1. MAIZE DISEASES
Dr. Jamba Gyeltshen
01/04/2010

2. Maize Diseases
Turcicum leaf blight (Northern leaf blight) (Exserohilum turcicum syn. Helminthosporium turcicum)
Grey leaf spot (Cercospora zeae-maydis)

3. 1. Turcicum leaf blight Northern Corn Leaf Blight
(Exserohilum turcicum)
Syn. Helminthosporium turcicum

4. TLB Pathogen Anamorph (asexual phase)
Exserohilum turcicum (syn. Helminthosporium turcicum)
Teliomorph (sexual phase)
Setosphaeria turcica

5. 1. Turcicum Leaf Blight (TLB)
Conidia are septate, spindle-shaped, and have a protruding hilum.

6. TLB
Major constraint to maize production where humidity is high and temperatures moderate (17 to 27°C). 
Cause yield losses as high as 70%

7. TLB Distribution

8. TLB Symptoms Cigar shaped lesions that are 3 to 15 cm long
Lesions are elliptical and tan in color, developing distinct dark areas as the fungus sporulates 
Lesions typically first appear on lower leaves and spread upwards.
Under severe infection, lesions may coalesce, blighting the entire leaf.  

9. TLB Symptoms

10. Disease cycle
Overwinters as mycelium and chlamydospores in infected crop debris. 
Fungi in crop debris sporulate in response to higher temperatures and humidity. 
Spores (conidia) are then disseminated by wind and rain splash to freshly planted maize.  Conidia can be carried vast distances in the wind.
They germinate in temperatures ranging from 17 to 27°C and during periods of extended leaf wetness (6 to 18 hours), infecting host tissue. 
Secondary cycles of disease occur where conidia produced in disease lesions are disseminated within the crop and to other fields by rain splash and wind.   

11. Damage
Mechanism of damage: Yield loss is caused predominantly through loss of photosynthetic leaf area due to blighting.  Under severe infestation, sugars can be diverted from the stalks for grain filling leading to crop lodging. 
When damage is important: If Turcicum leaf blight establishes before silking and spreads to upper leaves during grain filling, severe yield losses can occur. 
Economic importance: Yield losses as high as 70% have been recorded but typically range from 15 to 30%.

12. Disease management Grow resistant varieties: Yangtsepa
Management of overwintering infected crop residue will reduce the amount of available inoculum at the onset of the subsequent growing season.
Fungicide application can effectively control Turcicum leaf blight when applied at the right time. 
Fungicide should be applied when lesions first become visible on the lower leaves.

13. 2. Grey leaf spot Pathogen: Cercospora zea-maydis and Cercospora zeina
Gray leaf spot (GLS) is a serious foliar disease of maize in many temperate and tropical highland regions of the world. 

14. GLS Symptoms
GLS has characteristic rectangular, tan-colored lesions that are contained within leaf margins, as the fungi is not able to penetrate sclerenchyma tissue in the leaf veins.
As lesions mature they assume a graying cast due to sporulation of the fungi.  Lesions are typically 2-4 × 10-60mm in size and usually develop on the lower leaves, gradually spreading upwards on the plant during the season.  Under severe disease pressure, entire leaves can be blighted and lesions can develop on cob sheaths. Symptoms of GLS caused by Cercospora zeae-maydis and C. zeina are indistinguishable.

15. Symptoms as seen against light

16. GLS symptoms

17. GLS symptom severity

18. GLS conidia

19. Disease development
In spring, conidia (spores) are produced and disseminated to corn plants by wind and rain splashing. They require several days of high relative humidity to successfully germinate and infect corn leaves. Several weeks may be needed for the development of mature lesions on leaves. Conidia for secondary spread are produced from two to four weeks after initial leaf infection

20. Management
Damage, disease cycle and management are same as TLB

21. References http://www.apsnet.org/online/feature/grayleaf/gallery.htm