How to Manage Pests

UC Pest Management Guidelines


Crop Rotation Impacts on Pests

(Reviewed 3/17, updated 3/17)

In this Guideline:

Crop rotation has the ability to reduce the weeds, diseases, and nematodes that harm alfalfa. Avoid planting alfalfa directly into a field from where an alfalfa crop was recently removed; instead, have at least one or two rotations to a different crop. Rotation to a nonhost crop can significantly reduce pest numbers and types in the field. The table below provides information on nonhost crops that suppress alfalfa-associated nematode and pathogen populations. Also included is a list of rotation crops that can use herbicides that may not be registered for use in alfalfa.

If your field is infested with stem nematode or pathogens listed in the key below, consider choosing a nonhost crop from the table. A 3- to 4-year nonhost crop rotation is ideal. A rotation of lesser duration is still beneficial, but to a lesser degree.

Rotation crops have different effects on various weed species. Winter weeds can be effectively controlled with small grain plantings accompanied by an appropriate herbicide application. Summer weeds can be controlled by growing a summer annual rotation crop (corn, bean, sunflower, cotton, and tomatoes), and using selective herbicides and cultivation.

Volunteer alfalfa around the field edges of a rotation crop may perpetuate nematode populations. If your field has a history of nematodes, be sure to remove all volunteer alfalfa.

Recommended Rotation Strategies To Control Pests Common To Alfalfa
Pest Rotation Information
Northern Root-knot nematode 2 to 3 year rotation with nonhost crops such as cotton, blackeye cowpeas, and some lima bean varieties
Stem nematode 3 to 4 year rotation with small grains, beans, cotton, corn, sorghum, lettuce, carrots, tomatoes, or forage grasses1.


Bacterial wilt

Common leaf spot

Spring blackstem


3 to 4 year rotation with small grains, beans, corn, sorghum, forage grasses1.
Winter weeds A minimum of 1 year (preferably longer) in crops such as small grains (wheat, oats, barley, triticale) or winter forage grasses (e.g. ryegrass) that allow the use of selective herbicides that might not be registered in alfalfa.
Summer weeds A minimum of 1 year with crops that compete well with summer weeds, such as small grains, beans, cotton, corn, sorghum, or summer forage grasses (e.g.sudangrass or teff grass) and allow the use of selective herbicides that are not registered in alfalfa.
Gophers At least 3 years rotation to an annual crop along with tillage.
Dodder At least 2 years with nonhost crops such as cotton, small grains, beans, corn, sorghum, or forage grasses. Avoid rotations with crops that also serve as a host for this weed (e.g., tomato, onion, and carrot). However, management in season with glyphosate in Roundup Ready alfalfa is highly effective, so a 2-year or longer rotation may not be necessary in this case.
Nutsedge Two-year rotation with corn or sorghum that includes application of herbicide to control nutsedge. A rotation to Roundup Ready alfalfa that can be managed in season with glyphosate is useful to control yellow nutsedge.
1Three- to four-year rotations may give satisfactory results, depending on the severity of the infestation. A rotation for fewer years will give some suppression.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430

General Information

P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier

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