Sorghum Diseases

Sorghum diseases

1. Covered kernel smut

• Covered kernel smut disease (Sporisorium sorghi) affects the panicle damaging developing sorghum grains.
• It manifests with cone-shaped capsules developed within the panicles.
• They may cover some parts or the whole panicle with capsules containing spores that once broken spread to contaminate other sorghum plants causing further infection.

Control

• Use of sorghum disease-free seed which is dressed with thiram or any other effective chemical.
• Cutting off the infected panicle and bury in the soil to prevent further spread of the disease.
• Plough down to burry and destroy disease-carrying crop residues.
• Crop rotation with non-host crops especially legumes.
• Use of resistant varieties.
• Integrated disease management where a combination of the above strategies to reduce crop damage is adopted.

2. Ergot

• Ergot disease, caused by Sphacelia sorghi, also known as sugary disease affects the panicle producing mycelium in the affected grain.
• The affected spikelet produces honeydew which is a concentrated suspension of conidia.
• The disease affects sorghum at flowering and severe during rainy and humid conditions.
• The disease is spread through infected seed with sclerotinia germinating and releasing spores that infect the sorghum spikelet ovary.
• Insects and rain splash also spread the disease.

Control

• Adjusting planting dates to have sorghum flower at the time when there is low rainfall and low relative humidity.
• Plant clean seed dressed with thiram or any effective chemical
• Burn crop residue; deep plough soil at planting.
• Crop rotation; and where possible spray fungicides such as mancozeb 80 Wp (2kg/Ha) or Cabendazim (500gm/Ha) at panicle emergence.
• Repeat the spraying after a week, especially if rain occurs.

3. Anthracnose

• Anthracnose disease caused by Colletotrichum graminicola, that commonly attacks sorghum leaves, stems, and panicle.
• Symptoms include brick red coloration in a lengthwise split stem.
• Small circular leaf lesions develop into mature lesions with straw-colored centers that are reddish and blackish purple and later coalesce into larger necrotic tissue.

Control

• Practicing crop rotation with leguminous crops to break the disease lifecycle.
• Field sanitation where sorghum residues should be collected and destroyed before the onset of the rains to reduce disease spread.
• Use of resistant or tolerant varieties.
• Integrated disease management reduces damage due to anthracnose disease.

4. Northern leaf blight

• Symptoms of Northern corn leaf blight disease include long elliptical shaped lesions with grey centers and tan to red boarders.
• Control measures include; burning crop residues; deep ploughing at planting and crop rotation.

5. Sorghum rust

• Rust disease, caused by Puccinia purpurea, manifests as brown blister-like pustules formed on the upper and lower side of the leaf.
• The pustules rapture and release the powdery mass of reddish brown spores which are commonly dispersed by wind and animal contact.
• Other hosts include: Citronella grass, Creeping wood sorrel, Columbus grass, Johnson grass and Sudan grass.

Control

• Practicing crop rotation with leguminous crops to break the disease lifecycle.
• Field sanitation where sorghum residues should be collected and destroyed before the onset of the rains to remove the primary source of the disease.
• Use of resistant or tolerant varieties.

6. Striga (witchweed)

• Striga, commonly known as witchweed, is a parasitic weed the affecting many cereals including sorghum. It causes 20-80% grain yield loss under severe infestation.
• The common striga in Uganda is Striga hermontheca.
• Symptoms of striga damage to sorghum include stunted growth, yellowing and sometimes failure to bear panicles under severe infestation.
• The damage occurs when striga parasitizes the sorghum plant by colonizing roots, taking up the water, mineral nutrients, and photosynthetic assimilates thereby retarding growth and development of the host.
• Striga plants produce thousands of small seeds in a season which remain viable in soils for up to 15-20 years and a few can grow in a season where host plants exist.

Control

• Striga weed is mainly managed and controlled Inter-planting sorghum with a “chaser” Celosia argentea.
• Practicing crop rotation with trap crops such as cotton.
• Use of resistant/tolerant sorghum varieties and regular weeding before the weed flowers.