INTEGRATED WEED MANAGEMENT IN REDUCED TILLAGE SYSTEMS

JOHN T. O'DONOVAN

SENIOR RESEARCH SCIENTIST (WEED MANAGEMENT)

ALBERTA RESEARCH COUNCIL, VEGREVILLE

INTRODUCTION

The concept of integrated weed management (IWM) has been around for a long time but has not been taken very seriously. One of the main reasons for this is that herbicides have generally proven to be a very effective and relatively non-laborious means of controlling weeds in crops. In recent years, however, the development of weed resistance to herbicides has cast doubt on the sustainability of depending too much on this "magic bullet" approach to weed management. In western Canada, some of our most serious weeds (including wild oats, green foxtail, chickweed, kochia, wild mustard) have become highly resistant to one or more of several classes of herbicides with which they were once controlled. This more than any other issue is spearheading the move towards more integrated approaches to weed management.

Traditionally, tillage and summerfallow have been integrated with herbicide use as a means of weed control. Producers adopting reduced or zero tillage systems can no longer depend on these practices as components of an IWM system. These producers have to re-examine the concept of IWM and combine other agronomic principles with herbicide use if their weed management systems are to be effective and sustainable.

IWM can be defined as a system of sustainable weed management that combines rational and judicious herbicide use with other principles and practices in order to reduce the impact of the weeds to an economically acceptable level. While many of the principles discussed in this paper apply to both conventional and reduced tillage systems, they have particular application in situations where tillage is reduced or eliminated.

COMPONENTS OF AN IWM SYSTEM FOR REDUCED TILLAGE SYSTEMS

The goals of an IWM system should be to reduce the movement of weed seed into the soil and to reduce the impact of weeds on crops to an economically acceptable level. The emphasis should be on management rather than eradication, since many years of continuous herbicide use have failed to eradicate weeds from soil seed banks.

An important first step in an IWM program is to prevent the movement of weeds into the field. This can be achieved by planting clean seed, cleaning tillage and harvesting equipment between fields, tarping grain trucks, avoiding transfer of soil from roadsides to crop land, and controlling weed infestations along roadsides, fence rows and waste areas. Perennial weeds such as quack grass, Canada thistle, perennial sow-thistle, toadflax and foxtail barley growing along the perimeters of fields in reduced tillage systems can rapidly encroach into the field if allowed to do so. The success of an IWM system for reduced tillage will be influenced considerably by the proper management of weeds in these non-crop areas.

While prevention and sanitation are very important components of an IWM system, virtually all farmers already have weed seeds present on their land. A number of factors will influence how effectively these weeds are managed, and how much weed seed is returned to the soil. These include the type of direct weed control methods employed such as the use of synthetic herbicides or biological control agents, and agronomic weed management practices such as crop rotation. The essence of an effective IWM system is to combine one or more of these practices with strategies that maximize the competitiveness of the crop relative to the weeds. These include planting vigorous, high quality seed, growing competitive crops and cultivars, promoting early crop emergence, choosing optimum crop row spacings and seeding rates for weedy situations, and placing fertilizer to favour the crop.

Biological control methods may be a feasible option in the future. At present biological control with insects is proving successful in some non-cropping situations (e.g. leafy spurge flea beetle), but there is nothing available for situations where crops are grown intensively. Similarly, there are no mycoherbicides (based on plant pathogenic organisms) currently registered in Canada, and it is unlikely that this will change in the near future. The rest of this paper will therefore focus on the integration of herbicides with agronomic practices that favour the growth and development of crops relative to weeds.

Use Herbicides Judiciously

Herbicides can be the most important but should not be the only component of IWM for reduced tillage systems. If spring tillage is eliminated, a pre-seeding burn-off with a non-selective herbicide (e.g. Roundup® at 0.45 L/acre+350 ml surfactant/100 L water) may be necessary. This will control most annual weeds and suppress winter annuals. Effective quack grass control may also be obtained at this rate if environmental conditions are optimal and the weed is actively growing.

When fall tillage is eliminated, winter annuals such as stinkweed, shepherd's purse, flixweed, bluebur and narrow-leafed hawk's beard tend to increase. Fall is the most appropriate time to control these weeds. MCPA or 2,4-D at 6-8 oz. active per acre is a very cost-effective treatment. Hawk's beard is somewhat more tolerant and requires 10 oz. per acre. These weeds are more susceptible to herbicide applications in the fall than in the spring. A study conducted at Scott, SK showed that considerable stinkweed and flixweed biomass remained following spring herbicide application, whereas fall control virtually eliminated the weeds (Table 1).

Table 1. Effect of application timing on dry weight (gm/m²) of stinkweed and flixweed in winter wheat. Weeds were collected and weighed in late June.

Source: K. Kirkland, Agriculture and Agri-Food Canada, Scott, SK.

The risk of crop injury due to residues of these herbicides will also be considerably less if winter annuals are controlled in the fall rather than the spring.

Management of perennial weeds such as quack grass, Canada thistle, sow-thistle and toadflax is also best accomplished in the fall. In the spring, waiting for sufficient regrowth to maximize herbicide efficacy can delay seeding and result in reduced crop yields. Early competition from these weeds in the spring can also reduce crop yields.

One of the problems associated with fall perennial weed control, especially post-harvest, is the risk of reduced efficacy due to frost and cold temperatures. At least 2 weeks of frost-free weather is recommended after herbicide application. Effective fall control of perennial weeds has become much more feasible with the recent registration of pre-harvest Roundup® (1 L/acre). The treatment is registered for wheat, barley, canola, pea, dry beans lentils and flax. It is not recommended for crops grown for seed. The grain should contain 30% moisture or less (7 to 14 days before harvest). Comparisons of pre-harvest compared to post-harvest Roundup® application is presented for quack grass (Table 2). Pre-harvest application was generally more effective and more consistent.

Table 2. Quack grass control (%) with pre-harvest compared to post-harvest Roundup® (1 L/acre). Ratings were taken 1 year after treatment.

Source: M.N. Baig, Monsanto Canada Inc.

The use of pre-harvest Roundup® was the key factor in managing toadflax under zero tillage. After one application toadflax dry weights were reduced considerably by Roundup® at 0.5 L/acre (Table 3).

Table 3. Effect of pre-harvest Roundup® on toadflax dry weight in a barley/canola/barley rotation.

Harker, O'Donovan and Blackshaw (unpublished).

Further reductions occurred at 1 L/acre. After two applications, toadflax control was as effective at the low as at the high rate. Crop yields were also increased following application of the herbicide (data not shown).

In-crop weed control in the spring may or may not be required. Special attention should be paid to weed economic thresholds and herbicides should be used only when necessary. Every effort should be made to avoid the development of resistant weeds. Refer to the publication "Resistance of weeds to herbicides" prepared by the western Canadian provincial departments of agriculture. Rotate among the herbicide groups listed in the publication. For example, do not use wild oat herbicides of the same group more frequently than one year in three. Following this practice is especially important in reduced tillage systems, where herbicide use may increase in the short term. It is also important to realize that rotating herbicides is just one strategy in the battle against resistance. Effective, long term weed management is best achieved by paying attention to some of the agronomic principles discussed below.

Grow Competitive Crops in Appropriate Crop Rotations

Several studies suggest that including competitive crops and cultivars in a rotation, and combining appropriate crop rotations with herbicides can reduce the effects of weeds on crop yield and weed populations over time. Of the principle field crops grown in western Canada, barley is the most competitive followed by canola and wheat. Crops such as flax, peas and lentils are considerably less competitive with weeds. As indicated in Table 4, the effects of weeds on crop yield will be considerably less in barley than in most other crops.

Table 4. Effects of wild oats (100/m²) on % yield loss of various crops.

Adapted from Dew (1972)

The effectiveness of barley in reducing the build­up of wild oat populations over time is illustrated in Table 5.

Table 5. Wild oat population changes as influenced by cropping system.

Adapted from O'Donovan (1988)

The increase in wild oat populations over 4 years was considerably less in continuous barley and the canola/barley rotation than in continuous wheat (Table 5).

This study illustrates how problem weeds are often associated with a particular crop (e.g. wild oats in wheat). As well as being less competitive, wheat also takes longer to mature than barley (or Polish canola) thus giving wild oats ample opportunity to produce plentiful amounts of viable seed. Appropriate crop rotations can also minimize weed problems by maximizing control options. Rotating non­cereal with cereal crops can maximize herbicidal control of serious grass weeds such as wild oats and quackgrass. For example, in a 6 year field experiment in Idaho, the use of herbicides reduced wild oat populations in the soil by 41% in a winter wheat­spring barley­spring pea rotation compared to only 21% in continuous winter wheat (D. Thill, University of Idaho, Moscow, unpublished). In experiments conducted under reduced tillage in Saskatchewan, rotations of spring and winter wheat with mustard or flax, together with herbicide use, reduced quackgrass shoot populations from 800­1200/m² to 0­200/m² in 4 years (Loeppky and Derksen 1994). This study suggests that where appropriate crop rotations are combined with herbicides, quack grass may become less problematic over time in reduced tillage systems.

Plant Vigorous Seed and Promote Early Crop Emergence

A very important first step in an IWM system for reduced tillage is to plant vigorous high quality seed. This is crucial during the first few weeks of establishment when the crop and weeds are competing vigorously for moisture nutrients and light. Research conducted at the University of Manitoba (E. Stobbe) showed that crop seed size can make a big difference during early crop establishment. Large seed was considerably more vigorous than small seed and thus promoted early crop emergence.

Numerous studies have shown that crops that emerge early compete better with weeds, suffer less yield losses, and less weed seed is returned to the soil. In a study conducted at Vegreville, AB, wild oats that emerged a few days before the crop caused substantial yield losses, whereas those that emerged a few days after had little effect on crop yield (Table 6).

Table 6. Effect of relative time of emergence of wild oats (20 plants/m²) on yield loss of barley and wheat. DB = days before crop, DA = days after crop, ST = same time as crop.

Adapted from Cousens et al. (1987)

Green foxtail is considerably less competitive than wild oats. Even at very high densities its effect on crop yield can be strongly influenced by the time it emerges relative to the crop. Studies at Vegreville have shown that when barley or wheat emerged a few days ahead of green foxtail, crop yield losses were minimal, even at green foxtail densities of several thousand plants/m² (O'Donovan 1994a).

By striving to ensure that crops emerge as early as possible ahead of weeds, producers can minimize crop yield and financial losses due to weeds. Early crop emergence can be promoted by planting vigorous crop seed at relatively shallow depths when the seed bed is moist and firm (as is often the case in zero tillage systems). The crop can also be given an advantage by seeding as soon as possible after the last tillage operation in a conventional tillage system, or pre-seeding herbicide application in a reduced tillage system. Otherwise, weed seed present in the soil may begin germinating even before the crop is planted. Weeds that emerge late relative to strong competitive crops such as barley may not require in-crop control with herbicides. Omitting herbicide application in these situations could result in considerable monetary savings, and would delay or prevent selection of herbicide resistant weed biotypes.

Establish a Good, Vigorous Crop Stand

Crop density (stand) can strongly influence the competitive effects of weeds, and the yield and financial losses caused by weeds. In many cases, recommended crop seeding rates have been developed based on weed-free situations. Where weeds are present and where herbicide use may be limited, increasing the crop seeding rate can increase crop yield and reduce the amount of weed seed returned to the soil.

For some weeds in canola (e.g. Tartary buckwheat, stork's bill, cleavers and corn spurry), there are few if any post-emergence herbicides available. Research conducted at Vegreville suggests that relatively high canola seeding rates can reduce the competitive effects of Tartary buckwheat (O'Donovan 1994b). Where no Tartary buckwheat was present, there was little advantage to increasing the number of canola plants per unit area. However, where the weed was present, canola seed yield increased and Tartary buckwheat seed yield decreased with increasing canola density (Table 7).

Table 7. Effect of Tartary buckwheat (50 plants/m²) on canola and Tartary buckwheat seed yield at various canola densities.

Adapted from O'Donovan (1994b)

The results suggest that a canola density of 200 plants/m² provides the crop with a considerable advantage over weeds compared to lower canola densities (e.g. 50-100 plants/m²). Relationships between canola seeding rate and plant density can be difficult to determine especially under western Canadian dry land conditions. However, based on these results, in most cases a seeding rate of at least 8 kg/ha would be required for maximum weed suppression.

The above, and most other experiments designed to determine the influence of crop seeding rate on crop/weed interactions have been conducted in conventional tillage systems. There is little similar information available for reduced or zero tillage systems. An experiment was conducted at Vegreville AB from 1994 to 1996 to investigate the effects of different barley seeding rates on competition from wild oats in a zero tillage system. The results indicated that the extent of the yield loss due to wild oats was less at the higher barley seeding rates (Table 8). Yield loss due to wild oats was least in 1995 (the driest year) and highest in 1996 (the coolest year) (Table 8).

Table 8. Percentage barley yield loss due to wild oats at various barley seeding rates in a zero tillage system.

O'Donovan, Harker and Blackshaw (unpublished)

Each year, wild oat seed production decreased as barley seeding rate increased (Table 9).

Table 9. Effect of barley seeding rate on wild oat seed production in a zero tillage system.

O'Donovan, Harker and Blackshaw (unpublished)

Averaged over the three years, wild oat seed numbers dropped by about 130% when the seeding rate increased from 50 to 300 kg/ha. Increases in spring wild oat plant populations between 1994 and 1996 were greater at the lower barley seeding rates. For example, at a seeding rate of 50 kg/ha, the wild oat population increased from 80 plants/m² in 1994 to 235 in 1996, whereas at 200 kg/ha the population remained constant at 80 plants/m² from 1994 to 1996.

The study showed that, in most cases, yield losses were greatest at the lowest barley seeding rate (50 kg/ha). Averaged over all wild oat densities, yield loss from the wild oats lessened as barley seeding rate increased up to 200 kg/ha. There was no yield advantage to seeding at 300 kg/ha. In fact where no wild oats were present (weed-free checks) yield tended to decrease at the highest seeding rate, especially during the dry year (1995). The recommended seeding rate for barley in the thin black and black soil zones is 86-144 kg/ha. Our study suggests that for optimum wild oat management and crop yield in zero tillage systems, barley should be seeded at the high end of this range or higher, but should not exceed 200 kg/ha. Seeding at a relatively high rate in areas of the field where wild oats and other weeds occur at high infestations (e.g. low spots) may be more feasible than seeding at a high rate over the whole field.

It is unlikely that increasing the seeding rate alone would be sufficient to manage wild oats or other weed populations over the long term in a zero tillage system. A combination of limited herbicide use and relatively high seeding rates would be a more feasible approach. Herbicides would almost certainly be required during some years, particularly pre-seeding applications for weeds that emerge prior to seeding. No herbicides were used over the course of this study since the focus was on determining effects of seeding rate only. Wild oat populations were relatively heavy, and crop yield losses were unacceptable in 1994 and 1996, even at the higher barley seeding rates. Wild oat competition was strongest in 1996 when the spring was cool and wet, and weakest during the relatively dry and warm spring of 1995. This suggests that wild oats may not be as much of a problem in zero tillage systems under relatively dry soil conditions, and may not require control with herbicides, especially at high crop seeding rates. Seed production by wild oats is also likely to be much less under these conditions.

Will Narrower Crop Row Spacings Reduce Weed Competition?

The results of an experiment conducted at Scott, SK under conventional tillage show advantages to reducing barley row spacing (Kirkland, 1993). Weed biomass (wild oats, wild mustard and volunteer canola) increased and barley seed yield decreased as row spacing increased from 11 to 46 cm (Table 10). These results indicate that wider crop row spacings may promote weed competition and decrease crop yield in the absence of herbicides.

Table 10. Effect of barley row spacing on competition from weeds.*

*Data are averaged over different barley seeding rates and years.

**Numbers represent tillers rather than plants.

Adapted from Kirkland (1993).

Because of crop residue problems, decreasing row spacing to manage weeds may be less feasible in conservation tillage systems. On the contrary, the trend is to increase row spacing from the more common 22 cm to 33 cm. In this study (Kirkland, 1993), increasing the row spacing to 33 cm resulted in a 13% decrease in barley yield and a 34% increase in weed biomass. It is possible, however, that the increased weed competition at the wider row spacing resulted more from a reduction in barley plant populations per unit area (see shoot counts in Table 10) rather than from a direct effect of the wider spacing. Thus increasing the crop seeding rate to maintain high plant populations at the wider row spacings may enhance the competitiveness of the crop and alleviate the negative effects of the weeds on crop yield.

In other studies under conventional tillage, similar crop densities per unit area were maintained among row spacings, and there was little difference in yield of barley seeded in 9 or 18 cm rows(Barton et al. 1991) or canola seeded in 10 or 20 cm rows(O'Donovan 1994b). Slight increases in weed biomass occurred at the wider row spacings in both studies but this was not sufficient to have a major effect on crop yield. Similarly, in spring wheat seeded under no-till, wild oat plant counts and biomass did not differ between 20-, 30- and 40-cm spaced rows (Reinertsen et al. 1984).

Place Fertilizer to Favour the Crop over the Weeds

Both crops and weeds compete for nutrients (e.g. nitrogen, phosphorus) present in the soil. There have been a lot of studies conducted over the years to try and determine if the addition of extra nitrogen or other nutrients can reduce competition from weeds. The results have not always been as expected. In many cases added nitrogen actually benefited the weed over the crop. For example, in experiments conducted in California, wild oats were better able to utilize added nitrogen than wheat, and therefore gained a competitive advantage over the crop (Carlson and Hill, 1986). In a more recent study, researchers at North Dakota State University reached a similar conclusion with green foxtail (wild millet) (Peterson and Nalewaja, 1992). Doubling the nitrogen rate did not increase wheat growth, but increased green foxtail weight by 41%.

Does this mean that nitrogen will always benefit weeds over crops? Apparently not! Results from a study conducted in northeaster Alberta tell a very different story (O'Donovan, McAndrew and Thomas, unpublished). Evidently, how the nitrogen is applied can make all the difference in terms of whether the crop or weeds benefit.

The effects of tillage and nitrogen on green foxtail populations present above-ground in the spring, and in the seed-bank in the fall are presented in Table 11.

Table 11. Effect of banded nitrogen and tillage on green foxtail populations. Data were averaged over 1991 and 1992

O'Donovan, McAndrew and Thomas (unpublished)

Herbicides used to control green foxtail and broadleaved weeds were Hoe-grass II® (1989, 1990, 1991) and Stampede 360 plus MCPA® (1992). The results are very different from the U.S. studies referred to previously. Not only did the addition of nitrogen dramatically reduce green foxtail populations, but the populations tended to decrease as nitrogen rate increased. Furthermore, green foxtail populations were reduced more under zero than conventional tillage. Stinkweed populations also decreased as nitrogen rate increased.

Why the big difference between our results and those from the U.S.? In the U.S. studies the nitrogen was broadcast and soil-incorporated. Thus the weeds and crop had equal access to the nutrient. In our study, however, the nitrogen (urea) was banded 10 cm deep in 40 cm spacings, while phosphorus was applied with the seed. This provided an advantage to the crop which was able to access the nitrogen and phosphorus much more readily than the shallowly rooted green foxtail.

A related study (Blackshaw et al. 1996), showed that an integrated management approach that included banding nitrogen may allow producers to manage foxtail barley successfully in conservation tillage systems. Roundup® applied preharvest, postharvest or preseeding reduced foxtail barley biomass but did not eliminate the weed. Increasing wheat seeding rate reduced foxtail barley biomass and increased wheat yield by 16 to 32%. Finally, deep banding compared to surface broadcasting nitrogen reduced foxtail barley biomass and increased wheat yield up to 58% (Table 12).

Table 12. Effect of banded vs broadcast nitrogen on foxtail barley biomass and wheat yield.

Adapted from Blackshaw et al. (1996)

Other studies suggest that banding nitrogen may also favour crops over wild oats. In wheat growing under zero tillage, there were 27-57% less wild oat plants when nitrogen fertilizer was band-applied in the seed row compared to broadcast-applied prior to seeding the wheat (Reinertsen et al. 1984). Similarly, in spring barley, there were 28-60% less wild oat shoots when nitrogen fertilizer was band compared to broadcast-applied (Lish and Thill, University of Idaho, Moscow, unpublished).

These studies indicate that banded nitrogen can be an important component of an integrated weed management system. The strategy was especially effective for green foxtail management under zero tillage. Above-ground populations were reduced to 2 or 3 plants/m² at the higher nitrogen levels (Table 9). These low infestations would have virtually no effect on crop yield, and would not be expected to replenish the soil seed-bank to a great extent since a large proportion of the seed produced was in the surface residue. Dependence on herbicides for green foxtail control may therefore be reduced resulting in less selection pressure for herbicide resistance and greater savings for producers. These studies clearly show how integrating herbicide use with sound agronomic practices can be far more effective than herbicide use alone.

SUMMARY AND CONCLUSIONS

Farmers adopting reduced or zero tillage systems of crop management do not need to become over-reliant on chemical herbicides for weed control. To do so could lead to selection of weed biotypes that are resistant to herbicides, especially where herbicides of the same mode of action are used continuously. While it is true that reducing or eliminating tillage can result in short-term increases in some weeds (notably perennials and winter annuals), long term weed problems in reduced tillage systems can be alleviated considerably by integrating control practices with sound agronomic principles and practices.

An important first step in an IWM program is to prevent the movement of weeds into the field. This can be achieved through proper sanitation, and by controlling weed infestations (especially perennial weeds) along roadsides, fence rows and waste areas. Then it becomes a question of managing the weeds already in the field. The emphasis should be on managing weeds to an economically acceptable level rather than weed eradication, since it is becoming increasingly evident that continuous herbicide use will fail to eliminate weeds from a field.

A more rational approach would be to integrate herbicide use with practices that maximize the competitiveness of the crop over the weeds. Planting high quality, vigorous seed of competitive crops in appropriate rotations, and manipulating factors such as crop seeding rate, row spacing and fertility placement to favour the capture of resources by the crop can reduce the impact of weeds on crop yield and reduce the amount of weed seed entering the soil. Adopting agronomic practices that ensure early emergence of the crop relative to the weed can also confer a major advantage to the crop. For example, planting crops relatively shallowly into a moist and firm seedbed as soon as possible after a pre-seeding herbicide application will likely result in the crop emerging ahead of the weeds with minimal impact in terms of crop yield loss and weed seed production. Each of these practices when considered alone may not be sufficient to provide adequate weed management. However, combining these practices and integrating them with judicious herbicide use will result in long-term, more cost-effective and sustainable weed management systems for reduced tillage systems compared to where herbicide use is the dominant or sole weed control practice.

REFERENCES

Barton, D. L., Thill, D. C., and Bahman, S. 1992. Integrated wild oat (Avena fatua) management affects spring barley (Hordeum vulgare) yield and economics. Weed Technology 6: 129-135.

Blackshaw, R. E., Semach, G., Harker, K. N., and O'Donovan, J. T. 1996. Hordeum jubatum management in conservation cropping systems. in Proc. 2cnd. Int. Weed Contr. Conf., Copenhagen, Denmark, p. 993-996.

Carlson, H. L. and Hill J. E. 1986. Wild oat (Avena fatua) competition with spring wheat: effects of nitrogen fertilization. Weed Science 34:29-33.

Cousens, R., P. Brain, O'Donovan, J. T., and O'Sullivan, P. A. 1987. The use of biologically realistic equations to describe the effects of weed density and relative time of emergence on crop yield. Weed Science 35: 720-725.

Dew, D. A. 1972. An index of competition for estimating crop loss due to weeds. Canadian Journal of Plant Science 52: 921-927.

Kirkland, K. J. 1993. Weed management in spring barley (Hordeum vulgare) in the absence of herbicides. Journal of Sustainable Agriculture 3: 95-104.

Loeppky, H. A., and Derksen, D. A. 1994. Quackgrass suppression through crop rotation in conservation tillage systems. Canadian Journal of Plant Science. 74: 193-197.

O'Donovan, J. T. 1988. Wild oat (Avena fatua) infestations and economic returns as influenced by frequency of control. Weed Technology 2: 495-498.

O'Donovan, J. T. 1994a. Green foxtail (Setaria viridis) and pale smartweed (Polygonum lapathifolium) interference in field crops. Weed Technology 8: 311-316.

O'Donovan, J. T. 1994b. Canola (Brassica rapa) plant density influences Tartary buckwheat (Fagopyrum tataricum) interference, biomass and seed yield. Weed Science 42: 385-389.

Peterson, D. A., and Nalewaja J. D. 1992. Environment influences green foxtail competition with wheat. Weed Technology 6: 607-610.

Reinertsen, M. R., Cochran, V. L., and Morrow, L. A. 1984. Response of spring wheat to N fertilizer placement, row spacing, and wild oat herbicides in a no-till system. Agronomy Journal 76: 753-756.

JOHN O'DONOVAN - BIOGRAPHICAL DATA

Dr. John O'Donovan received B.Sc., M.Sc. and Ph.D. degrees in plant science in Ireland. In 1977 he moved to Canada and worked as a postdoctoral fellow at the University of Alberta.

He returned to Ireland in the fall of 1978 to lecture in plant physiology at University College, Cork. In 1979 he moved back to Canada as a research associate at Agriculture Canada's research station in Lacombe, Alberta where he conducted research on management of zero tillage cropping systems.

He joined the Alberta Environmental Centre (now Alberta Research Council), Vegreville, Alberta in 1983. There he has conducted considerable research on weed ecology, the economics of weed control, weed resistance to herbicides, integrated weed management in conservation tillage systems, and the effects of tillage and other agronomic practices on weed seed population dynamics.