Michigan is still leads the nation in pickling cucumber production, but a readily spread disease infecting up to 50 percent of the state's cucumber acreage threatens to change that.



The culprit is Phytophthora capsici, a fungus-like organism that infects plant roots, fruits and foliage and causes a blight, or rot, to appear on the infected  plant parts of several crops, including cucurbits, tomatoes, eggplant, peppers and snap beans.



Infection reduces yields and can kill plants outright within a few days. In 2006, Michigan growers produced $132 million worth of these vegetables on more than 83,000 acres. When weather conditions are favorable for Phytophthora (warm with rain), crop losses can reach 25 percent or higher.



"The economic losses from Phytophthora can be devastating," says Mary Hausbeck, Michigan State University professor of plant pathology and lead researcher on the Phytophthora project in East Lansing. "When a farm in southern Michigan was unable to harvest 300 acres of diseased pickling cucumbers because of Phytophthora, an estimated $300,000 was lost. This was in addition to a $40,000 loss on approximately 100 acres of processing tomatoes."



Because of the threat that the disease presents to the state's growers, plant pathologists are seeking to strategies to understand and control Phytophthora, which can persist in soils in the absence of a host for more than 10 years. They cite two findings as key.



The first dates back to 1999, when they learned that Phytophthora had become highly resistant to the primary fungicide that growers had been using to control it.



"This finding caused the pickle industry to shift to using alternative products that did work and helped Michigan acquire a Section 18 registration that some other states did not have," Hausbeck says.



The second is that some of the water sources that farmers were using to irrigate their crops were contaminated with the Phytophthora pathogen. In standing water, Phytophthora produces swimming spores that can be spread through moving water. The pathogen can survive and cause infection for eight to 10 hours, long enough to be spread over many acres through irrigation.



"Discovering that this pathogen can be spread through irrigation water has been the hardest one for growers to resolve," she says. "Irrigating with well water is safe, but using surface water from ponds, rivers, creeks or ditches is not, especially if there is a history of Phytophthora in the region. Phytophthora is not visible to the naked eye, and the cleanest-appearing ponds can be contaminated with it, so it can be difficult for growers to understand why they must shoulder the expense of digging a well."