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Extension > Yard and Garden News > Look for Leaf Spots

Thursday, June 29, 2017

Look for Leaf Spots

Angular Leaf Spot on Cucumber
M. Grabowski, UMN Extension
M. Grabowski, UMN Extension Educator

Recent rains and warm weather has provided ideal conditions for many leaf spot plant pathogens to spread and infect young vegetable plants. Leaf spot diseases are caused primarily by fungi and sometimes by bacteria. These plant pathogens survive from one season to the next in previous years infected plant debris and garden soil. Rain splashes fungal spores or bacteria from the soil onto the lower leaves. If the conditions are favorable (typically warm and wet) the pathogen infects and a leaf spot forms.

Young early blight leaf spots can
result in fruit rot later in the summer.
M. Grabowski, UMN Extension 
Leaf spots will soon produce a new set of fungal spores or bacteria that will spread to form new leaf spots. This cycle can continue throughout the summer as long as weather conditions are favorable. By August, entire leaves or plants are blighted brown and some leaf spots have become fruit spots or rot.

What’s a gardener to do?

  • Inspect plants now. Look at the lower leaves that are closest to the soil.
  • Pinch off leaves with leaf spots and remove them from the garden. They can be disposed of in a backyard compost pile that heats up to 148 F or brought to a municipal compost facility. Never remove more than 1/3 of the total leaves on the plant or you will be doing more damage than the pathogen!
  • Do not work in the garden when leaves are wet from rain, dew, or irrigation. Leaf spot
    pathogens are easily spread on hands and tools when leaves are wet.
  • Mulch the soil. Straw, wood chips, and plastic mulches provide a barrier between leaf spot pathogens in the soil and the lower leaves. Mulch also reduces humidity in the plant canopy.
  • Stake vining plants like runner beans, cucumbers, tomatoes, and peas. This will lift the plants farther away from pathogens in the soil and will help the leaves dry quickly after rain or irrigation.
  • Tomatoes staked and mulched, with the
    lower leaves pinched off.
    M. Grabowski, UMN Extension 
  • Pull those weeds! Weeds crowd the crop and create a moist humid environment favorable to leaf spot pathogens. Some weeds can also become infected with leaf spot pathogens and allow the pathogen to remain in the garden and spread to the vegetable crop despite a gardener's best efforts.


It is difficult to slow down a leaf spot disease once it has spread throughout the plant. Use the cultural control practices now to slow down these pathogens before they get started. Learn more about how to grow healthy vegetables at the University of Minnesota Extension Garden webpage

1 comment:

  1. is there a way to save a grapevine that has had this for 2 seasons?

    ReplyDelete

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