IPM Packages for Crops

diseases

DISEASES

Ascochyta blight [ Ascochyta rabiei (Pleosporales: Didy- mellaceae)] (syn. Phoma rabiei and teleo- morph Didymella rabiei ) This disease attacks all aboveground plant parts at every growth stage. Ascochyta blight can cause up to 100% yield loss and can reduce crop quality on untreated susceptible varieties. Fungus spreads by infected seed and crop residues, long-range dispersal of sexually produced ascospores, or within the crop by short-range dispersal of asexually produced pycnid- iospores. It causes severe lesions on leaves, petioles, stems, and pods. Water-soaked pale spots on young leaves will emerge as the first symptom, which will enlarge quickly under cool, wet conditions and coalesce to cause blighting of leaves. When severely infected, lesions girdle the stem and cause the death of all tissues above the lesion. It also causes shriveling, discoloration of seeds, and reduction in seed quality and yield, and if infected seeds are planted, the seedlings will develop dark brown lesions at the base of the stem and may dry up and die. This disease is prominent in Asia, the USA, Canada, and Australia. Resistant va- rieties are available for this disease but not durable because of the variability of the pathogen. Delay in sowing seeds and deep sowing (to avoid the emergence of infected seeds) and application of pesticides help in the management of this disease.

Rust [ Uromyces cicerisarietini (Pucciniales: Pucciniaceae)] It infects all aboveground plant parts. Small, round, brown postules appear first on the leaves and then they coalesce and turn dark brown. It is prominent in spring-sown crops. Severe infection causes defoliation and complete crop failure oc- curs, producing small shriveled seeds. Hot and dry conditions are favorable. Usually, if epidemics occur later in the season then it does not cause much loss, but in the early season, it can cause severe damage. No resistance varieties are known for this disease. Powdery mildew [ Leveillula taurica (Erysiphales: Erysipha- ceae)] Powdery mildew causes diffuse and powdery sporulation on leaves, stems, and pods. Affected parts are usually small but at later stages, they turn into larger areas. When heavily infested, leaves turn purple and become chlorotic, curled, and necrotic before abscission. This disease causes a reduction in yield. Cool and dry weather is favorable for this disease. Field and crop sanitation, timely sowing, crop rotation, and resistant cultivars are useful in manag- ing this disease.

Botrytis gray mold [ Botrytis cinerea (Helotiales: Sclerotinia- ceae)] It affects aboveground plant parts includ - ing leaves, stems, flowers, pods, and seeds. The most affected parts are growing tips and flowers. Symptoms initially occur as water-soaked lesions that later turn gray and dark brown. A series of cool, wet summers are ideal for its development. Af- fected leaves and flowers turn into rotting masses. Severely infected leaves wilt and fall and ultimately plants can die. Flower drop is also common due to this disease, which leads to poor pod formation and low grain yields. Botrytis cinerea is also asso- ciated with seedling disorders (soft rot) of chickpea. Infected seeds are shriveled and discolored. Bacteria, Pseudomonas fluo - rescens, Penicillium griseofulvum , and the fungi Trichoderma spp. reduce the severity of botrytis gray mold. Downy mildew [ Peronospora ciceris (Peronosporales: Peronosporaceae)] It infects all the aerial plant parts and causes curled, twisted leaves, and dwarfed tips. Cool and humid conditions are favorable. Initial symptoms include white mycelial patches on the lower leaf surfaces and chlorotic to yellow spots on the upper surface. Infected plants remain stunted and form bushy apical growth. Late planting and resistant germplasm lines help manage this disease.

Ascochyta blight, Mary Burrows, Montana State University, Bugwood