IPM Packages for Crops

diseases

DISEASES

Smut ( Sphacelotheca reiliana ) (Microbotryace- ae) Smut is distributed in Asia, Africa, the Americas, and Europe and invades plants during emergence or at the seedling stage through soilborne teliospores. It grows systemically with the meristem and does not get transmitted from one plant to the other. Infection is visible at a late stage of plant development on tassels and ears (large smut galls) of the maize plant. The infected corn ear looks very small and tear- drop shaped, and the cob looks empty. A relatively low percentage of infection in the fields (10%) can cause significant yield reduction (about 80%). Once the infection occurs, there are no effective treatments for reducing or eliminating the damage on affected plants. Head smut spores can sur - vive in the soil for several years. Balanced soil fertility should be maintained, with an emphasis on sufficient nitrogen. Tolerant hybrids are available and hybrids with fast emergence are less prone to head smut infection.

Leaf spot [ Cercospora zeae-maydis (Mycosphaerellaceae), Phaeosphaeria maydis (Physodermataceae)] Cercospora zeae-maydis only infects corn. This disease causes considerable yield loss in most maize-growing areas of Afri- ca. The disease is usually associated with an increase in the maize production area, continuous planting of maize on the same plot of land year after year, and the use of minimum tillage practices. The initial symptomsof grey leaf spots are small, dark, moist spots that are encircled by a thin, yellow radiance. Spots are initially brownish and yellow and later on turn into grey color due to the production of grey fungal spores. Phaeosphaeria maydis also causes small, pale green lesions scattered over the leaf surface. With maturation, lesions dry and develop dark brown mar- gins. Lesions also coalesce and become irregular in shape and blight the entire leaf. Maize plants on the edges of the fields are more prone to this disease. This disease is pronounced in cold conditions. Spores overwinter on crop debris and in favor- able climatic conditions (high rainfall and moderate temperatures); spores get disseminated through rain splash and wind. Crop rotation, residual management, and planting dates can manage this disease. Susceptible varieties should not be planted in previously infected areas.

Ear rots [ Fusarium verticillioides (=Fusarium moniliforme) (Nectriaceae), Diplodia maydis (=Stenocarpella maydis) (Diaport- haceae)] Fusarium verticillioides is a seed-borne endophyte in maize. It is very common and also difficult to eliminate. Warm dry weather early in the growing season, fol- lowed by wet weather during the devel- opment of the cob increases the infection. Fusarium verticillioides is associated with high levels of disease-causing mycotox - ins—fumonisins—on infected kernels. These mycotoxins are harmful to humans and cattle. Diplodia maydis causes ear rot, stalk rot, and seedling blight of corn. Corn is the only host for this pathogen. Ear rots overwinter on the diseased stalk and ear tissues that have not been buried. In the spring, the fungus reproduces on the plant debris and produces spores that are moved by rain and wind to the new crop. The fun- gal spores land on the plant and commonly infect at the base of the ear if sufficient water is available. Symptoms of ear rot be- gin as tan spots on the base of the husk and ear leaf, which expand over the ear, and at later stages white fungal growth spreads over and between the kernels. Resistant varieties are also available. Crop rotation is very useful to manage ear rots because the fungus survives poorly overtime on infested debris.

Southern leaf blight (Helminthosporium maydis), Pioneer.com