1. International Training Workshop on Maize production in Laos.pptx

Training on Maize diseases

1. Identification and management of major diseases of maize International Training Workshop on Maize Seed Production and Distribution in Bhutan November 13 - 15, 2023 | ARDC- Wengkhar , Mongar , Bhutan Dr. Suresh, L.M. Maize Pathologist, CIMMYT.

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3. Turcicum Leaf Blight: Fungal foliar disease Affects maize and causes a crop loss: Requires a humidity of 75-90% RH and temperature of 17-27 C. Spreads through crop debris, arial spread. Maize disease in Bhutan Grey Leaf Spot Fungal foliar disease Affects maize and causes a crop loss: Requires a humidity of 65% RH for survival and 90% for spread and temperature of 22 -27 C. Spreads through crop debris, arial spread. Ear rot Fungal ear rot disease Affects maize and causes a significant crop loss: Requires a humidity of 75-90% RH and temperature of 20-27 C. Spreads through crop debris, soil , insect vectors and arial spread.

4. Northern Leaf Blight ( Setosphaeria turcica Syn. Exserohilum turcicum ) Distribution: The disease is occurring worldwide. Plant species affected (Host range): Maize, Sorghum, and other wild grasses. Symptoms: Early symptoms are pale gray-green, elliptical, or cigar-shaped lesions that are initially less than 1 cm long. The disease usually begins as a few scattered lesions in lower leaves and progresses towards upper leaves. The disease can develop very rapidly after anthesis resulting in complete blighting of the leaves. Large oval gray elongated light brown spots. Symptoms often occur on lower leaves. Conditions for disease development : E. turcicum overwinters as mycelia and conidia in and on leaf debris. Conidia can be carried by wind over a long distance. Secondary spread within and between fields occurs by conidia produced abundantly in leaf lesions on susceptible plants. Symptoms often progress from lower leaves to upper leaves as conidia produced in lesions on lower leaves serve as inocula for the infection of the upper leaves. Northern corn leaf blight is found sporadically in most humid areas of the world where corn is grown but is most damaging when moderate temperatures (18-27 C) and prolonged periods of dew prevail during the growing season. Impact: Cause significant grain yield loss in the hot and humid medium to highland altitudes. If the disease is established before silking, losses in grain yield of up to 50% may occur. If the infection is moderate or delayed until 6 weeks after silking, yield losses are minimal. Management: Plant-resistant and certified seed Practice crop rotation with legumes Collect and decompose previous crop residue in one spot. Whenever is necessary, spray recommended fungicides at the early disease stage.

5. Disease progression of Turcicum leaf blight (TLB) Initial infection Long elliptical lesions Blight symptoms near ear position Blight symptoms near flag leaf Complete blight

6. Disease progression of Turcicum leaf blight (TLB) Cigar shaped lesions Blight Symptoms Coalesce of lesions Initial symptoms

7. Grey Leaf Spot (Cercospora zea maydis) Distribution : The disease occurs in temperate, to warm, humid areas of various parts world. Plants species affected (Hosts): Maize Symptoms: Early lesions are small, necrotic spots with a chlorotic halo that gradually hallo that gradually expands to full-sized lesions, which can blight entire leaves. Expanding lesions are tan and turn grey as the pathogen, Cercospora zeae-maydis or C. zeina , begins to sporulate on the underside of the leaf. In some cases, lesions have a dark border or yellow halo. The diagnostic feature of grey leaf spot lesion is the sharp edges of the lesions results from the inability of the fungus to penetrate sclerenchyma tissue in the major veins of the leaf, which limits the lateral expansion of the lesions. The opacity of the lesion is caused by stromatic tissue, i.e., dark hardened mycelium produced by the fungus, in the stomatal cavities. Rectangular elongated, parallel lesions. Conditions for disease development: Severe grey leaf spots are usually found in the field where corn follows corn and residues of the previous crops remain in the soil surface. Germinated conidia of C. zeae-maydis can survive at 60% relative humidity on the leaf surface but require a relative humidity of 95% or higher for germ tube growth and appressorium formation. Impact: Although the disease is not a problem until sometime after anthesis, it can develop rapidly, completely blighting leaves and causing premature death of the plants. Prolonged periods of dew, fog, and cloudy weather are conducive to severe grey-leaf spot epidemics. Reduce grain yields due to loss of photosynthetic leaf area. Management: Plant resistant and tolerant genotypes Practice crop rotation with legumes Collect and decompose previous crop residue in one spot. Disease cycle of GLS. Source: Ward et al . (1999).

8. Disease symptom progression – Grey leaf spot Blighting of leaves Coalescing lesions Rectangular parallel lesions Grey Mature lesions Expanding immature lesions Initial lesions

9. Ear rot Disease Fusarium Ear rot Fusarium verticilloides Common in all maize growing ecologies Hot dry weather after flowering favors Fusarium ear rot Symptoms Whitish/pink mycelium on/between kernels Starburst symptoms on kernels Fungi overwinters in crop debris and airborne conidia infect silks at flowering Control through host resistance and proper storage Quantitative Resistance (composition of kernel is important) Prevalent when wet weather follows silking White / grey mycelial growth over husks and kernels Infected kernels may be very light and appear to be glued together Black pycnidia are produced late in the season Fungi overwinters in infected stalks Most serious under high temp and drought Production of aflatoxins Overwinters in crop debris and spores are dispersed by wind or insects Host resistance offers best control. Rotation has minimal effect as a lot of alternate hosts Difficult to phenotype. R is likely to be quantitative but difficult to phenotype reliably Diploidia ear rot Stenocarpella maydis Aspergillus ear rot Aspergillus flavus Source: Iowa State University Source: University of Illinois

10. Ear Rots Significant yield damage Mycotoxin risk Highly environmentally variable Major Ear Rots Aspergillus ear rot (Aspergillus flavus) Fusarium Ear Rot (Fusarium moniliforme and other species (Gibberella)) Diplodia Ear Rot (Stenocarpella maydis)