1 - Conifer aphids may persist through winter, but other aphids will disappear until spring.

Yard and Garden - December 4, 2010

Q.

I have been noticing many aphids in my garden and on my evergreen trees recently. I thought the cold weather would have killed them. What should I do?

A.

Many aphids will disappear once the cold weather really sets in. They will probably reappear in the early spring once the weather warms, but once the weather is cold enough and their host plants have frozen, they will not be apparent in your garden. In the case of aphids on herbaceous plants and most deciduous plants, you may not need to apply any treatment at this time.

You mentioned aphids on your evergreen trees; there is a conifer aphid that may remain active on conifer trees through the winter. They have long legs and look like an aggregation of small spiders on the stems of the conifers. They are capable of piercing the tough skin of conifer twigs to feed and of remaining active in relative cold weather. Even if you do not see the insects themselves, you may notice a wet appearance on the ground under the infested tree, or shining needles on the tree. This is due to the honeydew excreted by the aphids.

As with most aphid infestations, strong jets of water may be sufficient to dislodge many of them from the trees and reduce their impact on the trees. This may need to be repeated on a monthly basis. Horticultural oils may also be applied now according to the label direction on the oil product to kill aphids. Both treatments will be effective and you can choose the method you prefer. The horticultural oil treatment may also be used on deciduous trees to reduce the population of aphids or other insects trying to overwinter in the bark crevices and under bark flaps.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

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