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Cultural Practices
Alfalfa is the principle legume used for hay in Illinois. Alfafa is seeded by itself on about 50 to 60 percent of the hay acreage in the state. To increase dry matter production of the stand, forage grasses such as orchardgrass, perennial rye, fescue, and kentucky bluegrass may be sown along with alfalfa. When pure stands of established alfalfa begin to decline, forage grasses may also be overseeded into the legume to boost production and improve the stands' competitive ability with weeds.
In the northern most counties, a companion crop such as oats, is typically seeded with alfalfa in early spring. Two or three cuttings of alfalfa can be harvested the first year in Illinois. The field is first cut, sun-dried, raked into rows, and then chopped for haylage or baled as hay. Alfalfa on average yields about one ton or more per acre per cutting.
The use of pesticide treatments by producers depends mainly upon the final use of the crop. Top quality alfalfa is sold to dairymen and horsemen, each having their own specifications. Some weeds, such as mustards, affect the flavor of milk and must be avoided. Horsemen judge hay quality according to percent of leaves and the absence of toxic weeds and blister beetles (which can be fatal to horses). Beef cattle and other livestock also use alfalfa in their diet, but do not require the highest quality. Therefore, the need for a pesticide is directly correlated with the end use; dairy cattle and horses having the greatest need for high quality hay.
Alfalfa is called a seedling crop if it has been planted within the last twelve months. Older fields are classified as established stands. It is easiest to control weed pests in the seedling year if no grasses have been seeded with the legume. The first cutting, or harvest, occurs in late May to mid-June. With adequate moisture and temperatures, succeeding cuttings occur every 28 to 34 days ending in mid- to late September. A late cutting in October may be taken, but the crop will need extra nutrients in the early spring to overcome winter stress. Alfalfa may grow well for four to seven years before reseeding or rotating to a row crop becomes necessary due to dieback of the stand.
Insect Pests
Major alfalfa insect pests destroy or stunt vegetative growth. These insects eat the leaves delaying photosynthesis which the plant uses to convert water and soil nutrients. The leaves are a major source of digestible nutrients for animals. Some fields will have a gray cast when infestations cause the majority of leaves to be eaten. Other fields may look yellowish due to plant wilting. All insecticide applications approved for Illinois are foliar treatments. Most treatments must occur two to three weeks before a bloom stage (this is essentially the same time before harvest). When treatments occur during bloom stage, bees attracted by the flowers are adversely affected by the insecticides.
Trends for infestations waiver only slightly. Alfalfa weevil populations are declining, while the state is really focusing on the rise of potato leafhoppers in the last two years.
Major Arthropod Pests
Alfalfa weevil 4
Adults weevils lie dormant in brushy or wooded borders of alfalfa fields during the summer. Adults lay eggs in fall and spring; after hatching, young larvae crawl to the growing tips of leaves. Late complete four instars while feeding on increasing amounts of leaves. The larvae then spin cocoons and pupate on plants or on the ground. Adults emerge, feed briefly, then leave the alfalfa fields when summer temperature increase.
Extended warm weather, mild winter weather, and a warm, early spring favor increased amounts of egg laying. Hot, dry weather (conditions that are unfavorable for natural enemies and diseases of weevils) favor weevil survival.
Damage: Damage is usually most severe in the southern half of Illinois. Early harvest of the first crop of alfalfa is sometimes effective in preventing severe damage; Insecticides are the only other option. During outbreak years, as mush as 50% of alfalfa is treated for this insect. On average, about 10% of fields are treated for alfalfa weevil.
Potato Leafhopper
Potato leafhoppers are carried into Illinois by prevailing spring winds off the Gulf Coast. Female leafhoppers lay eggs in stems and large leaf veins. The eggs hatch within one week, and the larvae feed on the plant. The larvae has five larval instars until adulthood. An entire generation can be completed in three weeks; there are several overlapping generations per year.
Damage: The potato leafhopper can cause major damage to alfalfa as it feeds on the undersides of the leaves. The obvious signs of damage include the stunting of the plant height and the yellowing of the leaves. The leafhoppers preferably like to feed on the plants in hot or dry seasons. This damage is becoming more significant as they are on the increase in many Illinois fields. If the winds and storm fronts are not especially B, the prevalence of potato leafhopper inIllinois can be reduced. However, for control, use an effective insecticide.
Diseases
Diseases contribute up to 15 percent of crop loss5. Most diseases remain unreported within the state. Many of the control methods employed are the planting of disease resistant seed varieties and rotation with row crops.
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