TechNotes Feb. 12 - Ice Storms, Chemical Rotations

TechNotes are provided by Syngenta GreenCast.

Ice Storms in the South  

In the southern United States the storms that have been moving through the United States recently have had a component of ice falling on many areas.  Ice accumulation on plant material may be potentially damaging. 

Evergreens, such as yews, arborvitae and junipers, are often damaged by heavy accumulations of ice. In addition the brittle branches of many hardwoods, such as  maples, and birch, may be seriously damaged in ice storms. Improper removal of ice from the tree or shrub might do more damage than good. 

If ice accumulates on trees or shrubs, prop the branches up to prevent breakage. Never break ice off trees or shrubs by beating the ice covered branches. This only increases the damage and causes further breakage.   Where ice has caused breakage of branches, the branch stubs should be pruned back to the main stem to promote healing and callus formation prior to the resumption of growth in the spring.

Mode of Action and Chemical Rotations

Growers producing ornamental crops must often use chemical pesticides to control various insect and disease organisms.  Chemical pesticides are divided into various classes depending on the type of pest they are effective at controlling. For example, insecticides are used to control insects, miticides are effective at controlling mites, and fungicides are used to control various plant pathogens.

Pesticides are usually most effective at controlling a pest when it is applied to a particular life cycle, or stage of development, of an insect or disease.  Chemicals applied to non- responsive life stages will result in less overall control achieved.  Growers should first pick chemicals which are appropriate for controlling the desired pest, and apply them to the life stages which will yield the greatest results.  Improper applications will result in inadequate levels of control, wasted time, money, and pesticide.

The method a pesticide acts against the living systems of the pest is called the mode of action.  Generally, the mode of action within the same chemical class of pesticide is similar.  If the desired level of control is not achieved using one product, understanding which chemical class, or family, it is from will help growers to pick an alternate chemical, which has a different mode of action, belongs to a different class of chemicals, and has a greater likelihood of providing an improved level of control.

Today’s growers need to be concerned about pests building up resistance to the chemicals being applied to control them.  Pest biology, the intensity of past and present pesticide applications, and commercial production practices, are all contributing factors leading to resistant insect and disease organisms. 

The first step to reducing potential pest resistance is to reduce the reliance on synthetic pesticides. When and where possible, growers should try to use non-chemical methods of controlling pests such as implementing cultural, mechanical, physical and biological management options.

For managing resistance, the best chemicals are those that work quickly after application, and quickly disappear from the crop area, reducing the length of time pests are exposed to these products.  Pesticides that are long lasting, or degrade slowly over time, often only kill the most susceptible portion of the pest population and leave behind the resistant pests, which reproduce and produce an even more resistant pest population.

Growers use several approaches to determine when to rotate the chemicals being applied. Long term rotations consist of using one product throughout at least the duration of one pest generation before rotating.  With overlapping pest populations containing all life stages present, many growers use the same pesticide for a least two generations prior to rotating.  Other growers practice rotating chemicals with each application.  When rotating pesticides, it is important to rotate to chemicals found in different chemical classes, or having different modes of action, than the one previously applied.

Additional information regarding resistance management and tables containing pesticide mode of actions can be obtained from the following websites.  For insecticide resistance and mode of action: www.irac-online.org and for fungicide resistance and mode of action: www.frac.info/frac/index.htm.