It’s not that I am unpatriotic, but in this context “flags” refer to isolated dead alfalfa stems with dead leaves still attached that are surrounded by healthy stems. The “flags” are usually light colored and the tips are often curled over like a shepherd’s crook or staff.

“Flagged” stems can be caused by several pathogens but when they appear in summer, are light tan in color and have the characteristic crook at the top, it is probably because the stem is infected with the fungus Colletotrichum trifolii (Figure 1).  The disease this fungus causes is called anthracnose (it has also been called southern anthracnose).  The most obvious symptoms...

I recently received a call from a PCA who had questions about nematodes that infect alfalfa. He had observed stunted crop regrowth after the first cutting and had reason to think that nematodes could be the cause.

There are three nematodes that tend to be the most problematic in alfalfa. Stem nematode (Ditylenchus dipsaci) is a nematode that feeds on above-ground plant parts, unlike most plant-parasitic nematodes that feed on roots. To recap a blog by Rachael Long and Dan Putnam, stem nematode symptoms include stunting, shortened internodes, and even plant death when infections are severe. It is a fairly easy pest to diagnose if...

When is nitrogen fertilization of alfalfa beneficial? Almost never!

Nitrogen (N) fertilizer is generally not required for alfalfa production since alfalfa can obtain its own N from N-fixing nodules (Figure 1).  Alfalfa fixes most (70-90%) of its N needs from the air through Rhizobium bacteria residing in alfalfa root nodules (Figure 1). Since 78% of our air consists of nitrogen gas, this supply of ‘free fertilizer' is inexhaustible. A recent unpublished UC Davis-CSU Fresno study showed 90% of N in alfalfa originated from the atmosphere -- but less when soil N levels were high, for example, in manured fields.

Although there have been some reports of yield and forage quality...

Of all of the insecticides evaluated against blue alfalfa aphid (BAA) by Eric Natwick of Imperial County, almost every insecticide applied to alfalfa this spring gave initial knockdown of BAA. Blue alfalfa aphid populations resurged in 7-10 days. Treatments giving 70–75% control (reported by PCA’s) were combinations of a pyrethroid with an organophosphate.

Possible factors for our BAA issue:

• High initial aphid populations

• Smaller than expected populations of predators and parasites; particularly the seven-spotted lady beetle

                May be weather related or pesticide...