Field peas are a valuable pulse crop grown for their high protein content and nitrogen-fixing abilities. For growers aiming to maximize yield and ensure seed quality, harvest timing plays a crucial role. One common harvest management practice is desiccation, the process of applying a chemical or natural agent to speed up the dry-down of the crop. Knowing when to desiccate field peas is critical, as incorrect timing can lead to reduced seed quality, staining, or harvest loss. Understanding the ideal window for desiccation and the signs to look for in the field helps ensure a clean, efficient, and profitable harvest.
What Is Desiccation in Field Peas?
Desiccation involves applying a harvest aid usually a non-selective herbicide or drying agent to terminate plant growth and accelerate drying. This technique is often used when natural dry-down is delayed due to weather or uneven crop maturity. Desiccation helps reduce green matter, making combining easier and minimizing moisture-related storage issues. It is especially useful for field peas, which can have uneven maturity across the field and tend to retain moisture in lower pods and leaves.
Reasons to Desiccate Field Peas
Desiccating field peas is not always necessary, but it offers several benefits when timed properly. Reasons for choosing desiccation include:
- Evening out crop maturity
- Reducing weed pressure at harvest
- Minimizing green material in harvested grain
- Speeding up the harvest timeline
- Reducing disease and pest risks in the late season
These advantages make desiccation a valuable tool in managing harvest logistics, especially when field conditions are variable or time-sensitive.
When Is the Right Time to Desiccate Field Peas?
Timing is critical in field pea desiccation. Applying a desiccant too early can damage seed development, while applying it too late reduces its effectiveness. The ideal time to desiccate is when the crop reaches physiological maturity and most pods have dried down naturally.
Signs Field Peas Are Ready for Desiccation
- Bottom pods: Brown and dry, with mature seeds that rattle inside.
- Middle pods: Turning yellow, with firm and well-formed seeds.
- Top pods: Still green, but beginning to lose color and shrink.
- Leaves and stems: Yellowing or drying, with signs of senescence.
- Seed moisture: Below 30% in the majority of pods.
Generally, when 75%-80% of the field pea plant has reached maturity and the lowest pods are fully dry, it’s time to consider desiccation. The target is to wait until the crop has stopped actively filling seeds and can tolerate the drying process without quality loss.
Choosing a Desiccant Product
Several desiccation products are available, and each has its advantages and restrictions. Common choices include:
- Diquat: Fast-acting contact herbicide that quickly dries plant material but does not control regrowth or weeds.
- Glyphosate: Systemic herbicide that works slower but offers weed control; not approved in some regions for pre-harvest use on peas.
- Saflufenacil or carfentrazone: Contact herbicides with variable effects depending on crop stage and tank mix partners.
Always read the label and check local regulations. It is essential to follow pre-harvest intervals and ensure the chosen product is approved for field peas to avoid residue issues and ensure crop safety.
Application Timing and Weather Conditions
For desiccation to work effectively, proper application conditions are important. Key factors to consider include:
- Time of day: Apply during warm, sunny periods for faster drying and better absorption.
- Humidity: Low humidity enhances drying speed, while high humidity can slow the process.
- Wind speed: Moderate wind helps with coverage but should not be too high to avoid drift.
- No rainfall: Avoid spraying before or during rain to prevent dilution or wash-off.
Uniform application and full canopy coverage are essential, especially when plants are tall or still have significant green tissue.
Safety and Pre-Harvest Intervals
Every desiccation product has a specified pre-harvest interval (PHI), the minimum number of days that must pass between application and harvest. This ensures that residues degrade to safe levels before the crop is harvested for consumption or sale. Common PHIs include:
- Diquat: 4 to 7 days
- Glyphosate: 7 to 14 days, depending on rate and formulation
- Saflufenacil: Typically 3 to 5 days
Failure to observe these intervals may lead to grain rejection, export issues, or food safety concerns. Always consult the product label for specific guidelines based on the region and intended market.
Alternatives to Chemical Desiccation
In some cases, mechanical or natural drying may be used instead of chemical desiccation. These alternatives include:
- Swathing: Cutting and windrowing the crop to dry in the field.
- Natural dry-down: Allowing the crop to mature and dry without intervention.
- Direct harvest: Waiting until all pods reach harvestable moisture levels.
These methods reduce the use of chemical inputs but require optimal weather conditions and careful management to prevent losses from lodging, shattering, or disease.
Impact on Seed Quality and Yield
When done at the correct time, desiccation has little to no negative impact on yield. However, if applied too early, it can halt seed fill prematurely, resulting in shriveled, lightweight seeds with reduced germination potential. Late desiccation may lead to uneven dry-down, delayed harvest, or exposure to weather-related damage.
Growers should balance the need for an earlier harvest with the risk of reduced quality by evaluating each field individually and using tools like moisture testing, seed color, and pod maturity to make the best decision.
Tips for Successful Desiccation of Field Peas
- Scout the field regularly and record crop progress.
- Use moisture meters to verify seed maturity.
- Apply desiccant during favorable weather conditions.
- Follow label instructions and pre-harvest intervals precisely.
- Ensure uniform application to all parts of the plant.
- Harvest as soon as the crop reaches safe moisture levels post-desiccation.
Timing Is Key for Effective Desiccation
Desiccating field peas is a useful strategy to improve harvest timing, reduce green material, and enhance crop uniformity. However, its success depends entirely on choosing the right time when the majority of the crop has matured and seed fill is complete. By watching for visual cues, testing moisture content, and applying desiccants under the right conditions, farmers can protect seed quality and ensure a smooth, efficient harvest. Like any agronomic decision, desiccation requires careful observation, timely execution, and adherence to safety guidelines to deliver its full benefits.