No known control measures exist for Aphanomyces and root rot complex in pulses. The best management practice most effective at reducing root rot infections is prevention, not growing peas or lentils in that field, and knowing your root rot risk. Other best management practices include knowing your field’s history, testing your soil, managing crop rotation by limiting the frequency of susceptible crops, utilizing good soil management practices (good soil fertility and reduced compaction), maintaining good field records and knowing the low areas and waterways; how water flows and pools in your field, as those are high-risk areas for root rot complex infections.
Questions to consider when planning your pea and lentil rotation include: How well did the crop do last time? What were moisture levels then and in subsequent years? Were there dead/dying patches in the field? Did you identify where these were? Has an Aphanomyces infection been confirmed in that field? Have you done soil or tissue tests to confirm the culprit is root rot complex?
Table 1. Management Decisions to Consider Before Planting When Fields are Low to Intermediate Risk of Developing Root Rots
|
Agronomic Factors |
Recommendations for Lowering Risks |
|---|---|
|
Seed Quality |
Choose a seed that is good quality and disease-free. Consider using seed treatments to manage disease on seed and protect against early infection by Aphanomyces. |
|
Varities |
Choose varieties with tannins in seedcoat and varieties with improved Fusarium resistance where possible. |
|
Nutrient Levels |
Consider a balanced fertility plan to ensure nutrients are available and easily accessible. |
|
Soil Management |
Address any compaction in the field and do not move heavy equipment across the field if there is higher moisture (including rolling under wet conditions) |
|
Pest Pressure |
Proactively managing weeds, insects and other pests that cause plant stress and exacerbate root rot infections. |
Crop Rotation
If there is a history of root rot, individual fields should be tested for Aphanomyces euteiches and other root rot pathogens.
Fields confirmed to have Aphanomyces should wait a minimum of six years and up to ten years, depending upon the risk of future infections and the level of oospores per gram of soil.
Though inoculum levels will be reduced after a few years away from peas or lentils, fields with moderate inoculum levels will require several years of non-host crops to reduce the inoculum to a level that will not impact yield. Yield is affected at 100 oospores per gram of soil.
The best pulse crop options for these fields are partially resistant varieties of faba beans, chickpeas, or non-host crops like soybeans, fenugreek, or lupin.
Aphanomyces can infect various crops in the rotation, including peas, lentils, alfalfa, dry beans, some varieties of red clover, and possibly some of the native weedy legume species. The susceptibility of dry beans and alfalfa to Aphanomyces root rot infection varies among the different varieties and classes. Cicer milkvetch is also very susceptible to infection by Aphanomyces.
Cereals also contribute to issues since they are susceptible to Fusarium spp. Combined infections of Fusarium and Aphanomyces can cause crops to suffer more than from Aphanomyces root rot, making crop rotation the critical tool for pulse growers when managing root rot complex.
Since the effectiveness of crop rotation directly depends on its length, the longer the lapse between susceptible host crops, the more inoculum reduction will occur in the soil. However, complete eradication of Aphanomyces root rot through long-term rotations may not be achievable.
How long do we need between pulse crops to manage Aphanomyces? Consider the following:
- What are the results of soil tests? Is Aphanomyces present? Avoid avoiding pea and lentil for six or more years if there is the presence of 100 spores per gram of soil or more.
- What was the planting frequency of the susceptible pulse crops, pea or lentil, in each field?
- What was the moisture level the last time a pea or lentil crop was planted? Dry, average, or wet conditions? Do planting dates matter? Keep good records of your fields and exact planting dates. Determine if a later planting date changes the susceptibility.
- Rotation intervals may vary, as short as four years, up to six or more years; yields may improve, but the pathogen may still be there.
- Consider incorporating a resistant pulse crop into the rotation. Faba beans and sainfoin exhibit good partial, quantitative resistance to Aphanomyces, and chickpeas are moderately resistant. Soybeans and fenugreek are both non-host crops.
Key Takeaways
- Increasing the time between pea or lentil crops on a given field will decrease the risk of developing a yield-robbing Aphanomyces or root rot complex infection.
- Practicing four- or more-year crop rotations of peas and lentils and utilizing risk assessment tools on a field-by-field basis can help mitigate the development of a severe Aphanomyces infection.
- This includes referencing previous cropping history and weather data from the last time peas or lentils were grown on a particular field to determine if the risk of Aphanomyces is low, moderate, or high.
- Check your field’s Aphanomyces risk using the Aphanomyces Risk Evaluation Application (AREA). The Root Rot Task Force app and Aphanomyces risk checklist are below.
Decision-Making Tree
Checklist to identify risk for Aphanomyces root rot infection and severity in specific fields for the upcoming year.
|
Considerations |
Higher Risk |
Lower Risk |
|---|---|---|
|
STEP 1: Major Influencing Factors |
||
|
Soil test for Aphanomyces |
Positive test result |
Negative test result |
|
Environment the last time or times peas/lentils grown |
Above average moisture (wet) |
Below average moisture (dry) |
|
Symptoms last time peas/ lentils grown |
Patchy to the whole field affected; late season lodging |
No symptoms; healthy field |
|
Action |
If one or more checked above = HIGH RISK. Do not seed peas or lentils into the field. Choose a different field, wait until the soil test is negative, or field out of peas/lentils for at least 8–10 years. |
Consider Intermediate Risk Factors. |
|
STEP 2: Intermediate Influencing Factors |
||
|
Field Conditions |
Heavy texture with poor drainage Field has compaction issues |
Lighter texture with good drainage No compaction issues |
|
# of times peas/lentils grown in the past 20 years |
> 5x or unknown |
< 5x |
|
Last time in peas or lentils |
≤ 4 years |
≥ 8-10 years |
|
Action |
If most checks are in this column, consider the field Intermediate Risk. Consider Minor Influencing Factors before planting peas or lentils in this field. |
If most checks are in this column, consider the field Lower Risk. Minor Influencing Factors can help reduce potential infections and severity. |
|
STEP 3: Minor Influencing Factors |
||
|
Rotation – crops included |
Limited diversity (canola or wheat) |
More diverse and include oat and mustard |
|
Rotation – managing Fusarium |
High residue levels infected with Fusarium from the previous crop (cereals) |
Low or no Fusarium-infected stubble from the previous crop |
|
Weed control – the presence or absence of susceptible weeds (alternative hosts) |
Weeds have been out of control on the field with high levels of host weeds |
Field is relatively weed-free going into pea/lentils |
|
Action |
Intermediate Risk – Consider Management Decisions (Table 2) before seeding to address minor influencing factors or plan to seed peas and lentils in a different field.
|
Low Risk – The field has a low risk for Aphanomyces infection but no guarantee of no risk. Consider Management Decisions in Table 2. |
Field Choice
Your field choice is the most important thing to consider when planting your pulse crop.
Choose lighter-textured, sandier soils with good drainage that are not compacted, have good soil tilth, and have a low frequency of peas or lentils in recent cropping history. Address any compaction in the field, and do not move heavy equipment across the field if there is higher moisture (including rolling under wet conditions).
Choose a field that did not have signs of root rot the last time peas or lentils were grown on it.
Try to avoid fields where herbicide residues might be a problem. These residues can add stress to the plants, making it easy for root rot to develop.
Consider your soil pH. Peas and lentils are sensitive to low-pH soil, and Aphanomyces prefers acidic soils, pH 4.5–6.5. Avoid highly acidic fields or consider management practices to adjust the pH before growing pulses.
Fields with high residue levels infected with Fusarium head blight may be at greater risk of root rot developing. When Aphanomyces is combined with Fusarium, the severity of root rot infections is much worse.
Utilize sound rotation strategies—no peas/lentils for at least three years (four-year rotation) and six to ten years if Aphanomyces and other root rot pathogens are positively identified.
Keep these four practices top-of-mind when planning your pea and lentil crops to prevent root rot.
- Record the state of your crops from year to year. Pay attention to signs of disease, such as stunted growth or yellowing in low-lying or damp areas. Know what year you last planted peas or lentils and what the environment was like then. Above-average moisture tends to increase outbreaks. Check and test your roots and look for signs of root rot in your fields.
- Reduce: If your soil tests return positive, do not plant peas or lentils in that field. Depending on the level of pathogens, it can take up to ten years to reduce spore counts. During that time, keep the field clean of weeds, as several common weeds can be vectors for the disease. Aphanomyces begins to impact the health of plants at a level of 100 oospores per gram of soil.
- Revisit: If the field has signs of root rot, test the soil using a soil bait or DNA test. Monitoring and testing areas of the field where water flows and accumulates can help catch a root rot complex infection before peas and lentils can no longer be grown there.
- Rotation: Diverse rotations improve soil health, which provides resiliency and protection against soil infestations and disease.
Fertility Management
Proper nutrient management can help promote the development of healthy plants and root systems that can better withstand disease pressure and adverse environmental conditions.
Managing pulses requires a nutrient plan to address soil deficiencies and supply the necessary macronutrients for healthy and vigorous growth.
Apply nutrients as needed. Know the safe rates of nutrients that can be safely applied. See the Prairie Nutrient Removal calculator for more information on pulse nutrient requirements.
Nitrogen
Peas and lentils fix their nitrogen, but until the nodules form, the crop relies on soil nitrogen.
Starter nitrogen is not usually recommended with peas and lentils, as extra nitrogen can delay nodulation and maturity.
A proven rhizobia inoculant compatible with the seed treatment should be used at the recommended rate.
Under conditions where soils are low in nitrogen, less than 15 pounds per acre (lb/ac) in the top 12 inches, 10–20 lb of nitrogen may be beneficial at the start of the season. As a rule, no additional nitrogen is needed if soil tests indicate more than 20 lb/ac of nitrate nitrogen. If it is below 15 lb/ac, consider starter nitrogen.
Phosphorous
Good phosphorus management is essential for growth, nodulation, and yields. Phosphorus levels are crucial for early plant growth, especially under cool conditions associated with early seeding.
The maximum safe rates of seed-placed phosphorus for lentils is 20–25 lb/ac and 15-20 lb/ac for peas, based on the narrow opener,15% seedbed utilization, and good moisture conditions. If higher phosphorus rates are required, banding fertilizer away from the seed is the best strategy.
Research Results
Initial results from a project led by Jessica Enns with Western Applied Research Corporation (WARC) have demonstrated that well-balanced fertility can help to protect yield when grown on Aphanomyces-infested land. WARC showed that using a blend consisting of nutrient levels of 20-50-20-10 lb/ac of nitrogen, phosphorus, and potassium, sulphur (N-P-K-S) had a 9-10 bushel per acre (bu/ac) yield advantage over straight monoammonium phosphate (MAP) at 4.5-20-0 actual lb/ac in an Aphanomyces-infested field.
Weed Management
Though they are not crop hosts, weed-host plants can also contribute to the amount of oospore inoculum in the soil.
Volunteer alfalfa, white clover, shepherd’s purse, chickweed, and field violet (field pansy) can all be infected by Aphanomyces under the same wet conditions as peas and lentils.
Diligent control of weedy host plants and crop rotation is essential to achieve spore reduction in the soil.
Soil & Plant Testing
If a root rot complex or Aphanomyces infection is suspected, you should confirm your suspicions with a plant or soil sample. Diagnostic laboratories can examine freshly infected roots for spores, plate samples for fungal identification, or confirm disease using DNA testing. Some labs can simultaneously test for pathogens such as Fusarium, Pythium, and Rhizoctonia.
Individual labs may differ in testing methods and sample requirements. Please check with the lab before sending samples. For more information on sample testing and interpreting results, see Scouting and Diagnostics.
Seeding Decisions & Seed Treatments
- Choose a seed that is good quality and disease-free.
- Consider using seed treatments as warranted to manage disease on seed and protect against early infection by Aphanomyces or if planting early into cool soils.
- Use appropriate inoculants and suitable application methods.
- Choose varieties with tannins seed cost and varieties with improved Fusarium resistance when possible.
- Choose more resistant pulse crop options – faba bean, chickpea, and soybean (only for Aphanomyces).
- Minimize seed damage and watch the airspeed of the seeder.
- Seed into warm, moist soil – the quicker the emergence, the more vigorous the seedlings.
- Optimizing seeding rates, seed quality, seed handling, and plant nutrition is essential to maximizing growth and yield.
After Seeding
- Monitor crops for signs of stress by focusing on low areas where water flows or pools.
- Follow herbicide labels – increased injury can occur when plants are stressed.
