Though once found only in the western part of our country, the Colorado potato beetle (Leptinotarsa decemlineata), is well established and here to stay. In the South it is potatoes’ worst enemy; uncontrolled, these beetles can completely destroy a potato crop by stripping the plants of their leaves.
Adult potato beetles burrow into the soil where they over-winter until late spring. Then they emerge, migrate to your potato crops, and begin mating. Eggs usually occur in clumps of 25 or so. For this reason, emerging larvae also appear grouped on plants where they have recently hatched. They crawl up on top of the leaves when it is warm and feed on the plants’ leaves.
A voracious herbivore, this beetle not only targets potatoes but also feeds on tomatoes, eggplant, cabbages, and even tobacco! For these crops, the use of floating row covers (a breathable, lightweight fabric) may help reduce pest pressure on the potato plants. It also feeds on jimson weed, henbane, thistle, and mullein, so these weeds may or may not be effective in luring the beetle away from crops.
Since this beetle is resistant to many commercial pesticides, you may find organic methods to be more useful. Appropriate crop selection is a great place to start. Several early-maturing potato varieties put on enough leaves before Colorado potato beetle populations explode and thus can better resist defoliation. These varieties include: Caribe, Norland, Pungo, Redsen, Sunrise, Superior, and Yukon Gold. Another control method is the use of wheat or rye straw mulches to restrict beetles’ movement into and through potato fields. Interestingly, research has shown that straw mulch also creates a favorable habitat for the beetles’ predators. Certain plants such as catnip, tansy, and sage are believed to have some efficacy in suppressing Colorado potato beetle infestations, but research has yet to confirm their usefulness.
One of the best organic management plans for the Colorado potato beetle, though, is routine scouting. We spend time walking through our potatoes, looking for insects and the damage they inflict on plants. Often the damage is more visible than the pests themselves. They leave the tell-tale chewed up leaves. Turn over the leaves to find the bright yellow-orange colored eggs attached to the undersides. These are soft and crush easily between your fingers. Later, the larvae are a little bigger and juicier. Be careful! You might get squirted! This is a great stage to treat with an organically approved pesticide. It is best to knock them out at this stage of development, to prevent them from reaching the adult stage and breeding a whole new patch of trouble.
Neem-based products such as Neemix™, BioNeem™, and Margosan-O™ have limited success. Caution should be used, though, since spray concentrations exceeding 1% can result in phytotoxicity on potato plants. Further, recent research has shown that neem products can be lethal to beneficial insects such as the ladybeetle, especially during their larval stages. Since Bt is only effective if ingested by the pest in its larval stage, it is important to catch them early.
For these reasons, don’t go overboard with the sprays. Always follow the directions on the label and keep in mind that adult plants can tolerate a fair amount of insect damage to their foliage and still produce a terrific crop. Implemented correctly, organic pest control works well, and the results are healthy plants and delicious, chemical-free organic potatoes!
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