September 10, 2004 | By: Aimee Heald-Nielson
LEXINGTON, Ky.

The 2004 apple crop in the central United States, including Kentucky, is forecast to be about 1.12 billion pounds according to a report by Minnesota’s Agricultural Statistics Service. That number represents a 7 percent decrease from 2003, but a 36 percent increase from 2002.

Several things can affect the final apple crop, and in Kentucky the numbers may be impacted by a wet spring and summer.

“Rainy periods in spring and summer were obstacles that apple growers faced when trying to manage apple diseases,” said John Hartman, plant pathologist for the University of Kentucky College of Agriculture. “Rains interfered with late dormant pruning and sanitation efforts, and prevented timely applications of preventative fungicides.”

Kentucky continued to experience above average rainfall and below average temperatures throughout the summer, which likely affected the kinds of diseases affecting apples, especially fruit rot diseases.

“Spring and summer of 2004 have not been typical in Kentucky,” said Tom Priddy, meteorologist in the UK Ag Weather Center. “We’ve had cooler temperatures than we normally do and more rainfall.”

Hartman said that based on weather patterns of the spring and summer, black rot fruit decay, sooty blotch and flyspeck will be the predominant near-harvest apple diseases.

“Unless the weather becomes typically more hot and humid, white rot and bitter rot may appear somewhat less frequently than normal,” Hartman said.

Black rot is caused by a fungus that infects blossoms and leaves. Prime conditions for the disease to begin are temperatures in the 70s with prolonged wetness, which has happened a lot this year in Kentucky.

“We’ve had several long periods this summer with temperatures in the 70s, when we should’ve been in the 80s and even the 90s,” Priddy said. “Couple that with above average rainfall and you’ve got the right conditions for these apple diseases.”

White rot is also caused by a fungus and it can infect woody tissue and cause cankers, but it does not infect the apple leaf tissue. The infection can occur throughout the growing season, Hartman said. Under warm conditions, above 80 degrees, the decay is soft, watery and a light tan color. Under cooler temperatures, the decay usually is firmer and a darker tan.
Bitter rot prefers hot, humid weather, which Kentucky has not had much of this year. 

“Dry eye rot and calyx end rot are usually minor diseases in Kentucky because they appear when very wet weather occurs during bloom, which was the case this year since that time was wetter than normal,” Hartman said. “If harvested, fruit infected with dry eye rot will develop gray mold in storage.”

Hartman said sooty blotch and flyspeck are important summer apple diseases, but they do not cause fruit rot. 

“Sooty blotch and flyspeck are caused by a complex of different fungi and they grow superficially on apple fruit surfaces and that lowers their quality and market value,” he continued. ”We know from previous research that there is a correlation between accumulated leaf wetness hours and appearance of symptoms of these two diseases.”

Hartman explained that beginning 10 days after petal fall, the number of hours of leaf wetness from dew or rain each day is added together. When that total approaches 200 hours, sooty blotch problems typically start appearing on fruits of untreated trees. In many Kentucky locations, that total was reached in early June, so this disease complex has been present on fruits for a long time this summer, he said.

Priddy said the long range outlook for fall shows near-normal temperatures and near-normal precipitation.

Contact: 

Writer: Aimee D. Nielson 859-257-4736, ext. 267
Source: John Hartman 859-257-7445, ext. 80720