Fungicide Resistance Is Frustrating
February 6, 2012 
From fire blight to powdery mildew, fruit and vegetable growers always seem to have some new disease problem. Part of the problem is human nature. When you find something that works, you use it, again and again. The only drawback with that strategy is it leads to resistance problems.
For this second of our four-part series on crop protection, we talked with representatives of a few companies that are focused on helping growers with resistance, as well as other disease problems. Our experts include Julian Smith, domestic sales director for specialty formulations for Brandt Consolidated; James Barrentine, director of technical services for Cheminova, Inc.; and Herbert S. Young, senior product manager, horticulture fungicides for Bayer CropScience.
Q: What are the biggest challenges fruit growers are facing regarding disease control these days? Please be as specific as possible.
Smith: The issue that is first and foremost is resistance management. Other major challenges regarding disease control are the identification of new bacteria-like pathogens and the control of the vector. We often get hung up on controlling the disease when we should be controlling the vector.
Barrentine: The biggest challenge is the lack of any new fungicides with different modes of action. This requires the growers to integrate older products into their disease program even if some resistance exists.
Young: The biggest challenge is globalization. MRLs (Maximum Residue Levels) are such a limiting factor and the systems are changing and evolving. Luna fungicide (fluopyram) was Bayer’s first attempt at a globally traded product. EPA selected Luna for CODEX (an organization that develops international food standards) before it was registered, but Luna was turned down by global Codex organization JMPR, because there were too many crops that were going to be included on the label.
Q: Have any diseases emerged in recent years that are particularly challenging for growers?
Smith: I think in particular it’s the diseases that have come from offshore, such as HLB (greening) in citrus. The solution lies not so much in disease control, but controlling the vectors, these unwanted pests, through APHIS and any other means we have at our disposal. Other potentially challenging diseases are those easily spread by environmental factors such as wind, or insect vectors. Examples of these include Erwinia, which causes fire blight in apples, which has several non-host plants it can grow on so it can be spread by many vectors. A bird can land on a hawthorn tree, and then spread the Erwinia to an apple orchard. We need a little more work to model the lifecycles of diseases so we can better adjust our control methods.
Barrentine: No new diseases have emerged, but what has happened is a shift from one disease to another. For example, powdery mildew in Eastern U.S. apple production has become more of a problem disease because of the demise of SI fungicides being used for scab control.
Young: They are always changing. We have greening on citrus and zebra chip on potato, and Alternaria is essentially new on almonds because of a change in production practices.
Q: A lot of researchers are concerned about resistance. Are there any crops where that’s a particularly acute problem? What is your company doing to address resistance problems?
Smith: Addressing fruits as a whole, first and foremost we’ve made an effort to make materials in a number of different Fungicide Resistance Action Committee (FRAC) groups, which differentiates modes of action, and therefore resistance. We’ve addressed soft chemistries such as TriTek, a petroleum oil product for both insect and fungal control. It controls both the disease and the insect vector. We also have the copper product Nordox 75, which provides a wide range of fungal and bacterial disease control. In addition, we are continuing to develop botanical oil products that are both fungicidal and insecticidal which are in yet a different FRAC. The key is to develop control chemistries while not encouraging resistance.
Barrentine: Resistance is a potential problem with all crops where fungicides are used to manage diseases. Rotation of fungicides with different modes of action is a recommended practice. Cheminova has three fungicides, Topguard, Koverall, and Sovran, with different modes of action that are available to growers so they can avoid resistance problems.
Young: The challenges are new and ongoing. We like to partner with growers to protect the products they have by preventing resistance. University researchers do a good job preaching resistance, but if growers cut the label rate down and stretch out timing intervals, it won’t work. We need their partnership to be successful.
Q: Has your company come out with any new products and/or label additions?
Smith: TriTek is a unique formulation of petroleum oil as an inverse emulsion material. It blooms really quickly and there’s no separation of oil and water, so you end up with superb leaf coverage and maximum disease and pest control. It has wide label range, and is labeled for in-season use. It’s important to emphasize that Brandt’s advice is built around a more holistic approach using all IPM tools. For example, top nutritional status can help overcome disease, as can optimum water management, and plant genetics. We don’t just concentrate on chemistry. Healthier plants better resist disease, which is why our nutritional products are likewise important.
Barrentine: Cheminova introduced Topguard fungicide and it is currently labeled for use on apples. Topguard fungicide is a stable, systemic fungicide. It translocates throughout the leaf to provide excellent curative and preventative activity. Topguard fungicide provides excellent control of powdery mildew, Cedar apple rust, and Quince rust of apples, and provides top-notch apple scab control when used with a protectant for resistance management. We anticipate registration on grape and stone fruit including cherry, peach, and plum in 2012.
Young: In early January we launched three Luna fungicides, which feature a new class of chemistry. The products will be available to growers this coming season. The fungicides include Luna Experience, Luna Tranquility, and Luna Sensation. The Luna products feature the new active ingredient, fluopyram. Each Luna product has two modes of action. It is a new chemical class mixed with one of our standard fungicides.
Specifically, Luna Experience will be for use on winegrapes, almonds, pistachios, and watermelon. One of the key diseases Luna targets in watermelon is gummy stem blight. The next Luna product, Luna Tranquility wil be for use on potatoes. Finally, Luna Sensation is slated for use on apples, cherries, almonds, and pistachios. The plan is to expand the labels to include additional fruit and vegetable crops sometime in 2014.
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