Summer 1995 (v7n3)
Lodi-Woodbridge WineGrape Commission
[Editor's Note: The Grower Profile series is from a chapter in a forthcoming SAREP publication on cover cropping in vineyards. The publication includes contributions by numerous UC and Natural Resource Conservation Service researchers. It is edited by Chuck Ingels and Robert Bugg of SAREP; Glenn McGourty, Cooperative Extension director, Mendocino County; and Peter Christensen, Cooperative Extensive Viticulture Specialist at the UC Kearney Agriculture Center in Parlier. For another perspective on cover cropping in vineyards, please see "Integrating cover crops into grapevine pest an nutrition management: The transition phase," page 11 of this issue.]
by Chuck Ingels, SAREP
When Dennis Culver first began working with the Lodi-Woodbridge Winegrape Commission in May 1992, many growers were already very interested in cover cropping. The Commission is a marketing and research organization, and includes 650 growers who farm over 45,000 acres in this important viticultural region north of Stockton. According to Culver, the Commission's IPM program consultant, growers had two primary reasons for using cover crops. First, cover cropping was viewed as an important strategy for increasing biodiversity in the vineyards. Cover crops provide a habitat and food source for beneficial insects and spiders which may reduce the need for pesticide applications. The second goal in cover cropping was to improve the soil and vine root environment by building soil organic matter and improving water penetration.
In August 1992, Culver organized a meeting on cover crops which further stimulated interest. Following the meeting, cover crop plantings increased dramatically. That fall, Culver set up side-by-side trials in several vineyards comparing cover-cropped versus fallowed middles in five-acre blocks. Although there were few pest problems in 1993, Willamette mite populations did appear to be reduced where the annual clover mixes were planted. In these clovers and in some high-nitrogen blends there may be a buildup of two-spotted mites, according to Culver, which result in increased numbers of beneficial arthropods in these cover crops. These beneficials, in turn, may move into the grapes and be responsible for reducing Willamette mite populations in the grapes. Similar trials will be conducted each year to determine the long-term effects on pests.
While the jury is still out on the effects of individual cover crops on grape pest management, Culver has specific recommendations depending on the method of irrigation, soil type, and nutritional needs. With furrow irrigation, he recommends the annual clover mix (subterranean, crimson, and rose clovers and barrel medic) or a legume green manure mix (bell bean, field pea, common vetch, and Lana woollypod vetch), sown in alternate middles the first year. The unplanted middles are eventually furrowed out in late spring for irrigation. Depending on the grower's preference, alternate middles can be sown each year or the same middles can be used. If the same middles are used, growers are finding that the annual clover mixes, in particular, are reseeding themselves quite nicely. According to Culver, the best strategy to facilitate reseeding is as follows: 1) allow the cover crop to go to seed, 2) shred it down in late spring (rather than disking it under), and 3) after the first substantial fall rain, run a springtooth harrow lightly through the middle.
Where drip irrigation is used, the cover crops of choice are perennial native grass mixes, such as Molate fescue, Idaho fescue, and pine bluegrass. The perennial grass species used are summer obligate dormant, which means that they do not compete or compete only minimally with the vines for water and nutrients during the critical late spring/summer months. Overhead sprinkler irrigation gives the grower the flexibility of planting either the annual or perennial cover crops noted above. For vineyards with very heavy or very sandy soil, or where a hardpan is present, Culver recommends Merced rye or barley to help improve these soils.
Regardless of the cover crop species used, Culver recommends that growers create a good seedbed and pre-irrigate where possible for best results. Depending on the time of seeding, a pre-plant irrigation may be the only irrigation needed. Culver also strongly recommends that growers monitor the nutritional status of the vines, especially nitrogen, since cover crops are capable of either adding or removing nitrogen from the soil.
Other mixes are also being used by growers in the Lodi area. Some growers have planted various insectary blends, which contain species attractive to beneficial insects and spiders. A number of these mixes have proven largely unsuccessful in this location because the species and/or seeding rates of the mixes create a stand which is poorly competitive with cool-season weeds. Also, it has been difficult to judge whether these mixes are attracting sufficient beneficials to significantly reduce leafhopper and mite populations.
Several growers have planted California native perennial grasses. Randy Lange of Lange Twins has planted over 300 acres of vineyard to a mix of various native grasses. Initially concerned about the effects of dust (from tillage) on mite predators and parasitoids, he first started using resident vegetation ("weeds") as the ground cover. However, some of the weed species became unmanageable and many became very competitive with the vines for water and nutrients. He had seen some vineyards planted to native grasses, which formed a dense cover and did not appear to compete with the vines.
To prepare the soil for planting native grasses after harvest, Lange applied two tons per acre of compost and then disked twice. In order to level the ground as much as possible during the first disking, he placed a triangular-shaped drag implement behind the disk to fill in the furrows created by the disk. Two weeks after the first disking, which tilled to a depth of six inches, he sprayed Roundup® on the berms to control the germinating weeds. The second disking was shallower, to prevent the soil from fluffing up too much, and included the use of a ring roller behind the disk to pack the seedbed before planting. In late October, he planted the seed blend at a rate of 20 pounds per acre. He calibrated the Truax drill (currently the only drill that can plant native grasses properly) frequently because he wanted to ensure uniform seeding and because of the high cost of the seed. He then sprinkle-irrigated the vineyard for three hours, and did not enter the vineyard until it was mowed in late winter. The berms were immediately treated with Roundup® in early March. Before mowing, weeds dominated the stand and had him worried. But after mowing, the thin green lines of the drilled grasses were clearly visible. No further irrigation was needed until early April. Lange admits he doesn't yet know the drawbacks involved with this mix, but he thinks the benefits will outweigh the risks.
[ Back | Search | Feedback ]