Check Alfalfa Stands And Make A Plan

Low forage inventories and increasing risk for alfalfa winter kill makes assessing spring alfalfa health essential. Walking fields early this spring to determine alfalfa population; assessing if plants are dead or unhealthy or if the stand has thinned is a proactive strategy to maximize management options such as re-seeding. Deciding to manage a reduced stand, or replace it, can be a tough decision, but with tight forage inventories there isn't much room for ignoring the issue until you find yourself with a feed shortage. Don't wait until it is too late to implement useful options, such as reseeding in the rotation.

Alfalfa Winterkill Risk Factors

Although it is always difficult to predict alfalfa winterkill, there are some risk factors lining up for this spring.

  • Alfalfa was stressed in 2013 with low yields.
  • There was significant potato leafhopper damage across much of the province.
  • Aggressive 4 cut systems are at a higher risk of winterkill and stand thinning than 3 cut systems.
  • Cutting during the Critical Fall Harvest Period due to forage shortages
  • Alfalfa prefers cool, dry fall weather for good winter hardening, but much of Ontario was wet into October and November.
  • 2012-13 winter temperature fluctuations, melted snow followed by cold temperatures and some ice sheeting.
  • Hopefully, we will not experience late-winter freeze-thaw cycles that result in alfalfa heaving.

(Refer to Risk of Alfalfa Winterkill http://www.omafra.gov.on.ca/english/crops/facts/91-072.htm

Frost Damaged Alfalfa http://www.omafra.gov.on.ca/english/crops/facts/frostdamaged.htm. )

Check your older fields, fields that are slow to green-up, poorly drained fields, fields with low fertility and pH, and fields that were aggressively cut last fall during the Critical Fall Harvest Period.

Plant Counts

Assessing whether to keep an alfalfa stand or not, can begins early spring at green-up after the plants have broken dormancy. Counting the number of plants (crowns)can give you an estimate of stand density. The limitation of using plant counts is that it doesn't account for the size of the crown or the number of stems potentially growing from each plant.

Alfalfa plant populations decline with age, but crowns get larger with more stems. Table 1 provides the minimum number of healthy plants per square foot for a desirable alfalfa stand. Mature stands (3rd year after establishment or older) should ideally have 3 or 4 plants/sq ft, but crown size and health should also be considered.

Table 1 - Alfalfa Plant Count Guidelines (per square foot)

Stand Age Good Stand Consider Replacement
Seeding Year
25 - 40
<15
1st year
>12
<8
2nd year
>8
<5
3rd year
>6
<4
4th year or older
>4
<3

Stem Counts

Stem density is the best indicator of yield potential from a stand. Initially, counting stems per square foot seems very tedious, but with some practice it can be done visually fairly easily and accurately. The limitation for measuring stem counts is that you can't do this until there is enough growth to count, about 4 - 6 inches. This may delay your decision and possibly the seeding date of resulting necessary new seedings. Like plant counts, stem count numbers assume no significant additional yield contribution from grasses. As a general rule, 55 stems per square foot provide a maximum yield. The critical level of 40 stems per square foot or less will result in a 25% yield reduction and should be rotated.

Dig & Check For Plant Health

It is very important to consider the health of alfalfa plants in addition to plant or stem densities. To properly assess forage stands you must inspect the field in several locations. This involves digging up plants with a shovel to get at least 6 inches of root. Look for large, symmetrical crowns with good leaf and bud vigour, and resistance to bark peeling. Lateral roots should be healthy and with good nodulation. (Figure 1) Using a sharp knife, slice the crown and root longitudinally. (Figure 2) Healthy plants will have a good internal root colour (white to cream colour) and firm in texture. Diseased plants will have dark brown, mushy areas of crown and root rot. Damage from disease get worse with time, not better. Dead or dying plants won't contribute to yield.

Cost of Reseeding Easily Covered By Rotational & N Benefits To Corn Crop

Although there is sometimes a tendency to think planting new forage stands is expensive, it is relatively cheap considering potential yield losses in old stands and the benefits to the corn crop following in the rotation. Trying to squeeze an extra year out of a stand can be costly. New alfalfa stands reach maximum yields in the year following establishment. Yields gradually decline with age. By the third year, yields sometimes decline by 20 - 25%. That is a lot of lost hay yield that cannot be justified compared to the cost of shortening stand age by a year or two!

The recommended nitrogen (N) credit to a corn crop following alfalfa is 100 lbs N worth about $60 - 70. Research shows that there is also a yield benefit to corn following alfalfa of about 10 - 15%. Assuming 20 extra bu/ac at $5/bu, this is worth $100. Together, the N credit and rotation benefit goes a long way to covering forage establishment costs in another field in the rotation.

Figure 1 - Assessing alfalfa for plant health - things to look for. (Banks, OMAFRA),leaf & bud vigour, cut open to access internal root colour, look for later roots, resistance to bark peeling

Figure 1 - Assessing alfalfa for plant health - things to look for. (Banks, OMAFRA)

Figure 2 - Cut alfalfa crowns and roots to assess internal root colour and texture.(Banks, OMAFRA), cut open to assess internal root colour, leaf & bud vigour, look for lateral roots, resistance to bark peeling

Figure 2 - Cut alfalfa crowns and roots to assess internal root colour and texture.(Banks, OMAFRA)


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca