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Both the potato and tuber flea beetle species exist on the Prairies. Both types produce “shot holes” in the leaves, but only the tuber flea beetle causes tuber injury.
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The potato flea beetle sometimes reaches economic threshold levels in Manitoba, but it is not a problem pest in Saskatchewan and Alberta. The tuber flea beetle was first reported in Alberta in 1974, but has not yet become a significant pest. There is no evidence that it has expanded its range eastward.
Potato flea beetle adults are black beetles about 1/10" (2 mm) long; their legs and antennae are brown.
The beetles jump actively, particularly when disturbed, but they seldom, if ever, fly. The potato flea beetle over winters as an adult among litter or undergrowth either in, or close to, the potato fields in which it fed the previous summer. In spring, the adults move to potatoes, where they feed on the foliage of newly emerged potato plants. If potatoes have not yet emerged, the adults feed on weeds or volunteer plants. In Manitoba, the spring adults are generally present in relatively small numbers. They feed on potato foliage making small round holes “shot holes” or scars in the leaf tissue. The eggs are laid in the soil. The larva, which is a slender white grub with a brown head and tiny legs, feeds on rootlets, and occasionally penetrates into developing potato tubers. When larvae are mature, they are about 1/5" (5 mm) in length. They moult into pupae, which are found in cells close to plant roots. Adults emerge from pupae and feed on potato foliage in late July and August. Populations of adults at this time may be high, and considerable "shot-holing" of potato foliage can result.
Direct damage from potato flea beetle is mainly attributable to defoliation “shot holes” of plants during late summer. Occasionally, larval feeding may cause tubers to be pimply or to have short tunnels bored into the tuber to a depth of 1/10" (3 mm) or less. Most of this injury can be removed by peeling. Fungal diseases, such as Verticillium wilt, Fusarium dry rot, rhizoctonia and common scab have been reported to be associated with potato flea beetles. Transmission of bacterial diseases and spindle tuber viroid may also occur.
Cultural control measures for potato flea beetles include crop rotation, field rotation where there is a separation of this year's potato fields from last year's potato crops and control of weeds in the nightshade family. It has been noted that beetles are more abundant where potato crops are adjacent to uncultivated areas.
Insecticides should be applied to the late summer generation of flea beetle adults if feeding damage is severe. Early maturing potato varieties are more susceptible to feeding damage than late maturing varieties. Emergence of flea beetles from pupation occurs over several weeks, so applications should be delayed as long as possible after the beginning of emergence, as insects in the soil will be unaffected by the insecticide. At the time of this application, Colorado potato beetle adults may also be on the plants, so it is important that the insecticide used to control flea beetles not be from the same group that was used to control of Colorado potato beetle larvae earlier in the season.
Late summer populations of potato flea beetles below 65 per plant for Norland and 300 per plant for Russet Burbank do not cause economic yield loss in unstressed potato plants. However, plants, which have previously experienced defoliation from other insects are very sensitive to potato flea beetle injury, and may suffer economic loss with late summer populations of as few as 22 flea beetles per Russet Burbank plant. Economic injury can also be estimated by assessing the percent defoliation. Early in the season, healthy plants can withstand 10% defoliation (regardless of the insect causing defoliation) without an economic loss. Later in the season (August), healthy potato plants can withstand up to 25% defoliation without suffering a serious yield loss.
Written by B. Elliot |
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