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Monsoon Impact
September 1st, 2014
Peggy Fiandaca

One of the many aspects that make Arizona a truly unique wine growing region are monsoons. A monsoon is defined as any regular weather pattern that brings significant rain fall. The Arizona monsoons are activated by moisture coming from the Gulf of Mexico and Gulf of California that increases humidity and causes rainfall. So far this year, over eight inches of rain has fallen at Lawrence Dunham Vineyards as a result of the monsoon weather pattern.

 Monsoon at Lawrence Dunham Vineyards

These summer storms starting in June in the mountains of southeastern Arizona run into September, have an impact on the vineyard and pose challenges to grape growers. Arizona is one of the few places in the world growing fine wine grapes that has a predictable wet season around harvest.

 Grapes at maturity
  The greatest challenges posed by the monsoons are moisture in the vineyard and possible hail.

Moisture is a concern because it can lead to bunch rot. Bunch rot is a combination of ripening grapes, bacteria, and water. We start to deal with bunch rot long before the rains start.

Early in the growing season we apply fungicides that eliminate the bacteria that cause bunch rot. Additional applications are made just prior to grape clusters closing while they are still green.

This is done in hopes that when the rains start there is less bacteria in the vineyard that would cause bunch rot.

We also carefully manage fruit density by removing clusters that are in contact with each other that causes a warm, moist environment and little air circulation – a perfect environment for bunch rot to begin. We also manage the canopy to increase air circulation and sun light. Bunch rot destroys the fruit and makes it unusable for winemaking. Hail is a threat to the ripening fruit as it gets softer as well as the plant itself.

Hail can damage fruit, damage the vegetation of the plant, and worst case scenario wipe out a vineyard.


Monsoon at Lawrence Dunham Vineyards

A positive aspect of the monsoon is the changing environment that occurs during this period. The temperatures can swing significantly from day-to-day and from hour-to-hour. For example, the temperature in our vineyard in the morning can be in the 90s, after a monsoon rain the temperature drops to the 50s in the afternoon, then rebound to the 80s by sunset, and then back to the 50s at night.

These temperature differentials impact the sugars and acids in the grapes making our wines unique. The cloud cover during the heat of the day increases the hang time of the grapes allowing them to develop more complex flavors.

Though challenging, the monsoons help create our unique mountain fruit that is the foundation for our distinctive Lawrence Dunham Vineyards’ wines.