Notes on New Fungicides for Grape Disease Control

Michael A. Ellis

Department of Plant Pathology
The Ohio State University
Ohio Agricultural Research and Development Center
Wooster, Ohio 44691

| Strobilurin fungicides | Abound (azoxystrobin) | Sovran (kresoxim-methyl) | Flint (trifloxystrobin) | Fungicides For Control of Botrytis Bunch Rot |

Several new fungicides have recently been registered in the U.S. for use on grapes.  Much of this new chemistry is highly effective for control of many of our major grape diseases, and should prove to be valuable tools for use in our grape disease management program.  The following information provides a brief description of these new fungicides.

 

Strobilurin fungicides

The strobilurin fungicides represent a new class of fungicide chemistry that is highly effective for controlling many of the major fungal diseases of grapes in the Midwest.  The strobilurin fungicides were first discovered or isolated from wood-decaying mushrooms, such as Strobilurus tenacellus.  This new class of chemistry is a valuable addition to our current arsenal of fungicides for grape disease management.  Perhaps one of the most exciting characteristics about the strobilurins is their spectrum of activity.  Most of them are registered for control of black rot, downy mildew, powdery mildew, and Phomopsis cane and leaf spot.  Some recent research suggests that have fair to good activity for control of Botrytis.  Although these materials do have a very broad spectrum of activity (control a large variety of fungi), they do differ in their activity to specific diseases.  All of them have good activity against black rot and powdery mildew.  None of them are highly active against Phomopsis cane and leaf spot, and they vary greatly in their activity against downy mildew.  Even though they differ in their activity to specific fungi, they will be important tools for use within the grape disease management program.  Until now, we have never had a fungicide that would provide simultaneous control of all of these diseases.  Prior to the development of the strobilurins we had to rely on tank-mixes of fungicides to control all these diseases.  For example, the sterol-inhibiting fungicides such as Nova provide excellent control of black rot and powdery mildew, but are not effective against downy mildew or Phomopsis.  Thus, we have recommended a tank-mix of Nova plus mancozeb to control all of these diseases simultaneously.  The Nova for black rot and powdery mildew and the mancozeb for downy mildew and Phomopsis.

The strobilurins are very good protectant fungicides.  They have good residual activity and have provided good control in 10-14 day spray schedules.  They are also “locally” systemic and provide some level of “after-infection” activity.  One problem with the strobilurins is that they are at high risk for fungicide resistance development.  Fungicide resistance development is a serious problem we are facing with these new fungicides, as well as our previously registered materials such as the sterol-inhibitors (Bayleton, Nova, Rubigan, Procure, and Elite).  When Bayleton was first registered in the U.S., it could be used at 2oz product per acre on a 21-day schedule and provide excellent powdery mildew control.  After years of continual use, the powdery mildew fungus has developed a high level of resistance to Bayleton.  Although Bayleton is still highly effective for control of black rot, we no longer recommend its use for powdery mildew control in Ohio.

The remaining sterol-inhibiting fungicides are also facing the threat of fungicide resistance developed by the powdery mildew fungus.  This is another reason why the introduction of the strobilurin fungicides is extremely timely.  Strobilurin chemistry is very different from chemistry of the sterol-inhibiting fungicides.  In short, they attack the fungus in a very different way.  One of the main recommendations for preventing or slowing down the development of fungicide resistance is to alternate the use of different fungicide chemistries in the spray program.  The introduction of the strobilurins allows us to do that.  Alternating strobilurin fungicides with a sterol-inhibiting fungicide combined with a good protectant fungicide will probably become a standard recommendation in fungicide programs for wine grapes in the Midwest.  Further information on fungicide resistance management will be provided as we discuss each of these new strobilurin fungicides individually.  There are three strobilurin fungicides currently registered for use on grapes.  They are: Abound (azoxystrobin); Sovran (kresoxim-methyl); and Flint (trifloxystrobin).  Although Abound, Sovran and Flint are all closely related and are all excellent fungicides, they do differ to some extent in their effectiveness against specific diseases.  In addition, some of them have specific or “special” problems that grape growers need to be aware of.


Abound (azoxystrobin)

Abound flowable (2.08F) was first registered in the U.S. in 1997.  Thus, most growers have some degree of experience with Abound, and all the grower comments I have heard have been quite positive.  Abound is registered for control of Black rot, powdery mildew, downy mildew, and Phomopsis cane and leaf spot.  It provides good to excellent control of all these diseases except Phomopsis, for which it provides fair control.  Research in New York indicates that it provides fair to good control of Botrytis bunch rot.  The following information was taken from the label.

Begin ABOUND flowable applications prior to disease development and continue applications throughout the season every 10 to 14 days. For resistance management: Do not apply more than 3 sequential sprays of Abound before alternating with a fungicide that has a different mode of action. For wine and table grapes, do not make more than 4 applications per acre per year. For all other types of grapes do not make more than 3 applications per acre per year. Do not apply within 14 days of harvest.

NOTE: ABOUND Flowable is very phytotoxic to apples of the variety McIntosh or varieties related to McIntosh. Do not use the same sprayer to apply ABOUND to grapes that will be used to apply other materials to apples. Do not allow spray to drift from grapes to apples.

Please note that label information is subject to change. Always read the most recent label.

The problem with phytotoxicity to apples can be very serious.  In Ohio, this is not much of a problem because most grape growers do not produce apples.  This could change to some extent in the future.  In states like New York, Michigan and Pennsylvania, where several grape growers also grow apples or where vineyards are situated next to apple orchards, the phytoxicity is a serious concern and significant losses have occurred in a few orchards.  Abound is registered for use at 11 to 15.4 fluid oz/A.  In the last couple of years, Ohio growers have used Abound at the rate of 11 to 12 fluid oz/A on a 10 to 14 day schedule with good results.  Abound is excellent for control of black rot and downy mildew.  It provides fair to good control of powdery mildew, but is weaker against powdery mildew than Sovran or Flint.  It is stronger against downy mildew than Sovran or Flint.  None of the strobilurins appear highly effective against Phomopsis, and they all have some activity against Botrytis.  Abound is a product of Zeneca Corp.


Sovran (kresoxim-methyl)

Sovran 50WG fungicide was recently registered (1999) for use on grapes for control of Phomopsis cane and leaf spot, black rot, powdery mildew, and downy mildew.  Sovran is a product of BASF Corp. and was the second fungicide in this new class of chemistry (strobilurin) to be registered for use on grapes in the U.S.  Sovran is similar to Abound in that it provides good to excellent control for most of our major grape diseases.  Unlike Abound, Sovran is not phytotoxic (damaging) to McIntosh apples and other related apple varieties.  Although Sovran and Abound are closely related and both are excellent fungicides, they do differ in their effectiveness against certain diseases.  Both Abound and Sovran provide very good control of black rot with about equal efficacy.  Both fungicides are also very effective against powdery mildew; however, Sovran is more active against powdery than Abound.  The biggest difference is with downy mildew.  Abound is more effective for control of downy mildew than Sovran.  Sovran will provide good control of downy if the highest label rate is used (6.4 oz/A).  Sovran is registered for use at 3.2 to 4.8 oz/A for black rot, 3.2 to 4.8 oz/A for powdery mildew, and 4.0 to 6.4 oz/A for downy mildew.  The 4 oz/A rate has provided good control of black rot and powdery mildew in fungicide trials.  Obviously, using the higher rate of 6.4 oz/A for control of downy mildew will greatly increase cost.  Both Sovran and Abound will provide only fair control of Phomopsis, and both have at least fair activity against Botrytis.

The following information was taken from the label.

Use Sovran* fungicide as a protective spray at 3.2-6.4 ounces per acre.  Make applications of Sovran* fungicide in sufficient spray volume to ensure thorough coverage. Do not use less than 10 gallons of water per acre. Black rot and Phomopsis cane and leaf spot control should begin at bud break and continue on a 14-day schedule through 1/4-inch berry. Use 4.8 ounces of Sovran per acre during periods of heavy infection pressure.         

For powdery mildew control, begin sprays at bud break and continue on a 14-day schedule. Form more susceptible grape varieties or under conditions that favor rapid powdery mildew development, use 4.8 ounces of Sovran per acre. When disease pressure is low, the spray interval can be extended up to 21 days.

For downy mildew control, begin sprays at bud break and continue on a 7-10 day schedule. Under conditions that favor severe downy mildew development, use 6.4 ounces of Sovran per acre.

Crop-Specific Restrictions and Limitations

To limit the potential for development of resistance:

*On wine and table grapes, do not make more than four (4) applications of Sovran or other strobilurin fungicides per season. On grapes for other uses, do not make more than three (3) applications per season.

*Do not make more than 3 sequential applications of Sovran.

*Apply Sovran in alternation with non-strobilurin fungicides with a different mode of action.

Sovran cannot be applied within 14 days of harvest.

Please note that label information is subject to change. Always read the most recent label.


Flint (trifloxystrobin)

Flint 50WG fungicide was also registered for use on grapes late in 1999.  Like Abound and Sovran, Flint is also a strobilurin fungicide.  Flint is registered for control of black rot and powdery mildew.  It is registered for “suppression” of downy mildew and is not registered for control of Phomopsis.  Of all the strobilurins, it has the best efficacy for control of powdery mildew.  The use of Flint for grape disease control in Ohio has been limited due to the following factors:

1) Flint cannot be used on Concord grapes.  The label states “Do Not Apply Flint to Concord Grapes or Crop Injury May Occur”; and

2) Flint is not highly effective for control of Downy mildew.  In fact the label states that it provides “Disease Suppression” not control of Downy mildew.

For these reasons, Ohio growers will probably select Abound or Sovran as the strobilurin fungicide of choice for use on grapes.  In growing regions such as California where downy mildew is not a problem and Concord grapes are seldom produced, the use of Flint is more practical.  If Concord grapes are not a problem and the main diseases of concern are black rot and powdery mildew, Flint will do an excellent job in the Midwest.

The following information was taken from the label.

Grapes: Do not apply Flint to Concord grapes or crop injury may occur.

Flint is registered for use at 1.5 to 2 oz/A for powdery mildew control, 2 oz/A for black rot control and 4 oz/A for suppression of downy mildew.

Restrictions: Do not apply more than 8 oz. of Flint per acre per season. Do not apply Flint within 14 days of harvest. Do not apply more than 4 applications of Flint or other strobilurin fungicides to table or wine grapes per season. On grapes for all other uses, do not apply more than 3 applications of Flint or other strobilurin fungicides per season. To limit the potential for resistance to develop, do not apply more than 3 sequential applications of Flint or other strobilurin fungicides before alternating to a non-strobilurin fungicide.

Note that both Sovran and Flint cannot be applied more than 4 times per season on wine and table grapes, and 3 times per season on grapes for all other uses. The label also states do not make more than 3 sequential applications without alternating with a non-strobilurin fungicide with a different mode of action.

The reason for these restrictions is to prevent the development of Fungicide Resistance.

In summary, all of the strobilurins are excellent fungicides; however, each has certain distinct characteristics.  Cost and the various “special” characteristics of each fungicide will help to determine which is used.  The important thing to note is that these are excellent fungicides and should be incorporated into our fungicide spray program for grapes in the Midwest.


Fungicides For Control of Botrytis Bunch Rot

Vangard Fungicide (Cyprodonil) and Elevate fungicide (Fenhexamid) were both recently registered for control of Botrytis bunch rot.  These are welcome newcomers to our arsenal of fungicides for Botrytis control, which is actually very sparse.  At present, Rovral, Benlate, Vangard, and Elevate are the fungicides recommended for bunch rot control.  Many growers no longer use Benlate due to the development of fungicide resistance.  Rovral has been the “Cadillac” fungicide for Botrytis control, but concerns over fungicide resistance development also exist with Rovral.  This makes the registration of these new fungicide chemistries (Vangard and Elevate) especially important.  Where resistance is not a problem, Rovral is still an excellent Botrytis material.  The efficacy of Vangard and Elevate is similar to that of Rovral.  Vangard and Elevate are both good Botrytis materials.  However, in several fungicide trials, Vangard appears to be slightly more efficacious than Elevate.

Vangard is registered for use at 10 oz/A when used alone or 5 to 10 oz/A when used in a tank mix.  More than 20 oz. of Vangard cannot be applied per acre per crop season, and Vangard can not be applied within 7 days of harvest.  Vangard fungicide is a product of Novartis Crop Protection.  To prevent fungicide resistance development to these fungicides (Rovral, Elevate, and Vangard), they should be tank-mixed or alternated with each other in the spray program for Botrytis bunch rot control.  Some research in New York suggests that there may be an additive effect from tank-mixing (half rates) of Rovral at 1 lb/A with Vangard at 5 oz/A.

Elevate 50WDG fungicide was registered for control of Botrytis bunch rot on grapes in 1999.  Elevate is a product of Tomen Agro, Inc. and has good activity against Botrytis.  Elevate is different chemistry than Vangard, Rovral, and Benlate.

The label states that for control of Botrytis bunch rot (gray mold) apply 1 lb. Product per acre.  The final application may be made up to and including the day of harvest (PHI=0 days).  Do not apply more than 3 pounds of product per acre per season.  Thus, you can not make more than 3 applications per season.

In summary, all of these “Botrytis” materials are costly and should be used correctly and only on the tight-clustered “more valuable” wine grapes that are highly susceptible to Botrytis.  Especially where Rovral has been used for many years, or where the efficacy of Rovral for Botrytis control appears to be reduced, these new materials (Vangard and Elevate) should be introduced into the fungicide program for Botrytis control.