The use of certified seed, rather than common seed, is strongly recommended. Only by planting varieties is it possible to know in advance whether the seed will provide the yield, persistence, disease resistance and maturity that is required for each specific field and farm operation.
Careful consideration of varietal traits will help match the right variety to environmental and management conditions in each field. There are no longer third-party alfalfa variety trials conducted in Ontario, so producers are encouraged to check results from neighbouring provinces and states.
Fall Dormancy and Winter Hardiness
Alfalfa varieties are assessed on how much growth occurs after a fall cutting and given a score from 1 to 11. The higher the number, the more aggressively the variety grows late in the fall and early in the spring. This faster regrowth contributes to higher yield. However, high fall dormancy scores (5 and greater) also translate into poor winter survival. These varieties may break dormancy too early in the spring and be injured by a late frost, and often do not start acclimating for winter early enough in the fall.
In most of Ontario, varieties rated fall dormancy (FD) 4 are best suited to growing conditions. However, growers should consider an FD 3 variety if winterkill is an ongoing issue and the following apply:
- Before winterkill, stand establishment is uniform and plant populations are good.
- A current soil test indicates fertility is adequate for alfalfa production.
- Pest and disease pressures have been minimal.
- The field has not been cut during the fall rest period.
Winter hardiness has been somewhat disconnected from fall dormancy in varieties with FD ratings between 1 and 4. Many varieties are given a separate score for winter hardiness. These range from 1–6, with lower values indicating more tolerance to cold conditions. A winter hardiness value of 2 will suit most of Ontario.
Insect and Disease Resistance
Disease Resistance Index
Diseases reduce the yield, quality and persistence of alfalfa. Alfalfa varieties are assessed for their resistance to the following diseases:
- bacterial wilt
- verticillium wilt
- fusarium wilt
- anthracnose
- phytophthora root rot
- aphanomyces root rot (race 1)
- aphanomyces root rot (race 2)
The disease resistance index (DRI) combines the resistance ratings of all these diseases (Table 1) into one number. Some trials do not test for aphanomyces root rot (race 2), so a perfect DRI rating without this test sums to 30 rather than 35. A variety that is susceptible to all the tested diseases would receive a DRI of 7/35, while a variety that was highly resistant to everything in the index would rate 35/35.
| Resistance Class | % Resistant Plants | DRI Rating |
| Susceptible (S) | 0%-5% | 1 |
| Low Resistance (LR) | 6%-14% | 2 |
| Moderate Resistance (MR) | 15%-30% | 3 |
| Resistant (R) | 31%-50% | 4 |
| Highly Resistant (HR) | >50% | 5 |
Potato Leafhopper Resistance
Varieties resistant to potato leafhopper have tiny glandular hairs on leaves and stems. However, the glandular hairs are not fully expressed during the establishment year, so while resistant varieties can dramatically reduce the potato leafhopper damage, yield reductions can still occur. Treatment thresholds for highly resistant (HR) varieties after the establishment year can be increased by 4 times those for conventional varieties. New seedings of potato leafhopper–resistant varieties should be monitored. Use conventional variety thresholds for potato leafhopper during the establishment year. See title and link for thresholds and more information about managing potato leafhopper in alfalfa.
Potato leafhopper–resistant varieties are particularly useful for farmers that do not scout or spray to control potato leafhopper. These producers may find the use of potato leafhopper–resistant varieties to be an easy and practical method to help manage the risk.
Root Morphology
Alfalfa roots can be tap, branching tap or rhizomatous (creeping-root), but most varieties grown in Ontario have taproots.
Varieties with branching roots were selected to be more tolerant of imperfect drainage than taproot varieties. Branch-rooted varieties have several taproots coming off the crown, but do not tend to root as deeply as conventional tap-rooted varieties.
Rhizomatous or creeping-root varieties have very wide crowns and develop lateral roots called rhizomes from which new alfalfa plants can develop. Creeping-rooted varieties have sunken crowns to withstand grazing pressure better than conventional tap-rooted varieties. Standard alfalfa normally requires a rest period of 30–35 days between grazing events, whereas creeping-rooted alfalfas may require a 45–50-day rest period.
Genetically Engineered Traits
Varieties of alfalfa with genetically engineered traits are available in Eastern Canada. Crops with these traits are not eligible for export outside North America. In addition, organic regulations do not accept any genetically engineered materials in Canadian certified organic crop production.
Glyphosate Resistance
Glyphosate-resistant alfalfa is marketed under the trade name RoundUp Ready. Alfalfa with glyphosate resistance will not be killed by label-rate applications of the herbicide glyphosate. This trait can be useful in situations with serious broadleaf weed challenges that require chemical control. The drawback is that planting a mixed stand is not an option. Some producers have planted glyphosate-resistant alfalfa in the spring, waited for weeds to emerge in the stand, sprayed the field with glyphosate, then planted grasses into the alfalfa in the fall. Otherwise, the trait is intended for managing pure stands of alfalfa.
Reduced Lignin
Genetically engineered reduced-lignin alfalfa was developed by Forage Genetics International and is marketed under the trade name HarvXtra. Lignin is a structural fibre in the plant that enables it to stand upright. Ruminants cannot digest lignin, so lowering the overall lignin content of alfalfa at a given stage of development makes the forage more digestible than normal. Higher digestibility in forage improves ruminant performance. Independent research in the U.S. has shown that the reduced lignin trait offers flexibility in alfalfa harvest schedules, as growers can choose to harvest higher-quality forage on their normal schedule or to delay harvest by 7–10 days to achieve higher yields of the same quality as their conventional production system. In some cases, this has resulted in the need for one less cut per year than under a conventional system. Reduced-lignin alfalfa should be grown and stored separately from conventional varieties, as animal performance will differ, and ration formulation should take this into account.