TIMELY TIPS

Plant Pathology 101

Plant diseases are an ugly reality for all gardeners. Whether you are a flower fancier, vegetable aficionado, native plant enthusiast or fruit fanatic, diseases are par for the course. You may be scratching your head right now as you try to figure out why your plants are wilting, rotting, spotted or spent. So, we thought a one page primer on plant diseases may be in order.

What's a plant disease? It is abnormal plant growth that results from an interaction between the plant, a disease causing agent and the plant's environment. Three things are necessary for the disease to develop: 1) - a susceptible plant; 2) - a favorable environment; and 3) - a disease causing agent (pathogen). If any one of these three is missing, disease cannot develop.

Hang in there; we'll see how this matters in your garden.

The most common plant disease causing agents are fungi. There are a few, important plant diseases caused by bacteria. Viruses severely injure many plants. But fungi are the pathogens (disease causing agent) that cause most of the spots, rots, mildews, cankers, blights, and wilts.

Here's a good example for you tomato growers. About now, your otherwise lovely tomatoes are probably beginning to show yellowish spots on the lower leaves. If you look more closely, you may see concentric rings of dead tissue that forms a "bulls-eye" or target shaped dead spot. This is the early blight fungus, interacting, if you will, with your tomato plant in the nice warm, wet environment. As the fungus grows, (microscopically within the tomato leaf) it destroys the plant tissue, causing it to turn yellow, then brown. As the disease develops, it produces spores (seed-like reproductive structures) that are splashed by rain to more leaves and the tomatoes themselves. Eventually the plant is defoliated (blighted) and some fruit rotting occurs. The diseased leaves fall to the soil. There, they survive for a year or more. When a susceptible plant (tomato) is present and the environment is right (warm and wet) the disease cycle begins again. This description fits many fungal plant diseases.

What's a gardener to do? Lets' go back to the three things needed for disease to develop…susceptible plant, pathogen, environment. When possible, buy plants that are not susceptible to the diseases that plague your garden. Plant breeders have done wonders creating plants that are immune or at least resistant to certain diseases. Penn State tomato breeders are close to offering resistance to the early blight describe above. Next, do what you can to make the environment less favorable for disease. By staking tomatoes, the foliage dries more quickly, reducing leaf wetness which the fungus needs in order to grow. Finally you can attack the fungus directly. Fungicides are chemicals that kill the pathogen. Sulfur and copper are fungicides that have been used for centuries and are available for organic gardeners. High tech fungicides such as chlorothalonil are even more effective. Crop rotation is another attempt to avoid the pathogen, but it has limits in small gardeners. Still, it is worth the effort.

Each disease has its own story. By learning the specifics you can understand and manage plant diseases more successfully in your own garden. See the back page of this newsletter for Penn State resources that can help you manage plant diseases.

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Master Gardener Corner

Bring your children to the Grange Fair August 16-20, 2006 to Catch the Gardening Bug at the Master Gardener Booth in the 4-H Building (building No. 2). Kids can talk to the BugMobile, see live bugs, and take home a live Lady Beetle, (a good bug) to release in their yard! Kids can also make a gardening project to take home and grow! (Click here to see more.) Bring a canned food item to add to the 4-H "Spider". Canned goods will be donated to a Bucks County food pantry.

The Master Gardeners have completed planting the Gardener Selects Demonstration & Trial Garden in front of the Extension Office. The garden contains some tried and true and some brand new plants. The garden is open for viewing 24 hours a day every day and brochures are available in the Box to describe the plants. The garden peaks in late July. The plants are evaluated by Master Gardeners from across PA and results are tabulated by Penn State to select the Gardener Selects Plant of the Year.

Horticultural Happenings

Visit the Bowman's Hill Wildflower Preserve Website (www.bhwp.org) or call 215-862-2924 for information on their summer programs. Learn about native plants, take a mushroom walk or how to build your own container bog garden!

The Henry Schmieder Arboretum at Delaware Valley College is a local horticultural jewel in Doylestown, PA. Their many plant collections can be viewed on the website (http://www.devalcol.edu/Arboretum/). The Arboretum also sponsors a spring and fall series of lectures open to the public for a fee.

Woody Plant Conference - Swarthmore Conference - Friday, July 28 at Swarthmore Conference.
The registration cost is $99, $49 with a student ID, and includes morning refreshments and lunch. The brochure can be downloaded or printed from this website:
http://www.chanticleergarden.org/pdffiles/woody_06.pdf

Check out the local nature centers for children's activities this summer:

Penn State Problem Solving Resources

This month we focused on plant diseases. Penn State has many excellent references that can help you diagnose and treat plant diseases. If you have web access try this site: http://www.ppath.cas.psu.edu/EXTENSION/PLANT_DISEASE/index.html. It has more than 100 fact sheets on diseases of woody and herbaceous plants. Control recommendations are included. All of our vegetable fact sheets contain a disease control section. You can check out these fact sheets by going to http://pubs.cas.psu.edu/Publications.asp and typing in your favorite vegetable. You can read the fact sheets on line and/or print them, order them form PSU or call our office for a copy. Fruit growers can access Penn State's Small Scale Fruit Production guide on-line at http://ssfruit.cas.psu.edu/

Let' s not forget the bugs. Penn State entomology fact sheet web site has information on everything from ants to wire worms. Go to http://www.ento.psu.edu/extension/fact_sheets.html to see the complete listing.

If the web is not for you that's OK, just give us a call and we can provide fact sheets on most common garden pests. Someone is available to answer garden questions Monday through Thursday, 9 till noon.

Scott Guiser, Extension Educator/Horticulture
and
Sue Schneck, Master Gardener Coordinator

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Penn State | College of Agricultural Sciences | Cooperative Extension & Outreach

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This page last updated Wednesday, July 1, 2009

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