Posts Tagged ‘fungicides’

Lima Bean Fungicide Update

Friday, September 3rd, 2010

Bob Mulrooney, Extension Plant Pathologist;

I was disappointed to learn that our 24c special local needs label for Phostrol fungicide for downy mildew has expired. This means that it is not registered for use on lima beans in Delaware. NuFarm Americas is pursuing labeling of Phostrol for legume vegetables, including limas, so by next season we may not need the 24c label to use this product. The active ingredients in Phostrol are mono- and di-potassium salts of phosphorous acid, this is one of several fungicides that we call phosphonate fungicides. These same ingredients are found in Prophyte and K-phite which have labels for use on beans for downy mildew. I have tested Phostrol and a product that was never marketed here called Fungi-phite — both are excellent for downy mildew control. I would feel very safe to say the other labeled products with these same active ingredients should perform as well. I have Prophyte in my trial this year so I will be able to say for sure, if the test is successful.

Pumpkins, Winter Squash and Gourds Added to Quintec Label

Friday, August 13th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Several additional cucurbit crops were added to the Quintec label and the changes are not in the 2010 Vegetable Recommendations book. Quintec is labeled for powdery mildew control on winter squash, gourds and pumpkin in addition to watermelon, cantaloupe and other melons such as honeydew and others. Rates range from 4-6 fl oz/A. See label for details. This is a good powdery mildew fungicide and should be used in rotation with other fungicides for powdery mildew. Be sure to read the label to avoid fungicide resistance.

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;

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.

Presidio Label Now Allows Application Through Drip Irrigation

Thursday, April 29th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Valent USA Corp. just announced that EPA has approved the drip irrigation label for Presidio on pepper and other fruiting vegetables, curcurbits, brassicas, and leafy vegetables. This will be significant for growers that have had problems with Phytophthora capsici crown rot on pepper and summer squash. This application method will not control downy mildew on cucurbits or other foliar diseases. The Presidio label is available here.

Resistance Management Strategies for Strobilurin Fungicides (FRAC Code 11)

Thursday, April 29th, 2010

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University;

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

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

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist;

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 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 We will soon have the 2010 Commercial Vegetable Production Guide online as well.

2010 Fungicide Update for Vegetables

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist;

There are some new additions and a few deletions:

Folicur 3.6F has been added for the control of common bean rust on snap beans. The section on soybean rust on snap and limas beans was removed. This disease has not developed on any other host other than soybeans and kudzu. At this time it is not a threat to snap and lima bean production. Omega 500F is labeled on snap and lima beans for white mold control. It also has good activity on downy mildew on limas. Hopefully by application time there will be a 2(ee) registration for downy mildew as well.

Cucumber, Cantaloupe, Pumpkin, Winter Squash and Watermelon
Switch and Folicur (tebuconazole) have been added for gummy stem blight control. The fungus that causes gummy stem blight has developed resistance to Pristine in South Carolina and may be occurring here. The addition of these two products is very important to control this important disease. Folicur has also been added to these crops and summer squash for powdery mildew control in addition to the other two triazole fungicides Rally and Procure.

Chlorothalonil (Bravo) has been labeled to replace maneb which is no longer being manufactured for anthracnose fruit rot control.

Sweet Corn
Maneb is no longer being manufactured for use on sweet corn.

Revus Top was added this year for control of leaf spots and late blight. Scala is labeled for early blight and gray mold control in the field as well as in the greenhouse and high tunnels.

Tanos was added for early blight control. Revus and Revus Top were added for late blight control.

Maneb is no longer being made but existing stocks can be used until maneb is gone.

Corn and Corn Fungicides

Thursday, July 2nd, 2009

Bob Mulrooney, Extension Plant Pathologist;

The following was written by Dr. Arv Graubaskas, Extension Field Crops Plant Pathologist at the University of Maryland in his Maryland Field Crop Disease Notes. The issue of applying fungicides to corn when part of the field is replanted is addressed. This question has been asked and this is the best answer we know.

In some parts of the state the earliest planted corn is close to developing a tassel. There has also been a lot of corn that had to be replanted due to drowning. In many other cases corn was only recently planted because the soil finally dried out enough to get equipment onto the field. There is thus a tremendous range of growth stages of corn out there and in many cases in the same field. Considering the weather pattern is still pretty wet the legitimate question of whether or not a fungicide program is warranted is raised.

First don’t get sold on the plant health or plant physiology response to strobilurin fungicides (Headline, Quadris, and to a lesser extent Quilt and Stratego) alone. Key word here is alone. The usual sales pitch involves stating that millions of acres have been treated and the average response has been 8, 10 or even 15 bu/A. These averages include cases that had significant foliar diseases as well as cases with little or no disease. These fungicides are great disease management tools and when diseases like gray leaf spot are significant will outperform other classes of fungicides. The performance of these fungicides when diseases are clearly yield limiting is so outstanding that it skews the average response number.

Let me illustrate with my data from last season. I had 16 replicated “trials” across the state across a range of crop histories, planting dates and hybrids that compared untreated corn vs. a strobilurin fungicide. The average response across these trials was 7.3 bu/A, but in only five of these trials was the positive (yield beneficial) response statistically significant. More importantly in those five trials gray leaf spot was a serious problem and the actual responses to the fungicide in those five cases ranged from 24 to 38 bu/A. In other words, where I did not have enough gray leaf spot to cause losses and thus the fungicide could only provide a yield advantage through alteration of plant physiology the average response was -0.7 bu/A. The overall average looks good but it is skewed by the cases that really benefited which were those cases where the fungicide primarily worked as a disease control agent. The plant physiology or plant health type effect occurs in concert with disease control to often outperform other classes of fungicides when diseases are a problem. Where there is no disease the plant physiology side benefits have little or no effect on yield or stand on a consistent basis. The bottom line is an insurance program where there is no need for insurance will only cost you money. Use a fungicide when you have a real risk of a foliar disease. The highest risk of getting gray leaf spot, the primary foliar disease of corn, involves three factors: 1) a susceptible corn hybrid, 2) no-tilling corn into corn stubble, and 3) a relatively wet season.

There is one additional factor that needs to be considered regarding fungicides in corn, especially this season. It gets us back to the comment that there is quite a range of growth stages out there and in many cases in the same field. Fungicides applied by air in a fullgrown corn crop generally perform better if surfactants are used. The surfactants help the fungicide to penetrate the canopy and be better distributed throughout the canopy. Arrested ear syndrome, where the development to corn ears is damaged resulting in a percentage of small malformed ears, has been associated with fungicides applied with a non-ionic surfactant (NIS) or sometimes other products (certain formulations of tankmixed products) especially if the corn is in the late vegetative stages of development just before tassel. Most of the damage seems to be associated with NIS surfactants but the fungicide formulation and tank-mixed products are not completely exonerated. It is therefore important that if one decides on using a fungicide that it is applied at or after tassel formation is completed. If it is close or there are parts of the stand that are not yet in tassel then NIS surfactants should not be used and be wary of any tank-mix products. One final comment on fungicides in corn, these products have not been shown to directly reduce stalk rots. Fungicides affect stalk rots and therefore improve stand, when there is a foliar disease. There is no direct action of the fungicides applied at or near tassel on the stalk rot pathogens that develop much later in the season. However, significant loss of effective leaf area from foliar diseases predisposes plants to stalk rots. Therefore, when there is a foliar disease problem and you manage it with a fungicide you get the additional benefit of reducing stalk rots.

The bottom line is fungicides have been proven to be excellent disease management tools for foliar diseases in corn and have an indirect effect on lodging due to stalk rots of the crop. The additional benefits of strobilurin fungicides are the reason they often outperform other fungicide classes with regard to yield when diseases are an issue. They should be considered when the risk of a foliar disease is high. Otherwise they are expensive insurance with a relatively low chance of a return if significant foliar diseases do not develop.

Fungicide Update for Vegetables 2009

Friday, March 27th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Lima Beans
Ridomil Gold/Copper is now labeled nationally for control of downy mildew on lima beans. A 24c label is no longer needed for DE and MD.

Fungi-Phite is a phosphorus acid salt fungicide similar to Phostrol and is now labeled for downy mildew on lima beans. I have had this product in my tests for two years and it has performed extremely well, comparable to Ridomil/Gold Copper and Phostrol. Availability may be limited. It is not listed in the 2009 Commercial Vegetable Recs.

Cantaloupe and Watermelon
Quintec 2.08SC from Dow AgroSciences was labeled during last season and is a good powdery mildew fungicide in a new FRAC group 13 that can be alternated with Rally or Procure in addition to Pristine.

The Bravo label has been expanded to include peppers (bell pepper, chili pepper, cooking pepper, pimento, sweet pepper), gourds, eggplant, okra, rhubarb, and cabbage. These new changes are not in the 2009 Commercial Vegetable Recs. With the phasing out of maneb these Bravo additions will replace many of the maneb applications on these crops that might be grown in DE.

Vegetable Diseases in the Greenhouse

Friday, March 6th, 2009

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; 

As vegetable transplant production in greenhouses gets underway, remember that the potential for disease can be minimized by using certified, tested, and treated seed. Sanitation is the most important management practice. Walls, benches, hand tools, pots and transplant trays should be sanitized with 5% commercial bleach. New potting mix should be used each year. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Once seed is planted, seedlings should be watered early in the day so that the foliage dries quickly and, if possible, watered at the seedling base to reduce moisture on leaves.

Provide good air exchange throughout the greenhouse to minimize periods of high humidity (high humidity favors pathogens). Even after careful sanitation and good practices for managing disease, disease may develop in the greenhouse. Most fungicides are not labeled for greenhouse use. Do not use unlabelled fungicides because the lack of a greenhouse label indicates that there are problems with safety, phytotoxicity, or resistance development risk associated with a fungicide.

The following table, which is modified from the Vegetable Management Guide 2008-2009 New England Region is a good summary of available fungicide options. Please note that Ridomil is not labeled for use in the greenhouse. Please follow label directions carefully.

Please follow link below for table:
Selected Fungicides and Bactericides Labled for Greenhouse Use 2009