I think most of us can agree that so far this year, northern Nevada has experienced a rather mild winter. However, if you look at the temperatures recorded in Lovelock, Nevada for the months of December and January they ranged from a high temperature of 61.0 degrees Fahrenheit to a recorded low temperature of 5.0 degrees Fahrenheit. These temperatures are very close to the normal average temperatures for theses months. The big difference was in precipitation, the normal average precipitation for these winter months is 1.06 inches. So far, this year we have recorded only 0.54 inches of precipitation for December and January.
With that weather data in mind, how does a dry and mild winter affect overwintering insects? Some might think warmer temperatures would increase the chances of insect survival. Perhaps that is true. But there are many factors that influence successful overwintering and are worth strong consideration. Some winter survivorship factors are highlighted here:
• Insects that overwinter above ground (e.g., alfalfa weevils) may be more likely to survive with fewer cold days. But a lack of snow cover can expose insects to those days with below-freezing temperatures, and could increase mortality compared to year with insulating snow.
• Insects that overwinter below ground (e.g., Mormon Crickets) will not likely be affected by a mild winter because soil temperatures are more constant. However, there could be more survivors than normal if the frost layer is shallow.
• All insect’s development is based on temperature. A warm winter day could cause insects to become active when they normally would be dormant. Activity uses up stored fats they depend on to survive until the spring. Without access to food, these active insects could starve to death before food becomes available.
• Most insects adapt to cold winters by slowly preparing in the fall and staying dormant until the spring. Therefore, large temperature swings can be detrimental to insects; the body can be injured or death can occur. We would expect some insect mortality due to cold intolerance when temperatures regularly fluctuate from 0-50 degrees.
• Also, there are other factors to understand before we can predict insect populations in the spring and summer. The same survival factors outlined above also apply to beneficial insects, like predators and parasitoids, and insect-killing pathogens. So ultimately it might not matter too much if more pests survive in a mild winter, because more beneficial insects will likely survive and help regulate spring populations. The uncertainty of insect survival in the winter can make predicting pest populations very difficult.
No matter what the winter weather is, both farmers and home gardeners should follow a good integrated pest management program (IPM) when using measures to control insect pests. A good IPM program includes chemical, cultural, and biological control methods to prevent economic yield loss, to mitigate resistance development, and to protect populations of beneficial insects.
Beneficial insects in this context include both the pollinators and the predators and parasites of insect pests that help to maintain pest populations below damaging levels.
Successful IPM begins with scouting/monitoring. Growers should monitor most pest and beneficial insect populations consistently throughout the season. Both population counts and the developmental stage of pest and beneficial insects and mites in relation to economic thresholds are used to determine management strategies. The “Economic Threshold” is defined as the pest population level that produces damage equal to or greater than the costs of preventing damage. In addition, continuous monitoring of pest and natural enemy populations can result in reduced use of chemicals, improved timing of pesticide applications, and less disruption of natural enemy and pollinator activity.
For more information on alfalfa IPM strategies and methods go to: http://www.unce.unr.edu/publications/files/ag/other/fs9811.pdf or call the Pershing County University of Nevada Cooperative Extension Office at 775-273-2923.
