Late blight on tomato plants

Wed. Oct. 11, 2017

Click below to listen to my 2 min. Garden Bite radio show:  Late blight on tomato plants

To say it’s been a wet summer and into Fall seems an understatement.  With that is the appearance of late blight on tomatoes.  Many folks are reporting this fungal disease.  Late blight is caused by the pathogen Phytophthora infestans, a fungus like organism that thrives in wet conditions. The scientific name translates to ‘plant destroyer’ and it is.

Late blight

So what does it look like?  First it starts with leaves that have large, dark brown blotches with a green gray edge.  The stems can become firm and dark brown.  The disease progresses rapidly in cool wet weather and the entire plant MAY turn brown and collapse in a few days.

Fruits have firm dark brown blotches. If the tomato is cut open, dry brown rot can be seen extending into it.  Fruit will become soft and mushy when bacteria invade after the initial infection. In high humidity, thin powdery white fungal growth appears on infected leaves, fruit, and stems.

Late blight with mold in high humidity

Once late blight has been found in a garden, there is little that can be done to help the plant. The disease simply moves too quickly.

Harvest what you can and be sure to keep checking to see if the fruit starts to show the disease in storage, if it does, get rid of it.

More information from the University of Wisconsin Extension.

Infected plants should be removed or destroyed as soon as possible to prevent the thousands of airborne spores forming on the leaves from spreading to neighboring plants.  Infected plants can be placed in a plastic bag or under a plastic tarp and left to cook in the sun for several days. Once all of the plant material is killed, the plant can be composted or buried.  Plants can also be shallowly buried in soil, as the freezing winter temperatures will kill both the plant and pathogen.