Weeds compete with alfalfa for water, nutrients, light, and space. This competition can decrease yields, lower forage quality, increase disease and insect problems, create harvesting problems, and initiate or poison the animals which will consume the forage. Premature loss of alfalfa stands is usually the result of the interaction of the pest complex - diseases, insects, and weeds

Witt, William W.

English

University of Kentucky

-27-WEED MANAGEMENT IN ALFALFA William W. Witt Department of Agronomy, University of Kentucky Introduction Weeds compete with alfalfa for water, nutrients, light, and space. This competition can decrease yields, lower forage qua-lity, increase disease and insect problems, create harvesting problems, and initiate or poison the animals which will consume the forage. Premature loss of alfalfa stands is usually the result of the interaction of the pest complex - diseases, in-sects, and weeds. Forage crops such as alfalfa differ from most grain and fiber crops in that the weeds are not seperated but harvested along with the crop. This addition of weeds to alfalfa forage decreases per acre yield, and probably more importantly, will lower forage quality. This decrease is often in the form of lowered protein content and digestibility. Successful weed man-agement in alfalfa is an attainable goal for producers. However, to accomplish this, an understanding of the alfalfa-weed eco-system is needed. Weed problems can be divided into three categories - annuals, biennials, perennials. Each type has characteristic traits that need to be understood if they are to be controlled culturally or chemically. Annuals are plants that complete the germination, vegetative, and reproductive growth stages in one growing season or year. The terms "summer annual" or "winter annual" refer to the portion of the year in which they grow. Biennials are plants that live during two growing seasons. The first season's growth is vegetative with the second season's growth being vegetative and then reproductive. Perennials are plants that live for more than two years and usually reproduce by seeds and vegetatively. Fleshy taproots, tubers, rhizomes, stolons, bulbs, and bulblets are examples of vegetative reproductive organs. As a general rule, perennial weeds are more difficult to control because of their multiple reproductive mechanisms. However, the amount of alfalfa yield reduction by weeds will be determined by the individual weed species and when it is growing in association with the alfalfa. There are two distinct growth stages of alfalfa that must be considered when developing a weed management program. In new seedings, the alfalfa plant acts as an annual and is usually in competition only with annuals during the first few weeks of growth. Cultural and chemical means need to be used that will shift the competitive edge to alfalfa - that is, provide control of the annual weed species. -28-Established alfalfa stands are composed of perennial plants and may be in competition with both annuals and perennials at some time during the year. Cultural Practices New seedings - Several cultural practices can be utilized in new seedings to provide weed control and allow the new emer-ging alfalfa plants to begin growth without competition from weeds. Some of these practices are (1) liming and fertilizing as soil analysis recommends; (2) seeding well adapted varieties that will provide vigorous early season growth; (3) purchase weed-free seed; (4) control of insects and diseases if appli-cable; and (5) rotation with other crops. These practices are the same for either conventionally prepared or no-tillage seed-ings. However, in no-tillage seedings, control of existing weeds will be necessary prior to alfalfa emergence. Established Stands - The following practices will help to maintain a vigorous, dense alfalfa stand and reduce competitive-ness from weeds: (1) maintenance of lime and fertility require-ments; (2) proper timing of harvests; (3) control of insects and diseases. Herbicide Control The aggressive nature of some weed species will allow them to become established regardless of any preventive measures that have been utilized. Many herbicides are available for alfalfa and will provide acceptable control of most alfalfa weeds in Kentucky. New seedings - Herbicides used prior to seeding are pri-marily for control of annual weeds such as large crabgrass, giant fox·tail, or chickweed. See tables 1 and 2 for herbicides recommended in Kentucky. Herbicides should always be used in spring seedings and are usually beneficial in late summer seed-ings because the foxtails and crabgrasses are summer annuals that will germinate and grow with the newly emerging alfalfa to dras-tically affect the stand and subsequent yields. Table 1. Herbicides applied prior to planting newly seeded alfalfa in prepared seedbeds. Amount Herbicide per acre Balan l. SE 3 ·to 4 qt. Eptam 7E 3.5 pts Weeds Controlled Crabgrass, fall panicum, fox-tails, goosegrass, lambsquarters, pigweeds Crabgrass, fall panicum, fox-tails, goosegrass, seedling johnsongrass, shattercane, lambs-quarters, pigweeds -29-Table 2. Herbicides applied prior to seeding in no-tillage alfalfa plantings. Amount Herbicide per acre Paraquat 2Ea l to 2 pt Roundup 4E 3 pt Weeds Controlled All existing vegetation. Peren-nial species may recover and grow. All existing vegetation. aA non-ionic surfactant should be added to increase control. Established stands - Herbicides (Tables 3, 4, S) can be ap-plied to both dormant and actively growing alfalfa for control of grasses and broadleaves. Recommended rates should be closely followed to prevent alfalfa injury. Table 3. Herbicides applied to dormant alfalfa. Amount Herbicide per acre Lexone SOW 1 to 2 lb Lexone 4L l to 2 pt Lexone DF 0.7 to 1.3 lb Paraquat 2Ea 2 pt Sencor SOW l to 2 lb Sencor 4 l to 2 pt Sencor DF .7 to 1.3 lb Sinbar BOW l to l. S lb Velpar 90W l lb Weeds Controlled Chickweed, henbit, jimsonweed, lambsquarters, mustards, pigweeds, purslane, ragweed, shepherdspurse, smartweed, spurge, yellow rocket, crabgrass, foxtails, fall panicum Same as Lexone SOW Same as Lexone SOW All existing vegetation. Some per-ennials and large annuals may recover and grow. Chickweed, henbit, pepperweed, shepherdspurse, yellow rocket, dandelion, barnyardgrass Same as Sencor SOW Same as Sencor SOW Chickweed, henbit, lambsquarters, mustard, peppergrass, prickly lettuce, shepherdspurse, yellow rocket, crabgrass, foxtails Annual bluegrass, chickweed, dan-delion, groundsel, lambsquarter, crabgrass, field pennycress, fleabane, foxtails, pigweed, shepherdspurse, yellow rocket aA non-ionic surfactant should be added to increase control. -30-Table 4. Herbicides that can be applied to either actively grow-ing or dormant alfalfa. Herbicide Butyrac 200a Furloe 4Ecb KERB 50Wc Amount per acre 2 qt 1 to 2 qt (Oct. -Jan.) 2 to 3 qt (After Feb.) 1 to 3 lb Princep 80Wd 1 to 1.25 lb Princep Caliber 90d 0.9 to 1.1 Weeds Controlled Lambsquarters, pigweed, penny-cress, common mustard, ragweed, yellow rocket Chickweed, cress, dodder, pur-slane, shepherdspurse, smartweed Chickweed, orchardgrass, sheep sorrel, quackgrass, mustards, shepherds purse Pigweed, chickweed, henbit, pep-perweed, lambsquarters, shepherds-purse, field pennycress, yellow rocket Same as Princep SOW arn new seedings spray 2 to 4 weeks after alfalfa emergence. bApply to new seedings after true leaves of alfalfa have formed. CAlfalfa should have trifoliate leaves formed prior to spraying. duse the lower rates for stands less than one year old. Table 5. Between harvest applications of Paraquat 2Ea Amount Herbicide per acre Paraquat 2Eb 1 pt Weeds Controlled Annual grasses and broadleaves. Suppression of some perennial species. aAppllcatlons must be made wlthln 5 days of cutting to prevent alfalfa injury. bA non-ionic surfactant should be added to increase control. Weed Management Programs Development of successful weed management programs for al-falfa is the result of the following items. (1) weed problem -know what weed species are present in your alfalfa that are causing problems. A few curley dock plants might be very evi-dent, but low growing species such as chickweed or henbit could be much more of a problem. (2) Application Options - know and -31-understand the options available to you with your application equipment. This will determine in some cases the herbicides you can choose. (3) Herbicide options - Select the herbicide that will control your weed species with your equipment. Use only recommended rates to prevent alfalfa injury and follow all warnings and precautions on the label. (4) Cultural prac-tices - These were discussed previously but are an integral part of an alfalfa weed management program. 

Weed Management in Alfalfa

https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1310&amp;context=ky_alfalfa

Weed Management in Alfalfa

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