Hurricanes and Emerging Plant Diseases

by Nikkita Patel

With the hurricane season in full swing, most media attention is focused on its devastating affects on infrastructure and human life. However, another important story relates to how this destructive force can ravage plant health and food security through the spread of plant diseases.

For example, gale-force winds, excessive amounts of rain and saturated soils provide favorable conditions for the spread and introduction of pathogens into new areas. Bacterial and fungal diseases tend to increase in severity after hurricanes.

Winds twist and break branches, damage leaves and injure fruits. Injuries to plants provide entry sites for pathogens, especially bacteria. Fungal spores are often kicked up from their resting states in the soil and are carried long distances in the weather currents. Predictive models show that they can persist for 48 hours in the air and travel hundreds of miles. Vectors, insects that act as carriers of a pathogen from one plant to another plant, also can be displaced great distances in hurricane conditions and spread plant diseases to distant locales.

Leading Factors of Plant Diseases   

A recent study explored factors that drive plant diseases of cultivated and wild plants, which have increased in incidence, increased in geographical or host plant range, or are newly recognized. A systematic analysis was conducted of seven years of ProMED postings (January 1996-December 2002). ProMED is a global electronic reporting system for outbreaks of emerging infectious diseases and toxins.

Of the 400-plus reports, the leading factor driving plant diseases, with 56%, was the human movement of plants (and their pathogens) from one location to another. This included the exporting and importing of flowers, fruits and vegetables. A positive aspect of this is that this factor is capable of being controlled through stricter quarantine measures and more rigorous inspections.

The second leading cause of plant disease emergence, with 25%, is severe weather conditions, which includes hurricanes, heavy rains and strong winds.   Unlike the previous factor, weather is not something that is controllable. Furthermore, global warming is likely to bring changing patterns of climate variability, including extreme meteorological events.   However, with increased surveillance and control measures, these diseases can be detected before extensive damage has occurred.

The ranges of several plant diseases have been steadily expanding northward, following the trajectories of most hurricanes. Citrus canker has spread throughout Florida, facilitated by hurricanes and strong rain-driven storms. In 1994, it was thought that citrus canker had been eradicated in the US; however in 1995, it was found near Miami International airport.   Since then, various hurricanes, including hurricanes Charley, Frances and Jeanne, have propelled this bacterial disease to 22 counties in Florida. Citrus canker weakens the tree and reduces the number of fruits produced. In attempt to control this disease, almost two million trees have been destroyed, yielding a loss of over US $200 million.

Another disease threatening the food security of the US is soybean rust.   This fungal disease causes soybean leaves to drop early, which reduces soybean yield. Soybean rust is thought to have moved from Brazil or Venezuela into North America for the first time in the fall of 2004 with Hurricane Ivan. Fortunately, this was the end of the harvest season, so damage was minimal. Yet, this disease has been steadily increasing in geographic distribution. Soybeans account for 16% of all U.S. crop production. Hurricane Dennis in June 2005, threatened to spread rust further north into the Midwestern states.

Recent hurricanes have impacted other plants including peanuts, tomatoes, peppers and cucumbers with bacterial, fungal and viral diseases. With the inevitable yearly hurricane season, the best protection is surveillance. Any suspected plant diseases should be reported to the local plant health authorities.