Walking through an alfalfa field the other day, I saw numerous leaves infected with downy mildew.  Because only young leaves are susceptible, symptoms are near the top of the plant and easily visible. Early stage symptoms include a light green blotchy area on the leaf surface (Photo 1). In time the area will turn yellow and eventually may dry out (Photo 2). These diseased areas on leaves are usually localized.  In the morning when humidity is high, on the underside of the leaf you can see light gray or violet “fuzz” (Photo 3). Look at the “fuzz” with a hand lens.  It is the mycelium and spores of the fungal pathogen Peronospora trifoliorum, the cause of downy mildew in alfalfa. The main...

This is the time of year that alfalfa fields provide a lush green carpet, outgrowing the damage from 4 months of cold and frost in California’s Central Valley.  But not all fields are emerald green-some show the ugly, patchy, stunted evidence of a nasty little invader: stem nematode.

Of course you can’t see the nematodes (ugly or not) with the naked eye but they sure make the alfalfa look ugly.

Stem nematodes (Ditylenchus dipsaci) are causing significant damage to alfalfa fields again this year in the Sacramento and San Joaquin Valleys. These microscopic worm-like pests primarily move through fields in water and infect the above ground portion of the plants (crowns and stems)....

It’s that time of year again when we need to start thinking about controlling weevils in alfalfa hay production. Egyptian alfalfa weevils are the most damaging insect pests of alfalfa in California, as the larvae feed on the foliage, causing yield and quality losses if left untreated.

The life cycle of the Egyptian alfalfa weevil is predictable. Adults spend the summer outside fields in protected areas, such as behind tree bark (for example, eucalyptus trees) and in crevices. In late fall or early winter, adults emerge and migrate into alfalfa stands. Soon after entering fields, they begin laying eggs in new and old or dead alfalfa stems. Hatching larvae make their way to the terminal buds and feed on the developing...

Dodder is a troublesome annual parasitic weed that infests alfalfa fields.  Initial infestations are usually caused by sowing dodder infested seed (a good reason to purchase Certified seed) and by “sheeping off” fields with sheep that came from an infested field.  Perhaps no weed problem is worse than an alfalfa field heavily infested with dodder.  As a parasite, it lives at the expense of the alfalfa plant and literally sucks the vigor and life out of the plant.  If left uncontrolled it can actually kill the alfalfa plant.  It emerges as a rootless shoot and must attach itself to a suitable host within a few days or it dies.  After it embeds its sucker-like structures (called...