerant canola will provide some economic attractive weed control options in the near future. Registration of Pursuit in peas will also provide a good economic alternative.

FUTURE ROLE OF SURFACE APPLICATION

The main advantages of surface applied 'incorporated herbicides' will be as rows:

Canola and Mustard:

good alternative for herbicide rotations

(good alternative for varieties not tolerant to glyfosinate, glyphosate, imazethapyr, etc.

in heavy weed pressure it may be economical to apply both a pre-emergent as well as a post-emergent

Peas

good alternative for herbicide rotations

while Pursuit will be a good product for weed control in peas, it is in a class of chemicals (SU's)

to which weeds such as chickweed and kochia can quickly develop resistance

Lentils

good alternative, very few other choices exist

lentils can be sensitive to higher rates of Edge

In some situations due to a lower level of efficacy, weed control may be lower than desirable due largely to the poor competitive nature of lentils.

Sunflower and other broadleaf crops

little or no data, but these products may also have a fit

CONCLUSION

The development of surface application for trifluralin and ethalfluralin is good news, bad news story.

Good news - It works, most of the time.

Bad news - We are about 20 years behind where we should be in the use of these products in zero till.

Summary: Surface application provides zero till farmers with a much needed alternative for weed control in broadleaf crops, however that need may diminish with introduction of new herbicides and herbicide tolerant crop varieties.