Lentil is a very poor competitor to weeds. Good weed control in lentil requires a long-term strategy involving the entire crop rotation. Perennial weeds, such as Canada thistle and sow thistle, should be controlled in the years prior to lentil production. Volunteer wheat and barley are difficult to clean from small-seeded lentil and should be controlled in the field. Weeds that germinate late in the season, such as Russian thistle, kochia and wild tomato, cause severe competition to the crop. They interfere with harvesting, increase dockage and increase staining and moisture levels in the harvested seed.
A late fall application of a phenoxy herbicide such as 2, 4-D or MCPA can be used at rates of 280 g ai/ha or less to control winter annual broadleaf weeds in fields planned for lentil production. Spring applications or applications that include dicamba should be avoided to prevent possible crop injury. A pre-emergence burnoff treatment of glyphosate can be used in lentil to control weeds before the crop emerges.
The introduction of Clearfield® technology has given lentil growers additional in-crop herbicide choice. Research on Clearfield® Lentils concluded the optimum timing for herbicides was between the five to six node stage and the 10 node stage. Weeds emerging after the 10 node stage did not reduce yield but may lead to harvesting issues.
See Saskatchewan Agriculture’s Guide to Crop Protection to check herbicides that are registered for grassy and broadleaf weed control in lentil. Make sure to follow label directions and apply the herbicide at the correct time of plant development. Some herbicides can move in the soil after heavy rainfall, so if the use of these products is anticipated, lentil must be planted at least 5 cm (2 in.) deep to prevent injury to seedlings. For example, do not use SENCOR in soils with less than four per cent organic matter.
Edge and trifluralin (RIVAL, TREFLAN) are registered only for fall application. A spring application, especially in lighter soils, can cause seedling injury and may lead to increased incidence of seedling diseases such as rhizoctonia wire stem.
Glyphosate is registered for pre-harvest weed control in lentil. This application is used to control perennial weeds, such as Canada thistle, sow thistle and quack grass in-crop before harvest begins. Do not use seed from crops treated with a preharvest application of glyphosate, as abnormal germination and seedling development will likely occur. Always read and follow label recommendations when using crop protection products.
Herbicide-resistant weeds: herbicide choice should take into account herbicide rotation to slow the development of resistant weeds. Resistant weeds can have a huge impact in lentil crops simply because it is a less competitive crop and there are limited herbicide options. A few examples of herbicide resistant weeds that are particularly troublesome for lentil growers include Group 2 resistant kochia, wild mustard and cleavers, as well as Group 1 and Group 2 resistant wild oat. Rotating herbicide groups away from Group 1 and 2 products, especially in rotational years where pea is not grown, can help prevent or manage resistant weeds. BASF recommends that Group 2 products be applied no more than twice in a four-year period, and never twice in the same year. Research indicates that alternating between two modes of action for wild oat control will double the number of years for resistance build-up, and alternating with a third mode of action will increase the time of resistance build-up to four times as long as for a single mode of action for wild oat control.
Minimizing crop injury to herbicides: during periods of crop stress (heat, drought, frost or after land rolling) the ability of the lentil crop to tolerate herbicide application may be reduced. Crop injury can be reduced by waiting approximately four days after the crop stress occurs before applying herbicide, by maintaining water volumes at label recommendations, and by applying the product during the evening.
Lentil can be damaged easily by some herbicides registered for other crops. Sprayer tanks should be thoroughly cleaned before applying any crop protection product to lentil and care taken not to drift herbicides from other fields onto lentil fields.
Alternatives to chemical weed control: non-herbicide options may be considered as well and include tillage, harrowing and higher seeding rates. Tillage may be a tool to reduce kochia populations. Burial of kochia seed to at least one cm or deeper can result in reduced germination or death of the germinated seed prior to emergence.
Alternatives to chemical weed control Research completed at Agriculture and Agri-Food Canada, Scott showed that post-emergent harrowing with a tine harrow can be used to control weed seedlings when the crop is very short (less than 10 cm), provided that the foliage is dry and the operation is done on a warm, sunny day. An increased lentil seeding rate should be used to offset the plant losses during harrowing.
Higher seeding rates are a great option for improving weed competitiveness. Research at the University of Saskatchewan suggests higher seeding rates reduced weed populations and increased lentil yields.