Rotate & Combine Crops & Controls | Prevent Resistance Buildup in Pests & Pathogens

When the same crop or crop family goes into the same ground year after year, its pests and diseases tend to build up and can become resistant to the controls used against them.

Crop rotation is one of the best ways to stop crop-specific pathogens from building up in the soil and growing area, and to cut down on pests that overwinter there. Rotating crop families is best, but switching crops within a family, or varieties within a crop, also helps. Varieties respond differently to disease and pests, so when you know you have a particular disease, choose resistant varieties. Changing varieties also makes it harder for a pathogen to adapt.

When crop and variety rotation aren't enough, alternating your controls also slows resistance, and some controls work better together. That means either spraying different products in turn or mixing compatible products in one tank.

Alternating controls to prevent blight.

In our trial plots, to prevent early and late blight on tomatoes, we usually start with OxiDate^® (a hydrogen peroxide–based fungicide and bactericide) to clean up the plants, then follow with a copper fungicide.

At the next spray we might use OxiDate again and follow it with a different product, such as Actinovate^®.

Tank mixing can help against European corn borer and cucumber beetles.

Mixing products with different modes of action slows resistance because each attacks a different target. Against European corn borer, for example, spinosad, the active ingredient in Monteray Garden Insect Spray, acts on the insect's nervous system, while Bacillus thuringiensis, the active ingredient in DiPel^® DF, attacks the gut. A tank mix of products like these can work better than either one alone.

Likewise, against cucumber beetles, PyGanic^® (a pyrethrin insecticide) can be mixed with Surround^® WP (a kaolin clay repellent) for a quick knockdown followed by ongoing repellency.

Some controls are both gentle on the environment and very hard for pests to resist.

Pests generally can't develop resistance to certain physical controls. Diatomaceous earth is made of fossilized diatoms whose sharp edges damage insects' outer layer, killing them by drying them out after contact or ingestion, usually within a couple of days. Highly refined paraffinic oils smother the eggs, larvae, nymphs and adults of soft-bodied insects and mites, and other horticultural oils and insecticidal soaps also control pests with little risk of resistance.

Sluggo^® is a granular bait based on iron phosphate, a naturally occurring mineral that breaks down into plant nutrients, mixed with bait that draws in slugs and snails. Iron phosphate baits are considered low in toxicity to people, pets and wildlife when used as directed, and slugs and snails don't become resistant to them.

These are only a few of the ways to get the control you need while limiting resistance. Whether you farm commercially or garden at home, keep good records of which pests and diseases show up, what you used and how well it worked. Always read and follow the label exactly when applying any control. Used sensibly, crop rotation, control rotation, combining controls and resistance-proof options are safe, effective and good for the environment.

Learn More

• Tips for effective, sustainable pest and disease control • Article
• Integrated pest management (IPM) principles • U.S. EPA
• A conceptual framework for integrated pest management • Trends in Plant Science
• Pest and disease controls • Products