Weather has dampened the plans of many gardeners and homeowners this growing season. In fact, this May was the wettest on record in the Chicago area since 1871, according to the National Weather Service.
“Cool, wet weather promotes foliage diseases, such as leaf blights, needle cast diseases, crown and stem rots on a host of woody ornamentals, perennials and vegetables,” said Richard Hentschel, University of Illinois Extension Horticulture Educator for DuPage, Kane and Kendall counties. “While foliage diseases on trees and shrubs are rarely fatal, that is not the case for needle evergreens where older infections spread to 2019 new growth.”
Even those plants that have known disease resistance are more likely to have disease problems the longer the current weather pattern continues.
“While the cool temperatures have allowed for more growth early on, perennials, iris, daylily, phlox and others have grown larger than expected,” Hentschel said. “This is the time fungal disease spores are in the air moving along to infect all the young tender vigorous growth.”
For example, fruiting apple trees and flowering crabapples will have strong outbreaks of Cedar Apple Rust and Apple Scab in cool, wet weather. More infection spores will survive than if the air was hotter and drier. Under these conditions, home orchardists are having to treat their apples more often and over a longer period of time.
Vegetable transplants expecting warmer soils will just “sit there” and will often lag behind in development even if the soils do warm and dry out. Vegetable seeds without a protective fungicide seed treatment are likely to rot in place before they have a chance to germinate.
“When it rains, soil-borne fungal pathogens will be splashed up onto foliage causing infections to start at the base and interior of our garden plants, with tomatoes suffering the worst,” he said. “If the wet soil persists, fruits forming on our vine crops like cucumbers and summer squash will develop fruit rots where they touch the soil.”
Hentschel added that vegetable gardening could be modified this year by growing in pots, raised beds, and grow bags instead of the traditional in-ground beds. Planters and raised beds will warm up quickly and grow mixes will not waterlog as they are designed to drain well.
Soils with naturally poor drainage will maintain the wet conditions longer, promoting root rots and crown rots. Landscape plants damaged by extreme cold weather may have symptoms show up later this summer.
“We already know many flower buds did not survive. If plants are healthy otherwise, had vegetative buds killed and not vascular tissue, it can take four to six weeks to create another set of buds to leaf out with,” said Hentschel. “With all that is going on, the best practice now is to take a wait-and-see approach.”
If plant replacements are needed, consider plants that are hardier than those you are taking out.
“All this wet, cool weather along with the winter temperature extremes we had, will make for a very unusual growing season with more plant problems ahead.”
To get help with your lawn and garden questions, contact your local Master Gardener Help Desk. Find hours and contact information for DuPage, Kane and Kendall counties at https://go.illinois.edu/MasterGardenerHelpdkk