Cover crops, hedgerows, maintenance in vineyard landscape

Most North Coast wineries use a winter annual cover crop that is disced before the growing season. Common problems with cover crop management are mentioned and Elizabeth Lovall at Morningsun Herb Farm in Vacaville is cited as a resource on specific plants. Other hedgerow information can be found in the CAFF handbook (pdf).

Cover crop selection and management:
Issues to be aware of in a vineyard landscape where cover crops, hedgerows are being implemented and maintained.

• Mowing too closely can kill off your cover crop.
  Mowed too closely only subclover and brome survive, oat and vetch will die. Mowing height depends on where the plant resprouts from — how close to the base of the plant. All cover crops are rejuvenated (or increase in biomass) if mowed at 6-12 in. The take-home is find out the correct mowing height for your cover crop.
• Preventing arthropod movement from cover crop to vine
  Establish non-host plants, and diverse cover crops, maintain the understory vegetation (cover crop) and extend its flowering by irrigating, use strip mowing or tillage to maintain phenological diversity and retain some flowering plants.
• Why arthropods move from cover crop to vine
  Arthropods move from understory to the vine if the cover crop uniformly matures, dries down, or is under drought stress, lack of diversity or density of host plants (the plants they live on), or the understory is mowed, tilled or herbicided.
• Nitrogen gains from cover crops
  This varies quite a bit depending on the mix of plants in the cover crop and when it started decomposing (i assume it was mowed since the data says no-till). “Low-grow” mix has overall lower N content and higher biomass than “rich” mix. The order of greatest N by dry weight are: vetches (4% N by dry weight), then black mustard, clovers, grasses. % N released is consistently highest if decompose at late bloom stage and lowest at late vegetative state (right before bloom), and roughly two-thirds of total N is released after decomposing for 4 months.
• Water infiltration benefits when incorporated as green manure
  Cover crops that have the highest water infiltration when incorporated are: barley and cereal rye.

Maintenance of Vineyard and surrounding area

• Problematic plants in riparian areas near vineyard
  Himalayan blackberry, common periwinkle, California mugwort are all hosts for blue-green sharpshooter, a vector of Xylella fastidiosa (Pierce’s disease).
• Problematic plants in areas with young vines
  Pre-emptive mowing before budbreak (particularly London rocket) is recommended to discourage high density of false chinchbugs. They can migrate as surrounding vegetation dries down and feed on young vines.
• Keeping ecosystem healthy in vineyard:
  Drain ponds in late summer to reduce predators and do not stock fish. Retain logs, rocks, and rodents!, encourage emergent and riparian vegetation on pond and creek banks, retain native upland vegetation, maintain connectivity among different required habitats, reduce use of pesticides and soluble fertilizers

Pest control by other natural enemies:
Grape Mealybug (a grape pest) is protected by gray field ants but the ants can be diverted by common vetch nectaries in cover crop. (walt bentley et al). Trachylas sp. and Theridion sp. are two spiders that are natural enemies of leafhoppers.

Further reading:
see Natural Enemies, Hedgerows, and other books in the reading list.

credit: R.L. Bugg lecture 101C