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Cooperative Extension San Joaquin County
University of California
Cooperative Extension San Joaquin County

Posts Tagged: viticulture

NEW: Grape Pest Management—Third Edition

Grape pests and diseases cause significant economic losses to California’s wine, raisin and table grape vineyards annually. Grape growers rely on University of California researchers and others for information that allows them to make sound management decisions.

 Grape Pest Management—Third Edition

In the much anticipated 3rd edition of Grape Pest Management, more than 70 research scientists, cooperative extension advisors and specialists, growers, and pest control advisers have consolidated the latest scientific studies and research into one handy reference. The result is a comprehensive, easy-to-read pest management tool.

What’s new? Well, for starters, more information on destructive vineyard pests. The new edition, the first in over a decade, includes several new invasive species that are now major pests. It also reflects an improved understanding among researchers, farmers, and growers about the biology of pests. With nine expansive chapters, helpful, colorful photos throughout, here’s more of what you’ll find:

  • Diagnostic techniques for identifying vineyard problems
  • Detailed descriptions of more than a dozen diseases
  • Comprehensive, illustrated listings of insect and mite pests,including the recently emerging glassy winged sharpshooter and Virginia creeper leaf-hopper
  • Regional calendars of events for viticultural management
  • Up-to-date strategies for vegetation management



Posted on Friday, December 6, 2013 at 6:07 PM
Tags: grape (2), IPM (2), viticulture (48)

VOC's Contribute to Ozone Formation

It’s that time of year again when hot weather fuels the creation of ozone, or smog. Some pesticides emit volatile organic compounds (VOCs) that contribute to ozone formation. Using pesticides that release VOCs may be restricted in certain California locations between May 1 and October 31.


If you plan to apply a pesticide, use the Department of Pesticide Regulation’s VOC calculators to determine emissions from fumigant and nonfumigant pesticides. Get there by clicking on the Air Quality button at the top of each treatment table in the UC IPM Pest Management Guidelines: Grape.


Simple steps can minimize the release of VOCs into the air: 

  • Use pesticides only when necessary.
  • Decrease the amount of pesticide applied if appropriate.
  • Choose low-emission management methods.
  • Avoid emulsifiable concentrate (EC) formulations and fumigants.


Ozone, or smog, is caused by mixing VOCs, nitrogen oxide, and sunshine. High levels of ozone can harm people and crops. Regions in California that do not meet federal or state air quality standards for ozone, called nonattainment areas, may restrict the use of pesticides that release VOCs.

Posted on Friday, June 28, 2013 at 2:57 PM
Tags: smog (1), viticulture (48), VOC (1)

Preparing Your Vineyard For Frost

Low temperatures experienced during the winter do not usually damage dormant grapevines in the San Joaquin Valley. However, succulent green shoots are much more sensitive to low temperatures, so spring frost damage is serious concern. Damage from spring frost can vary within and between vineyards. Some factors that determine the extent and severity of frost damage include vineyard location, stage of shoot growth, the minimum temperature reached, and the duration of time that the tissues are at or below critical temperatures (Table 1). A mild frost shortly after budbreak may only damage a few leaf cells, causing necrotic (brown to black) spots (Fig. 1, inset) which will appear to be unevenly distributed throughout the leaf blade or shoot. If enough cells are damaged, the leaves may become distorted, or killed. As frost intensity and duration increases, shoot tips and flower clusters may be killed (Fig. 1). Vines in low lying areas of a vineyard will experience the most damage since cold air will settle and not warm until late morning or later (Fig. 2). Severe frosts will kill entire shoots to the cane. When temperatures are low enough to kill whole shoots, the damage is often uniform throughout the vineyard. Shoots killed by frost will turn a dark brown to black color within a few days of freezing.

On clear nights when frost forms, the coldest air is found near the ground. As night progresses, a cool layer of air continues to build and the shoots nearest the ground are the first to experience damage. Thus, training grapevines to higher heights decreases their susceptibility to frost damage. For example, a Thompson Seedless vineyard trained to a height of three feet will be more susceptible to frost than one trained to a height of four feet. 

Previous research has shown that temperatures during radiative freezes generally increase with height above ground before decreasing again at some height to form an inversion layer. For example, air temperature may be 28°F one foot above ground, but 30°F three feet above ground. At twenty to twenty-five feet above the soil line the temperature will gain another two degrees. The greater the temperature change between the soil line and the inversion layer, the greater the chance of avoiding frost damage. Wind machines can help mix the cold and warm air, increasing the temperature and providing relief for green tissue.

When frost has been predicted, growers should take note of their vineyard’s growth stage so a strategy can be developed. Vineyards that are not yet at bud break may not require special attention. However, when green shoots are longer than six inches, soils need to be prepared well in advance of cold weather. Table 1 shows the relative susceptibility of grapevine tissue at different growth stages and critical temperatures.


Table 1. Frost damage to various growth stages of grape.

Growth Stage

Critical Temperature*

 Buds—tight, closed


 Buds with wool (eraser stage)

< 26°F

 Budbreak—green tissue showing

< 30°F

 Shoots< 6” in length

< 31°F

 Shoots > 6” in length

< 32°

*Critical temperatures are based on research under controlled environments. Vineyard characteristics (location, cultivar, etc.) may increase or decrease susceptibility to frost damage. These values should only be used as a point of reference when developing a frost protection program.


If a significant frost event occurs and all the green shoots are killed, secondary or tertiary buds will push within one to two weeks. However, secondary and tertiary buds will not be as fruitful as the primary buds and growers can expect substantial losses. Vineyards that have experienced significant frost damage should be irrigated regularly in order to develop a full canopy and prepare them for the following season. Vineyards with substantial frost damage should not be neglected.

Soil Characteristics

In order to minimize damage caused by frost, vineyard soils should be prepared for maximum heat absorption during the day and release at night. Optimal conditions include soils that are free of vegetation, firm in texture, and moist. Moist dark soils improve their ability to absorb heat during the day and radiate it at night as ambient temperatures drop. Soil texture will also have an impact on heat absorption. Vineyards planted to sandy soils are more prone to frost damage because they retain less water. Additional water may be needed if winter precipitation has not been adequate to maintain soil moisture. Prior to a predicted frost, the goal should be a uniformly distributed irrigation that allows for maximum heat absorption. Table 2 shows the benefits of a bare, firm moist soil in contrast to less optimal vineyard floor conditions. Soils that have been recently cultivated or disked do not retain heat well because they are dry and have numerous air pockets and thus should be irrigated soon after cultivation. Native vegetation or cover crops that insulate soils from absorbing heat should be mowed, disked, and irrigated, unless significant precipitation makes irrigation unnecessary. Irrigation during a frost event can be beneficial. On nights that low temperatures are expected pumps should be turned on early enough that the entire vineyard is covered with water. In some vineyards, it may not be feasible to saturate the whole vineyard. In such cases, focus efforts on the most susceptible areas (low lying) portions where cold air tends to drain. Doing so will improve the chances of protection.

Vineyards that are drip irrigated should not have their row middles cultivated. Drip irrigation should be turned on to wet as much soil as possible. Growers will have to be especially vigilant to the weather forecast in order to start irrigating well in advance of the frost event. Cover crops or native vegetation should be mowed prior to budbreak and regularly thereafter until the risk of frost has passed (typically mid-April). Row middles should not be cultivated unless a significant rain event has been predicted. Doing so could result in significant losses if frost should occur. It only takes a single frost event (one night at freezing or below) to experience a complete loss.


Table 2. Comparisons between optimal soil conditions for frost.

Soil   Characteristics


Temperature   Benefit


 Bare, firm, moist




Least optimal


 Shredded cover crop

         0.5 °F


 Low growing cover crop

         1-3 °F colder

 Dry, firm

 Freshly disked

           2  °F colder

 Dry to moist

 High cover crop

           2  °F colder



Posted on Monday, March 25, 2013 at 9:12 AM
Tags: frost (1), Rubired (1), Thompson Seedless (1), viticulture (48)

Embryo Rescue: Making the Impossible Happen

Grapes like DOVine, Selma Pete, Sweet Scarlet and Scarlet Royal likely would not exist were it not for ARS scientists’ expertise with a laboratory technique known as “embryo rescue.” The technology “allows us to use two seedless grape plants as parents for new, seedless offspring,” says grape breeder David W. Ramming with USDA Agricultural Research Service (ARS) at Parlier, California.

“Seedless” grapes actually have a small seed inside, “but it’s so small that your tongue can’t detect it,” says Ramming. What’s the point of embryo rescue? To literally rescue the embryo within the minuscule seed so that it can be grown into an experimental vine for testing in the research vineyard.

DOVine, developed by the USDA ARS in 1995, as an early ripening raisin was the first variety released from the hybridization of two seedless grapes using embryo rescue techniques. DOVine resulted from a cross of 79-101 x Fresno Seedless made in 1983. 79-101 is a blue seedless grape of unknown parentage, probably bred by Elmer Snyder of USDA; Fresno Seedless is a sibling of Flame Seedless and resulted from the cross of (Cardinal x Thompson Seedless) x [(Red Malaga x Tifafihi Ahmer) x (Muscat of Alexandria x Thompson Seedless)].

As might be expected, when two seedless grapes are chosen as parents, the seeds inside the grapes of their offspring are also extremely small. Says Ramming, “In nature, those seeds would abort” instead of developing into hard little spheres, each with a healthy embryo inside.

To save otherwise-doomed embryos, Ramming and colleagues excise them with surgical precision from the developing berry (Fig.1). Then, the researchers nurture the embryos on a gel-like bed of nutrients until they form seedlings hardy enough to transplant.

Ramming pioneered the use of embryo rescue several decades ago to breed superb seedless grapes. Today, it still remains the survival secret of many of the team’s most innovative grapes and used by private breeding programs. 

Posted on Friday, February 15, 2013 at 1:48 PM
Tags: embryo rescue (1), grape breeding (2), grapes (4), raisin (5), table (1), viticulture (48)

Grape Breeder, David Ramming Retires

After 38 years, David Ramming has retired from the USDA Agricultural Research Service (ARS)-Parlier, California, where he bred grapes for California’s raisin and fresh market industries. Starting in 1975, he replaced John Weinberger who had just released ‘Fiesta’, the first grape developed to replace ‘Thompson Seedless’; the primary raisin grape for 100+ years. Since 1995, David has introduced four raisin grapes that helped make mechanized harvest a reality. ‘DOVine’, which ripens 2-3 weeks earlier than ‘Thompson Seedless’ was the first to be grown by San Joaquin Valley growers over large acreages. Trained using quad cordons, it is a vigorous variety that needs a large overhead trellis to grow. His most recent release in 2001, ‘Selma Pete’, was named after the late L. Peter Christensen, a world renowned UC Cooperative Extension Specialist who worked closely with David in developing cultural practices for new varieties. ‘Selma Pete’ has become the most widely planted raisin grape to date from David’s program and is grown on both open gable and overhead trellis systems. Additionally, two Muscat flavored raisin grapes were released prior to ‘Selma Pete’.

A technique pioneered by David known as embryo rescue has greatly shortened the breeding timeline for seedless grape advancement. Embryo rescue allows for seedless by seedless crosses by removing the small seeds and placing them on a nutrient-rich media, which allows them to grow into viable plants. All of David’s raisin and table grape varieties have been developed using this novel technique, which also has benefited California’s private grape breeding programs.

David’s most recent work has focused on incorporating resistance to powdery mildew and Pierce’s disease. He has been working with colleagues to determine what North American grapes have resistance and then using them to improve his breeding lines. Using molecular markers to find the progeny that have disease resistance in them, he has shortened the screening time. Young plants grown in incubators has saved time and money by not having to grow plants out in the field for evaluations or trials

In retirement, David plans on spending more time with his family and grandkids.

Posted on Friday, January 18, 2013 at 3:59 PM
Tags: grape breeding (2), raisins (4), Ramming (1), table grapes (3), viticulture (48)

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