Phytophthora Blight Is A Destructive Force

Phytophthora blight (caused by Phytophthora capsici), some may say, is synonymous with destruction. Causing problems in numerous areas of the U.S., Phytophthora blight historically has been an issue for pickling cucumber growers in Michigan, for pumpkin growers in New York and Illinois, and for growers in Georgia, North Carolina, Texas, California, and Florida — just to name a few places.

Its main “victim” seems to be bell peppers, but several crops, including tomato, eggplant, and other cucurbits, can also fall victim to this pathogen. This species of Phytophthora isn’t
just a concern in the U.S., it is an issue worldwide. To respond to this problem, the University of Florida and the University of Georgia are hosting the First International Phytophthora capsici Conference in November 2007 to discuss what needs to be done to manage this disease. (For additional information on the meeting, go to http://conferences.dce.ufl.edu/pcap/).

According to Pam Roberts, associate professor of plant pathology at the University of Florida, growers must constantly be on the lookout for P. capsici. Yellow squash seems to be the most susceptible in Florida. “Phytophthora wilts the entire plant and the fruit turns brown,” she says.

Making the situation more difficult for growers, the symptoms of Phytophthora differ from crop to crop. For example, on watermelon, growers only see the problem when they are harvesting, and by that point, the watermelons are unmarketable, she says. On pepper, however, the fruit turns brown.

Ronald French, assistant professor and Extension plant pathologist at Texas A&M University, says that for peppers, “growers can look for wilting as one of the symptoms or a dark purple to black lesion in the stem or crown.”

Survival Techniques

To survive, P. capsici likes moderate temperatures and wet weather, says Roberts. “It needs moisture to move around. Considered a water mold, the pathogen moves in water toward roots so it can spread.”

On top of that, the pathogen is believed to be able to survive in the soil for up to five years, although some have put that number even higher. “Current research should address that longevity issue in order to have a better understanding of this pathogen,” French explains. “The pathogen can also survive in old plant tissue. So, it could be possible that it could survive until the next growing season, and infect the new crop.”

The growers most at risk are the ones growing in fields that have had P. capsici in the past. For those growers, they need to avoid planting in areas where the pathogen has been present. (For additional information on managing P. capsici go to http://edis.ifas.ufl.edu/VH045.)

Finding Solutions

What are growers to do? To prevent an outbreak or future outbreaks, French suggests crop rotation with crops not susceptible to P. capsici. He also recommends using tolerant varieties (if available), providing good soil drainage, and having a good scouting program. A good scouting program, he says, will help growers find the disease before it becomes a major problem. Therefore, better results could be obtained when implementing a plant disease management strategy.

Once it is established, P. capsici  is difficult to eradicate. There are preventive fungicidal treatments available, he says, and growers should check with their county extension agent for more information on what can be applied in their areas.