Monthly Archives: July 2015

Watch for Late Blight in Tomatoes and Potatoes

This is Late Blight Season: Know the Symptoms and Get Disease Confirmation

By: Ken Schroeder, Agricultural Agent

UW-Extension, Portage County


Late Blight Phytophthora infestans, has been confirmed on potatoes and tomatoes in Wisconsin every year since 2009.  As I write this, July 9th late blight has been reported in 3 central Wisconsin counties.

Late blight caused the Irish potato famine of the 1850’s.  It is often referred to as a ‘community disease’ because it is extremely destructive and easily spread by wind.  Left unmanaged, a small outbreak can lead to an epidemic, devastating gardens and commercial vegetable fields.

This disease has the potential to completely defoliate fields within 3 weeks of the first visible infections.  Spores are easily spread by wind, rain, machinery, workers, and wildlife.  Because the fungus produces so many spores that can travel long distances through the air it is very important that everyone, farmers and gardeners alike, who grow potatoes and tomatoes are able to identify late blight.

Know the Symptoms:  Leaf symptoms appear as pale green, water-soaked spots that often begin at Late Blight leavesthe leaf edges or tips where water from rain and dew accumulates.  Spots can be circular or irregular and bordered by pale yellow to green blending into healthy tissue.  They enlarge rapidly (expanding ¼ to ½ inch per day) turning brown to black over time.  When relative humidity is in excess of 90% leaf lesions are often surrounded by cottony white mold on the lower leaf surface.  This white, cottony growth distinguishes late blight from several other foliar diseases of potatoes and tomatoes.  Infected stems and petioles turn brown to black and may also be covered with white masses of sporangia.  Stem lesions frequently appear first at the junction between the stem and leaf, or at the cluster of leaves at the top of the stem.  Entire vines may be killed very rapidly.  A characteristic odor similar to that produced by Late Blight tomatoesgreen tissue after a severe frost can often be detected.  Visit the University of Wisconsin Vegetable Pathology website and the UW-Extension Horticulture website for additional late blight photos and links to other late blight information including options for gardeners and organic producers.

Get Disease Confirmation:  Twice weekly check potatoes and tomatoes closely for symptoms of late blight.  If you suspect late blight on your crop contact your local University of Wisconsin Extension office and have a sample sent to the University of Wisconsin plant disease diagnostic lab for confirmation.  If confirmed, destroy infected plants by burying or putting in plastic bags for disposal.  Don’t compost!!!

Late Blight Look-Alikes:   Early Blight – appears as brown to black lesions with concentric rings on the leaves.  Typically, lesions are produced on older, lower leaves and progresses upward.  Significant yellowing may accompany the lesions.  Moderate temperatures (75 to 85 oF), high humidity, and prolonged leaf wetness are conducive to development of early blight.  Alternating periods of wet and dry weather tend to increase progression of this disease.  See UW-Extension Early Blight fact sheet .

Botrytis/Gray Mold – Gray mold appears late in the season on the foliage, and may be mistaken for late blight.  A grayish-green, wedge-shaped, spreading lesion with concentric rings appears on the leaves, often near an injury or a dried blossom.   Lesions begin on the margins or tips of leaves.  With severe infections, leaves are blighted and a soft gray rot attacks the stems and exhibits a fuzzy gray fungal growth.  When vines are disturbed, spores billow from them like a cloud of dust.  Cool temperatures and high humidity promote disease development.  Gray mold is often found in fields where a lot of fertilizer is used.  Typically, gray mold is not of economic importance in Wisconsin.  See Gray Mold fact sheet .

Septoria Leaf Spot – A very common leaf disease of tomato, however, not necessarily a look-alike.  Symptoms begin on the foliage closest to the ground and then move on up the plant.  Leaf spots tend to be small and circular with dark borders and gray or tan centers.  Eventually, multiple spots on a single leaf will merge.  Warm, wet, humid weather increases the severity of the disease that can progress to the point where all the foliage is killed and falls from the plant.  This disease does not advance nearly as rapid as late blight.  See UW-Extension Septoria Leaf Spot fact sheet .

For assistance in identifying this potentially disastrous late blight disease, contact your local University of Wisconsin Extension Office


Master Gardener Level 1 Training 2015 – Wood County

I hate the thought of summer coming to an end so soon, but am excited to announce another Master Gardener Training class for fall of 2015.  The Master Gardener program is a volunteer program designed and sponsored by University of Wisconsin Cooperative Extension to educate community members interested in gardening who, in turn, volunteer each year to further educate the public and provide community support.  The first step in becoming a certified Master Gardener Volunteer is to attend the Level 1 training course.  In Wood County, we try to hold one Level 1 training class per year, alternating between the Wisconsin Rapids area and the Marshfield area.  This is the year we are going to be in Marshfield.  The Level 1 training classes have been evolving over the years to incorporate more hands-on learning activities rather than just lecture.  We are also using internet technology for better access to learning modules and state specialists located throughout Wisconsin.  Participants will need to be able to access these modules on their own time.  The classes will be held on Tuesday evenings, beginning in September and concluding in November.  The Tuesday classes will be from 6-9pm held in the auditorium at Marshfield Ag Research Station.  There will be 36 hours of training in all horticultural related subjects including fruits, vegetables, perennials, annuals, trees and shrubs, landscape design, weeds, insects, diseases, soil and plant health, composting, wildlife management, natives and invasives, houseplants, plant propagation and lawn care along with volunteer training.  We always have live presenters during the class hours, and will have distance education incorporated as well for off-site learning opportunities.

The Wood County Master Gardener Association is a strong group with wonderful members passionate about gardening, community service, and education.  We have many projects and activities throughout Wood County and surrounding areas that help enrich the beauty of our communities and enlighten our community members.  If you would like to be part of our team, consider taking the Level 1 training.  Once complete, each person is required to volunteer 24 hours of community service before you are awarded the status of Certified Master Gardener Volunteer.  To maintain the certification, 24 hours of service is required each year along with 10 hours of continuing education.  Most of our members achieve this amount without even having to think about it!  After the Level 1 training is complete, there are more opportunities for advanced Level 2 trainings on specific topics.  We have educational events at all of our monthly meetings along with garden tours and socialization with fellow members.

If interested in participating in the Level 1 training and joining this dynamic group of volunteers, please register with the Wood County Extension office.  Our registration brochure is available at the link below or call 715-421-8440 and we can send you information.  We also require the background check form and volunteer agreement form to be sent in at the time of registration.  The fee for the Level 1 training class is going to be $135 per person and includes all training materials and handouts.  Registration is open until August 27th.  The classes will begin Tuesday, September 8th but you must be registered by August 27th to attend.


Master Gardener Training Brochure

Background Check Form

UWEX-MG Volunteer Agreement Form

MG Newsletter July 2015

Warming up July with MG Newsletter July 2015