Alfalfa Diseases

• Anthranose – mainly a disease of southern and eastern United States

• Aphanomyces root rot (ARR) – mainly a disease of eastern and western United States, in wet soils. Symptoms similar to nitrogen deficiency.

• Bacterial wilt (BW) – in the south and central prairies. Cause serious stand losses in 3-5 yr stands. Plants start out yellow-green and advance to stunted with spindly stems.

• Blossom blight (BB) - common in cool, wet conditions. Can reduce seed yield.

• Brown root rot (BRR) - affected plants become yellow and growth is stunted.

• Common leaf spot (CLS) – in the south and central prairies. Occurs in 1st and 2nd cuttings and in fall regrowth. Causes reduced yield and lower forage quality.

• Crown bud rot (CBR) – common in irrigated or moist soils. Progressive decline in stand and yield. Control – delay spring harvest, leave 25 cm on plant after the last harvest.

• Damping-off/seedling blight (DO) - occurs in the prairies in areas with crown rot. Severe in fields where germination is slowed by low seed vigour, cold wet soil, poor seed to soil contact, etc.

• Downy mildew (DM) - common in the prairies during cool, humid weather.

• Fusarium wilt (FW) - in the south and central prairies. Causes gradual stand thinning. Symptoms are similar to bacterial wilt, but plants are not stunted. Control – control pea aphids and potato leafhoppers.

• Lepto spot (LS) - mostly in central Alberta and southern Manitoba. Attacks young regrowth and yield and quality are reduced. There are no resistant cultivars available.

• Phytopthera root rot (PRR) – a problem in the south and central prairies, in wet or slowly drained soils. Plants have reduced root mass and growth rate, and can die rapidly. Control – crop rotation is not effective, avoid untimely cutting (plants stressed, before a heavy rain), control leaf-feeding insects, use tillage and land-leveling.

• Root lesion nematodes – moderate problem in eastern Canada and along the southwest coast of B.C.

• Sclerotinia – moderate problem in eastern Canada.

• Spring black stem - in the south and central prairies. Causes leaf drop, stem girdling and infection of the crown and roots resulting in death. Reduces yield and quality.

• Summer black stem – mainly a disease of the eastern and western United States.

• Verticillium Wilt – a problem in pockets of south central B.C., and southern Alberta and Manitoba. Leaves yellow, leaving a green stem. Crown infection results in death. Yield can be reduced up to 50%. Control – harvest non-infected fields first.

• Winter crown rot or snow mold (WCR) – dark brown rot of crown. Control – plant winter hardy cultivars

• Yellow leaf blotch (YLB) - most destructive in northern Alberta. Yellow blotches form on the leaves and older lesions will appear brownish-orange. Causes defoliation, yield loss, and a reduction in feed quality.

• Resistant Varieties – CBR, ARR, BW, CLS, DO, DM, FW, PRR, SBS, VW
• Crop Rotation – BRR, CBR, DO, DM, VW, YLB
• Maintain Stand Vigor – WCR, CBR
• Maintain Good Fertility – CBR, FW, PRR
• Harvest Early – CLS, SBS, YLB

• Although spring frost injury is not considered a disease, its effects can be similar to the productivity and vigor of alfalfa plants.