Summer and fresh vegetables! This is the time my spring plantings are now bearing fruit. Of course, along with harvesting the veggies, I also need to be careful about fungal infections that will weaken and eventually kill my plants. One fungal pathogen is powdery mildew and there are two very distinct fungal pathogens, powdery (Podosphaera xanthii) and downy (Pseudoperonospora cubensis) that affect my cucurbits (pumpkins, squash, and cucumbers). These two diseases have very different symptoms and control strategies.
Powdery mildew is a white fungus that mainly grows on the top and underside of the leaves and does not usually attack the squash fruit.
The yield of infected plants can be reduced because infected plants have less energy to invest in fruit.
The best way to prevent powdery mildew is to plant disease resistant varieties and provide good air movement around the plants. If susceptible cultivars are growing in an area where powdery mildew has a history of causing yield losses, fungicides may be required. An interesting 1999 article (Crop Protection, Vol.18, Issue 8, Sept. 1999) found that spraying with 30-50% cow’s milk was as effective as using the fungicides fenarimol or benomyl.
People also read…
Downy mildew is often referred to as water mold because it thrives in humid conditions. Downy mildew is not seen in Minnesota every year because it cannot overwinter here and must be transported here by spores blown in from the southern states.
But once here, this disease can be recognized by the almost square yellow to brown spots that appear on the leaves. Once downy mildew has started an infection it is very difficult to control and there is nothing that can be done to save the plant.
The best solution is to remove infected plants as soon as symptoms appear.
The good news: The pathogen will not survive the winter in Minnesota.
There is a website that tracks downy mildew infections and can be found at https://cdm.ipmpipe.org/.
There is more information on fungal diseases and other diseases that could infect your garden plants and a great resource is at https://extension.umn.edu/vegetables/disease-management.
Do you have an active interest in gardening? Have a desire to share your gardening interest with others? Contact Marianne Duffy Hohenner at [email protected] to learn how to become a University of Minnesota Extension Master Gardener Volunteer.