How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Integrated Pest Management

(Reviewed 3/17, updated 3/17)

In this Guideline:


Integrated pest management uses a combination of crop management, careful monitoring of pest populations, and timely control activities to prevent and manage pest outbreaks. Common methods in alfalfa production include biological control by natural enemies, modification of cutting schedules, crop rotation, pest-resistant varieties, and the use of pesticides when needed. Proper stand establishment, irrigation management, and effective crop management are critical to encourage a vigorous alfalfa crop that is better able to withstand weed infestations, insect feeding, and disease incidence.

Weeds

Weeds are often the most important yield- and quality-reducing pest problem, especially in older stands. An integrated pest management (IPM) program begins with effective weed management during stand establishment, the correct identification of weed species at different times of the year and an effective weed management strategy. Proper stand establishment, harvest timing, crop rotation, and irrigation management all help prevent weed intrusion. Overseeding older depleted stands with other forages (grasses or legumes) can extend stand life and assist in preventing weed infestations. When herbicides are needed, use proper timing to achieve maximum efficacy. In addition, take care to avoid off-site movement of herbicides with irrigation or rain events.

Insects

Although alfalfa fields are home to many beneficial insects, there are also several very damaging arthropods as well. The most damaging insects in alfalfa hay in California are

  1. Alfalfa weevil (occurs primarily in late winter),
  2. Aphid complex (occurs in spring, summer, and fall, depending on species),
  3. Summer worm complex (armyworms, alfalfa caterpillars, etc.), and
  4. Leafhoppers (can occur at various times).

Proper identification of insect pests and natural enemy species is essential to an IPM program for pest control. Many insect species, particularly in the immature stages, are similar in appearance and may be easily confused. For example, lygus bug nymphs, which are pests of alfalfa seed, may be confused with aphids. Pea aphid and blue alfalfa aphid are similar in appearance and can easily be mistaken for each other. Because economic treatment thresholds are specific for the pest species, proper identification is critical. Likewise, failure to properly identify natural enemy species may lead to unnecessary pesticide applications if predator or parasite numbers are sufficient to maintain pest numbers below economic treatment levels.

Disease & Nematodes

There are very few pesticides for the management of most diseases and none for nematode control in established alfalfa stands. Selection of resistant varieties, irrigation management, soil drainage, crop rotation and prevention of mechanical spread of pests and diseases are important IPM strategies.

Use of Pesticides

When pesticide intervention becomes necessary, follow the label for proper pesticide rate and application method. Choose pesticides that are relatively safe to natural enemy species and honeybees, while maximizing control of the pest. Selection of a pesticide product for an application depends on several factors including registration status, activity on the pest, preharvest interval (PHI), cost, length of residual control, harm to natural enemies and pollinators, and environmental toxicity hazard. Design herbicide use strategies to prevent weed resistance and shifts in weed species.

Use the year-round IPM program for guidance in carrying out a comprehensive IPM program for alfalfa hay.

For more information on integrated pest management in alfalfa, see Irrigated Alfalfa Management for Mediterranean and Desert Zones, UC ANR Publication 3512 and Intermountain Alfalfa Management (PDF), UC ANR Publication 3366.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430

General Information

L. D. Godfrey, Entomology, UC Davis
E. T. Natwick, UC Cooperative Extension, Imperial County
P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier
R. F. Long, UC Cooperative Extension, Yolo County
V. M. Barlow, UC Cooperative Extension, Riverside County and UC IPM Program

Acknowledgment for contributions to Insects and Mites:
D. R. Haviland, UC Cooperative Extension, Kern County
M. Rethwisch, UC Cooperative Extension, Riverside County (Blythe)
C. G. Summers, Entomology, Kearney Agricultural Center

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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