UC scientists are perplexed and concerned about the condition of California alfalfa fields this spring. Alfalfa should be a lush, green carpet, but in many areas, there are patches that appear dead; in some cases, entire fields have been reduced to bare ground, according to UC Davis Cooperative Extension alfalfa specialist Dan Putnum.
Although scientists caution that there may be several factors contributing to this damage, stem nematode symptoms are present and the pest has been observed in lab tests. Alfafa stem nematode is a voracious microscopic pest that is generally present in Valley soils, but rarely becomes such a severe problem.
UC News and Information Outreach distributed a news release yesterday to get the word out about possible causes of the poor alfalfa stands, but the situation in alfalfa continues to unfold.
Putnam said that, in touring the fields on Tuesday, he could not identify a pattern related to alfalfa variety or pesticide regime. Different dormancy groups seemed equally affected.
"There was a little phytophtora damage deep on some roots, but most roots were relatively healthy. There were some fields with very great damage, and others without as much damage, but this could certainly be a result of crop rotation factors or lack of equipment or water transfer, as much as variety or pesticide patterns," he reported.
Putnam said most symptoms appear to be from stem nematode. However, because it is so unusually severe, scientists are keeping their options open.
UC Davis CE nematology specialist Lynn Westerdahl said scientists are considering gene sequencing to try to understand the pest and why it appears to be wreaking havoc in California alfalfa.