Assessing an alfalfa stand in fall determines which fields are likely to suffer winter injury and allows time for spring planning.
Sample plants from four representative areas of the field and use stem counts to estimate yield potential. Yields will not be limited in stands with 40 to 55 stems per sq. foot. Stands with fewer than 40 stems per sq. foot will experience some yield reductions.
To determine the stand’s ability to survive winter, assess root and crown health. Cut the top 15 centimetres of the root lengthwise and check for rot or discoloration in the crown and root.
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Healthy stands will have fewer than 30 percent of the plants with 40-50 percent rot or discoloration.
Stands with few stems and significant rot will have a greater chance of experiencing winterkill and subsequent yield reduction.
Herbicides perform best when alfalfa plants have reached 20 cm and are actively growing.
September is not too late to spray, if moisture is adequate for growth and there is enough time for the herbicide to translocate to the roots before the first killing frost.
If dry, leaving alfalfa removal until after the first cut in the following year is advisable.
A mix of Roundup (0.75L/ac) and Banvel (0.5L/ac) is effective if there are grass and broadleaf weeds. Banvel (0.5L/ac) and 2,4-D (0.4L/ac) mixes are effective if there is no quackgrass.
When using Roundup alone, do not drop below one litre per acre. Note the recropping restrictions on the product label when using Banvel.
Some alfalfa regrowth will likely occur in the following summer so be prepared for an in-crop broadleaf treatment.
