Gardening season is in full bloom in Wisconsin, but while your perennials and their pollinators are peaking, so too are those nasty plant diseases that can filter into your flowers and victimize your vegetables
Brian Hudelson, the director of the University of Wisconsin Extension’s Plant Disease Diagnostics Clinic, recently joined Jill Nadeau on WPR’s “Garden Talk” to discuss what ailments may be plaguing your plants
The common, the infected and the ugly
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Hudelson has encountered countless plant diseases in his 30-year career, but he claimed the most common is likely Rhizosphaera needle cast, which primarily affects spruce trees. “The fungus gets in there, infects the newer needles, but then just kind of sits around and becomes active as those needles end up farther towards the interior of the canopy, and then will cause the needles to drop prematurely,” Hudelson explained. “It causes a lot of problems in spruce trees and makes them look ugly over time,” Hudelson continued.
So ugly in fact that Hudelson advised gardeners to not even bother with this common conifer: “It’s an overused tree. It’s not well adapted to our weather here in Wisconsin.”
A flood of fungus
Several other fungal plant diseases causing havoc for Wisconsin gardeners are currently on Hudelson’s watch list
Powdery mildew is having a moment thanks to current Wisconsin weather
“Because it’s our muggy July weather. Powdery mildew prefers dry leaves but really high humidity.”
Another dreaded fungal disease on Hudelson’s radar is Verticillium wilt
“This fungus hangs out in the soil and infects through the roots, colonizes the water-conducting tissue inside the plant and blocks it off,” Hudelson explained. “And so that prevents water from getting from the root system up into the branches. It is a lethal disease.”
Blowin’ in the wind
For a treacherously transmissible disease, Hudelson points to gray mold, also known as Botrytis blight
“Botrytis Blight is pretty common in the environment,” Hudelson said. “So even if you get rid of all your infected material, you can still have problems with the fungus. The spores will blow around for a long distance.”
Dialing back on branch dieback
Hudelson advised on how to counteract against deadly canker diseases that kill plants by preventing water from entering branches
“The way to deal with that is to basically find that interface between live and dead branches and come down about 4 to 6 inches below and then cut off the top of the tree,” Hudelson recommended
To prevent further contamination, Hudelson strongly encouraged using rubbing alcohol to clean cutting tools for about 30 seconds between each trim.
Trouble for the tomato
Septoria leaf spot is a potentially ruinous fungal disease that can trip up your homegrown tomatoes
“You get the browning of the leaves at the bottom of the plant and it kind of works its way up the tomato plant. Eventually the browning will get so bad that the leaves will entirely dry up,” Hudelson explained
Hudelson said tomatoes are also highly sensitive to not only unmanaged leaf debris but also herbicide exposure
“Tomatoes are very sensitive to very low dosages,” Hudelson said of weed killers. “Check for symptoms on tomatoes if herbicides are drifting around.”
Hudelson advised not consuming any vegetables on a plant suspected to have been exposed to herbicides
Monochrome maladies
White mold is another fungal disease that paradoxically forms in little black structures that Hudelson described as looking like “mouse or rat droppings.”
“If you see those, dig up the plant as quickly as you can, remove the soil around the plant and get that out of your garden,” Hudelson urged
Conversely, Hudelson described black rot as a bacterial disease that typically affects brassicas or cold crops
“The typical symptoms will be some kind of browning,” Hudelson elaborated. “Often times starting around the margins of the leaves and then working its way back along the veins. And you’ll see kind of a yellow halo.”
How about them apples
Hudelson admitted that he may be partly to blame for a newer fungal disease found in Wisconsin called Marssonina leaf blotch, which he compared to apple scab
“I had been pushing for people to grow varieties of apples that are naturally resistant to apple scab instead of using fungicide treatments,” Hudelson said. But he theorized that this new fungal pathogen might previously have been controlled by fungicides that he was discouraging others from using
“Nature has a way of making us kind of look foolish sometimes,” Hudelson laughed
The diagnostic duo
For home horticulturists vexed by their underperforming vegetation, Hudelson accepts digital photographs or physical samples that he reviews and sometimes shares with the director of the UW-Madison’s Insect Diagnostic Lab
“I work very closely with PJ Liesch,” Hudelson said. “We trade samples all of the time and things that sometimes we think are disease problems are really insect problems, and sometimes things that we think are insect problems turn out to be diseases.”
Hudelson joked that he’s become an expert on plant diseases the hard way
“I have a talk that I give called ‘Confessions of a Black Thumb,’” Hudelson laughed. “It’s all about plants that I have killed or at least thoroughly maimed.”
