Central Coast Vineyard Team
On three beautiful, July mornings, the Central Coast Vineyard Team held a series of educational “tailgate” meetings in both English and Spanish. The tailgate meetings were held at Premier Vineyards in Los Alamos, Stone’s Throw Vineyards in Paso Robles and Zabala Vineyards in Soledad. They addressed insect pests and the predatory and parasite insects that prey upon them. Translations in both directions were conducted by many of the attendees, which led to an extensive exchange of information between vineyard managers, winemakers, owners, farm workers and entomologists. Here is a summary of the key points from the presentations that were conducted by Ron Whitehurst, biologist, and Julio Roque, entomologist, of Rincon-Vitova Insectaries, which is located in Ventura, Calif.
Importance of Refuge
A diverse habitat for beneficial insects (“beneficials”) is necessary to promote a diverse population of beneficials. In terms of a beneficial refuge, a diverse mix of flowers and grasses is desirable. Whitehurst recommends dill, coriander, and fennel in coastal areas because nectar is available to both tiny and large insects. The refuge should also contain pollen from early spring flowering grasses, like wheat and rye. It is necessary to have a mix of plants that have different types of flowers that bloom at different times of the year. This will allow a variety of insect species of insects to feed and reproduce during different seasons.
A flowering, nectar-producing habitat should be provided throughout the year, especially during times when the vineyard floor is normally dry. Maintaining 5% (1 row our of 20) of the vineyard floor as habitat to start a transition to a bio-control program is suggested. Once the beneficial insect populations are established, Whitehurst suggests that an area as small as 1% of the vineyard floor can provide sufficient refuge assuming a diverse mix of plants is sustained. Borders are great areas to convert to insect refuge. They can often be irrigated and manipulated separately from the crop. Borders can also be used as a trap crop where the refuge is more attractive to migrant pests than the vines and thus can help keep pests out of the vineyard.
Biology of Beneficials
Understanding the biology of the beneficials reinforces the idea that nectar and pollen are necessary to support their feeding and reproduction. Many predatory beneficials are predators only during their nymphal stages. Once they become adults, they become nectar feeders. Most of the life stages of the predators can actually feed on sap or nectar but they also forage on pest predation. Many parasitic beneficials need nectar and pest hosts to deposit their eggs. Parasitoids lay their eggs in the pest insect, where the young complete their life cycle and emerge to attack more and more pests. For predatory or parasitic insects to survive between seasons and continue on naturally without reintroduction, there must be prey insects present.
Assessing the Chemical Program
An important element for encouraging beneficial insects is to avoid applying disruptive pesticides in the vineyard. Broad-spectrum pesticides that attempt to clean up the field disrupt beneficial populations, allowing the pest populations to resurge quickly and require more pesticides. Organophosphates (i.e., Diazanon and Lorsban) can devastate beneficial insect populations. Even common fungicides for powdery mildew (i.e., sulfur) can affect beneficial insects. Herbicides affect spiders, ground beetles and beneficial fungi, all of which play important roles in biological control. Imidachloprid (i.e., Merit, Avid) does not directly affect the predatory insects at first, because they do not feed on the fluids of the plant. As time goes on, and the predator consumes prey that is sick but not yet dead, there is a “feed through” effect (biomagnification) on the beneficial insects. For example, lacewings don’t reproduce well after eating aphids containing Imidachloprid.
Fortunately, many of the insecticides now used in vineyards do not remain toxic for long periods of time. Each season presents a fresh start for beginning a bio-control program by encouraging refuge and possibly releasing beneficial insects. Natural biological control can be augmented with a release of key beneficials. A beneficial release is not the first part of a biological program, but rather a last tool available to growers when natural biological controls are absent. Remember that the refuge needs to be developed, and the disruptive materials need to be eliminated from a pest program, before a beneficial release should be considered. In fact, simply providing the habitat encourages diverse insect populations. (“If you plant habitat, they will come.”) At Zabala Vineyards, an aggressive planting and management of flowering cover crop hosted a wide variety of general predators and parasitic wasps, without purchasing and releasing these beneficials.
If a grower is interested in a beneficial release, it is suggested to release general predators at a low rate in the cover crop or refuge in spring, when aphids and other pests are plentiful. They will multiply and benefit the vines later on. This is usually before budbreak in vineyards. To minimize risk, budget half the money spent on insecticides for an appropriate beneficial insect release. As soon as you see the target pest (look in the habitat as well as the vine), release a small number of beneficial insects frequently in pest hot spots.
Julio Roque, a bio-control entomologist trained in Nicaragua, used a “D-Vac” to collect insects from both the vines and the vineyard floor. The D-Vac is essentially a converted leaf blower with a squirrel cage fan replacing the paddle blade fan. It vacuums the insect life from the plants into a screen bag. Samples were emptied into a two-cubic-foot, plywood box with a glass lid. When demonstrated, the diversity of types, and the sheer numbers of insects, were dramatically different between the vineyard floor with cover crop and vineyard canopy areas. The vineyard floor had many more insects, especially small flies, which can be important natural enemies of plant feeding pests.
Insect and mite populations can also be monitored using a standard sweep net. The sweep net harvests the larger insects but under-samples the many tiny parasites, immature eggs, small nymphs and larvae of predatory species. One must look at both pests and beneficials and the distribution of the various life stages in order to predict the progress of natural biological control processes. For example, egg-laying adults may dominate a pest population, but the young 1- to 2-day-old larvae are not surviving beyond this early development because of predation of beneficials. This indicates that the population will decline. When monitoring suggests the presence of all life stages and no beneficials, the pest will surely increase in the future.
Insects (especially mites) are not as evenly distributed throughout the vineyard where pesticides are not applied regularly. Therefore, scouts should cover more area of the vineyard, seeking out the hot spots of insect activity. By monitoring the rise of beneficials and the fall of pests in hot spots, it is possible to predict future populations. Beneficials seek out hot spots and reproduce more rapidly where prey are present. Hot spots that clean up with little or no damage benefit by increasing the natural biological control in the vineyard, and eventually the whole plantscape.
Beneficials tend to seek out a particular part of a plant, so to monitor for multiple species, scouts need to cover more area. One of the challenges to effectively monitor insects is their territoriality and nocturnal behavior (i.e., many predatory beetles are nocturnal and spiders can be territorial and difficult to shake loose from the vine or floor). This territorial nature of both pests and beneficials is a challenge for scouts when determining economic and damage thresholds. It is easier to monitor conventional chemical control fields because there is not as much diversity and variability. The goal is to farm in ways that benefit beneficials and minimize practices that interfere with the functional groups of natural enemies, particularly unnecessary pesticide applications. Instead of “if in doubt, spray,” the slogan should be not to spray, and to follow with more intensive monitoring of the beneficials’ effects on pest populations.
With an estimated 29 million species of insects in the world, only a small fraction of them are pests. It is daunting to consider examining insects and identifying tiny life forms in order to control pests. It is easier to look at functional groups: predators, parasites, plant feeders and decomposers. For insect identification, the grower has many tools and educational materials available. Whitehurst recommends a 30X microscope with light available from Radio Shack for about $10 that is a perfectly useful and valuable grower tool.
The UC Cooperative Extensions and local county Agricultural Commissioners have entomologists available to help growers identify pests and beneficials. After they’re identified, study sources to learn about their life cycles and how they interact in the vineyard.
Remember, the experiences of every grower will be different, because every agricultural site is different. Therefore, it is necessary to collect information on the farm itself and not rely completely on research done by other people at other sites. Finally, do not be afraid to design your own method for measuring the insects in your vineyard. As long as you’re consistent and record the information, you will be able to use the information in the future to help you make decisions.
Note: Rincon-Vitova Insectaries is a 2002 CCVT Associate.
(For more information, contact the Central Coast Vineyard Team at P.O. Box 840, Templeton, Calif. 93465, phone (805) 434-4848 or fax (805) 434-4854.)
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