What Does the Loss of Chlorpyrifos Mean for Farmers? (09/23/21)
How widespread is the use of chlorpyrifos in North Dakota?
Chlorpyrifos is registered for use in a wide variety of crops grown in North Dakota, including field corn, alfalfa, soybean, sugarbeet, sunflower, wheat, and dry edible beans. Chlorpyrifos is probably best recognized by its original brand name Lorsban. There are liquid, water-soluble powder (WSP), and granular formulations now available under a number of other brand names like Govern, Warhawk, Yuma and other generics. Chlorpyrifos is also available in premix products, such as Cobalt Advanced that also contain a pyrethroid insecticide. Registered uses vary by crop. For example, registered uses in soybean include granular at-plant applications and post-emergence foliar liquid applications. In dry edible beans, chlorpyrifos can be used as a seed treatment slurry (WSP formulation) or as a pre-plant broadcast application, but cannot be used for post-emergence foliar applications. In summary, chlorpyrifos is widely used for control of many insect pests of field crops in North Dakota.
What insects do most ND farmers control with this technology?
Chlorpyrifos is a broad-spectrum insecticide that controls a wide variety of soil and above-ground insect and mite pests. Soil pests include seed corn maggot, corn rootworm larvae, sugar beet root maggot larvae, white grubs, and wireworms. Examples of above-ground pests include alfalfa weevil, aphids, armyworms, cutworms, foliage-feeding caterpillars, grasshoppers, leafhoppers, lygus bugs, corn rootworm adults, sugarbeet root maggot adults, banded sunflower moth, sunflower head moth, red sunflower seed weevil, wheat midge, and spider mites. Chlorpyrifos is also available as a residual bin spray and grain storage protectant against stored grain insect pests like red flour beetles and rice weevils. Other characteristics of chlorpyrifos is its short residual activity, usually about 3-5 days. It also is volatile and is able to penetrate closed canopies and crop floral structures better than other insecticides.
What, if any, other pesticide options are there for growers?
Most crops have several alternatives for controlling insect and spider mite pests. Broad-spectrum insecticides include neonicotinoid seed treatments, granular and liquid pyrethroid formulations for at-plant use, and neonicotinoids, pyrethroids, and other organophosphates for foliar use. There are also several newer alternative chemistries that have specific activity against certain insect pests, such as diamides (Prevathon, Exirel) for foliage-feeding caterpillars like thistle caterpillars and green cloverworms in soybeans or banded sunflower moths and sunflower head moth in sunflowers; and pyropenes (Sefina Inscalis), sulfoximines (Transform) and butenolides (Sivanto) for control of soybean aphids. There are also specific miticides such as abamectin (Agri-Mek) and etoxazole (Zeal) registered for use in soybean and corn to control spider mites, but these products are more expensive than chlorpyrifos.
Some crops such as sunflower have only a few chemistries available for use. Red sunflower seed weevil is best controlled using straight chlorpyrifos or a chlorpyrifos + pyrethroid premix because chlorpyrifos is better able to penetrate flower bracts and other floral structures where the larvae are hiding. Due to an increase in growers’ complaints about pyrethroid failures to control of red sunflower seed weevils in some areas of South Dakota (pers. comm. Dr. Adam Varenhorst, SDSU), pyrethroids alone may or may not give adequate control. Currently, there are no other alternative chemistries to control red sunflower seed weevil. The development of pyrethroid resistance is a major concern with red sunflower seed weevil and other insects like soybean aphids, spider mites and diamondback moth.
Pyrethroids are the most widely used mode of action for foliar insecticides, and that comes with an increased risk of insecticide resistance. Resistance to pyrethroids has occurred in soybean aphids in multiple states (Minnesota, Iowa and South Dakota) including eastern North Dakota. While we do have other effective chemistries to control pyrethroid-resistant soybean aphids, the loss of chlorpyrifos means that we have one less tool in our insect control arsenal. This may lead to overreliance on pyrethroids and pyrethroid resistance developing in other insect pests.
How does this change how farmers manage for insects?
The loss of chlorpyrifos forces farmers to use alternative chemistries. In the case of spider mites, where multiple foliar applications may be necessary and rotating products with different modes of action is a must to prevent resistance, the loss of chlorpyrifos may force growers to use a more expensive miticide, which increases their overall monetary input in the crop. It is vital that farmers practice sound integrated pest management (IPM) principles regarding insecticide use, and to adopt non-chemical IPM strategies, such as crop rotation, host plant resistance and conversation of biological control agents. Scouting fields regularly and using established economic thresholds is more important than ever now. An important IPM strategy when more than one insecticide application is needed for control of a specific pest, is to rotate to a new mode of action to help prevent the development of insecticide resistance and to keep our current insecticides in our IPM toolbox.
State IPM Coordinator and Research Specialist