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Understanding Pesticide Applications

With every application of fungicides or insecticides it is crucial to read and comply with the labeled instructions.  At the end of each year it should be your goal to have achieved control of your pest and disease problems with as little applied chemicals as possible. Not only does this make sense financially, but applying greater amounts of chemicals with greater frequency than recommended by label can lead to build up of resistance to such pesticides or become environmental or health hazards.

At times some labels can seem to be a bit interpretive.  There was one recent example of this that  I wanted to share with you that a producer brought before Dr. Brannen, UGA Fruit Pathologist.  These were the questions  and answers given.

Question 1: If a product gives a maximum amount per acre per season and also lists a maximum number of sprays per season, which do we follow?

For example:

The rate per application of Dithane is 1.2 to 3.2 qts per acre. I spray 1.2 qts per acre.  The maximum amount per season per acre is 19.2 qts. and the maximum number of sprays is 6 according to the label.  Obviously those numbers coincide if you spray the maximum rate per spray and spray 6 times you get 19.2 qts.  If I am only spraying 1.2 qts per acre, does that mean I can spray 16 times? I guess the question is are they trying to keep the amount of Dithane put in the environment to 19.2 qts/acre?

A: The applicator can only spray the max seasonal rate and max number of applications.  For our example, you would be restricted to six applications without regard of amount. So… any time a label takes the restrictions one step further beyond just total rate per year by restricting number of applications in a season, then that number trumps the total seasonal rate regardless of the rate you chose. The user is to adhere to both rules.  The idea is that by limiting the number of applications ultimately reduces the possibility of resistance build up.  This is especially important when using FRAC codes

Question 2: When a label specifies a quantity per season, what defines a “season”?

A: One full year is really a season, but the label may specify a timing on application; applying outside the use pattern specified is also generally considered off label.

For example:

If the label specifies bloom application for x disease, you are not really supposed to use it in December, though sometimes there are gray areas.

Further considerations:

It is also important to consider canopy growth stage as well as research regarding chemical concentrations that produce the most efficacious results.  For example, a small, sparse canopy  may require less material for complete coverage compared to a large, dense canopy.  Further, research results may have found that a particular product only provides control of ___ disease at the maximum labelled rate.  These considerations can guide effective chemical control of fungal diseases. Last, remember that many chemicals have labelled pre-harvest intervals (PHIs).  You can only legally spray your vineyard using these pre-harvest guidelines.  Since this year is on track to be an early harvest, please keep these PHIs in mind.

Please practice good environmental stewardship and use your honest understanding to guide your spray schedule.  If you have questions, reach out to reputable grape pathology sources such as Dr. Phil Brannen at UGA or Mizuho Nita at Virginia Tech.