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Insect Offense or Defense

This has been one of the driest autumns on record in the Sierra foothills. The new year was dry as a bone as well. The parched landscape and water-starved trees are definitely more vulnerable to infestation by insects. Being on the offensive for insects or plant diseases really comes down to the basics of Integrated Pest Management, or IPM.

IPM focuses on long-term prevention of pests or their damage by managing the ecosystem.
In preventing pest problems, we need to use a combination of biological, cultural, physical (mechanical) approaches. Chemicals like pesticides should be used only as a last resort. This year could be just a total anomaly: no rain, not very cold, and unseasonably warm weather with very little chill hours that plants, especially fruit trees, require. The University of California IPM website is a valuable resource for identifying and fighting garden pests. On UCDavis Website Home, Garden, and Landscape Pests you will find a wealth of information for identifying and managing insect infestations in the garden.

Insects alter their patterns during dry times. They go deeper underground, searching for moisture. On the bright side, there are fewer mosquitoes and gnats when the season is dry. On the down side, we may see an increase of bark beetle activity in conifers. Yellow jacket populations could increase, and mites just adore dry weather. One of the main reasons for insect survival during droughts is that the nutrients in the plants are more concentrated without water to dilute them. Lack of moisture also increases insect detoxification systems. Insects feeding on drought or heat-stressed plants may be more efficient in breaking down certain plant defense compounds that would normally discourage them.

The key is to monitor. Keep an eye out for insects early on or, if winter actually comes, late. The storms this past weekend notwithstanding, the weather has been warm and we yearn to get an early start on gardening. But plants can get burned if fertilized too early when they are dry, or get frost damage if they are pushing to the budding stage when winter finally arrives. The nectar flow could be low for foraging pollinators this year, and the unwelcome insects will take advantage of the stressed plants. Insects will also move into structures during dry months in search of water and food, so don’t forget your garage and adjoining structures when you look for insects.

Another option is sanitation or cultural controls. Remove diseased or dead and dying branches and old fruit from the ground because they become part of the life cycle for damaging insects or diseases. Ants just love to build nests in trees, so check that firewood you cut after the wind event in December to make sure you are not bringing pests into your home. Weed growth is minimal now, but can sprout up later if wet weather comes. Insect pests like to use weeds for shelter then, when the delicate plants are put in the ground, they go for the smorgasbord!

Aphids, scales, thrips, and fruit tree borers are a problem in a garden stressed by lack of rainfall. Instead of spraying insecticides, many of which are bad for the environment, try using soapy water to discourage aphids. Scales can be scraped from plants by hand. By keeping your garden clean, and by regular cleaning of garden tools, you reduce the ability of bugs to spread from one plant to another.

The winter of 2011 left us wondering if anything would survive its heavy onslaught. Trees were waterlogged and hillsides slid down the mountain. Now in 2012 we wonder what will survive for a different reason. It’s all a balancing act, so good luck and happy new year.

Marian Chambers has been a UCCE Tuolumne County Master Gardener since 2006. She is the retired Tuolumne County Deputy Agricultural Commissioner, has a wealth of knowledge about bugs, but prefers to spend her winters skiing.