This article suggests different pesticide sprays to use in controlling grape insects and diseases in Southwest Michigan. It was originally written as suggested sprays for juice grape growers but can be modified to be of use to commercial growers of wine and table grapes. I am not suggesting that growers need to apply all the sprays recommended. Growers should only apply the sprays they need. Some growers need as few as 2 sprays just before and after bloom. Most commercial growers find they need 5 to 9 sprays, 3 or 4 before bloom and 3 or 4 after bloom.

The weather of determines disease severity by providing infection periods for disease and a spray program that works well one year will fail in another. Generally disease control drives a growers spray program and insecticides are added to fungicides sprays when appropriate, but insects such as climbing cutworm, grape berry moth and Japanese Beetle will often require control when no fungicide is needed. I have not attempted to include all the pesticides used in grapes, see the MSUE Bulletin, E-154 'Michigan Fruit Management Guide' for more complete pesticide use information. For the home owner and small grower 'Pest Control in Small Vineyards' E-2698 ($2) is an excellent publication and serious hobbyists or owners of small acreages of wine or table grapes should order it for their library.

National Grape Cooperative, the major grape processor in Michigan, forbids the use of Captan and restricts EBDC fungicides to use before bloom. Wine and table grape grower could use these materials as they wish but many use a similar program to the ones given here.

Grape Varieties vary greatly is their susceptibility to grape diseases. Concord is moderately resistant to most diseases and somewhat sensitive to Copper and very sensitive to Sulfur. The schedule for Concord juice grapes reflects a low maintenance resistant grape. Niagara is more susceptible to downy mildew and phomopsis and the sprays used here are closer to those used for wine and table grapes.

Schedule for Concord Juice Grapes,
Schedule for Niagara Juice Grapes
Schedule for Wine and Table Grapes

Using Grape Fungicides

Fungicides have different modes of action and each one has strengths and weaknesses. To use a fungicide effectively, it is important to understand its unique characteristics. Several diseases affect grapes and no one fungicide was effective against all grape diseases. Fungicide choice and application timing are driven by what diseases need to be controlled, when they are most easily controlled and how effective a given pesticide is against the diseases targeted for control.

There are two ways fungicides work. One is as a protectant and the other is systemic. Protectant fungicides cover the outside of the plant, killing fungus spores as they germinate. Protectants need to be applied before infection. Once the fungus infects the plant and becomes established, they do not work. The EBDC (ethylene-bisdithiocarbamate) materials (Polyram, Dithane, mancozeb) and Ziram are protectants and do not provide control if applied after a disease infection period. Protectants can redistribute on the plant during a light rain or dew but heavier rains will wash them off. My rule of thumb is that they need to be reapplied if one inch of rain has fallen. Once you see disease symptoms, using a protectant fungicide can only slow the progress of the disease. At that point in time you have lost the battle and playing catch up. Protectants usually poison the fungus in several ways and resistance to protectant materials is unlikely to occur.

Systemic fungicides are absorbed into the plant and kill the fungus early in the infection process before symptoms appear. Systemic fungicides kill fungi by blocking specific biological pathways in the fungus. Since a minor change in the pathway is all that is needed to get past this "roadblock", development of resistance in target pathogens can be a problem. Systemic fungicides need to be applied before the infection process is too advanced and the fungus is big enough to shake off the dose and continue growing. (Think of this as stepping into to boxing ring with Mike Tyson. We could’have all beat Mike when he was 6 years old, but no one wants to fight him now.) With systemic fungicides we talk about days of "back action" or post-infection activity. This is actually the amount of time we have before the fungus becomes too big to control. We can apply a systemic fungicide after a rain (infection period) and get control. Since these fungicides are absorbed into the plant we do not need to worry about washoff. Systemic fungicides also provide protection for several days before plant growth or fungicide movement within the plant dilutes them. My rule of thumb is that if the material has been on for a day, most of it has been absorbed so you don't need to reapply. Systemic fungicides do not protect new growth. In grapes we have three types of systemic fungicides: 1) The SI’s or sterol-inhibiting fungicides, such as Nova and Elite, 2) the strobilurin fungicides or strobys: Abound, Sovran, and Flint, and 3) Ridomil.

The SI fungicides have about three days of back action and ten days of protection against black rot and powdery mildew. These fungicides provide excellent control of black rot and powdery mildew but not Phomopsis or downy mildew. Grape growers in Michigan have used these materials for many years to control black rot and powdery mildew. They do an excellent job when sprayed on a 14-day interval. Because we have used the SI fungicides for so many years, fungicide resistance is a real problem. Powdery mildew is resistant to the SI materials in California and this is one of the reasons the strobilurin fungicides are registered in grapes.

The strobys should be used in rotation with the SI fungicides and sprayed no more than two times in a row. These materials provide control against all the major grape diseases except Botrytis. Abound and Sovran should be the materials of choice for Concord and Niagara vineyards. Flint is phytotoxic to Concords and weak on downy mildew in Niagara grapes. Abound is slightly better than Sovran for downy mildew control. Resistance development is a major risk with the strobilurin fungicides, but none has been found so far in grape pathogens. This is why we want to rotate the use of strobys with other fungicides with different modes of action. Resistance in the SI fungicides is incomplete meaning we can get control by increasing the rate. Laboratory tests indicate that resistance to strobys, when it occurs is complete, meaning these materials will not work at all. There is also evidence in apple scab that where there is SI resistance then the after infection "back action" effectiveness of the strobys is reduced. The strobilurins have at most two days of back action and 10 days of protection. One mistake that growers make is that they want to use strobys at the same spray timing as the SIs, every 14 days. Use them, as protectants on a 10-day rotation and you will be happy. Don't abuse the weakest part of these fungicides action spectrum. They are excellent protectant materials.

Systemic fungicides protect the foliage and fruit that they are applied to. New growth since the last fungicide application is unprotected. Many protectants can redistribute on the plant surface when they are wet and this redistribution will cover part of the plant. Systemic fungicides cannot do this; they only protect the leaves where they were absorbed. Strobys redistribute over the surface in the wax layer, they are surface-systemic. Over time, the fungicides in the leaves are diluted, which is why we need to reapply at 14 or 10-day intervals to maintain the fungicide protection in the plant and protect new leaves.

Ridomil is a systemic fungicide that is very effective against downy mildew, but has no effect on other diseases. Ridomil is premixed, Ridomil Copper and Ridomil MZ. This is for fungicide resistance management. Ridomil Copper is used mainly after bloom. Concords and Niagara and somewhat sensitive to copper. Ridomil MZ has mancozeb as its partner and is used prebloom. Be sure to add addition EBDC material to bring the per acre rate up to a full rate to get the full benefit of the MZ. Ridomil is the only fungicide that will eradicate downy mildew after the symptoms are visible. This makes it very effective to use at bloom time or any other time that you see downy mildew symptoms. Using Ziram, Educes, or strobys after you see the symptoms will only slow the spread of the disease. Once downy has started, there are always new infections that are still too small to see. I recommend that any time you see downy mildew and you have 66 days before harvest, that you consider using Ridomil to clean up the vineyard, otherwise mildew will just get worse.

The last thing I want to talk about is spray coverage. In order to control diseases you need to put the fungicide everywhere the fungus can infect the grapevine. This is easy to do early in the season when there are few leaves on the vines. It is much harder after the canopy has filled in and the fruit clusters are under two or three layers of leaves. These leaves act like shingles on a roof. It is difficult for sprays to penetrate. If you are going to skip every other middle you need to blow the spray all the way through the row you are spraying and into the next. This is the only way that you can be sure that you are protecting the fruit inside the canopy. Since this is difficult to do, you may need to slow down so the airblast can penetrate the canopy, and/or spray every row middle.

I think there are several reasons we seem to be seeing more disease problems in grapes. Some of our disease problems are due to poor spray coverage after bloom. Coverage that is good for a systemic where you get some material on part of every leaf is total inadequate for a protectant which needs to cover the entire surface of the leaf. With a systemic concentrate spraying works only if you get enough on each leaf and berry. If the dose is too small than disease control is lost. Some of our systemic materials are not as effective as when they were introduced 10 years ago so coverage and dose are more important and disease control is less forgiving. The rest I think is due to poor timing and early infections before bloom. Growers are saving money on early sprays but paying for it in lost crop at harvest.

Disease control in the early season is important. Focus on preventing diseases from becoming established in your vineyard. Mid and late season eradication is impossible once diseases become established. Disease pressure only increases and substantial losses will result.

Early season disease control is focused on the use of protectants against phomopsis and black rot. These diseases overwinter on infected canes. EBDC materials, such as Dithane and Penncozeb, provide excellent protection against Phomopsis and black rot. Try for two or three EBDC sprays before bloom. These sprays should be timed for regular applications to protect new foliage from infection during and following rains. Phomopsis is becoming a big problem in Michigan. It causes fruit drop at veraison. Phomopsis symptoms become apparent long after infection. We believe that the berry cluster is susceptible at all times during the season. To reduce Phomopsis, begin protecting the flower cluster as it becomes exposed during early shoot growth. Regular EBDC applications should protect the flower cluster and keep black rot leave lesions to a minimum. Concentrate on controlling black rot on the fruit.

Where powdery mildew is a problem or after a long rainy period (black rot and powdery mildew infection periods), use the Educes in combination with a SI (sterol inhibitor) fungicide, such as Nova and Elite. The SI fungicides have about three days of back action and ten days of protection against black rot and powdery mildew. The SI’s provide excellent control of black rot and powdery mildew but not Phomopsis or downy mildew. The strobilurin fungicides, such as Abound and Sovran, and Flint should be used in rotation with the SI fungicides and sprayed no more than two times in a row. Flint is an excellent material for powdery mildew control in wine or table grapes. The strobilurins short back action and 10 days of protection. Use them, as protectants on a 10-day rotation and you will be happy.

If Downy Mildew symptoms appear before bloom apply Ridomil Gold MZ with enough EBDC fungicide for a full rate of EBDC to provide Phomopsis protection.

The bloom sprays (just before, during and after) are the most important sprays for disease control. Flowers and young fruit are very susceptible to infection by all grape diseases. Downy mildew becomes a problem at bloom. An EBDC spray applied immediately preceding bloom helps to control this disease. The EBDC should be tank mixed with a SI to provide a broad spectrum of disease control. The SI fungicides do not control downy mildew. The SU (strobilurin) fungicides, such as Abound and Sovran, and Flint should be used in rotation with the SI fungicides and sprayed no more than two times in a row. Bloom is a good time to use a strobilurin and control all the major diseases. You can then alternate between strobilurins and SIs in your spray schedule.

Ridomil can kill downy mildew. Some growers with downy mildew problems are using it as a mixing partner at bloom time.

A tank mix of Ziram and a SI is recommended in the post bloom period and provides about 14 days of control. Ziram and a SI should provide protection for downy and powdery mildew. The SU (strobilurin) fungicides should be rotated with the SI fungicides. Ziram as a protectant will only slow the spread of downy mildew. Ridomil CU should be used if you see active downy mildew after bloom (remember the 66 day PHI). Bunch closing (when the berries begin to touch) is the last opportunity to completely cover the fruit leaving fungicide residues in the interior of the fruit cluster. For varieties that are susceptible to Botrytis a spray of Rovral, Vangard, or Elevate is applied at bunch closing.

Late season development of both powdery and downy mildew can take place if the diseases got established early and warm humid days with heavy dews occur. Abound or Ziram (less effective) are recommended for downy mildew control at this time, while Nova or Elite are recommended for powdery mildew control. Black rot will no longer infect the fruit after veraison, but Botrytis bunch rot becomes a problem as the cluster ripens. For varieties that are susceptible to Botrytis a spray of Rovral, Vangard, or Elevate is applied at bunch closing, again at veraison and during ripening if the weather is wet. A spray is advisable at bloom only if the variety is highly susceptible to Botrytis rot and the weather is very wet during the bloom period. Rovral may not be effective at sites where Botrytis has become resistant.

The major insect pests of grapes in SW Michigan are climbing cutworm, grape flea beetle, grape berry moth, rose chafer, Japanese beetle, and grape leafhopper. Minor pests are grape root borers, phylloxera and European red mite. The main insecticides used in grapes are the organophosphates (Lorsban, Imidan and Guthion), carbamates (Sevin and Lannate), and the pyrethroid Danitol. Other materials include Provado, Pyramite and Kelthane. Attention to an insecticide’s pest spectrum, length of activity, effects on natural enemies, pre-harvest interval and re-entry interval should be considered when selecting an insecticide.

It appears that Guthion will not be used in grapes due to EPA restrictions. Lorsban 4E can only be used for climbing cutworm early and not post bloom.

Climbing cutworm are controlled in the early spring at budbreak with Lorsban 4E or with Danitol. These products are applied to the vine when bud feeding is first seen in the spring. Danitol will control climbing cutworm and grape flea beetle.

A key time for gaining control of insect pests in Michigan juice grapes is around bloom. Depending on pest abundance in a particular growing season, effective control of grape berry moth and grape leafhopper before or immediately after bloom provides the foundation for effective insect control during the season. Insecticides are applied with the bloom sprays for control of the first generation of berry moth and rose chafer. Insecticides are also applied after bloom to control grape berry moth, Japanese beetle and grape leafhopper. Grape leafhopper is becoming resistant to Sevin in some regions of Michigan. Provado provides excellent long-term control of grape leafhopper and is fair against Japanese beetle and rose chafer. Provado provides no control of grape berry moth. If growers use Provado for leafhopper control, they need to time organophosphate sprays for grape berry moth, rose chafer and Japanese beetle.

*SI Fungicides are Nova, Elite, Rubigan and Bayleton
**Strobilurin Fungicides are Abound and Sovran do not use Flint on Concord grapes.

*SI Fungicides are Nova, Elite, Rubigan and Bayleton
**Strobilurin Fungicides are Abound and Sovran.

Early and complete coverage of the fruit rachis during early growth is important in reducing Phomopsis. Research in 2004 indicates that dormant sprays of Sulfur or EBDC sprays at budbreak are extremely important and effective in reducing Phomopsis.

*SI Fungicides are Nova, Elite, Rubigan and Bayleton
**Strobilurin Fungicides are Abound and Sovran.

Early and complete coverage of the fruit rachis during early growth is important in reducing Phomopsis.