Disease control

Maize streak virus

The virus is transmitted by leafhoppers (Cicadulina spp. (C. mbila / C. bipunctella zeae)).


Maize Figure 14: maize infected by streak virus

Maize Figure 14: maize infected by streak virus

Damage/Symptoms

  • The virus causes a white to yellowish streaking on the leaves.
  • The streaks are very narrow, more or less broken and run parallel along the leaves.
  • Eventually the leaves turn yellow with long lines of green patches
  • Plants infected at early stage usually do not produce any cobs.
  • Yield losses in East Africa vary between 33 and 55% under natural infection conditions

Control

  • Use of tolerant / resistant varieties
  • Early rouging
  • Eradication of grass weeds
  • control vector by spraying with dimethoate, malathion
  • Avoid overlap of two maize crops
  • Crop rotation
  • Use certified maize seed

Leaf blights

(Bipolaris maydis (Helminthosporium maydis / Cochliobolus heterostrophus)).

Disease development is promoted by prolonged wetness on foliage, extended dew, Relative Humidity (97-100%) and relatively warm temperatures (24-35° C).


Maize Figure 15: maize infected by blight

Maize Figure 15: maize infected by blight

Symptoms

Small yellow dots that become elongated between veins appear. They later become brownish to creamy white in colour with reddish to purplish brown borders. The spots may join together and result in blighting of entire leaves. Silks, portions of the husks and cobs may turn black. A black mould may develop on cobs.

Control

  • Use of tolerant / resistant varieties
  • Good field sanitation (removal of crop residue after harvest or deep ploughing of crop residues)
  • Use certified seeds
  • Crop rotation

Grey leaf spot

(Cercospora zeae-maydis) This disease is favoured by prolonged periods of high relative humidity. It can cause yield losses of 30 to over 50%.


Maize Figure 16: maize with grey leaf spot

Maize Figure 16: maize with grey leaf spot

Symptoms
Symptoms are similar to leaf blight but the spots are much narrower.
They are initially light brownish in colour, and with age they bleach to ashen grey surrounded by narrow light-brownish border. When wet, spore mass is formed on the spots with a light shade.

Control
As for leaf blight

Maize rusts

(Puccinia sorghi)


Figure 17: Necrotic rust lesions on maize

Maize Figure 17: Necrotic rust lesions on maize

Damage/symptoms
Highland rust produces yellow –brown linear postules on leaves while lowland rust produce light brown postules on upper leave surface.

Control

  • Use of resistant varieties
  • Crop rotation
  • Deep ploughing of crop residue
  • Destruction of weed Oxalis sp. (an alternate host)

Maize Smuts

(Common & Head smut)


Maize Figure 18: maize infected by head smut

Maize Figure 18: maize infected by head smut

Damage/Symptoms

  • The first symptoms become evident when tassels and cobs (ears) appear.
  • Large white to black galls on stalks, tassles and ears.
  • Masses of Black spores are released if galls are opened
  • The infested plant to do not produce any grains

Control

  • Use certified seeds
  • Crop rotation
  • Use resistant varieties
  • Rogue and destroy by burning the affected plants