Farm406

Foliar diseases can be some of the most devastating diseases of pulse crops and are oen noticed too late to implement management. It is very important to scout crops on a regular basis, particularly when humidity is high and following rain and hail events. Early action against foliar fungi such as Ascochyta can be very beneficial. However, growers must be very careful to discriminate between bacterial diseases, where there are no chemical options, and fungal diseases. Bacterial blight is very commonly seen in pea aer hail events or rain events associated with high wind that blows soil particles into plants, particularly at the edges of fields. It is caused by Pseudomonas syringae pv. pisi in pea and Xanthomonas campestris pv. cassiae in chickpea. It can be easily confused with Ascochyta blight, but management is very different. Bacterial blight is characterized by angular lesions (Figure 4) that are water-soaked at first (when held up to the light, you can see the tissue is translucent) and early in the disease could be confused with physical damage due to hail. Lesions of bacterial blight are stopped by leaf veins, making the lesion angular in shape. is is in contrast to Ascochyta blight (cover photo, center) where circular lesions expand beyond the leaf veins. As the tissue dries, the lesions turn from light green, water-soaked lesions to dry, brown, papery tissues which, if lesions occur at leaf edges, can cause tearing. Disease symptoms can also occur on stems, petioles, and pods (Figure 4). Symptoms include downward curling of leaf edges and leaflets, thick and brile stems at the soil line, discoloration of the vascular tissue (orange-brown or red to black) and discoloration and roing of secondary roots. If the plant is infected when it is older, a black canker may develop on the stem close to where the pod is aached and enlarge upward and downward from that point. Affected plants die more rapidly under dry soil conditions, and death occurs in circular to oval patches. Plants may also be more scaered if the level of inoculum is low or unevenly spread. Relatively warm soil temperatures (74 to 82°F) are optimal for disease development. Verticillium wilt is caused by Verticillium dahliae and V. albo-atrum and is reported as an economical disease only on chickpea, although V. dahliae can infect lentil and pea (Ligoxigakis et al. 2002). Foliage turns yellow before wilting, and the xylem is light brown in color when the stem is split. is is not considered a major cause of disease in the Northern Great Plains, but can be serious where it occurs. Crop rotation with non-hosts is the most effective method of control; resistant varieties may be available. FOLIAR DISEASES If weather conditions remain humid aer infection, the disease can progress very rapidly and defoliate plants. You may see cloudy droplets of bacteria along the edges of lesions, which as the leaves dry, become crystalline and flake off. If weather conditions become warm and dry aer infection, the disease is halted in its progress. It is not uncommon to see symptoms only on lower leaves. Yield losses are proportional to the amount of canopy lost due to disease. e pathogen is seedborne, and contaminated seed is considered the most important source of inoculum for field epidemics. e pathogen also survives on stubble and in the soil. FIGURE 4. Above, Symptoms of bacterial blight of pea. Angular lesions turn brown when the leaf tissue dies. Bacteria ooze from lesions under high moisture conditions and dry on the leaf surface. Below, water-soaked lesions and bacterial ooze where hailstones hit a petiole. Continued on page 54 Photo: Mary Burrows, Montana State University Photo: Mary Burrows, Montana State University farm406 52

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