Opportunities for cultural weed control
Weed competition
Herbicide choice

Opportunities for cultural weed control
Field beans are a useful cleaning crop in a rotation since their late autumn or spring establishment allows cultural control of many grass weeds that normally germinate before the crop is sown. Cultural weed control has increased in importance with the advent of herbicide resistant strains of weeds.

Most grass weeds e.g. blackgrass germinate almost solely in the autumn. Blackgrass germinates in September and October whilst ryegrass germinates rapidly after seed shed at harvest, providing environmental conditions are conducive. Both these weeds show herbicide resistance, blackgrass resistance to a range of herbicides is well established whilst Italian ryegrass and wild oat populations are increasing rapidly. Winter bean establishment occurs after the bulk of grassweed germination. Stale seedbeds therefore provide a non selective method of controlling resistant weeds as well as a method of controlling other early germinating species e.g. barren brome. Similarly, ploughing, an important establishment technique for winter beans is also an effective way to reduce grassweed populations.

Weed competition
Competitive effects of weeds can seriously damage yield of beans as shown in Figure 1. Grass weeds and tall growing species are the most competitive whilst grass weeds and cereal volunteers can also harbour cereal diseases such as take all. Couch is especially susceptible to take all and may aid disease carry over from one cereal crop to the next, diminishing the benefits of the break crop.
Little work has been conducted on the competitive effects of broad leaved weeds in field beans. The ‘Weed Research Organisation’ conducted research into the competitive effects of various species in cereals, which may relate in part to beans (Figure 2). Species, which spread through the canopy, may also cause harvesting difficulties.

Figure 1 Competition between barley volunteers and winter beans. Cv. Bourdon. c. Barbalola et.al., 1991. Aspects Applied Biology (27) Production and protection of legumes p. 179-82 Click here for a larger image

Figure 2 Competitiveness of certain weed species in winter wheat c. Cousens & Courtney, 1995. HGCA Project Report No. 107 Click here for a larger image

Herbicide choice
A pre emergence application of simazine at 1.7 to 2.3 kg ha^-1 (depending on soil type) provides a cheap base control and will partially control blackgrasBatallion (terbutryn + terbuthylazine) and simazine applications will no longer be permitted after December 31st 2007 but pre -emergence applications of simazine at 1.7 to 2.3 kg ha^-1 (depending on soil type) provide cheap base control and will partially control blackgrass (Figure 3) and meadow grasses with some broad leaved weeds (Table 1). Propyzamide (Kerb) at up to 840 g ha-1 provides additional grassweed control including wild oats and sterile brome plus some broad leaved weeds. Carbetamide (Crawler) is applied pre- or early post-emergence of weeds from November to the end of February. It controls annual meadow-grass, black-grass and barren brome (pre- and post-) and gives some control of volunteer cereals and wild oats post-emergence. It only controls a few broad-leaved weeds, including speedwells (pre- and post-) and cleavers and knotgrass (pre). It can be used on all soil types except soils with more than 10% organic matter.

Figure 3 Control of resistant blackgrass in winter beans. c. Cook et.al., 1991. Aspect Applied Biology (27) Production and protection of legumes p. 161-6. Click here for a larger image

Cleavers can be a difficult weed to control in many break crops. Clomazone (‘Centium 360 CS’) and now an off-label approval for prosulfocarb (Defy) both provide control of cleavers plus activity on a range of broad leaved weeds.(Figure 4). Defy also offers activity on grass weeds such as loose silky bent and annual meadow grass. Both are residual herbicide for pre emergence use only and can be used on most soil types but clomazone cannot be used on those containing more than 10% organic matter and very light soils and sands. They require good seedbed conditions. Other herbicide possibilities are listed below in Table 1.

Several pendimethalin products have off-label approval for use at 1320gai/ha in winter beans.

'Blois' is a pre emergence herbicide containing 128g/l linuron and 256g/l trifluralin. It will control annual meadow grass and a wide range of broad leaved weeds includng polygonums, brassica's such as charlock and orache; also speedwels, fools parsley, fumitory, groundsel, poppy and shepherds purse.

Nirvana (imazamox + pendimethalin) is a new product available for pre-emergence use in winter beans from this autumn and provides wide spectrum residual broad-leaved weed control. It shows excellent activity against polygonums, black-bindweed, redshank and knotgrass. Charlock is also effectively controlled as is chickweed. Nirvana also gives improved control of early emerging volunteer oilseed rape when compared to pendimethalin alone and at higher rates reduces cleaver numbers effectively.

Figure 4 Comparative activity of various herbicides on cleavers in winter beans c. FMC, 2001 Click here for a larger image

Table 1. Activity of various herbicides on broad leaved and grass weeds in field beans

*Expiry is on 30 September 2005. Check the approval after this date.

S – susceptible
MS – moderately susceptible
MR – moderately resistant
R – resistant

Contact graminicides also provide good control of grass weeds. ‘Laser’, ‘Pilot’, ‘Fusilade’ and ‘Falcon’ can all be used on beans and provide varying control of most species (Table 2). ‘Aramo’, containing tepraloxydim, is a new active ingredient, which has limited scope for dose rate reduction but provides good control of difficult species such as couch and resistant blackgrass (including target site resistance)(Figure 5). ‘Aramo’ should not be used alone for resistant blackgrass as resistance to this group of herbicides develops quickly (within 2 to 3 years of constant lone use) but should be used in sequence with other herbicides, including those mentioned above.

Table 2. Effective dose rates of various contact graminicides for use in broad-leaved crops.
These rates present a guide to the differential susceptibility of specific graminaceous species to each active ingredient and should be used in conjunction with manufacturers recommendations.

Figure 5. Control of resistant blackgrass with various contact graminicides [redrawn from data produced by BASF Ltd, 2000] Click here for a larger image

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