Garden diseases are in full swing


Harvest of backyard gardens should be in full swing this month. Staples such as beans, tomatoes, cucumbers, and summer squash should be picked every few days to ensure continued harvest and top quality.

Unfortunately, it is this time frame that unseen micro-organisms try to limit this garden fun. Two of the more devastating diseases, late blight and downy mildew, have made their appearance in Pennsylvania within the past week and can quickly bring an end to garden picking unless addressed.

Late blight, known as the “plant destroyer,” limits its attack to potato and tomato. When conditions are ripe, temperatures of 60∂-80∂F and high moisture, it can wipe out plantings within days.

The pathogen has a complex lifecycle and one of the key facts to know is that it has a difficult time overwintering in many areas of the US. Because of this, researchers and extension educators in many of the land-grant universities (of which Penn State is one) track the organism as it moves about. This is easily monitored by anyone, farmers and backyard gardeners, to better prepare for the approaching mayhem. Bookmark and check out USABlight at https://usablight.org/map/

A related disease, downy mildew, acts in similar fashion but on vegetables in the cucurbit family (cucumber, pumpkin, butternut squash, etc.). Like late blight, the micro-organism does not have the ability to overwinter. With personnel on the ground in growing regions throughout the US, the disease movement can be tracked with relative ease at http://cdm.ipmpipe.org/scripts/map.php.

Since the pathogens are closely related, management of the problem in tomatoes and cucurbits is also similar. Scout plants on a regular basis and remove any suspicious lesions on leaves (pull up pictures off the internet to help with identification) as this might slow down disease progression.

Avoid overhead watering as this creates an optimal environment for the disease to thrive.

Weeding can be a chore, but it is more than eliminating competition between crop and weeds for light, water, and nutrients. A dense weed crop can create a micro-climate around vegetables that encourage prime conditions for disease progression.

Finally, consider the use of fungicides to limit the spread of the disease. Always read and follow the label to make sure that the product is appropriate for intended use.


Tom Butzler is a horticulture educator with the Pennsylvania State University Cooperative Extension Service and may be reached at



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