The old saying, “Everything's fine until it's not,” comes to mind when dealing with some tough to control perennial weeds in alfalfa production during the summertime. Such was the case for an alfalfa field in the Sacramento Valley, where weed control seemed good up until mid-summer, and then it wasn't. Perennial weeds that started off small and overlooked, grew through the season, persisting through multiple cuttings, including curly dock, plantain, and nutsedge. For tough to control weeds in alfalfa fields, one needs to determine: 1) What types of perennial weeds are present, and 2) How many of them are there, to make a decision on how to manage them. These sorts of weed issues can creep up quickly in older alfalfa...

Yikes, my weed control didn't work!  It's springtime and you're looking at your seedling alfalfa field that you planted late last fall. You have a great stand, but you're not quite satisfied with the level of weed control despite an earlier herbicide application. You still see weeds out there, including bristly oxtongue, thistles, mustard, dandelion, and fiddleneck. You know that weed infestations can weaken young alfalfa plants, retard growth, delay the first cutting, reduce quality, and result in long term damage to crop yield and stand persistence.

The field is still a seedling stand, considered as such until at least the first hay cutting (around the 6-9 leaf stage and a crown is forming). The...

Put on that jacket!  This winter has been cold and dry, and many of our crops have felt it, including almonds, but also alfalfa!  Fortunately, alfalfa has a high degree of tolerance but yields can also be reduced due to frost.

Frost Damage. We had record high temperatures in early February (near 80^oF) followed by record lows (27^oF on Feb 24, CIMIS data, Davis site). This caused some frost damage to alfalfa fields in many areas of the San Joaquin and the Sacramento Valley, with tip burn and dieback in the upper canopy.

Established alfalfa has good frost tolerance and will readily regrow once the weather warms. Harvest may be delayed by a week or two, depending...

Picture 1: Adult alfalfa weevil

Alfalfa weevils, key pests of alfalfa hay, have been showing pyrethroid insecticide resistance within the Intermountain region, specifically in the Scott Valley area west of Mount Shasta. In some alfalfa fields, weevil counts have been off the charts with 100 weevils per sweep, FIVE times the economic threshold level. These same fields showed little efficacy on weevil control by pyrethroids. In a 2016 test only 3-15% of weevils collected from conventional fields died from exposure to pyrethroids. Weevils collected from organic alfalfa fields that had no exposure to pyrethroids showed a 92% mortality (