Ecological Agriculture Projects Logo

EAP Publications | Virtual Library | Magazine Rack | Search | What's new

Join the Ecological  Solutions Roundtable



Forage Alfalfa


Environmental Interrelationships

As we view pictures of our small planet from outer space, as taken from space machines, we become aware of the fact that life as we know it, is limited to this earth of ours. We also realize that the soil, water, air, weather, plant life, animal life and man all share an interdependence, one with another. We are all part of one earth, ours! Quality soil, air and water are limited and precious resources. They are essential to the good life we seek.

Not all is good. We share this earth with many biological organisms and physical factors which are hostile to our well-being. Pest insects, mites and vertebrates, weeds and plant diseases, all challenge our ability to live comfortably and to produce needed food and feed crops Man's survival requires him to combat, and if possible control these pests.

Breeding for Pest Resistance in Crops

ln recent decades, plant breeders have produced several crop varieties which are resistant to certain pests. These resistant varieties are able to withstand, or at least tolerate, the attacks of insect pests or diseases. They are often resistant because of protective structures such as thick or spiny leaves, or internal generic defenses The use of pest-resistant crops is usually inexpensive and their use minimizes or eliminates the use of pesticides

Cultural Control Practiced

The manipulation of pest populations by such methods as cultivation and crop destruction after harvest, are old and sometimes still effective forms of pest control. Plowing both aerates the soil, and disturbs the life cycle of soil inhabiting pests. The breeding places of some insect pests can be altered by destroying the remains of a crop, such as the stalks. Crop rotation is a proven method of minimizing many insect pest problems. Other cultural control methods include such practices as planting or harvesting crops at times which favor the plants, but discourage the pests.

Biological Control

One long known method of control is the use of natural enemies to control pests, especially pest insects. These predators and parasites may be native to an area, or they may be introduced by man. When effective, they will hold populations of pest species at or below economical levels. Unfortunately pesticide applications often destroy these beneficial insects, allowing the pest populations to rapidly build up to damaging levels.

Insect pathogens, or disease-producing micro organisms are sometimes used effectively in pest control for the following reasons.

a. They attack only the target pest.

b. They usually cause no damage to the environment

c. They may be highly compatible with other methods of control.

Conventional Chemical Pesticides

When properly used, most pesticides will provide needed control of pest species with a minimum of damage to the environment. However, accidental use, or overuse can result in serious problems. It is important that all pesticide applicators use these chemicals according to label instructions. IPM allows for the use of pesticides under rather restrictive conditions, and often in conjunction with other approved methods of control. Pesticides are tools used, in IPM programs when pest populations economically justify their use.

Other Techniques

There are many other techniques which can be used to control crop, livestock, range and public health pests. We have only mentioned a few of them

Protect the Environment

When controlling any pest, we want to avoid damaging the quality of the soil, air and water We also want to avoid injury to man and other non-target plants and animals.


Pest population monitoring by scouting involves the actual inspection of crops by pest management specialists These scouts determine the prescience of pest insects, diseases and weeds They then determine the implications of the infestations If the pest populations are large enough to threaten the yield, such a condition is referred to as the economic threshold At this point, the grower will need to make the decision to treat, and if so, what control procedure to use, or not to treat This approach differs from the fixed-schedule method of treating in that the grower treats only if his crop is threatened. There are situations where this pest management approach is more economical than the fixed-schedule routine.

Integrated Pest Management

A consideration of level of pest populations present, the economic implications and a selection of the best combination of control techniques available is termed integrated pest management, and that is what this is all about.

The Ideal

The IPM goal is to use control techniques, or pest suppression if you will, that reduces the numbers of real pests without a marked reduction in other life systems.


Alfalfa is the principal cultivated forage crop in this region. It is commonly irrigated but is also grown without irrigation under favorable conditions. No other forage crop can produce as much high protein feed (up to 10 tons) per acre, per year. Most dairy and beef cattle feeders depend upon alfalfa hay as the major protein, mineral and vitamin source in their animal rations.

Alfalfa is a perennial crop which persists for several years, thus spreading the high establishment costs over several seasons. From one to five crops may be harvested annually depending on the length of the local growing season and the availability of irrigation water. Some alfalfa. is grazed and some is green chopped for manger feeding, but the hazard of ruminant bloat and short season availability restrict such uses. Most alfalfa is preserved for future or distant use as haylage (silage) or as a dried product.

We have come a long way from the high labor requiring methods of the past to the sophisticated machine methods of the present. Nearly all alfalfa is now cut with a swather and dried in the field. Once dry, the producer may choose one of several handling systems, such as: (1) partial drying and ensiling, (2) chopping and stacking (3) wagon pick-up and small stacks (4) regular baling for bales up to 120 Ibs. each, (5) new balers for up to 1-ton bales (4' x 4' x 8') (6) cubing, and (7) dehydration and pelleting.

As much hay is now moved from point of production to a distant use point - even overseas - newer methods emphasize high density, machine loading and unloading, quantity handling and high quality for maximum milk or meat production.

Many new varieties are available every year requiring constant variety testing to determine yielding capacity, quality of hay produced, length of stand life, and resistance to diseases and insect pests. For example, some 25 new varieties were released in two years (1975-76) of which 19 were private (company-owned) and 6 were public (experiment station released) varieties. Alfalfa hay production is coming of age and price increases coupled with high demand have greatly stimulated production.

Fortunately, a certain amount of pest damage can be tolerated in the crop before control by pesticides is warranted. For this reason, alternate methods of pest control are often worthy of consideration. In the remainder of this text, we are going to examine various pests of alfalfa and briefly discuss different methods for their control.


Alfalfa is an excellent forage plant for most livestock It is also a host plant of choice for a large number of insects, and some mites. One of the major insect pests of alfalfa is the alfalfa weevil. It is widespread throughout the West and is often the most damaging pest of alfalfa.

Anyone of several different pests are capable of destroying an alfalfa field. When present in large numbers, they are considered major pests. When present in small numbers, they are considered minor pests Examples of such insects are, alfalfa weevil, alfalfa looper, armyworms, cutworms, wireworms, Lygus bugs, pea aphid, Blue alfalfa aphid, spotted alfalfa aphids and thrips Mites are usually present only in small numbers.

The farmer harvests what is left after the pest insects and mites have had first shot at the field. He harvests only a percentage of the potential yield. His share is often only 80 to 90 percent of what the yield would have been had it not been for the pests.

It isn't uncommon in a typical first crop alfalfa field to find a half dozen insect pests feeding on the crop Individually, these are rarely a problem unless they are present in large numbers. Collectively, they are rarely a problem unless their numbers are large and increasing Fortunately, indigenous insect predators and parasites usually hold the pest numbers in check. Usually by the time any pest insect is present in threatening numbers, the alfalfa can be cut and the problem is resolved for the moment.

Scouting and Surveillance

The key to determining the extent of pest inset t and mite infestations in forage alfalfa is by frequent monitoring of the fields, usually once a week during the growing season. This monitoring or scouting is usually done by a person trained in surveillance techniques, who knows the insects and the significance of the observations being made. The scout keeps the grower informed as to his findings. This can be done be recording the results on a c hart kept at the farmer's residence, usually in the barn. Growers can also be kept informed to some extent by means of a weekly newsletter

Management of Pests

Successful farm management practices, such as the selection of a good variety of alfalfa, one which is resistant to most aphids, good seed bed preparation, fertilization, irrigation, weed disease control, all contribute to healthy, fast-growing alfalfa, alfalfa which can tolerate some pest infestation. Fortunately, many insect and mite predators and parasites already exist in most alfalfa fields. These insects are the growers best friends and everything should be done to protect them Probably one of the most valuable, naturally occurring parasites of the alfalfa weevil is the tiny wasp (Bathyplectus curculionusl. This insect often parasitizes over 50 percent of the weevil larvae present in a field. Many other naturally occurring insect predators and parasites are: ladybird beetles, damsel bugs, Collops, lacewings, big-eyed bugs, minute pirate bug, syrphid fly larvae and predaceous mites The present e of these beneficial insects and mites in the fields is one very good reason why sprays should not be used unless the pest insect populations becomes threatening.

Careful monitoring of fields by scouts will indicate if the natural predators and parasites are keeping the pest insects and mites under control. If, for some reason such as the influence of weather, the pest populations are threatening and immediate control is warranted, then, after careful consideration, approved pesticides should be used Growers should not try to exterminate all of the insects and mites present in their fields, but rather, select a chemical which will provide reasonable control of the pests with a minimum amount of damage to the Beneficials, including the various kinds of bees which frequent the fields.

Essential Biological Data

Next, let us briefly consider the biological data essential to the development of I PM

We need to know the biology, distribution, host range and behavior of the pest species. As a reference point, we need a good index of the pest population levels that can be tolerated without a significant loss. Two additional points which need to be considered are as follows: We need a knowledge and evaluation of the seasonal and spatial (space) occurrence of significant predators, parasites, and pathogens and the factors affecting their effectiveness And last, we need information on both physical and biological causes of mortality in the life stages and generations of the pest species

IPM - Advantages

What are some of the advantages of IPM' Often there is a reduction in the total quantity of pesticides used resulting in less potential residues and less hazards to other organisms in the environment. With the use of less pesticides the grower can prevent or delay the development of resistance in the pest species With less pesticide usage the grower will conserve the beneficial species. Often with well-planned IPM programs total production costs will be reduced.

Cultural Practices for insect control:

1.Weed-free seed bed 2. Certified clean seed 3. Crop rotation when needed 4. Early cutting of first crop 5. Adequate irrigation 6. Weed control 7. Cultivation as appropriate


The amount of weed contamination in your alfalfa stand can determine the yield and value of your crop. The effects of weeds are many. Consider the following.

1. Fast growing weeds will out compete the slowgrowing alfalfa seedlings.

2 Weeds art host plants for other alfalfa pests, especially insects, mites and diseases.

3. Livestock may reject hay that contains unpalatable, thorney or irritating weeds, or if eaten, weeds may injure the animals' mouth or cause off flavors in milk.

4 Weedly alfalfa has a lower protein value, hence a lower nutritive value

5. And, alfalfa cubes, in demand for both local and foreign markets, cannot be made from weedy alfalfa.

Annual Weeds

Some of the common annual weeds m this area are, mustards, cheatgrass (Junegrass), peppergrass and kochia These weeds grow from seeds They mature, produce seed and die in one season or year The seeds lie dormant (some for as may as 25 years) and germinate when conditions are favorable.

' The number of annual weeds that will invade your field will vary from year to year There are usually a list of weeds after a wet spring. Pre-emergent e herbicides will kill the weed seedlings The longer you wait, the more difficult it is to control the larger weeds

Perennial Weeds

The creeping perennial weeds that most of you are likely to find in your fields are quackgrass and bindweeds (morning glory). These types of weeds ran live for more than two years. They can reproduce by seeds and by their underground parts The rootstocks can send up new shoots even after the above ground parts have been cut off

Creeping perennials are the most difficult weeds to control. The best time to control them Is before the new alfalfa is planted. Cultivation, crop rotation and herbicides can all be used. Apply control measures in late summer or fall before the weeds have had a chance to build up food reserves in their rootstocks

Dandelions are also a perennial, but they have a taproot Plowing and rotation to another crop will help control this weed Once the alfalfa has been established, mowing and competition from the deep rooted alfalfa plants will help keep the weeds under control Stands that art weakened by poor management, insects, or diseases are susceptible to weed invasion


Diseases in alfalfa can cause an estimated annual loss of 36 percent in yield and stand in the United States. Diseases can greatly reduce the life-span of a stand.

Diseased plants are usually easy to recognize because they are less vigorous and don't appear healthy. All parts of the plant can be damaged by disease and regular inspection of leaves, stems and roots is critical in evaluating disease losses. Determining the exact cause of a disease may require the inspection by a specialist. The first step in providing proper control of alfalfa diseases is the accurate recognition of the cause.

Some of the symptoms indicative of diseases are as follows: stunted plants, wilted plants, spotted leaves, dead plants, or yellow plants.

The infectious organisms that cause these symptoms are extremely small and most of them cannot be seen without the aid of a microscope. These microorganisms are included in 3 major groups: The fungi, bacteria and viruses

There are several fungi that attack roots, stems or leaves of alfalfa. These fungi are specific and generally attack only one part of the plant. For example: There are some fungi that cause root rots and others that cause leaf spots.

The environment greatly effects the kinds of diseases that occur, Foliar leaf spots occur when there is a heavy canopy and high humidity. Root rots are more common on heavy or water logged soils.

Bacteria can cause a very destructive wilt disease m susceptible alfalfa varieties. Bacterial wilt affects the root tissue causing gumming. The bacteria are spread by surface water, equipment, infected hay and animals Most new varieties of alfalfa are resistant to this disease

Viruses are usually carried by insects from infected to healthy plants. They multiply inside the cells of the alfalfa plant and reduce the vigor and production of the plants Viruses usually don't kill plants

There are approximately 40 infectious diseases of alfalfa in the United States. However, within a specific geographic area, only a small number of these diseases occur. Therefore, it is difficult to list specific control procedures for each disease and only generalizations can be made in this manual.

When thinking of disease control, it may be helpful to picture this diagram. (see below) Each part of the triangle can be manipulated to reduce disease losses. Whatever you do to one segment will have some effect on the other two parts.

The most critical decision in disease control is the planting of good quality seed of a well adapted variety for your area and a variety resistant to the major diseases However, these varieties are not immune to disease

Avoid planting in wet, poorly drained soils The quicker the seeds sprout and the seedling emerges, the more likely they are to escape infection by disease causing organisms.

Manipulation of the environment is possible by planting and cutting at the proper time of the year Winter injury can be reduced by allowing the plants to grow 5-6 weeks after the last harvest. This allows for food storage In the taproot and crown. Irrigate according to plant needs and avoid over-irrigation or water standing on the fields

Pesticides for disease control are rarely used, because the profit margin is not great. Control depends primarily on planting good quality seed of resistant varieties followed by sound cultural practices.


The alfalfa stem nematode is a tiny eelworm' that infests alfalfa. It spreads quickly and your stand will become unprofitable and eventually die.

If you have nematodes, you will notice damage before the first cutting because they are most active during cool, wet springs. The crown buds become distorted and swollen, leaves are small and white-topped and the stems become thickened and blackened. Large numbers of nematodes can be found inside the stem tissue.

One way nematodes are introduced into fields is by infected plant debris mixed with alfalfa seed. Once present, irrigation waste from infested fields carry the nematodes into irrigation canals, and then into uninfested fields.

Resistant varieties of alfalfa are available. Fall burning of fields for weed control also helps control nematodes however, spring burning will increase their numbers. Planting your fields with grain crops for 3 years will remove most of the nematodes. However, nematodes have survived for several years in fallow fields in areas in extremely dry climates.

A resistant variety in combination with the above control measures will keep nematodes at a low level Unfortunately, it is not economically feasible to eliminate nematodes completely.


The amount of damage to crops or pastures by large and small animals is limited. However, pocket gophers and other animals may sometimes cause forage problems

Gophers make tunnels below the ground and push the displaced soil into easily recognized mounds Subsequently gopher damage results from crop losses and equipment damage from hitting the mounds

Flood irrigation may drown gophers in their burrows while sprinkler irrigation may create favorable living conditions for them Therefore, extensive gopher control may sometimes by necessary.

The 'gopher-getter" may be purchased jointly by several farmers or it can occasionally be borrowed from the U.S. Fish and Wildlife Service. This machine will kill 80-100 percent of the gophers by using a system of artificial tunnels and treated bait.

Occasionally problems arise with jackrabbits or deer Deer are game animals and protected by law Farmers should contact the State Division of Wildlife Resources, or similar organizations, for help in controlling deer with scare techniques, trapping or hunting


At this point we wish to briefly define four common terms.



Refers to the dollars related to pest losses, loss prevention and pest control.

General equilibrium position

The average density of a population over a period of time in the absence of permanent environmental change.

Economic threshold level

That density of the pest insect (or other pest) at which control measures should be considered to prevent an increasing pest population from reaching the economic injury level

Economic injury level

The lowest population density that will cause economic damage. The level may vary from crop to crop, area to area, season to season or with men's scale of economic values

Next, let us briefly consider a few simple examples of bio-economics, especially the economic thresholds and

economic injury levels.

Example Number 1.

We will use the following as a base. Ten acres of alfalfa which can produce 5 tons of hay per acre, worth $50 a ton

Base: 10 acres alfalfa

5 tons/acre


Assume that without any control measures that the losses due to insects will be 2 percent of the crop This will amount to 2,000 pounds of hay (1 ton), worth $50.

Without control 2 percent of crop

Losses due to insects = 2,000 pounds (1 ton) = $50

The insect population is at the general equilibrium level, but the grower guesses at the damage and decides to spray The cost of spraying is $7/acre or $70/10 acres.

Cost of spraying $7/acre or $70/10 acres

The results, since the cost of spraying was $70 and the grower only saved $50 worth of hay, he is out $20 for his efforts

Cost of spraying $70

Hay saved $50

Net loss --$20

Example Number 2.

Using the same base as in Case Number 1, let us assume that without any control measures the losses due to insect pests will be 5 percent of the crop. In this example the insect population has reached the economic injury level.

Without control - losses = 5,000 pounds of hay

Due to insect 5% = 21/2 tons

= $125

The grower decides to treat. The cost of spraying is $7/acre.

Cost of spraying $ 7/acre

$70?10 acres

Since the potential losses would be $125 without spraying and the cost of spraying is only $70, the net gain for the 10 acres is $55.

Hay saved $125

Cost of spraying $ 70

Net gain $ 55

Example Number 3.

Using the same base as in the previous example, let us assume that without control measures the losses due to insect pests will amount to 10 percent of the crop.

Without control - losses = 10,000 Ibs. of hay

Due to insects 10% = 5 tons

= $250

The grower decides to treat. The cost of spraying is $7/acre.

Cost of spraying $ 7/acre

$70?10 acres

The results: Since the potential loss will be $250 without spraying and the cost of spraying is only $70, the net gain for the 10 acres will be $180 or 321% more than when the damage was 5 percent.

Hay saved $250

Cost of spraying S 70

Net gain $180

Example Number 4.

The following examples will provide us with further insight as to when it pays to spray and when it doesn't. For our base let's consider a 10 acre field of alfalfa which has the capacity to produce 5 tons/acre worth $50/ton.

Base: 10 acres alfalfa

5 tons/acre

= 50 tons/10 acres or 100,000 #

= $250/acre or 2500/10 acres

Let us assume that unless control measures are taken, the insects will do 4 percent damage, the weeds 3 percent damage and the diseases 2 percent damage.

Assume Losses due to insects. . 4%

Losses due to weeds . . 3%

Losses due to diseases. 2%

Here we see that a 4% loss due to insect damage amounts to 4,000 pounds of hay, or 2 tons; 3% amounts to 3,000 and 2% to 2,000 pounds, for a total of 9,000 pounds or 4.5 tons.

Losses in pounds of hay

Insects 4% = 4,000 pounds

Weeds 3% = 3,000 pounds

Diseases 2% = 2,000 pounds

Total 9% = 9,000 pounds

Dollar-wise, a 4% loss amounts to $100, a 3% loss to $75 and a 2% loss to $50, for a total loss to $225/10 acres or $22.50/acre.

Dollar value losses

Insects 4% = $100

Weeds 3% = $ 75

Diseases 2% =$ 50

Total 9% = $225

In this example, $22.50 is the point of decision. If control costs would exceed this amount, then control is not warranted. If control costs would be somewhat below $22.50/acre than control measures should be considered.

Example Number 5.

Using the same base as before, let us assume that without control the losses due to insects will be 10 percent of the crop.

Without control = 10,000 Ibs. of hay

Losses due to insects = 5 tons

= $250 for the 10 acres

The grower decides to treat. The cost of spraying is $7/acre.

Cost of spraying


$70/10 acres

But, he only obtains 80 percent control. Eighty percent of $250 is $200, so even with control he looses $50 worth of hay.

80% control = $200 hay saved

=$ 50 hay lost

The results: The potential loss would have been $250 without any control, but he sprayed and only obtained 80 percent control. Thus, he saved $200 worth of hay, he lost $50 worth. It cost him $70 to spray and he net $80.

Hay saved $200

Cost of spray $ 70

Difference $130

Hay lost $ 50 .

Net gain $ 80

Example Number 6.

Let us assume that unless control measures are taken the insects will do 12 percent damage, the weeds 6 percent d the diseases 2 percent

Pest Percent damage Pounds of hay Loss in dollars
Insects 12 % 12,000 $ 300
Weeds 6 % 6,000 $ 150
Disease 2 % 2,000 $ 50
Total loss 20 % 20,000 $ 500

Without Control

From this example, let us assume that the control measures were only 80 percent effective That means even we apply pesticides as needed, we will still lose 4,000 ponds of hay or $ 100

80 percent of 20,000 = 16,000 pounds

80 percent of $500 = $400

In this case, in order to save 16,000 pounds of hay (80 percent of 20,000) the breakpoint is $40/acre If it costs are than $40/acre to save the 16,000 pounds of hay, then won't pay to spray If it costs somewhat less than $40/acre n control measures could be justified

Reasoning: You can only save $400 worth of hay at 80% effectiveness of the spray.

$400 divided by 10 acres = $40/acre.

Example Number 7

Let us assume that if no pesticide were applied that the farmer would loose 20 percent of his crop to pest insects are we see that a 20 percent loss would amount to 20,000 pounds of hay (10 tons) and a dollar value of $500 for the 10 acres of hay

Losses in pounds of hay 20% = 20,000 pounds of hay Dollar value of losses 20% = $100

for simplification, let us assume that the major pest in this field is the alfalfa weevil larva and its major parasite is the wasp, Bathyplectus will control 70 percent of the weevil, the saving will be 14,000 pounds of hay (7 tons) or 50 for the ten acres, or $35 an acre

If the grower sprays and controls all of the weevil he losses $500 minus the $350 worth of hay the Bathyplectus would have saved him So, he really gains any $150 on the acres and in the process, destroys a very valuable ally in the parasite

What does it cost to spray in pounds of hay? Let us use the following base

Hay $50/ton

Spray $ 7/acre

The cheaper the value of the hay, the more hay it takes to pay for spray application At $45/ton, it takes 313 pounds, but when the hay is worth $65/ton, it only takes 215 pounds, or about 30 percent less

Value of Hay/Ton Pounds of Hay to pay for Spray
$45 313
$50 280
$55 254
$60 233
$65 215

Now, consider percentage of yield to pay for a spray application If the yield is 1 ton/acre, spray costs will be 14 percent of the yield If the yield is 4 ton/acre, spray costs will be less than 1 percent, namely 0.35 percent.

Percentage of yield to pay for a spray application
Tons/Acre % of yield
1 14%
2 7%
3 4.6%
4 0.35%

Thus we see that the greater the value of the hay, the fewer pounds required to pay for the spray application. Or stated another way, hay low in value, sprays costs will be proportionately high or hay higher in value, spray costs will be proportionately lower


Why I PM? Because we need to develop control systems for alfalfa which will manage the major pests using both systems and management that have been based on sound biological and ecological principles Pest management programs will be more effective if growers participate on an area-wide basis and utilize all available and appropriate suppression methods against the target pest species

There are two basic fundamental principles of IPM.

1. Consideration should be given to the agro ecosystem, and

2. Control decisions should be based on economic injury levels.

An ideal IPM program would include most, if not all of the following

1. Testing the soil for needed nutrients and then fertilizing as appropriate.

2. Proper seed bed preparation including control of weeds.

3. Selection of a pest resistant, high yielding variety of alfalfa. Some varieties are resistant to selected diseases and insects.

4. Maintain proper moisture levels. Irrigate as needed.

5. Weekly scouting of fields to determine the following.

a. Presence of diseased plants, including nematode infestations. b. Weed populations. c. Pest insect and mite populations. d. Populations of beneficial insects.

6.If pest insect or mite populations are developing near cutting time, cut the alfalfa a few days early rather than resorting to a pesticide application.

Cut the alfalfa before the field is more than 5 or 10 percent in bloom to avoid killing honey and wild bees.

7.Before any insecticide is applied, scout fields to determine presence of beneficial insects. If beneficials, such as predators and parasites are present in large numbers, determine if spraying can be avoided.

8. If the application of an insecticide is required, choose a chemical which will suppress the pest insect population with a minimum of damage to the beneficial insects which are present.

9. After cutting a crop, check field for infestations of diseased plants weeds or pest insects that might be retarding the development of the next crop.)

Copyright 1981 Cooperative Extension Service Utah State University (2C/6-81)

Info Request | Services | Become EAP Member | Site Map

Give us your comments about the EAP site

Ecological Agriculture Projects, McGill University (Macdonald Campus)
Ste-Anne-de-Bellevue, QC,  H9X 3V9 Canada
Telephone:          (514)-398-7771
Fax:                     (514)-398-7621


To report problems or otherwise comment on the structure of this site, send mail to the Webmaster