Weed Management
Successful weed control in lentils requires a long-term strategy involving the entire crop rotation – not just the season in which lentils are grown.
Perennial weeds, such as Canada thistle and sow thistle, should be controlled in the years before lentil production. Volunteer wheat and barley should be controlled in-crop as the seeds are difficult to clean from small-seeded lentil at harvest. Late-season weeds, such as Russian thistle, kochia, and wild tomato, can outcompete lentils. These late-emerging weeds can also interfere with harvest, increase dockage, and lead to increased staining and moisture levels in the harvested seed.
Post-harvest applications of herbicides, such as those with lentils as a recropping option the following spring, can be used to control winter annual and perennial weeds, thereby reducing weed pressure the following year. Understand that certain herbicides have soil and moisture label requirements to minimize the risk of injury to the following lentil crops.
Pre-seed or pre-emergence herbicides are essential for controlling weeds in lentil before the crop emerges. Soil-applied products may provide weed control during early crop growth but usually require moisture for activation. For in-crop applications of herbicides, the critical weed-free period for lentils is between two and five nodes of development.
Research on Clearfield® lentils found that the optimum timing for herbicide application was between the five to six-node stage and the 10-node stage. Weeds emerging after the 10-node stage were less likely to reduce yield but may cause harvesting issues.
Ensure that you follow the label directions and apply the herbicide at the correct stage of plant development. Some herbicides can move in the soil after heavy rainfall. Therefore, if these products are anticipated to be used, lentils should be planted at least 5 cm (2 in.) deep to prevent injury to seedlings.
Herbicide-Resistant Weeds
Herbicide rotation is imperative in slowing the development of resistant weeds. Resistant weeds can have a significant impact on lentil crops because lentils are a less competitive crop, and there are limited herbicide options.
Some 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 2-resistant wild oat. Rotating herbicide groups away from Group 1 and 2 products, especially in years where lentils are not grown, may help manage resistant weeds.
Research indicates that alternating between two modes of action for wild oat control doubles the number of years for resistance build-up, and alternating with a third mode of action increases 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 lentil crop may be less tolerant to herbicide application. 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 using the product during the evening when the sun and heat are less intense.
Lentils can be easily damaged by certain herbicides registered for use on other crops. Sprayer tanks should be thoroughly cleaned before applying any crop protection product to lentils. Care should also be taken to prevent herbicide drift from different fields from contaminating lentil fields.
Alternatives to Chemical Weed Control
Non-herbicide options include tillage, harrowing, and higher seeding rates. Tillage may reduce kochia populations. Burial of kochia seed to at least one cm or deeper can reduce germination or kill the germinated seed before emergence.
Research at Agriculture and Agri-Food Canada, Scott demonstrated that post-emergent harrowing with a tine harrow can effectively control weed seedlings when the crop is less than 10 cm tall, provided the foliage is dry. The operation is conducted on a warm, sunny day. Increased seeding rates should be used to offset plant losses from harrowing.
Higher seeding rates can also improve weed competitiveness. Research by Dr. Steve Shirtliffe at the University of Saskatchewan suggests that higher seeding rates, up to 240 plants per square meter, reduce weed populations and increase lentil yields.
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Disease Management
Disease can severely impact lentil yield if conditions are conducive.
These soil-borne fungal diseases can infect lentil seedlings and are caused by pathogenic species of Rhizoctonia, Pythium, Fusarium, and/or Botrytis, which are present in all Saskatchewan agricultural soils.
Lesions may develop on the base of the stem, causing discolouration and constriction. Diseased plants turn yellow and die. Typically, only scattered plants are affected, so these diseases rarely result in economic losses. Seedling stress or damage due to environmental or herbicide injury can increase incidences of seedling blight, especially wire stem.
Aphanomyces species and Aphanomyces euteiches can also cause root rots and have been identified across most of Saskatchewan. There are no seed treatments that control A. euteiches, and it can survive in the soil for many years. It is the most difficult to maintain among the root rot pathogens, as it can infect the plant at any stage and is most aggressive under wet conditions.
Ascochyta blight is a severe foliar disease of lentils in Western Canada. It can be seed-borne or residue-borne, resulting in infection of leaves, stems, pods, and seed. Lesions appear as tan or grey spots with dark margins and have tiny black fruiting bodies (pycnidia) in the centre. Cool, rainy weather is conducive to the spread of disease. It is most damaging to maturing pods and seeds if prolonged wet weather occurs during July and August. Severely infected seed lots may not be marketable or will be downgraded due to discoloration.
Ascochyta blight inoculum overwinters on lentil residue, so producers should implement crop rotations and avoid planting lentils on lentil stubble. Most modern lentil varieties have some level of resistance to Ascochyta blight.
Anthracnose is a foliar and stem disease found in most lentil-producing areas in Western Canada caused by the pathogen Colletotrichum lentis. There are two races of Anthracnose. Most lentil varieties now have resistance to Race 1 (Ct1). Race 0 is the more common and virulent race that lentil growers encounter in Saskatchewan, and efforts are underway to identify and introduce resistance to this race in future varieties.
Infection results in sunken, grey to cream coloured lesions on leaves and stems. The lower leaflets turn yellow and brown, then drop off. In early-season infections, lower stems become cankered, and the plants die prematurely, often before they produce seed.
Lesions and dead plant tissue may contain tiny black resting bodies (microsclerotia) similar in appearance to Ascochyta blight pycnidia, but smaller, more numerous, and irregular in shape. Diseased patches in the crop can expand rapidly and appear as yellowed or grey patches within an otherwise green field. The disease is favoured by warm, moist weather.
Anthracnose can be spread by wind-borne residue and dust during harvest and can persist in fields for several years. While there is no research showing that the disease is frequently transferred from the seed to the lentil seedling, producers should still use seed with low infection levels, as there are no seed treatment fungicides that control seed-borne Anthracnose. Extend crop rotations to avoid planting lentils in the same field for at least four years.
There are a few foliar fungicides registered for Ascochyta blight and Anthracnose in lentils. Generally, a fungicide should be applied before the plant canopy closes completely, which usually coincides with the timing of the first flower. However, follow label directions for the correct time of application. The goal is to protect healthy plant material if disease inoculum is present and weather conditions favour the disease. More than one application may be required if disease-favourable conditions persist.
Research has confirmed the presence of considerable levels of Group 11 (strobilurin)- insensitive and mixed sensitive/insensitive populations of anthracnose in Saskatchewan. Group 11 fungicides should not be applied on lentils for anthracnose as a standalone and should be tank mixed with other modes of action with activity on anthracnose.
Botrytis gray mould causes stem and pod rot during the flowering and seed-filling stages, resulting in significant economic losses. Soil-borne inoculum is present in all fields, but this disease is typically only a problem in heavy vegetative stands that have lodged due to wet, cool weather. Leaves wilt and drop off, pods fail to fill, and infected areas turn grey to brown. Clouds of gray spores are dispersed into the air as infected areas are harvested. There are foliar fungicides registered for the control of foliar blight caused by Botrytis gray mould.
Sclerotinia white mould may occur in maturing lentil crops under high moisture conditions that promote vegetative growth and lodging and can cause economic losses. Lentil crops are at an increased risk of Sclerotinia infection when grown in rotation with other susceptible crops, such as canola, peas, or sunflowers. There are foliar fungicides registered for controlling Sclerotinia stem rot on lentils. As with Botrytis, achieving the necessary coverage of infected stems often makes treatment difficult.
Research at the University of Saskatchewan revealed that all lentil tissues (i.e. leaves, stems, pods, and flowers) can be infected by spores of Sclerotinia. Testing Sclerotinia-infected plants at various ages showed that plants older than six weeks were significantly more susceptible. This decrease in resistance, combined with wet weather late in the growing season and a heavy plant canopy, may explain why Sclerotinia is more of a problem in maturing lentil crops.
Stemphylium blight has been identified in several lentil fields in Saskatchewan. The foliar disease exhibits similar leaflet drop symptoms to Anthracnose and produces lesions on leaves identical to those of Ascochyta blight. It has not yet been confirmed as causing significant yield losses because the disease typically appears later in the growing season. The fungus thrives under warm (25°C to 30°C) and wet conditions, but spores can germinate at temperatures as low as 5°C, which may indicate that infection can occur in cool, damp weather as well. Some lentil varieties appear to be more susceptible to Stemphylium blight than others. Infection can cause seed staining, reduced seed size, and decreased germination rates.
Management of lentil diseases begins with crop rotation. Some pathogens can survive in the absence of a host crop (e.g., Botrytis and Stemphylium) or will affect other host crops in the rotation (e.g., Sclerotinia). Lentil varieties with excessive vegetative growth tend to experience more frequent problems with late-season botrytis and sclerotinia in years or locations with higher moisture levels.
Viral diseases do not typically have an economic impact on Saskatchewan lentil crops. Lentil seed-borne mosaic virus is a potential threat to lentils, as it may be introduced with infected lentil seed and spread by aphids.
Heat canker occurs when young lentil seedlings are exposed to hot soil surface temperatures. Effected seedlings wilt quickly on extremely hot spring days. The pinched stem usually remains white, and often new shoots emerge from the scale nodes.
Managing Fungicide Resistance
As with herbicides and weed resistance, managing fungicide use to slow the development of fungicide resistance is essential. Use a foliar fungicide only when disease risk and potential loss are considered to be economically damaging (i.e., greater than the cost of control).
The development of resistance to Group 11 (strobilurin) fungicides in several fungal pathogens in other crops has been reported in Europe and Saskatchewan, and is of great concern. No more than two applications per year of any strobilurin fungicide should be made to the same field.
The following strategy should be considered and implemented to delay fungicide resistance/insensitivity:
- Rotate the use of fungicides from different groups that control the same pathogens.
- Tank-mix fungicides that have a high risk of developing insensitivity with fungicides from a different group, where both are effective on the target pathogen.
- Do not apply more than the maximum number of applications listed on the label.
- Avoid consecutive sprays of the same fungicide, or other fungicides in the same group, in a season.
Fungicide application should be based on an integrated pest management (IPM) program that includes scouting and accurate record keeping.
Monitor treated fungal populations for signs of fungicide insensitivity. If the disease continues to progress after fungicide treatment, switch to a fungicide with a different target site of action.
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Insect Management
Grasshoppers
Grasshoppers eat flower buds, open flowers, and developing pods. Feeding on early-developing pods can result in yield loss and delay maturity as the plant attempts to compensate for the lost biomass. Damage from grasshopper feeding is variable, but it is often not of significant concern in lentils. Slight damage to the pods may result in shattering, seed loss, increased risk of disease, and seed staining. At harvest, grasshopper parts, specifically heads, can be a problem to clean out.
The economic control threshold is two grasshoppers per square metre in lentils. If control is necessary, the optimal timing is mid-June, when nymphs are at the third instar. Grasshoppers prefer more open areas, so populations tend to be higher in field margins. A thick lentil crop will deter the insects from moving further into the field. If grasshopper populations only exceed the economic threshold in the field margins, an edge treatment with an appropriate insecticide can save time and money while providing adequate control. As of August 1, 2023, the Canadian Grain Commission has implemented a change that no longer considers grasshoppers, other insects, and insect parts as a downgrading factor in lentils; instead, they are included in dockage.
Cutworms
Cutworms can damage newly emerged lentil seedlings, potentially requiring insecticide application. Below-ground feeding cutworms (pale western and red-backed cutworms) cut plants off at or near the soil surface. Foliar feeding cutworms (dingy and army cutworms) feed above-ground, consuming the plant foliage.
The economic threshold for cutworms in lentil is 2 to 3 per square metre in the top 7.5 cm (3 in) of soil. Lentil crops can often recover from cutworm damage, provided favourable growing conditions are present, but maturity may be delayed. Scouting for cutworms is usually more successful in the evening, when they emerge to feed.
Wireworms
Wireworms are the immature stage or larvae of click beetles. Wireworms thrive in moist soils and shred below-ground plant tissue. Initially, symptoms may appear as wilting in the central leaves of the main stem but can eventually cause plant death. Damage may not be noticed early enough in the season to allow for reseeding. There is no established economic threshold for wireworm in lentils, and no in-crop insecticides are available. Controlling wireworm requires the use of insecticidal seed treatment.
Lygus Bug
Lygus bug can be a pest for lentils in the United States, but has not been a significant problem in lentils in Saskatchewan to date. The economic threshold for Lygus bugs in lentils is seven to 10 adults per 25 sweeps during blooming and podding. To monitor with a sweep net, make 25° to 180° sweeps (with a 38 cm or 15 in net) in at least five randomly selected places in the field.
Pea Aphid
Pea aphids can affect lentil yield and quality when present in sufficient numbers. Damage caused by aphids can be challenging to quantify because they rob plants of resources by piercing and sucking rather than chewing and defoliating. Adults can develop wings but are often wingless. Populations can increase rapidly due to their ability to give birth to live young without mating, and because they can easily migrate into areas on air currents. Research conducted at the University of Saskatchewan has identified an economic threshold for lentils of 29-43 aphids per sweep, which provides a seven-day lead time before reaching the economic injury level of 64-92 aphids per sweep. This research has also provided insight into the significant financial losses that can be attributed to aphids, amounting to a loss of 0.0014 bushels per acre per aphid per day. Reports of decreased efficacy of Group 3 (pyrethroid) insecticides have been noted in Saskatchewan, and monitoring has shown that some populations have developed more tolerance to this mode of action.