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Alfalfa Establishment

Seed alfalfa or alfalfa-grass mixtures only on well-drained soils. Seeding alfalfa following old alfalfa stands is not recommended, as this practice has led to stand establishment problems, which are thought to result in part from insect and disease buildup.

Alfalfa or alfalfa-grass mixtures may be seeded using conventional seeding equipment such as a cultipacker seeder or grain drill on a firm, well- prepared seedbed; or they may be seeded directly into corn stalk or small grain stubble using a special no-till seeder. No-till establishment requires special attention to weed and insect control, but if properly done it results in excellent stands with little or no soil losses. Plant as soon as a good seedbed can be prepared in spring or, for a mid- to late-summer seeding, in early- to mid-August. Late summer seedings need at least 8 weeks of growth before the first killing frost.

Band seeding no deeper than .25 inch is an excellent method of seeding. When band seeding or when using the no-till seeder, you may reduce recommended alfalfa seeding rates by one-third. Press wheels used in conjunction with conventional band seeding provide additional stand insurance. To ensure a firm seedbed, if seedbed is dry and press wheels are not used, cultipack before and after seeding in the same direction as band seeding. If annual crops such as oats or peas and triticale are used as a nurse crop, reduce the seeding rate of the companion crop by 30%, and harvest when the small grain is in the boot or early heading stage for silage, hay, or greenchop. Do not apply additional nitrogen for the nurse crop.

Fluid seeding-distributing seed in a carrier of water or fertilizer solution- is a new technique generally limited to forage legumes. Because fluid seeding requires special equipment for good seed suspension and distribution, custom application is recommended. Fluid seeding is a broadcast method, so for best results prepare the seedbed as in conventional seeding and cultipack after seeding.

Seeding rates necessary for successful stands are related to the condition of the seedbed and method of seeding.

Use preinoculated seed or treat seed with proper inoculant. If seed is preinoculated, look for the expiration date on the tag to see if reinoculation is necessary. This may occur if seed is not used soon after purchase or stored improperly.

Seed already treated with Apron (metalaxyl) fungicide is available to give protection against Phytophthora and Pythium. These fungal diseases can cause serious establishment problems in poorly drained fields or following extended periods of heavy rainfall. Apron fungicide is also available for self-treatment of seeds. The fungicide Ridomil is also available for soil application to protect against these same diseases.


Alfalfa Hay Harvest Management

Seeding Year - When alfalfa is spring seeded, the first cutting can be made 60 days after emergence if one cutting during the seeding year is allowed to reach early bloom before it is harvested. Normally up to two to three harvests may be made in the year of a spring seeding, depending on the length of the growing season.

Established Stands - Cutting management is an important tool in achieving high quality, high yields, and stand persistence. It also can be effective in reducing the impact of weed, insect, and disease pests. Harvest schedules depend somewhat on the quality goals of the producer. Progressive dairy farmers have recognized the economic importance of producing high-quality forage and often cut early in order to obtain greater than 20% crude protein, less than 30% acid detergent fiber, and less than 40% neutral detergent fiber. Such high-quality forage has the potential to increase forage dry matter intake and milk production while decreasing the requirement for grain.

For high-quality alfalfa, make the first cutting at mid- to full bud stage, so long as:

  1. Better adapted varieties with multiple pest resistance are used.
  2. Adequate levels of lime, phosphorus, and potassium are maintained.
  3. Insect pests are monitored and controlled.

Cutting pre- or early bud alfalfa is not recommended because there is a higher risk of losing the stand. Also, fiber levels may be undesirably low when cut extremely early. If an alfalfa stand has been weakened by winter stress, make the first cutting at the early- to midbloom stage.

Generally, summer cuttings are permitted to reach early bloom (approximately 35 days between cuttings). In Pennsylvania, the average cutting intervals between first and second cuts and second and third cuts, for producers who make four or more cuts per year, is 37 and 33 days, respectively.

In the past, it has been recommended that producers avoid cutting alfalfa during the critical 6-week period prior to the average hard frost date (generally between early September and mid-October). This should still be considered if the stand is weak due to such factors as low soil fertility, disease, or extreme climatic conditions (such as water-saturated soils). However, it has more recently been recognized that alfalfa can be cut even during this critical period as long as:

  1. Better adapted varieties with multiple pest resistant are used.
  2. Adequate levels of lime, phosphorus, and potassium are maintained.
  3. There are at least 45 days of regrowth prior to cutting.

If harvests are delayed until mid-October, leave a 4- to 6-inch stubble to protect the crown and to catch snow for added insulation over winter.

Harvest schedules for alfalfa-grass mixtures should be based on the growth stage of the alfalfa as it relates to the species of grass used in the mix. Because orchardgrass, perennial ryegrass, reed canarygrass, and tall fescue can tolerate more frequent cuttings without jeopardizing the grass stand, they are more compatible with frequently cut alfalfa. Stands of timothy or smooth bromegrass mixed with alfalfa should not be cut until the grass is in the early head-emergence stage, and cannot tolerate frequently cut alfalfa; therefore, they are more compatible with less intensely managed alfalfa (three cuts or less per year).


Alfalfa Grazing Management

Rotational grazing is a "must" for optimum returns in an alfalfa or alfalfa-grass grazing system. Rotational grazing is more labor intensive than continuous grazing because of the need to provide and maintain electric fencing and to move animals from one paddock to another on a carefully planned and executed schedule. Care also must be given to avoid damaging the alfalfa stand, because comparatively high numbers of animals graze on a relatively small area of alfalfa. However, the rewards can offset the extra effort.

There is no set rule on number of paddocks required or on paddock size. Most recommendations call for fields to be divided into a minimum of six to eight paddocks for most effective management. Paddock size depends on the number and size of animals being grazed. However, there should be enough animals in a paddock to harvest the available forage in less than four days.

As an example of a rotational grazing practice, a recent demonstration successfully grazing 24-beef cattle on a four-acre alfalfa plot. The field was subdivided into eight half-acre paddocks. After four days grazing on each paddock, the cattle were rotated. After all eight paddocks had been grazed, cattle were returned to the first paddock, which had recovered and was ready for another round of grazing.

Determining the number of animals that each acre of alfalfa will support in a grazing system is a difficult process. The number of animals per acre can be increased as alfalfa becomes more productive beyond the first year of stand life and as the management skills of the farm operator improve. A conservative suggested is 2 to 3 dairy cows or 3 to 5 stockers per acre during the early part of the grazing season.

The number of animals per acre is normally reduced when alfalfa production declines, such as during the typical mid-summer slump period. It is very important to closely monitor grazing to prevent overgrazing. Overgrazing can force animals to consume more supplement, if one is supplied, increasing production costs. Overgrazing also may force animals to eat the basal stems which are not very nutritious, thus limiting animal gain. Severe overgrazing also could damage the crowns of the alfalfa plants.

Undergrazing, on the other hand, can lead to uneven grazing. When unevenly grazed, the remaining plants become larger and less palatable. When the field is grazed again, the animals once more will favor the young tender plants. This in effect reduces the productive acreage unless the older, larger plants are clipped periodically.

One or more "sacrifice" paddocks also enhance a grazing program where alfalfa is the main forage. A sacrifice paddock is an area, preferably with grass sod, that can be used to hold animals during wet weather or to allow adequate regrowth of the alfalfa paddocks. Hay may be fed in sacrifice paddocks to keep pasture growing at an optimum rate.


Alfalfa Fertility

Before Planting -Information on adjusting soil nutrient levels before seeding is available.

During Establishment - Have a soil test taken to determine lime and fertilizer needs for alfalfa establishment. Fields to be seeded to alfalfa should be limed to pH 6.5 to 7.0. Needed lime should be applied at least 6 months to a year before seeding to allow the lime time to react with the soil and minimize triazine herbicide carryover. For maximum production, seed only in soils that are already at a pH of 6.2. Generally, for soils below this pH, lime should be applied but seeding delayed. Starter fertilizer applications of up to 20-60-20 per acre are desirable at seeding time. Band placement is highly recommended. Plant nutrients recommended in excess of this amount should be incorporated into the seedbed before seeding. If soil test recommendations are followed at planting, additional applications of fertilizer in the fall of the seeding year are not necessary.

Established Stands - High levels of phosphorus and potassium must be maintained in the soil for high crop yields and long-lived alfalfa stands. Determine lime and fertilizer needs by soil test. High alfalfa yields can reduce plant nutrient levels in soil rapidly. Thus, for top production and stand persistence, annual soil testing is recommended.

When a soil test indicates the need for fertilizer, topdress after first and/or last cutting. Split applications, one-half in fall and one-half after first cutting, may result in more efficient use of fertilizer, especially potash. Recent research suggests that, based on nutrient removal, a 0-1-4 ratio of N-P2O5-K20 is best when high yields are anticipated. If the soil test is 1 part per million (ppm) or less of boron (B), or plant tissue has 25 ppm or less B, then topdress with a fertilizer containing at least 2 pounds of B per acre.

At present, there is no evidence to indicate a general need for other fertilizer nutrients. Recent research does suggest that in certain isolated cases small responses from sulfur may be obtained.


Managing Weeds in Legumes

Managing weeds in forages requires a different approach than weed management in row crops. Over 95% of the weed control in a healthy forage crop comes from the competition provided by the forage. However, to maintain a relatively weed-free forage, proper fertilization, cutting management, insect control, the use of disease-resistant varieties, and selective herbicide use are necessary to keep the forage stand competitive.

If weeds become a problem, they can compete or interfere for light, nutrients, water, and space, directly influencing yield and standability. Common chickweed infestations in alfalfa have been reported to reduce forage stand by more than 30%. Common chickweed emerges in the fall and winter and early in spring develops a thick lush mat that can compete with the first forage cutting. Once the chickweed dies in early summer, summer annual weeds such as foxtails, lambsquarters, and pigweed or perennial weeds such as dandelion can replace the dead or dying winter annual weeds and continue to reduce forage yield and quality.

Unlike most grain or fiber crops from which weeds are separated at harvest, weeds are often harvested along with the forage crop, potentially reducing quality. Reductions in quality are often in the form of lower protein content and feed digestibility. Although weeds do have some feed value, this value differs among species. Dandelions come close to equaling alfalfa in protein and total digestible nutrients (TDN). Control of dandelion may not necessarily improve the quality of hay, but it may be of some value in reducing the time necessary to dry the hay, since dandelion dries more slowly than alfalfa. Increased drying time may mean greater harvest losses due to untimely rainfall.

Grassy weed quality can be similar to that of the forage. In general, weedy grasses have about 75% of the quality of alfalfa. However, controlling quackgrass in alfalfa can increase forage protein levels 4% to 7%. Weeds with woody stems or flower stalks, such as yellow rocket, white cockle, rough fleabane, curly dock, and broadleaved dock, have lower protein levels (about 50% of the quality of alfalfa), so controlling them is even more important.

When weeds are present or persist in spite of good management, herbicides can help improve yield and quality. Weed control at establishment or in the seedling year is most critical for maintaining a healthy forage stand. When weeds are controlled the seedling year, the forage crop seldom requires additional herbicide treatments for at least the first two years of the stand.

Weed management in forages can be divided into two phases: control in the establishment or seedling year and control in an established stand.

Control before and during establishment

Managing weeds in forages begins long before crop establishment. Certain types of weeds are potentially serious problems for forages, so it is important to eliminate them in advance. In particular, perennial broadleafs and grasses such as dandelion, curly dock, Canada thistle, and quackgrass are much easier to manage prior to planting a forage crop. In addition, biennial weeds including musk thistle and burdock should be eliminated before establishing forage. If these weeds are not removed before the seeding is made, they commonly persist throughout the life of the forage. The cost of controlling weeds before or at the time of seeding should be considered an investment that will be returned for the life of the stand.

Below are some general rules for managing weeds at establishment or in the seedling year:

  1. Weeds that emerge with the crop are generally more destructive.
  2. Maintain the forage relatively weed-free for the first 60 days.
  3. Weeds that emerge beyond 60 days will not influence that year's forage yield.
  4. Later-emerging weeds may still influence forage quality.
  5. Winter annual weed competition in early spring is most damaging to forages.
  6. Broadleaved or dicotyledonous weeds are generally more competitive against legumes than grassy weeds.

Herbicides are needed most often during establishment, and several options exist for managing weeds in pure legume seedings. In no-till seedings, adequately controlling the existing vegetation is very important, especially perennials. Weed control is also very important while the forage is young and prone to competition from invading species.

Control in an established stand

The best weed control in an established forage stand is achieved by maintaining a dense healthy stand through proper fertilization, cutting management, and insect control. Controlling weeds in established forages is normally of greatest benefit in the first cutting. Weeds generally contribute much less to yield in the second and succeeding harvests. Before using a herbicide in established stands, evaluate the forage to ensure it is worth the cost of the herbicide.

Below are some general rules to follow before using a herbicide in established forage stands:

  1. Thin or irregular stands will not thicken once weeds are removed. Be sure there are sufficient desirable species to fill in the gaps. A minimum of five alfalfa plants per square foot should be present.
  2. Weeds tolerant of the herbicide may invade the space left by susceptible species, ultimately creating a more severe weed problem.
  3. Only well-established vigorous stands should be treated with herbicides.
  4. If the forage stand is at least two years old and 25% to 30% are weeds, removing them with an herbicide application is of questionable value.
  5. If 50% or greater of the stand are weeds, it is time to rotate to a different crop.

If weeds become a problem in established forages, several herbicide options are available. Chemical control in established forage legumes is often limited to late fall or early spring applications. Also, many products have harvesting, feeding, or grazing restrictions following their use.


Managing Legume Insects

Management of forage insect pests is aimed primarily at the alfalfa weevil and the potato leafhopper in alfalfa. Other insect pests of forages are minor in comparison and must be dealt with on a field-by-field basis. Economic injury levels for the potato leafhopper and the alfalfa weevil are fairly well established. The economic injury level is the value of crop loss caused by the pests that is equal to the cost of a spray application. Thus, unless the value for the crop loss caused by the pests exceeds the cost of controlling them, it is not profitable to spray. On the other hand, some insect losses could have been avoided if a spray had been applied at the proper time.

A good pest management program requires proper identification of the pest species causing the damage, and determination if the economic threshold has been exceeded.

Alfalfa blotch leafminer can be found in practically all alfalfa fields in the state (Pennsylvania). However, damage will always appear worse than it actually is. The second cutting is usually most severely infested. Control may be justifiable if 30% or more of the leaflets have a mine present.

The adult fly is about .13 inch long and resembles a common housefly. The larvae (maggots) are pale yellow, soft-bodied, shortened, and thickened. At least three generations per year occur in Pennsylvania. Adult females emerge in the spring, cut shallow holes through the lower leaf surface, and deposit eggs under the leaf epidermis. A female lays one to three eggs per leaflet. To feed, the female cuts a hole in the leaf with her oviposter and laps up exposed sap and tissue, forming conspicuous pinholes in the leaves. After the eggs hatch, the larvae tunnel within the leaf, feeding on leaf tissue. The larval stage lasts approximately two weeks. Larval mining causes conspicuous white blotches on the leaflets, which are typically comma-shaped. Blotches and punctures can cause deterioration of foliage quality, loss of photosynthetic area, and defoliation.

Alfalfa weevil is primarily a problem in the first cutting of alfalfa in April and May. Larvae feed within the growing tips, on the upper leaves as they open, and later on the lower leaves. Plants become skeletonized from weevil feeding and the leaves dry, giving the field a frosted appearance. After cutting, the larvae may feed on the new emerging shoots, severely retarding alfalfa regrowth. Adults also feed on the alfalfa plant. Conditions that favor pest development are excessive pesticide use (which destroys biological control agents), mild winters, and warm dry spring weather. Several species of parasitic wasp and a fungus help maintain alfalfa weevil populations.

Black cutworms can cause extensive damage to new seedings in late May early June.

Pea aphid control is sometimes needed, but natural controls are usually all that is needed to keep aphid populations in check. Control may be warranted if populations reach 30 aphids per sweep of an insect net.

Pea aphids are small, green, long-legged insects about .19 inch long. They can be winged or wingless. Like other aphids, the pea aphid damages the plant by removing sap with its sucking mouth parts and possibly by poisoning the plant.

The insect overwinters on alfalfa, clovers, and other perennial plants in either the egg stage or as adult females. In the spring, populations increase on the winter host and begin migrating to other hosts about May 1. Winged females start colonies on new plants by giving birth to live young, which are ready to reproduce in 12 days. A female commonly produces 6 to 7 young per day. There are 7 to 20 generations per year. Pea aphids may be found in forage fields during June and July.

Potato leafhoppers are the most destructive insect pest on new seedings of alfalfa in the state. Stress to alfalfa seedlings caused by this pest can affect the vigor and later performance of the plants and influence stand longevity. New spring seedings are especially vulnerable to attack by leafhoppers. Regrowth of second and third cuttings of established stands is also frequently damaged.

It is essential to use sound control measures for this pest on new seedings in order to obtain optimum stands, yields, and quality. In most years, leafhopper populations are high enough in some fields to cause appreciable losses to newly established stands.

There are several ways to reduce leafhopper damage to the first cutting of new seedings:

  1. leafhopper populations can be monitored by periodical sweepings and applying an insecticide accordingly;
  2. Furadan (carbofuran) 4F can be broadcast and incorporated prior to seeding;
  3. Lorsban (Chloropyrifos) 4E can be broadcast and incorporated prior to seeding. Furadan 4F may be used at seeding time by mixing 2 to 4 pints of Furadan 4F in 15 to 40 gallons of water and spraying on the soil surface; then incorporating. If a herbicide is being used, mix it with Furadan 4F and apply both materials in the same operation. Lorsban 4E can be broadcast and incorporated prior to seeding.

At the time alfalfa is typically seeded in the spring there are no insect pests that will influence yield, with the possible exception of cutworms. Clover root curculio do not lay eggs in spring-seeded alfalfa, because they have already moved into established stands when new seedings are seeded. The same is true of alfalfa weevil, which migrate into established stands to lay their eggs in late March and early April. Furadan and Lorsban cannot be expected to provide adequate leafhopper control on alfalfa seeded before early May.

The effects of Furadan and Lorsban will not last much longer than 45 to 50 days; therefore, their effectiveness will be minimal by the time the leafhoppers arrive, usually in early June. Even when Furadan or Lorsban is used at planting, spray protection may still be needed before harvest, depending on the buildup of leafhoppers in the field.

Regrowth after the first cut must be monitored closely for insects, starting when the regrowth is 2 to 3 inches tall.

Currently, the only control method for potato leafhoppers on seedling alfalfa established in spring grains such as oats is malathion. However, this compound has a very short residual and application requires driving over the alfalfa and small grain.

Leafhopper populations often vary considerably from one field to the next. For this reason, it is advisable to make leafhopper checks with an insect net in each alfalfa field. Start checking new seedings in early June, and check the regrowth of established stands when the plants are about 3 inches high. Adult potato leafhoppers are yellowish green and about .13 inch long and .03 inch wide. The nymphs are similar in appearance but lack wings. Damaging populations may be more likely when temperatures are between 70 and 90 degrees F, harvest is delayed, or alfalfa is strip-cut or cut in blocks.

Meadow spittlebug damage is most likely on legumes seeded in small-grain stubble. Spray applications are not profitable unless there are one or more spittle masses per stem by mid-May.

The adult spittlebug is .25 to .38 inch long and resembles a frog; its head is short and blunt with large eyes. Adults vary in color and marking, ranging form light grey to dark brown, with spots, strips, or bands on the wing covers. Adults walk with their front four legs and drag their back legs. The nymphal stage is found within the frothy spittle mass that they secrete. They are about .03 inch long and orange. As they develop, they become greenish yellow and then green.

Eggs are laid during August and September in small-grain stubble, alfalfa, or weeds where they overwinter. They begin to hatch during April in Pennsylvania. The nymphal stage lasts approximately 5 to 8 weeks. Adults appear in late May and early June to lay the next year's eggs.


Managing Legume Diseases

The following management practices will help minimize disease losses in alfalfa. Most of these recommendations apply to other legumes as well.

  1. Use the best-adapted, disease-resistant varieties.
  2. Do not plant alfalfa in fields that are poorly drained. Red clover, birdsfoot trefoil, or a grass is a better choice. In fields that are moderate to poorly drained, Phytophthora-resistant varieties should be used along with a fungicide seed or soil treatment.
  3. Use a cereal, corn, or grass crop for at least 2 years in rotation with alfalfa.
  4. Keep soil pH, phosphorus, and potassium at optimal levels for crop growth.
  5. Control leafhoppers, as they interact with diseases.
  6. Clean all equipment of plant debris before storing for the winter, as some pathogens that do not survive well in the field survive well on equipment under shelter.
  7. Mow youngest stands first. This reduces the spread of pathogens by machinery from older, more diseased stands into healthier, younger stands. Mow after the dew has dried, as pathogens are easily spread in water films.
  8. Mow a few days earlier than usual when stands are hit hard by leaf spots, in order to retain more leaves and reduce inoculum in the field.
  9. Maintain a cutting schedule that ensures the recharging of root carbohydrates both during the growing season and prior to fall dormancy.

Wilt diseases can cause severe stand losses in Pennsylvania. Bacterial, Fusarium, and Verticillium wilts occur statewide, with Fusarium wilt worse in the southern counties and Verticillium wilt worse in the northern counties. Resistance to all these wilts is available in current varieties and is needed to obtain maximum production.

Anthracnose is a fungus disease that occurs statewide and is particularly severe in southeastern Pennsylvania. The causal fungus often cannot overwinter in the field, but it does so in infected plant debris on equipment in storage. Therefore, cleaning equipment before storing for the winter helps delay the introduction of this pathogen into young seedlings in spring. Resistant varieties are available and should be used statewide.

Phytophthora root rot can devastate young stands of alfalfa and can cause serious plant loss in older stands. Soils saturated with water for three or more days can trigger a disease outbreak. In perennially wet sites, the use of alternative crops is recommended. The use of resistant varieties, seed treatment with Apron fungicide, or soil treatment with Ridomil fungicide are effective control measures.

Crown and root rot complex, caused by Fusarium spp. plus other fungi and bacteria, is common in alfalfa. Resistant varieties are not available; therefore, growers must depend on proper crop management practices to minimize stress on the plants, which slows down the rate of root rot development. Root-rotting fungi "team up" with root-feeding insects, and root deterioration progresses with increasing stand age.

Aphanomyces root rot is a new disease that is causing establishment problems in other areas. As yet, no outbreaks of the disease have been reported in Pennsylvania, although both strains of the pathogen are known to exist in Pennsylvania soils. This disease is likely to occur under the same wet soil conditions as does Phytophthora, so it is possible that losses caused by this fungus have been occurring but have been attributed to Phytophthora. The fungicide treatments available against Pythium spp. and Phytophthora spp. are not effective against Aphanomyces spp.; however, resistance to one of the strains of the fungus is available in some newer varieties.

Foliar diseases are common in Pennsylvania throughout most of the growing season and can cause significant quality and yield loss through defoliation. When foliar diseases are severe, early mowing helps in leaf retention and reduces inoculum in the field. Some of the current varieties have improved levels of resistance, but all become diseased if favorable moisture and temperatures prevail.

Spring and summer blackstem occur in Pennsylvania, with spring blackstem usually more severe. Leaves, petioles, and stems are attacked, with the spring blackstem fungus also causing crown and root rot. As with other foliar diseases, early harvesting of severely diseased stands can increase leaf retention and reduce inoculum in the field. A few current varieties have improved levels of resistance, but all will become severely diseased if extended moist periods occur.

Nematodes generally do not cause serious problems on alfalfa in Pennsylvania, as long as rotations with corn, cereal, or grass crops are used.

Sclerotinia crown and stem blight can cause seeding failures. Late- summer or early-fall seedings using conservation tillage favor disease development. The infective stage for this disease usually occurs in October, and fall-seeded plants are very susceptible at this time. Because conservation tillage does not bury the fungus, disease severity is often much more severe than in seedings done with conventional tillage. Infected seedlings often survive until spring when the plants die and entire stands may be lost. Spring plantings, because of the plants' increased maturity in the fall, are not as likely to be devastated. Resistant varieties are not available.

Virus diseases are not considered serious on alfalfa in Pennsylvania. Viruses may be present, however, without causing obvious symptoms, and it is possible that viruses contribute to premature stand decline. No resistant varieties are available.


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This page was last updated on November 16, 2002