2001 Ohio Forage Performance Trials

Ohio State University Extension
Ohio Agricultural Research and Development Center
The Ohio State University

Horticulture and Crop Science
Series 195
December 2001

Alfalfa

     Alfalfa has the highest combined yield and quality potential of any adapted perennial forage grown in Ohio. It is the state's largest single hay crop, being grown on about one-half of the total hay acres. Alfalfa requires well-drained soils with near-neutral pH (6.5-7.0) for greatest production and persistence. Alfalfa trials are initiated each year and data is collected for at least four years unless the stand becomes so depleted that further testing is no longer worthwhile; variety performance should be evaluated over several sites and years.

Guidelines for Selecting Alfalfa Varieties

    To capitalize on alfalfa's potential, select high-yielding varieties with resistance to problem diseases. Consider these factors when selecting alfalfa varieties for Ohio:

1. Yield. Yield is the major factor in determining profitability of an alfalfa stand. Select varieties with high yields over several locations and years. Table 3 shows this comparison in percent of the average yield. Varieties that perform equally well across several locations and years are probably adapted to a wider range of environmental conditions. Stable yield performance across several environments is important because soils may vary on your farm and weather conditions vary from year to year. Conditions on most farms are such that several varieties may perform equally well.

2. Persistence. Another important consideration beyond yield is how long the stand will last. Study variety performance by age of stand to get an estimate of longevity of stand productivity. Some varieties may decline with age more rapidly than others. This may influence your choice of variety depending on how long you intend to keep the stand in production. For long-term rotations, choose varieties with good performance in the fourth or fifth year of production. If you plan to harvest alfalfa for three years or less, then high performance during early years of the stand should be given major consideration.

3. Fall dormancy (FD) Alfalfa varieties with fall dormancy ratings of 1 through 5 are considered adequately winter hardy for Ohio conditions while those of 6 or higher are not considered adapted. Varieties with higher fall dormancy ratings tend to grow at a lower temperature. Thus they begin to grow earlier in the spring and later into the fall, extending the growing season. Until recently it was generally felt that fall dormancy rating was very closely correlated with winter hardiness. This relationship with modern varieties seems less dependable. Now, for example, a variety with a "2" dormancy rating may not always have greater winter hardiness compared to one with "3" fall dormancy rating. Fall dormancy ratings provided by the seed industry are given in Table 1.

4. Disease and pest resistance. Variety selection based on yield performance alone is less satisfactory than selections that also consider disease resistance characteristics. Resistance to specific disease-causing pathogens may be the most important attribute in an alfalfa variety. Pathogens can dramatically reduce yield and persistence of susceptible varieties. For example, Phytophthora root rot resistance is often very important on s

oils that are less than well-drained. The disease resistance characteristics of alfalfa varieties included in this report and their local seed marketers are listed in Table 1. Below is an explanation of the information found in Table 1.

a. Bacterial Wilt (Bw) and Fusarium Wilt (Fw) Nearly all alfalfa varieties currently grown in Ohio have resistance to Bacterial Wilt and Fusarium Wilt. The widespread use of these varieties has greatly diminished the significance of these diseases. However, severe losses can still be incurred in stands of susceptible varieties.

b. Verticillium Wilt (Vw) First detected in Ohio in 1984, this disease still has limited distribution within the state, having been confirmed on 17 farms in 9 Ohio counties. It has been found in Ashland, Columbiana, Franklin, Holmes, Knox, Logan, Medina, Stark, and Wayne Counties. Verticillium Wilt is usually introduced into a field on infested seed and generally does not become a problem until the third production year. Scattered plants become yellow and stunted and gradually die, leaving a thin, unproductive stand.    

c. Anthracnose (An) Anthracnose occurs during hot, rainy weather. The fungus attacks individual stems and grows into the crown, causing a crown rot and eventual death of the plant. Severe losses can occur the second and third year after seeding in stands of susceptible varieties.

d. Phytophthora Root Rot (PRR) This disease typically occurs in heavy or poorly drained soils. However, when any soil becomes water saturated, the fungus may invade the taproot and destroy the plant. Even resistant varieties are fairly susceptible to Phytophthora in the seedling stage.

e. Root Knot Nematode (RRN) Damage from Root Knot Nematode is most likely to occur on sandy or organic (muck) soils. Small galls or 'knots' form on roots. These may be confused with nitrogen-fixing Rhizobium nodules.

f. Aphanomyces root rot (APH) may contribute to poor alfalfa establishment and reduced growth in wet soils. Seedlings may die (damping off) if infection occurs at an early stage of development. Older seedlings are yellowed and stunted. When aphanomyces and phytophthora occur together, they form a destructive disease complex.

5. Compare to check variety. For comparisons of varieties across several trials, always compare varieties to the same check planted within the trial. The variety Vernal is used as a check in all Ohio trials.

6. Use good management. No variety can produce well under poor management. Good management considers all aspects of alfalfa production: seed bed preparation, liming and fertilization, seeding, pest control, harvest, storage, and post harvest treatment. Many newer varieties are better adapted to intensive management.

The abbreviations for the column headings are: (FD) Fall Dormancy; (Bw) Bacterial Wilt; (Vw) Verticillium Wilt; (Fw) Fusarium Wilt; (An) Anthracnose; (PRR) Phytophthora Root Rot; (RKN) Root Knot Nematode; (APH) Aphanomyces Root Rot Race 1.

Resistance Key: 0-5% = susceptible (S); 6-14% = low resistance (LR); 15-30% = moderate resistance (MR); 31-50% = resistance (R); >50% = high resistance (HR). If the resistance rating for a variety is not listed, then the variety is susceptible or has not been adequately tested.

Summary of 2001 Alfalfa Crop Conditions

    The year began with a late spring but excellent stands for most varieties and vigorous spring growth at all locations. First harvest yields were average to high where alfalfa weevil infestations were controlled. Rainfall totals for April through August ranged from 4.42 inches above normal at S. Charleston to 4.40 inches below normal at Wooster (Table 2). Temperatures were well above normal In April, slightly above normal in May and August, and near normal to slightly below normal in June and July (Table 2).

    High forage yields were harvested from established stands at S. Charleston (Table 6) where rainfall was well above average. Forage yields were also high at Wooster, despite very dry conditions. This illustrates the tremendous ability of the alfalfa taproot to absorb moisture from deep in the soil profile. Alfalfa weevil damage was very heavy again this year and well above economic action thresholds at all locations in the spring. Insecticide application was used at all locations for control. Alfalfa weevil infestations were similarly high in growers' fields across the state. Early scouted fields suffered less yield lost if insecticide was used for control. Some fields were devastated in days once the alfalfa weevil began feeding. For more information on alfalfa weevil management see Ohio State University Extension Fact Sheet FC-ENT-32 (Alfalfa Weevil) available at the county extension offices and on the internet (https://ohioline.osu.edu/factsheet/ENT-32). Potato leafhopper (PLH) activity was low to moderate at North Baltimore, Wooster and Jackson but was very high for the second and third harvests at S. Charleston in trials where no insecticide was applied to control this pest (Tables 11, 14, 15). These trials are a continuing evaluation of the new glandular-haired alfalfa varieties that have improved resistance to potato leafhopper. 

    Three new alfalfa trials were seeded in April 2001. Trials were established at S. Charlestron (Table 8) and N. Baltimore (Table 9) to evaluate standard alfalfa varieties (not resistant to PLH). A trial was also established at S. Charleston (Table 15) to continue potato leafhopper resistance evaluations.