As field peas approach bloom, producers need to be thinking about potential diseases and management tools available.

Ascochyta/Mycosphaerella blight can be an economically important disease when cool, wet weather occurs during bloom and pod-fill. The disease is widespread throughout the growing region and spores can travel long distances, which can place even new fields at risk. The pathogens causing Ascochyta/Mycosphaerella blight overwinter on crop residues and produce aerial spores in the spring. This disease complex causes dark necrotic lesions on leaves, stems, and pods, with symptoms most severe in the lower canopy. Foliar symptoms develop as purplish-brown flecks and/or brown lesions with concentric rings; depending on conditions, either type of lesion or a mix of both types of lesions may develop. Stem lesions, which typically develop only at the base of plants, are brownish-purple and can cause lodging and, when severe, premature senescence. Foliar fungicides can decrease yield losses to the disease and also significantly improve harvest ease by reducing the basal stem lesions that can cause lodging. The optimal application timing generally coincides with full bloom and early pod development (when pods are still flat), but applying fungicides at bloom initiation may be advised if the canopy is very dense and conditions are highly favorable for disease (wet and cool). A single fungicide application generally provides adequate control. When considering fungicides, producers should be careful to rotate fungicide chemistries when more than one application is made in a season, or when a single fungicide application is made in sequential seasons. Some fungicide resistance has been seen in Montana.

Powdery mildew can be a very important disease when conditions are favorable. It reduces seed size and can sharply reduce yields if it develops during early to mid-pod development. Late planted peas are at greater risk for yield loss than early planted peas. The pathogen overwinters in small black reproductive structures that release aerial spores in the spring/summer. Powdery mildew infection and development is favored when dry, warm weather are accompanied by nights that are cool enough for dew to develop. The disease can develop very rapidly when environmental conditions are favorable. Powdery mildew causes white powdery fungal growth over all above-ground parts of the plant. The disease usually begins as small discrete white tufts. Once it appears, the disease can spread very quickly and the white fungal growth can quickly cover entire leaves and other green tissues. As the disease is developing, the white fungal growth can be easily rubbed off, and the tissue underneath may appear normal or slightly yellowed. As the disease progresses, black specs (fungal reproductive structures) often develop within the white fungal growth, and the peas take on a bluish color. Fungicide applications are highly effective against powdery mildew but it is critical to apply them before an epidemic begins; apply at either the first appearance of trace levels of powdery mildew in the lower canopy or on the basis of perceived risk if weather conducive to the disease occurs during bloom and pod-fill.

Bacterial blight is generally not considered an economically important disease of field peas, however there have been some severe losses to the disease. This disease is caused by a bacterial pathogen, therefore fungicides are not recommended for management. Bacterial blight is often confused with ascochyta blight, so it is extremely important that the disease is accurately distinguished before any treatment is applied.