In the Central Valley most winter annual weeds start to germinate in late September or October and continue to germinate until late January, whenever soil moisture and temperature conditions permit. Survey for weed seedlings just after alfalfa is cut.
Recording weed survey results assists in weed management decisions, including herbicide choice and cultivation practices. Information collected over a period of years tells you how weed populations are changing and how effective your management operations have been.
Weed identification
The most dangerous winter species are fiddlenecks and common groundsel. Identify common winter annual weeds and perennial weeds.
How to survey
Walk through each field in a random pattern, rating the degree of infestation for each weed species. Use either a numeric scale of 1 to 5 (1 being the lightest, 5 being the heaviest), or rate as "light," "medium," or "heavy."
- Check fencerows, ditch banks, field edges, and wet spots as these may be problem areas for weed growth.
- Check areas around the field edges as these areas could be potential sources for wind-disseminated seeds.
- Pay particular attention to perennial weeds.
- Sketch a map of the field and mark areas with major weed infestations.
- Indicate the growth stage of the weed (seedling or mature).
- Record results on a established alfalfa weed survey form .
The need for treatment depends on weed species, their competitiveness, the potential market for the alfalfa, and toxicity to livestock. In addition, vigor of the alfalfa stand is a complicating factor; weakened stands will require treatment when denser ones won't.