IPM Packages for Crops

diseases & viruses

Turcicum blight ( Setosphaeria turcica, Exserohilum turci- cum ) (Pleosporaceae) Symptoms of Turcicum blight include large, oval, grey, or light brown leaf spots, sometimes with dark margins, and cover large parts of the leaves. Symptoms occur first on the lower leaves. The disease caus - es the leaves to dry out, wither and die. Heavy dews, frequent light showers, high humidity, and moderate temperatures are favorable for the disease. This disease causes loss of grain and animal fodder. Resistant hybrid varieties and crop rotation with a non-host crop (legumes) can reduce the disease severity. Southern leaf blight of maize [ Helminthosporium maydis (= Coch- liobolus hetrostrophus , Bipolaris maydis ) (Pleosporaceae)] This disease is found around the globe and during the summer season it is considered the most important disease of maize. Helminthosporium maydis infects leaves, sheaths, ear husks, ears, cobs, shanks, and stalks. Infected seedlings wilt and die within a few weeks of the planting dates. Symptoms vary depending on the race of leaf blight. Lesion color can be tan with brown, red borders or yellow-green or chlorotic halos. The shape of lesions can bediamond, elliptical or spindleshaped. Resistant/tolerant hybrids are available (RML-4/RML-17 and RML-32/RML-17). Destruction of infected crop residue is highly useful.

Downy mildew ( Peronasclerospora spp.) (Peronospora- ceae) Downy mildew has a broad host range. Seedlings are prone to infection and infect- ed maize plants have leaf chlorosis. As the plant grows, it often shows stunting, and necrotic lesions begin to formon the leaves. As the leavescontinue to grow, a white, downy growth develops into the necrotic lesions. Several single-gene sources of resistance have been found, and many resistant varieties are commercially (Rhizoctonia solani) (Ceratobasidiaceae) This disease is particularly destructive with the rice-maize rotation. Usually, this disease infects the pre-flowering stage (plants 40-50 days old). White mycelium and irregularly rounded sclerotia develop on sheaths, husks, silks, cobs, and kernels. Leaves and leaf sheaths of infected plants appear blighted with prominent banding. Stripping the lower two or three leaves and leaf sheaths considerably reduces the inci- dence of disease but does not affect grain yield adversely. available. Crop rotation is useful. Banded leaf and sheath blight Maize dwarf mosaic virus (MDMV) (Potyviridae) MDMV is a serious maize pathogen and epidemic worldwide causing about 70% loss in corn yield globally. MDMV is a single-stranded RNA virus and is transmit- ted in a non-persistent manner by several aphid species. MDMV infected plants exhibit mosaic patterns, which occur near the lower part of the youngest leaves. Oth- er symptoms include mottling spots and irregular necrotic lesions. MDMV infected plants show a delay in flowering as well as a poor grain set and fill. VIRUSES

Maize streak virus (MSV) (Geminiviridae)

MSV occurs throughout Africa and causes severe damage. It is transmitted by sev- eral leafhopper species. This also infects several species of Poaceae. MSV causes continuous parallel chlorotic streaks on leaves, with severe stunting of the affected plant, hence, failure to produce complete cobs or seed. During epidemic years, MSV can cause 100% yield loss. Maize lethal necrosis disease (MLN) This disease is an emerging disease in sub-Saharan East Africa. This disease is caused by coinfection of maize with Maize chlorotic mottle virus (Tombusviridae) and one of several viruses from the Potyviridae ( Sugarcane mosaic virus, maize dwarf mo- saic virus, Johnsongrass mosaic virus or Wheat streak mosaic virus) . The coinfect- ing viruses act synergistically. Infection results in frequent plant death or severely reduced or negligible yield. Multiple maize crops per year, maize thrips ( Frankliniella williamsi ), susceptible maize crops, and soil and seed transmission play significant roles in development and spread of this disease. Best measures to manage this disease still need further studies.

Maize dwarf mosaic virus (MDMV), AgroAtlas