Here's an excerpt from our Newsletter of 2015:
"This year we’re experimenting with alternative under-vine treatments. I love having full grass cover all through the vineyard floor, with all the microbial/nutrient cycling, soil structure and “living mulch” benefits that this treatment provides. However, we do have some concern that grasses immediately under the vine can rob the vine of water and nutrients, particularly in a drier year. This year, we’re experimenting with varying under-vine covers to see if we notice any difference in the vine and fruit development – from fully sprayed out, partially removed and mulched. We’ll monitor vine vigour, take petiole tests (measurements of vine nutrition status) and ultimately measure fruit composition to see what we can learn. Research in this area is somewhat lacking."
Our experimentation was interesting - in a dry season (typical but not always the case) there was a definite impact on vine vigour from leaving full grass cover in place, with Cabernet being the most significantly effected, and Shiraz barely noticing. Now, in addition to cyclical mulch and compost treatments, we selectively use a knockdown herbicide in the spring, to just tip the advantage to our vines in the critical first few months of growth. The grasses bounce back and we get the continued "living mulch" benefits for the rest of the season. This year we're trialing an even softer organic herbicide treatment. Tilling remains an option, but I'm reticent to disturb our delicate soils.