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Posted 02/11/2021 in Agricuture by Patience Chizema

5 most common sugar beans diseases


5 most common sugar beans diseases

Anthracnose

Anthracnose can reduce bean quality, as well as yield. Losses can be severe during cool, rainy weather.



bean leaf infected with anthracnose

 

Anthracnose is caused by the fungus Colletotrichum lindemuthianum. This disease appears on all aboveground parts of the plant but rarely on roots. Lesions usually are dark brown and may contain pink spore masses during moist weather. Elongate, angular spots appear on lower leaf veins. As the fungus spreads into surrounding tissue, lesions eventually appear on the upper side of veins and infected seeds become discoloured. Plants grown from infected seed may develop lesions on the cotyledons. The most striking phase of the disease occurs on pods. Small brown spots appear and rapidly enlarge into dark sunken lesions. Often lesion margins will be dark brown while lesion centres remain light in colour.


Disease Management

  • Practice crop rotations using other crops that are not within the legume family.
  • Plant only clean, certified and disease-free seed since the fungus can be carried on the seed. 
  • Practice a good weed control program to destroy other alternative hosts for the fungus.
  • Deeply incorporate and remove plant residue just after harvest to reduce overwintering of the fungus at the production site.
  • If possible, avoid using overhead irrigation methods as they tend to facilitate the dissemination of the fungus.
  •  Fungicide sprays can also be helpful.


Bacterial Blights

Bean blights, caused by various species of bacteria, occur in most of the bean growing areas of the world. Under favourable weather conditions, these bacteria can spread rapidly through a field causing defoliation and pod damage.

Bacterial Brown Spot

bacterial brown spot

 


This disease, caused by Pseudomonas syringae pv. syringae is more common on lima beans than other bean types. Small, water-soaked spots on leaves become red-brown in colour. Spot centres dry out, turn grey, and may fall away. Veins on the underside of the leaves may turn red-brown. Spots on stems and pods are more elongated than those on leaves.


Bacterial Wilt


bacterial wilt on sugar beans

 

This disease is exhibited by large yellow halo (up to 1/2 inch in diameter) surrounding the leaf spot. Newly developing leaves may show yellowing due to systemic infection and plants can die rapidly. Leaf symptoms without halos may develop if temperatures are relatively high. Symptoms on pods are also similar to those of common blight; however, the bacterial crust on the surface of the spots may be white (halo blight) instead of yellow (common bacterial blight).n addition, plants are stunted, and leaves droop and appear wilted.



Common Bacterial Blight 



common blight

 

 


On common bacterial blight,  lesions on leaves first appear as small, water-soaked, light green areas. Leaf spots become dry and brown with a narrow yellow halo. As the disease progresses, spots may expand, eventually killing leaves. Similar watersoaked spots form on pods and can develop into broad irregular blotches. In humid weather, a yellow bacterial crust covers the surface of the diseased area. The margin of the spot or the entire spot may be red-brown in colour. In severe attacks, pods may shrivel and seeds may not develop.

Disease development of these bacterial diseases

These bacteria overwinter in seed, plant debris, and susceptible weeds. When infested seeds are planted, an early outbreak may occur on the new crop. The bacteria can spread to healthy plants via splashing rain, wind-blown soil particles, or on tools and implements moving through wet fields. The bacteria enter through natural openings (for example leaf stomata) or through wounds (for example those caused by cutting and chewing insects). Once introduced, these bacteria can colonize leaves without causing symptoms, and then cause sudden crop damage following heavy rains. Therefore, disease management should be centred around keeping the population of bacteria low and out of the field.

Disease Management

  • Use certified disease-free seed as using retained seed is very risky because the seed could harbour bacterial pathogens.
  •  Rotate beans to non-legume crops leaving 2 to 3 years between bean crops.
  • Spray bean plants at the first sign of disease with a fixed copper bactericide. 
  • Deeply incorporate and remove plant residue just after harvest to reduce overwintering of the bacteria at the production site.
  • If possible, avoid using overhead irrigation methods.


By Patience Chizema


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