Crown rot symptoms in alfalfa

Verticillium, Fusarium, Rhizoctonia, Phytophthora, Pythium, Phoma, Mycoleptodiscus, Stagonospora, and Macrophomina

Crown rot control• Variety selection• Promote vigorous growth with proper fertility and

irrigation practices.• Control foliar diseases and insect problems.• Avoid cutting hay when soils are wet.• Avoid heavy grazing.• Control weeds with herbicides and avoid cultivation

practices which damage crowns.• Avoid field sites with heavy or poorly-drained soils.• Rotate out of alfalfa for 2-3 years.• Heavy watering in the fall will delay dormancy

– Stop watering end of September

Stem nematode in alfalfa• Ditylenchus dipsaci

White flagging Stunted plants, shortened internodesSwollen nodes Crinkled leaves (between veins)

Stem nematode on alfalfa• Spread by surface water runoff, irrigation,

wind-blown crop debris, infested hay, soil and crop debris clinging to equipment, humans and livestock, and with seed

• Prevent introduction of nematodes into a field• Rotate with a non-host (not alfalfa or sainfoin)

and control alfalfa volunteers 2-4 years• Some resistant lines (not completely resistant)• Cut infected fields slightly higher and when dry

to reduce spread

Boron deficiency in alfalfa• Can result in hollow, corky stems;

bushy plant; yellow/reddish leaves

• Test soil; apply fertilizer containing boron

Alfalfa mosaic virus

• Vectored by aphids

• Symptoms masked by heat

• Wide host range: most legumes, many weeds, potatoes

• Transmitted mechanically and in seed

• Makes plants more susceptible to winterkill

Brown root rot of alfalfa• Phoma sclerotioides

• Most active in late winter and early spring

• Very broad host range, including grasses

2006 Survey

BRR survey• About 250 crowns collected from MT

• PCR analysis of crown lesions

• Zero positive so far (may have been too warm when collected?)

• Will test DNA for other crown rot pathogens– Stemphylium botryosum– Phytophtora medicaginis– Aphanomyces euteiches