Integrated Management of Grape Diseases

5A) Fungicides for Use in Organic Production Systems

The following is a brief description of some disease control materials that are commonly or traditionally used in organic production systems. Copper fungicides, elemental sulfur and liquid lime sulfur are the old "standard" fungicides, and have been used for many years in organic production systems.

Note: Prior to using any material in the organic system, it is important that the grower consult his/her organic certification agency or program to be positive that use of the material is permitted.

Copper Fungicides

When different formulations of copper are dissolved in water, copper ions are released into solution. These copper ions are toxic to fungi and bacteria because of their ability to destroy proteins in plant tissues. However, because copper can kill all types of plant tissues, the use of copper fungicides carries the risk of injuring foliage and fruit of most crops. Factors promoting this injury include: 1) the amount of actual copper applied, and 2) cold, wet weather (slow drying conditions) that apparently increases the availability of copper ions and, thus, increases the risk of plant injury. Because of the potential to injure plants and to accumulate in soil, the use of copper fungicides in conventional production systems has largely been replaced with conventional fungicides that are generally safer to plant tissues and often more effective.

Several terms are used when discussing copper as a fungicide. The original material used was copper sulfate (also known as blue vitriol or bluestone). When this material was combined with lime in the French vineyards, the combination became known as Bordeaux mixture.

Bordeaux Mixture

Bordeaux mixture is a mixture of copper sulfate and hydrated lime in water. It has long residual action and has been used for years to control many diseases, including downy mildew and powdery mildew of grape. It can be made (mixed) on site by combining copper sulfate with spray grade lime. It is also commercially available as a dry wettable powder.

Fixed Copper Fungicides

Following the discovery and use of Bordeaux mixture, several relatively insoluble copper compounds or fixed coppers were developed. Fixed copper formulations release less copper ions and are generally less injurious to plant tissues (safer to use) than Bordeaux mixture, but their use is still limited because of their potential to injure plants and lack of compatibility with other pesticides. Some of the more common commercial formulations of fixed copper include C-O-C-S, Kocide 101, Tribasic Copper sulfate, Champ, and Tenn-Copp 5E. There are several fixed copper fungicides registered for use on small fruit.

Sulfur Fungicides

Sulfur is available as liquid lime sulfur and as dry wettable powders or liquid (flowable) formulations of elemental sulfur.

Liquid Lime Sulfur

Liquid lime sulfur can be used at high concentrations as a dormant spray on raspberries and blackberries for control of cane blight, spur blight and anthracnose and on grapes for control of anthracnose. At high concentrations, it should be used only when plants are dormant. It can cause severe damage if applied after green foliage appears. Lime sulfur has a foul odor that many people dislike. It is also registered for use on grapes and caneberries as a more dilute concentration for use during the growing season.

Dry Wettable Sulfurs or Flowable Sulfurs

Sulfur for use as a fungicide is available under many trade names. The microfine wettable sulfurs or flowable sulfurs are usually much less injurious to foliage and fruit than liquid lime sulfur, but their use during hot weather (above 85F) may result in some leaf burning and fruit damage. Sulfur fungicides are very effective for control of powdery mildew on most fruit crops, but are not highly effective for control of most other fruit crop diseases. Sulfur is very toxic to foliage of certain grape varieties (mainly American grapes) including Concord, Chancellor, DeChaunac and Foch. Sulfur is relatively safe on most other varieties see Table 6, page 68. Applications after the fruit begins to ripen may pose problems during fermentation if the grapes are intended for wine making.

Growers should note that sulfur is lethal to some beneficial insects, spiders and mites. These beneficial insects are natural predators of harmful insects and mites that affect fruit crops. Killing these beneficial insects may increase certain pest problems, especially mites.

Specific comments on fungicide use will be made in the text for each crop where applicable.

5B) "New Alternative" Disease Control Materials for Small Fruit

Many products are currently available or currently being introduced as "biological control agents" or "biopesticides". These include living microorganisms, "natural chemicals" such as plant extracts, and "plant activators" that induce resistance in plants to disease. For most of these products, independent evaluations are currently being conducted; however, their effectiveness under moderate to high disease pressure is uncertain. Although many of these new products have great potential for use within organic production systems, their effectiveness needs to be determined in field tests. It is important to remember that registration of these materials for control of a specific disease on a crop is no guarantee that they will provide effective control

under moderate to heavy disease pressure. In addition, many products may be effective for only one or a few diseases and most have very limited residual activity (they have to be applied often). It is also important to remember that these are registered pesticides and growers need to be certain that their use is permitted within their organic certification program.

The IR-4 project is a federally funded program that facilitates the registration of sustainable pest management technology for specialty crops and minor uses. IR-4 has a very helpful searchable database for all registered biopesticide products. I think the following web sites probably have the best information on biopesticides that are avilable nationally and in your state.

For background go to:
http://ir4.rutegers.edu/biopesticides.html

For the searchable database on biopesticies go to:
http://ir4.rutgers.edu/Biopesticides/LabelDatabase/index.cfm

Also, the Biopesticide Industry Alliance recently updated their web site. On it there is some general information about biopesticides that should be useful to organic growers.
http://www.biopesticideindustryalliance.org

These web pages list all the products currently available along with information such as registered crops and diseases controlled. It also lists the name of the company that manufacturers or distributes the product along with phone numbers and web site addressess. These sites are updated regularly and should be a valuable resource for growers interested in these products.

The following are a few of the most common "alternative" disease control products currently registered for use on small fruit.

• -AC10 (Ampelomyces quisqualis) is a biofungicide registered for control of powdery mildew in grapes, strawberries, blueberries, raspberries, currants, and gooseberries. A. quisqualis is a fungus, that parasitizes powdery mildew fungi. Preliminary results in grapes in Michigan show moderate disease control. Adding an adjuvant such as Nufilm (0.02% v/v) enhances its efficacy. Application should start as soon as susceptible tissue becomes available and continue on a 7 to 14 day schedule. A minimum of 2 sequential applications if needed to maintain the population of A. quisqualis. The following chemicals cannot be tank-mixed with AQ10: sulfur and potassium salts of fatty acids.
• -Armicarb 100 (potassium bicarbonate) is a reduced-risk, protectant (contact) fungicide. Armicarb 100 is registered for control of powdery mildew and other diseases in grapes, blueberries, strawberries, and brambles. Preliminary results in grapes in Michigan indicate moderate control of powdery mildew. It provides little or no control of the other grape diseases. Start applications at the first sign of disease and continue on a 7-14 day schedule. The preharvest interval (PHI) on all crops is 0 days.
• -Kaligreen (potassium bicarbonate) is a reduced-risk protectant (contact) fungicide. Kaligreen is registered for control of powdery mildew on grapes, strawberry, brambles (raspberry and blackberry) and blueberry. It provides good control of powdery mildew when applied on a frequent-protectant program of 7 to 10-day intervals. It has little or no efficacy against most other fungal diseases on small fruit. It is formulated as a micro-encapsulated powder that is mixed in water and sprayed directly on the crop. Kaligreen has a preharvest interval (PHI) of 1 day on all small fruit crops.

• -Messenger (harpin) is a reduced risk product registered for use on grapes, blueberries, cranberries, strawberries, brambles, and currants. The active ingredient is derived from a protein produced by certain bacteria. This protein stimulates natural plant defenses. Messenger has no direct effect on pathogens. The efficacy of this material for disease control or suppression has not been sufficiently confirmed. Messenger has a 0 day PHI.
• -Mycostop (Streptomyces griseoviridis strain K61) is a biocontrol product registered for use on all fruit crops for control of several important pathogenic fungi that cause seed, root, and stem rot and wilt diseases. The active ingredient is the bacterium, Streptomyces griseoviridis strain K61. It is sold as a powder formulation that is mixed with water and applied as a spray or a drench. It's efficacy for control of grape diseases has not been demonstrated.
• -Oxidate (hydrogen dioxide) is a broad-spectrum bactericide/fungicide registered for use in grapes, blueberries, cranberries, strawberries, and brambles. It is a rather corrosive material and works by oxidizing fungal and bacterial cells. The efficacy of the material for disease control has not been sufficiently confirmed on several diseases. In one Ohio fungicide evaluation, it provided no control of grape black rot.
• -Serenade (Bacillus subtilis) is a biocontrol product registered for control of powdery mildew, Botrytis bunch rot and sour rot in grapes. Serenade is also reported to provide some suppression of downy mildew. This product needs further evaluation, but preliminary results show a moderate level of control of Botrytis bunch rot and powdery mildew. Serenade did not control grape black rot in Ohio. Good coverage is important for control. Applications are recommended on a 7-10 day schedule. Serenade has no maximum seasonal application rate and has a 0 day PHI.
• -Trichodex (Trichoderma harzianum) is a biofungicide registered for use on all small fruit crops for control of a wide range of diseases, but primarily for control of Botrytis fruit rot. It is sold as a wettable powder formulation that is mixed with water and sprayed directly onto the plants.
• -Trilogy (Clarified Hydrophobic Extract of Neem Oil). The label states that Trilogy is a broad spectrum fungicide of certain diseases and controls mites in citrus, deciduous fruits and nuts, vegetable crop, cereal grains and other miscellaneous crops. The label does not state what diseases are controlled on specific crops. Trilogy is registered for use on grapes, strawberry, brambles (raspberry and blackberry), and blueberry. Trilogy is a liquid that is applied for diseases as a 1% solution in sufficient water to achieve complete coverage of the foliage.

As the efficacy of these new materials is tested and validated, they will be included in these guidelines where appropriate.

5C) Fungicide Use Strategies for Organic Production

Unfortunately, there are not many options to choose from when one considers current fungicide use strategies. The current options are:

1. Do Not Use Fungicides

This is always an option, but may not be a wise decision for commercial grape plantings in the Midwest. This option should not be confused with "organic" production. Grape growers in "organic" production systems will most probably use Sulfur or Copper to some extent for disease control. Sulfur and Copper are fungicides. Growers that choose not to use fungicides must rely completely on cultural practices, disease resistance, or biological control agents or products for disease control.

2. Protectant Fungicide Program

In a protectant program, fungicides are used as a protective barrier on the plant surface. This chemical barrier prevents the fungus from entering the plant. It works much like paint on a piece of wood to keep out water. Protectant fungicides (such as sulfur and copper) are not systemic and cannot move into plant tissues. Once the fungus penetrates into the plant, protectant fungicides will not control it. As the protective barrier breaks down or new foliage is produced, additional applications are required to maintain the protective barrier.

Protectant fungicide programs have been, and still are very effective; however, they generally result in a fairly intensive use of fungicide. On grapes, protectant fungicides are usually applied on a 7-10 day schedule early in the growing season and on a 10-14 day schedule later in the season. Obviously, maintaining a protective barrier on the plant surface throughout the growing season requires several applications. It is important to note that the most critical period for disease control on grapes with fungicides is from immediate prebloom through 3 to 4 weeks after bloom. It is during this period when protection of fruit is most critical. Cover sprays later in the season may also be required to protect foliage and cluster stems (rachis) from infection by powdery and downy mildew.

5D) Fungicides for Organic
Grape Disease Control

Due to the complex of grape diseases in the Midwest (black rot, powdery mildew, downy mildew, Phomopsis cane and leaf spot, Botrytis bunch rot) some use of fungicide within the organic production system will probably be required. The use of sulfur and copper fungicides on grapes has a long history, and these fungicides are commonly used in conventional grape production systems today. The challenge for the organic producer is to develop a program using only these fungicides that will provide simultaneous control of the entire disease complex. Especially in wet growing seasons, all of the above mentioned diseases can develop within the vineyard simultaneously. The exclusive use of sulfur and copper, even in combination, may not provide acceptable disease control of all the diseases under moderate to heavy disease pressure.

Liquid Lime Sulfur

Lime sulfur is recommended for control of anthracnose as a dormant application in the spring. It is recommended at the rate of 10 gallons per acre. The dormant application is generally not recommended unless anthracnose is a problem. Some growers routinely make a dormant application of lime sulfur or copper, and feel they are getting some benefits for control of other diseases as well. University research indicates that a dormant application alone will not provide season long control of any grape disease; thus, foliar applications through the growing season will probably be required.

Sulfur is highly effective against powdery mildew if used in a protectant program with a minimum of 7 to 10 days between applications. Sulfur provides very good control of powdery mildew, but has little or no effect on all the other grape diseases. Under moderate to heavy powdery mildew disease pressure, a minimum of 7 to 10 days between spray intervals will probably be required.

There are many formulations of sulfur (wettable powders, dusts, dry flowables and flowables). The flowable formulations appear to most effective and result in much less applicator exposure when preparing sprays.

Note: On sulfur tolerant varieties that are susceptible to PM (Table 2), Sulfur will be a major component of the fungicide program. On highly susceptible varieties, spray intervals shorter than 14 days (7-10 days) will probably be required.

Although Sulfur is highly effective for PM control, it has little or no effect on the other grape diseases. It is important to remember that Sulfur can cause severe injury on some varieties. Sulfur should only be used varieties known to be sulfur tolerant (Table 2).

Note: Concord grapes are extremely sensitive to Sulfur. Sulfur injury may occur even on sulfur-tolerant varieties when temperatures of 80 to 85F or higher are experienced during or immediately after application.

Copper fungicides are highly effective against downy mildew and are moderately effective against powdery mildew. Copper fungicides are weak for controlling black rot, Botrytis Bunch, and Phomopsis Cane and Leaf Spot. A concern with the use of copper fungicides is the potential they have for phytotoxicity or "vine damage".

The following summary of recommendations are intended to reduce the danger of phytotoxicity when using copper:

1. Do not make a complete season-long spray program with any copper fungicides.

2. Use fungicides other than copper whenever possible.

3. When using copper fungicides, delay their use as late in the growing season as possible.

4. When using copper fungicides, avoid the use of copper sulfate. Always us a "fixed" copper formulation.

5. Use the full recommended rate of lime. Never eliminate the use of lime completely, unless the pesticide label indicates that lime should not be used.

6. Remember that cool, wet weather enhances the risk of copper injury. Be especially certain to use adequate lime levels during such periods or switch to other fungicides.

7. Make sure that any material you tank mix with copper is compatible. Many materials are incompatible (cannot be tank-mixed) with copper.

8. Avoid copper and lime sprays on fruit destined for fresh market.

Powdery mildew is different from most other grape diseases, because the fungus that causes it lives almost entirely on the surface of infected plant parts. The fungus may penetrate only one cell layer deep into the plant. Thus, it is exposed to eradication following topical treatment with a range of products that do not affect other diseases that colonize deeper into infected plant tissues, such as black rot. Research in New York and other locations has demonstrated that many new and "alternative" materials can provide effective control of powdery mildew if applied often enough (7 day schedule) through the growing season. These materials burn out the fungus growing on the surface, but do not provide protection against new infections; thus, repeated applications are important. These materials include: Nutrol (manopotassium

phosphate); Kaligreen and Armicarb (potassium bicarbonate-baking soda); oils such as Stylet Oil and Trilogy; and dilute solutions of hydrogen peroxide (Oxidate). In Australia, dilutions of milk and whey (the dairy by-product) have been effective for controlling powdery mildew.

Unfortunately, these materials have very little or no effect on the other grape diseases. In addition, organic growers need to consult with their certification agency or program to be sure that any material they use is "certified" or acceptable as organic.

Table 3 in section 5E shows the relative effectiveness of organically approved fungicides for control of the major grape diseases. It should be noted that none of the materials or highly effective against black rot, phomopsis cane and leaf spot, and Botrytis bunch rot. These diseases will be a major concern on susceptible varieties in organic production systems. Whereas, most varieties do not have complete resistance to these diseases, varieties differ greatly in their level of susceptibility. Organic growers should at least AVOID varieties that are highly susceptible to these diseases (Table 2). In addition, the use of cultural practices mentioned in these guidelines must be strongly emphasized.

There are many biocontrol materials and other products such as oils and salts currently registered for use on grapes. Most of these are registered for control of powdery mildew and Botrytis bunch rot, and their effectiveness under moderate to severe disease pressure needs to be determined. As information on these materials becomes available, they will be included in these guidelines.

5E) Table 3: Relative effectiveness of organically approved fungicides for controlling grape diseases.

H= highly effective

M= moderately effective

W= weak or not effective