When should multiple fungicide passes be considered for pulse crops?

As pulse crops in Western Canada continue to be intensively managed, protecting the yield potential from fungal diseases involves understanding disease cycles and risk. Peas, lentils and chickpeas often produce a dense canopy architecture that creates a favourable microclimate near the soil surface that becomes humid as the crop matures. This dense, humid canopy microclimate is very conducive to both the development and rapid spread of yield-reducing pathogens. Optimum disease control requires an approach that more often includes a multi-pass strategy for canopy management and seed health preservation at harvest.

The shifting pulse disease spectrum in Western Canada

Fungal diseases rely on environmental moisture and extended periods of humidity to develop, and often these conditions can arise during important stages in crop development. As a result, key diseases to watch for and protect against in the Prairies include:

• Ascochyta blight: Ascochyta blight, which can impact both chickpeas and lentils, is characterized by necrotic lesions on leaves, stems and pods. This disease relies on rain-splashed spores to spread, so early-season rain can lead to a quick outbreak.
• Mycosphaerella blight: This is one of the main diseases in field peas. It will typically begin on lower leaves and spread upward through the canopy. Untreated, it can result in premature defoliation and severe lodging.
• Anthracnose: A severe disease of lentils, anthracnose develops under warm, humid conditions, especially during flowering. This disease can cause stem girdling and rapid canopy dieback.

The agronomic rationale for a multiple-pass strategy

The rationale behind using multiple fungicide passes is based on the biology of the host plant and the pathogen. A single application delivers a finite period of residual activity, which often ranges from 10 to 14 days. However, the most vulnerable time period for disease development on pulses is often many weeks long and begins early in the vegetative stage and extends into late pod elongation.

In addition, pulses continually produce new vegetative tissue and flowers after an early-season pass. Since systemic fungicides have little to no downward translocation or movement back into new leaf tissue as it emerges, this new growth is completely unprotected from spore events late in the season. If the weather remains wet and humid, the pathogen can readily colonize the upper canopy or newly produced pods. A second pass is thus required to protect the new tissue from late-season infections that would otherwise impact grain fill or seed appearance.

Strategic product deployment: Gauntlet and Joust

Rotation is important to a successful multi-pass program. A combination of active ingredients that takes into consideration current and future needs and resistance can be very successful. Products in the modern management toolbox, such as Gauntlet or Joust, can be selected to provide control in the right disease window for specific needs, and/or structural needs.

Gauntlet was designed with a dual mode of action for specific strategic purposes. It is a Group 3 (prothioconazole) and Group 11 (azoxystrobin) chemistry. It is an excellent choice for first application timing in lentils, which is typically at the very beginning of flowering or at the first sign of disease. Two modes of action provide not only excellent preventative and curative control of Anthracnose and Ascochyta blight, but also a very strong resistance management barrier.

Joust is a Group 3 (prothioconazole) systemic chemistry that has broad-spectrum activity and fast cuticle absorption. It is an effective option to rotate with, and/or use as a stand-alone dedicated fungicide for peas and chickpeas. Joust is effective for the specific control of Ascochyta and Sclerotinia. It is a great option to maintain a clean middle and upper canopy through the important structural changes that occur later in the season.

Timing the applications for maximum efficacy

To ensure the full value of the fungicide investment is captured, applications must be synchronized with specific crop staging.

The first window (Canopy closure to early bloom)

The primary goal at this stage is to protect the lower leaves and stem bases before the canopy closes and limits droplet penetration. Applying a product like Gauntlet at this time halts early infections and keeps the lower canopy functioning. This pass is critical for preventing early-onset Ascochyta and Anthracnose from establishing a baseline inoculum in the field.

The second window (10 to 14 days later / full bloom to early pod)

This pass is executed to protect newly formed flowers and young pods from late-season flushes. It also creates a barrier against Sclerotinia, which targets the senescing petals as they drop into the canopy crotches. Rotating to a systemic option like Joust during this window ensures that fresh tissue is protected while the plant directs its energy toward pod development.

By utilizing high-performance solutions like Gauntlet and Joust at the correct biological windows, growers can successfully insulate their pulse crops from the devastating impacts of Ascochyta, Anthracnose and Sclerotinia. Protecting the crop throughout its entire vulnerability window ensures that the genetic potential of the seed is fully realized at the combine.