Master_gardeners_08-31

Jeff Green | Aug 07, 2008

Back toHome

Potatoes do, however, have two special requirements. First, they need to be hilled, that is, to have soil mounded around the stems to protect the developing tubers from sunlight. Tubers exposed to light not only turn green, but also develop solanine, a compound that makes the potatoes taste bitter, and can cause indigestion or illness.

The other special requirement is to control Colorado potato beetles. These orange and black-striped critters can chew potato plants down to the stems and drastically reduce crop yields.

The Colorado potato beetle used to be an inoffensive beetle that lived in Colorado and ate a plant called buffalo bur (Solanum rostratum). Then potatoes were introduced into the state in the early 1800s. The beetle gradually adapted its preferences to potatoes, and started to spread from Colorado across North America and into Europe.

The beetle has seven life stages: Adults overwinter in the soil, emerging in late spring. They walk or fly in search of plants from the nightshade (Solanaceae) family – preferring potatoes, eggplants and tomatoes.

Once they’ve found potato plants (or other hosts), they begin to eat and reproduce. Females lay eggs in bright yellowy-orange clusters on the undersides of the potato leaves. Eggs hatch in about 1-2 weeks, depending on temperatures.

The newly-hatched larvae eat even more voraciously than the adults. They are tannish-orange and have black spots on their abdomen. After going through four larval life stages, they burrow into the soil to pupate and emerge in a couple of weeks as adult beetles to start the cycle over again.

Handpicking these pests is the number one strategy for the home gardener. Not only is it an environmentally friendly option, it is also an effective one, as the Colorado potato beetle has developed resistance to many inorganic insecticides, and most botanical and biological insecticides are only effective at certain stages or for a short time.

Starting in early summer, check potato plants regularly for adults, egg masses (on the undersides of leaves), and larvae. Handpick adults and scrape off the larva and egg masses into a bucket of soapy water. An alternative for the super-squeamish is to suck them up with a battery-powered vacuum cleaner.

Cultural practices, such as yearly crop rotation, can help control the severity of Colorados. There is also some evidence that straw mulch makes it harder for beetles to find the potato patch, and that the mulch creates an inviting microenvironment for predators such as ground beetles, ladybugs and green lacewings. Other predators to encourage in the garden are birds and toads.

For gardening information, call Kathleen Lang 613-283-5982.