Posts Tagged ‘FRAC codes’

Grower’s Guide to Understanding the DMI or SI Fungicides

Friday, June 10th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The following article by Andy Wyenandt, Ph.D., Specialist in Vegetable Pathology at Rutgers University is particularly timely since many vegetable growers are spraying fungicides to prevent many foliar diseases at this time of year especially on vine crops where DMI or SI fungicides are used very frequently.

The DMI (DeMethylation Inhibitors) or Sterol biosynthesis Inhibiting (SI’s) fungicides belong to FRAC code 3, which include the triazoles and imidazoles. Some of these fungicides are commonly known as Tilt (propiconazole), Rally (myclobutanil), Folicur (tebuconazole), and Procure (triflumizole). SIs work by inhibiting the biosynthesis of ergosterol, which is a major component of the plasma membrane of certain fungi and needed for fungal growth.

Resistance by fungi to the SI fungicides has been characterized and is generally known to be controlled by the accumulation of several independent mutations, or what is known as ‘continuous selection’ or ‘shifting’, in the fungus. Such that, in any given field population the sensitivity to the SI fungicide by the fungus may range from extremely high (highly sensitive, i.e. will be controlled by fungicide) to moderate (partially sensitive) or low (mostly resistant to fungicide). This type of resistance is also known as quantitative resistance. With quantitative resistance there are different levels of resistance to the fungicide due to independent mutations, which is unlike the target mutations that occur in qualitative resistance associated with the QoI fungicides (FRAC code 11).

Because different levels of resistance to the SI fungicide may exist in the field, the fungal population may behave differently to different rates of the SI fungicide being applied. If that is the case, it is suggested that using a higher rate of a SI fungicide, may improve control when lower rates have failed. For example, let’s say that a powdery mildew population on pumpkin has 25% high, 50% moderate, and 25% low sensitivity to a SI fungicide. If fungicide is applied at the low rate, only 25% of the population (highly sensitive) may be controlled. Whereas, if the high rate was used 75% of population may have been controlled.

The main point is that if low rates of SI fungicides have been used and control seems to be weakening, bumping to a higher rate may improve control. Unfortunately, it is difficult to determine what proportion of the powdery mildew population is sensitive or not sensitive by looking at the field until you have begun spraying. The best advice, if you are using low rates and think those rates are not working like you feel the rate should be bumped up to the high rate the next time the fungicide is sprayed, and if the high rate doesn’t work, it may be safe to assume the fungal population has grown mostly resistant. Importantly, if the high rate fails, whether you bumped up to a high rate or started with one, and control does not seem adequate, do not continue to use the fungicide.

Recognizing if and when fungicide chemistries are failing and when fungicide resistance is developing is critical to producing successful crops and why scouting on a regular basis, at least before and after each fungicide application, is important. Regular scouting can help reduce unwarranted and ineffective fungicide applications and help reduce wasted costs. Remember to always tank mix SI fungicides with protectant (M) fungicides (i.e., chlorothalonil) to help reduce the chances for fungicide resistance developing. Always apply SI fungicides according to label rates and resistant management recommendations and always be aware of the fungicide rates you are applying.

 

Grower’s Guide to Understanding the Protectant Fungicides (FRAC Codes M1 – M9)

Friday, May 20th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The following article is excerpted from Rutgers Plant and Pest Advisory Newsletter and is a good refresher on fungicide basics. It was written by Andy Wyenandt, Ph.D., Specialist in Vegetable Pathology, Rutgers University

Protectant (or contact) fungicides, such as copper (FRAC code M1) and sulfur (M2), the dithiocarbamates (mancozeb, FRAC code M3) and chlorothalonil (M5) belong to FRAC groups which have a low chance for fungicide resistance to develop. Protectant fungicides typically offer broad spectrum control for many different pathogens. So, why wouldn’t fungi develop resistance to protectant fungicides? Protectant fungicides are used all the time, often in a weekly manner throughout much of the growing season. The answer is in their modes-of-action (MOA). Protectant fungicides have MOA’s that affect (i.e., prevent) fungal development in different manners. In inorganic compounds, sulfur (M2) prevents fungal growth (i.e., spore germination) by disrupting electron transport in the mitochondria. Coppers (M1), on the other hand, cause non-specific denaturation of proteins. Chlorothalonil (M5) inactivates amino acids, proteins and enzymes by combining with thiol (sulfur) groups. In all cases, a protectant fungicide’s chemistry disrupts fungal growth and development either non-specifically or in multiple manners. Because of this, there is a much lower chance for fungi to develop resistance to them.

Protectant fungicides are contact fungicides, meaning they must be present on the leaf surface prior to the arrival of the fungus and must then come into direct contact with the fungus. Protectant fungicides can be redistributed on the leaf surface with rainfall or overhead irrigation, but can also be washed off by too much of either! Remember, that with protectant fungicides, any new growth is unprotected until the next protectant fungicide is applied, in other words, protectant fungicides are not systemic and do not have translaminar activity like some of the newer chemistries. Protectant fungicides should be tank-mixed with fungicides with higher risks for resistance development. Protectant fungicides used in this manner will help slow (or reduce the chances for) fungicide resistance development on your farm. In any case, it’s best to always follow the label and tank mix protectant fungicides with those fungicides with a high-risk for resistance development when required to do so.

 

Grower’s Guide to Understanding the DMI or SI Fungicides (FRAC Code 3)

Thursday, May 13th, 2010

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

The DMI (DeMethylation Inhibitors) or Sterolbiosynthesis Inhibiting (SI) fungicides belong to FRAC code 3 which include the triazoles and imidazoles. Some of these fungicides are commonly known as Folicur (tebuconazole), Tilt (propiconazole), Rally (myclobutanil) and Procure (triflumizole).

SIs work by inhibiting the biosynthesis of ergosterol, which is a major component of the plasma membrane of certain fungi and is needed for fungal growth. Resistance by fungi to the DMI fungicides (FRAC code 3) has been characterized and is generally known to be controlled by the accumulation of several independent mutations, or what is known as ‘continuous selection’ or ‘shifting’, in the fungus. Hence, in any given field population the sensitivity to the DMI fungicide by the fungus may range from extremely high (highly sensitive, i.e. will be controlled by fungicide) to moderate (partially sensitive) or low (mostly resistant to fungicide). This type of resistance is also known as quantitative resistance. With quantitative resistance there are different levels of resistance to the fungicide due to independent mutations, which is unlike the target mutations that occur in qualitative resistance associated with the QoI fungicides (FRAC code 11).

Because different levels of resistance to the FRAC code 3 fungicides may exist in the field, the fungal population may behave differently to different rates of the SI fungicide being applied. Therefore, it is suggested that using a higher rate of a FRAC code 3 fungicide, may improve control when lower rates have failed. For example, let’s say that a powdery mildew population on pumpkin has 25% high, 50% moderate, and 25% low sensitivity to a DMI fungicide. If fungicide is applied at the low rate, only 25% of the population (highly sensitive) may be controlled. Whereas, if the high rate was used, 75% of the population may have been controlled. The main point here is that if low rates of FRAC code 3 fungicides have been used and control seems to be weakening, bumping to a higher rate may improve control. Unfortunately, it is difficult to determine what proportion of the powdery mildew population is sensitive or not sensitive by looking at the field until you have begun spraying. The best advice, if you are using low rates and think those rates are not working like you feel they should, the rate should be bumped up to the high rate the next time the fungicide is sprayed, and if the high rate doesn’t work it may be safe to assume the fungal population has grown mostly resistant. Importantly, if the high rate fails, whether you bumped up to a high rate or started with one, and control does not seem adequate do not continue to use the fungicide. Recognizing if and when fungicide chemistries are failing and when fungicide resistance is developing is critical to producing successful crops and why scouting on a regular basis, at least before and after each fungicide application, is important. Regular scouting can help reduce unwarranted and ineffective fungicide applications and help reduce wasted costs. Remember to always tank mix FRAC code 3 fungicides with protectant (M) fungicides (i.e. chlorothalonil, mancozeb) to help reduce the chances for fungicide resistance developing. Always apply FRAC code 3 fungicides according to label rates and resistantce management recommendations and always be aware of the fungicide rates you are applying.

Resistance Management Strategies for Strobilurin Fungicides (FRAC Code 11)

Thursday, April 29th, 2010

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

The strobilurin, or QoI, fungicides (FRAC code 11) are extremely useful in controlling a broad spectrum of common vegetable pathogens. You may know some of strobilurins as azoxystrobin (Quadris), pyraclostrobin (Cabrio), or Pristine (pyraclostrobin + boscalid, 11 + 7). All strobilurin fungicides inhibit fungal respiration by binding to the cytochrome b complex III at the Q0 site in mitochondrial respiration. Simply said, the fungicide works by inhibiting the fungi’s ability to undergo normal respiration. The strobilurin chemistries have a very specific target site, or mode-of-action (MOA). Although highly effective, fungicide chemistries like those in FRAC code 11, with a very specific MOA, are susceptible to fungicide resistance development by some fungi. For us, knowing the specifics on the technical jargon isn’t so important, its understanding what is at stake. So, if you read or hear someone speak about G143A resistance development to the strobilurin fungicides (where resistance is known in cucurbit powdery mildew and downy mildew, for example), you know what they are talking about and how important it is. So much so, if cucurbit powdery mildew develops resistance to one strobilurin fungicide it may develop what is known as cross resistance and become resistant to all other chemistries in FRAC code 11 — even if only one chemistry has been used!

How do we avoid the chances for fungicide resistance like this to develop? It’s simple, don’t let the fungus ‘figure out’ what it is being sprayed with and do this by rotating different fungicide chemistries (i.e. FRAC codes). Proper fungicides rotations are necessary when fungicides with specific MOAs are used in fungicide programs for controlling important diseases. That’s why it is important to follow a fungicides label precisely and be certain that some fungicide chemistries aren’t overused. All strobilurin fungicides should be tank mixed with a protectant fungicide, when possible. Remember tankmixing high-risk fungicides (i.e. FRAC code 11) with low-risk, protectant fungicides (FRAC codes M1-M9) helps reduce (and/or delay) the chances for fungicide resistance development. Never tank mix strobilurins together and never apply any strobilurin fungicide (either the same chemistry or different chemistry) in consecutive applications if stated by the label. Remember, azoxystrobin acts against the fungus the same way as pyraclostrobin does and so on. Even though you are spraying two different fungicides, each has the similar MOA and is acting against the fungus in the same exact way.

The publication”Fungicide Resistance Management Guidelines for Vegetable Crops in the Mid-Atlantic Region-2010” is available from the county extension offices or online at http://ag.udel.edu/extension/pdc/documents/FRACGuide_2010.pdf

Fungicide Guide for Managing Resistance of Fungi on Vegetable Crops Available Online

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

New Jersey Cooperative Extension has both the 2010 Commercial Vegetable Production Guide online as well as the FRAC guidelines for managing fungicide resistance on vegetable crops. There is much more at this site as well, and it is a good source of information at your fingertips. Both publications are also available free at the Delaware Extension offices. The website is http://njveg.rutgers.edu. The Production Guidelines are under Growing Crops and the FRAC Guidelines are under Controlling Pests-IPM. The FRAC Fungicide Guide for vegetables is also posted on the UD Plant Clinic site http://ag.udel.edu/plantclinic. We will soon have the 2010 Commercial Vegetable Production Guide online as well.

Fungicide Guide for Managing Resistance of Fungi on Vegetable Crops Available Online

Friday, March 27th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

New Jersey Cooperative Extension has both the 2009 Commercial Vegetable Production Guide online as well as the FRAC guidelines for managing fungicide resistance on vegetable crops. There is much more at this site as well, but it is a good source of information at your fingertips. Both publications are also available free at the Delaware Extension offices. The website is http://njveg.rutgers.edu. The Production Guidelines are under Growing Crops and the FRAC Guidelines are under Controlling Pests-IPM.

Grower’s Guide to Understanding the Strobilurin Fungicides (FRAC Code 11)

Friday, April 25th, 2008

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

The strobilurin, or QoI, fungicides (FRAC code 11) are extremely useful in controlling a broad spectrum of common vegetable pathogens. You may know some of the strobilurins as azoxystrobin (Amistar), trifloxystrobin (Flint), pyraclostrobin (Cabrio), or Pristine (pyraclostrobin + boscalid, 11 + 7). All strobilurin fungicides inhibit fungal respiration by binding to the cytochrome b complex III at the Q0 site in mitochondrial respiration. Simply said, the fungicide works by inhibiting the fungi’s ability to undergo normal respiration. The strobilurin chemistries have a very specific target site, or mode-of-action (MOA). Although highly effective, fungicide chemistries like those in FRAC code 11, with a very specific MOA, are susceptible to fungicide resistance development by some fungi. Why is that? In the strobilurins, a single nucleotide polymorphism of the cytochrome b gene leads to an amino acid substitution of glycine with alanine at position 143 of the cytochrome b protein. For us, knowing the specifics on the technical jargon isn’t so important, its understanding what is at stake. So, if we hear someone speak about G143A resistance development to the QoI fungicides (where resistance is already known in cucurbit powdery mildew and downy mildew), we know what they are talking about and how important it is! So much so, if cucurbit powdery mildew develops resistance to one strobilurin compound it may develop what is known as cross resistance and become resistant to all chemistries in FRAC code 11, even if only one chemistry has been used!

How do we avoid the chances for fungicide resistance like this to develop? It’s simple – don’t let the fungus ‘figure out’ what it is being sprayed with and do this by rotating different fungicide chemistries (i.e. FRAC codes). Proper fungicide rotations are necessary when fungicides with specific MOAs are used in fungicide programs for controlling important diseases. That’s why it is important to follow a fungicide label precisely and be certain that some fungicide chemistries aren’t overused. All strobilurin fungicides should be tank mixed with a protectant fungicide, when possible. Remember, tankmixing high-risk fungicides (i.e. FRAC code 11) with low-risk, protectant fungicides (FRAC codes M1-M9) helps reduce (and/or delay) the chances for fungicide resistance development. Never tank mix strobilurins together and never apply any strobilurin fungicide (either the same chemistry or different chemistry) in consecutive applications if stated by the label. Remember, azoxystrobin acts against the fungus the same way as trifloxystrobin does and so on. Even though you are spraying two different fungicides, each has the similar MOA and is acting against the fungus in the same exact way.

Grower’s Guide to Understanding DMI or SBI (sterol biosynthesis inhibitor Fungicides (FRAC Code 3)

Friday, April 18th, 2008

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

The DMI (DeMethylation Inhibitors) or Sterol Biosynthesis Inhibiting (SBIs) fungicides belong to FRAC code 3 which include the triazoles and imidazoles. Some of these fungicides are commonly known as Tilt (propiconazole), Nova or Rally (myclobutanil) and Procure (triflumizole).

SBIs work by inhibiting the biosynthesis of ergosterol which is a major component of the plasma membrane of certain fungi and needed for fungal growth. Resistance by fungi to the SBI fungicides has been characterized and is generally known to be controlled by the accumulation of several independent mutations, or what is known as ‘continuous selection’ or ‘shifting’, in the fungus. In any given field population the sensitivity to the SBI fungicide by the fungus may range from extremely high (highly sensitive, i.e. will be controlled by fungicide) to moderate (partially sensitive) or low (mostly resistant to fungicide). This type of resistance is also known as quantitative resistance. With quantitative resistance there are different levels of resistance to the fungicide due to independent mutations, which is unlike the target mutations that occur in qualitative resistance associated with the QoI fungicides (FRAC code 11). Because different levels of resistance to the SBI fungicide may exist in the field, the fungal population may react differently to different application rates of the SBI fungicide. Hence, it is suggested that using a higher rate of a SBI fungicide, may improve control when lower rates have failed.

For example, let’s say that a powdery mildew population on pumpkin has 25% high, 50% moderate, and 25% low sensitivity to a SBI fungicide. If fungicide is applied at the low rate, only 25% of the population (highly sensitive) may be controlled, whereas if the high rate is used, 75% of population be been controlled. The main point here is that if low rates of SBI fungicides have been used and control seems to be weakening, bumping to a higher rate may improve control. Unfortunately, it is difficult to determine what proportion of the powdery mildew population is sensitive or not sensitive by looking at the field until you have begun spraying. The best advice, if you are using low rates and think those rates are not working like you feel they should, the rate should be bumped up to the high rate the next time the fungicide is sprayed, and if the high rate doesn’t work it may be safe to assume the fungal population has grown mostly resistant. Importantly, if the high rate fails, whether you bumped up to a high rate or started with one, and control does not seem adequate, do not continue to use the fungicide. Recognizing if and when fungicide chemistries are failing and when fungicide resistance is developing is critical to producing successful crops and why scouting on a regular basis, at least before and after each fungicide application, is important. Regular scouting can help reduce unwarranted and ineffective fungicide applications and help reduce wasted costs. Remember to always tank mix SBI fungicides with protectant (M) fungicides (i.e. chlorothalonil) to help reduce the chances for fungicide resistance developing. Always apply SBI fungicides according to label rates and resistance management recommendations and always be aware of the fungicide rates you are applying.

Grower’s Guide to Understanding Protectant Fungicides (FRAC Codes M1 – M9)

Friday, April 11th, 2008

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

Bob Mulrooney Notes: The following is an article by Andy Wyenandt on protectant fungicides that we have published in the past. Hopefully it will be a good review of some basic information that growers and fieldmen should know.

Protectant (contact) fungicides, such as the inorganics (copper, FRAC code M1) and sulfur (M2), the dithiocarbamates (maneb, mancozeb, thiram, M3) and chloronitriles (chlorothalonil, M5) belong to FRAC code groupings which have a low chance for fungicide resistance to develop. Protectant fungicides typically offer broad spectrum control for many different pathogens. So, why wouldn’t fungi develop resistance to protectant fungicides? Protectant fungicides are used all the time, often in a weekly manner throughout much of the growing season. The answer is in their modes-of-action (MOA). Protectant fungicides have MOAs that affect (prevent) fungal development in different manners. In inorganic compounds, sulfur (M2) prevents fungal growth (i.e. spore germination) by disrupting electron transport in the mitochondria. Coppers (M1), on the other hand, cause non-specific denaturation of proteins. Chlorothalonil (Bravo, M5) inactivates amino acids, proteins and enzymes by combining with thiol (sulfur) groups.

In all cases, a protectant fungicide’s chemistry disrupts fungal growth and development, either non-specifically or in multiple manners. Because of this, there is a much lower chance for fungi to develop resistance to them. Protectant fungicides are contact fungicides, meaning they must be present on the leaf surface prior to the arrival of the fungus and must then come into direct contact with the fungus. Protectant fungicides can be redistributed on the leaf surface with rainfall or overhead irrigation, but can also be washed off by too much of either! Remember that with protectant fungicides, any new growth is unprotected until the next protectant fungicide is applied. In other words, protectant fungicides are not systemic and do not have translaminar activity like some of the newer chemistries. Protectant fungicides should be tank-mixed with fungicides with higher risks for resistance development. Protectant fungicides used in this manner will help slow (or reduce the chances for) fungicide resistance development on your farm. In any case, it’s best to always follow the label and tank mix protectants with higher risk fungicides when suggested or required to do so.

Understanding FRAC Codes is Important for Managing Fungicide Resistance Development

Friday, March 28th, 2008

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

FRAC, or the Fungicide Resistance Action Committee, was developed to help provide resistance management guidelines for fungicide use. Remember, high-risk fungicides have a high probability of resistance development because of their modes-of-action (MOA). Those fungicides with chemistries that have a specific target site against fungal pathogens, unfortunately, will have a high risk for losing efficacy because of resistance development in the pathogen. Importantly, fungicides with similar chemistries and MOAs that belong to the same FRAC code may also be prone to cross-resistance, where a fungus that develops resistance to one fungicide in the FRAC group may also develop resistance to other fungicides in the group, even if those other fungicides haven’t been used.

With the recent influx of new fungicide chemistries on the market great lengths have been taken to reduce the risk of fungicide resistance development for many fungi where ‘high risk’ fungicides are used. There are currently 43 numbered FRAC groupings and 4 lettered groups. As new fungicides with new MOAs are released on the market, new numbered groups will be added to the list. For many vegetable crops many of the most common fungicides used fall into a few of these groupings, most notably:

Multi-Sites (M) or Low Risk FRAC Groups
M1 and M2, inorganics such as sulfur and copper
M3, Maneb or Mancozeb
M5, chlorothalonil such as Bravo

Higher Risk FRAC Groups
Group 3, triazoles such as Nova or Rally
Group 4, mefenoxams such as Ridomil
Group 11, strobilurins such as Quardris, Flint, Cabrio

Some of the newest fungicides labeled for use in vegetable production include Quintec (quinoxyfen, FRAC code 13) and Revus (mandipropamid, 40).

Knowing which fungicides belong to which FRAC code will have an impact on spray schedules, disease control, and resistance management. Protectant fungicides, such as those in the FRAC code M, have a low risk for fungicide resistance development and have less stringent restrictions. However, for those chemicals with a higher risk of fungicide resistance development the product labels are more stringent and labels should be followed precisely. Labels often require that high-risk fungicides be tank-mixed with protectant fungicides to reduce the chances for fungicide resistance development. In general, tank mixing high-risk fungicides with protectant fungicides is always a good resistance management strategy. For example and, in general, the strobilurin fungicides in FRAC code 11 should not be sprayed consecutively. Such that, if Quadris (azoxystrobin, 11) is sprayed one week, it should not be followed the next week with another Group 11 compound such as Flint (trifloxystrobin, 11) or Cabrio (pyraclostrobin, 11) or a compound containing a Group 11 fungicide (Pristine, pyraclostrobin + boscalid, 11 + 7). A simple way to remember what to use next in your fungicide rotation is to use a labeled fungicide with a different FRAC number or letter. FRAC codes can be found in the fungicide table at the beginning of each crop section in the 2008 Commercial Vegetable Production Recommendations to help growers learn what fungicides belong to what FRAC groups and to help them chose fungicides for use in rotations. A complete list of fungicides and FRAC groups can also be found in Table E-8 on pages E30 and E31 in the Vegetable Production Recommendations. Efforts in learning and using new chemistries with new modes of action along with knowing their FRAC grouping will ultimately pay off in the long run by reducing the chances for fungicide resistance development.

Delaware Growers – Fungicide Resistance Management Guidelines for Vegetables were distributed at Ag Week with the Vegetable Production Recommendations. If you did not receive one and would like a copy, request one from the county Extension office or stop by and pick one up. These guides were developed as a project directed by Andy Wyenandt at Rutgers assisted by the other plant pathologists in the mid-Atlantic region and funded in part by the Northeastern IPM Center and USDA/CSREES.