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Q&A: You Ask…the Experts Answer

Q: Is the tomato blight still a problem for upstate gardeners?

Steve Reiners and Spikes

This issue’s guest expert is Steve Reiners,  an associate professor with the department of horticulture at the NYS Agricultural Experiment Station in Geneva.

A: Unfortunately, tomato (and potato) late blight will always be a potential problem for gardeners in New York as well as the rest of the country.  The disease is caused by the same pathogen that caused the 19th Century Irish Potato Famine and is still with us today.  Up until 2009, we saw it occasionally and usually only later in the season.  2009 was different. There are three things needed for a plant disease to thrive. First, we need the pathogen to be present.   That year, some tomato transplants for sale in the spring were already infected. Second, we need a susceptible host and we have that with tomatoes and potatoes grown everywhere in gardens and farms.  Finally, we need the perfect weather conditions.  Late blight thrives during wet and mild summers.  Day temperatures of 70 to 80F and night temps of 50F to 60F are ideal, but if the season is dry and hot, the spread will be limited.  The airborne spores can travel several miles but will only germinate and infect susceptible plants if “free moisture” is present.  That means leaves are wet from dew, fog, rainfall or sprinklers.  The spore and disease will have a hard time surviving more than an hour in hot and dry conditions.

The pathogen can only overwinter on living tissue.  So if tomato plants were infected last year, it won’t survive on those.  The plants die with frost and so does the pathogen.  Where it can survive is on potato tubers that overwinter in soil and “volunteer” the following spring.  As of mid-June, we have not seen the disease exploding throughout the Northeast as we did in 2009, so we won’t have that early inoculum. With a hot and dry summer, we should be fine.  Gardeners should try watering using trickle irrigation to keep leaves dry and reduce disease spread.  If you need to use sprinklers, water in the morning so leaves are dry by evening.  In addition, some excellent varieties are being bred with resistance to the disease.  Finally, Google “late blight Cornell” and you can find updates on where the disease has been found this season.  Cornell, along with other Universities, is tracking the disease so we can sound the alert if it is spreading.

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