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DuPont has just announced that it will voluntarily withdraw the use of all forms of benomyl (Benlate) on fruit and vegetable crops at the end of the year. No sales will occur after December 31, 2001 and existing stocks will likely be out of circulation by the end of 2002. The company spokesman states that the decision is economic in nature—citing the high costs of meeting the increased regulatory requirements due to the Food Quality Protection Act (FQPA). This announcement caught most of us by surprise as EPA lists of products slated for re-registration didn’t indicate that benomyl would be addressed until 2002 or 2003.
I spoke with Walt Stevenson, vegetable plant pathologist and Patty McManus, fruit crop pathologist about how this cancellation will affect Wisconsin’s fruit and vegetable growers.
In Wisconsin vegetable production, benomyl is registered for use on carrots, celery, beans, and vine crops. It is used in snap bean production for Sclerotinia white mold and Botrytis gray mold control. Benomyl is also used on dry, lima, and wax beans. Alternative fungicides for beans include Topsin-M, Rovral, and Ronilan. Recently, a new microbial fungicide, Contans WG (Coniothyrium minitans) was labeled for the control of white mold on beans. This product has a broad range of crops for which it’s registered and is applied to soil and plant residue to reduce the amount of sclerotia that serve as inoculum for the disease. Crop rotations of at least 2 years between bean crops or other susceptible crops are also recommended to reduce disease pressure in beans.
Benomyl is used by carrot growers for the control of Rhizoctonia crown rot and cottony rot caused by Sclerotinia. Loss of this product may cause problems for some commercial carrot growers as there are no suitable alternatives for the control of either disease.
Wisconsin celery growers use benomyl to control Cercospora and Septoria blights. However, thiophanate-methyl (Topsin-M), a registered fungicide that has the same mode of action as benomyl, is available for use on celery and will control both blights.
Powdery mildew, gummy stem blight, and anthracnose on vine crops including cucumbers, melons, pumpkins, and squash are three other plant diseases for which benomyl is registered for use. Several alternatives exist in the absence of benomyl. Trifloxystrobin (Flint) and myclobutanil (Nova) are two very effective fungicides that recently received labels for use in these crops. Thiophanate-methyl will also control these diseases in vine crops.
Of a more serious concern is the impact that the loss of this product will have on fruit production in Wisconsin. Currently it is registered for use on apples, strawberries, raspberries, and cherries. In many cases there are no alternative products available for substitution that will maintain high quality fruit while still allowing growers to produce the crop economically.
On apple, benomyl is currently used in combination with captan to manage the flyspeck/sooty blotch disease complex, especially in southern Wisconsin. To a lesser extent, growers use benomyl to mange powdery mildew. Topsin-M (thiophanate-methyl) is in the same fungicide class as Benlate and can be used as an effective substitute. The strobilurin fungicides, Flint and Sovran, are effective against flyspeck/sooty blotch, but there are restrictions on the number of applications in order to delay fungicide resistance to this class of fungicides.
Benomyl is currently used in combination with captan to manage a number of diseases on strawberries, including anthracnose, powdery mildew, gray mold, and various fungal leaf spots. Topsin-M is registered on strawberry and can be used as an effective substitute.
Raspberry growers currently use benomyl in combination with captan to manage a number of diseases, including anthracnose, powdery mildew, cane blight, spur blight, and gray mold. There are other fungicides, which when combined with good cultural practices, will help control these diseases. However, Topsin-M is NOT registered on raspberry.
Benomyl is not used extensively in cherry production, but is sometimes mixed with captan to manage the blossom blight phase of brown rot. More often growers depend on the sterol inhibitor (SI) fungicides for control of brown rot. However, loss of Benlate puts more pressure on the SI fungicides in the way of resistance. Topsin-M is registered on cherry.
Benlate is not registered for use on cranberries in Wisconsin.
The loss of benomyl is just another reminder of the impact of FQPA on agricultural and horticultural production in the state. Keep in mind that many of the alternative products discussed above will also be re-evaluated as part of FQPA and may either be voluntarily withdrawn from sale or canceled by the EPA. It is therefore important for growers and pest management specialists to implement an integrated approach to pest management in lieu of sole dependance on chemical pesticides.
