Tuesday, October 21, 2008

Cleaning up garden will reduce diseases next season

A big end-of-season chore is garden cleanup. This practice reduces the potential for plant diseases the next season and can reduce some insect problems.

Although this was not a banner year for many diseases because of the dry weather, several diseases might have been a problem in gardens where plants were watered from above.

Splashing water, wet plant parts and higher humidity around plants can contribute to disease development. Diseases we heard about this season included powdery mildew, black spot on roses, septoria leaf blight on rudbeckias, bacterial blight on geraniums, botrytis blight on peonies, canker and dieback on vincas, crab apple scabs, and septoria leaf spot on tomatoes.

Disease management includes cleaning up infected leaves, flower heads and other plant parts, and cutting infected stems back close to the ground. The debris can be put in yard waste for collection or removed from the garden.

Other management strategies include turning plant debris into the soil in annual gardens or adding it to a hot compost pile where it will degrade quickly. Plant pathogens are less likely to survive winter if the organic debris decomposes quickly.

Infected plant debris can be hot or "fast" composted by raising the compost pile's temperature so the debris decomposes quickly, thus killing plant pathogens. Shredding or chopping plant debris before it's added to a pile allows more surface area for the decomposing organisms to work on, which speeds up the process.

The minimum pile size should be 1 cubic yard, and the internal pile temperature must reach and sustain 120 to 160 degrees for two to three weeks to kill pathogens.

Making hot compost involves a good mix of green and brown debris initially, turning the pile frequently, keeping it at 50 percent to 60 percent moisture (moist but not wet) and making sure enough nitrogen is in the pile to fuel the decomposition process for the microbes. This can be added in the form of a synthetic fertilizer or as coffee grounds, grass clippings and other green debris.

Piling debris and letting it sit unattended for several months won't kill disease organisms, and such a compost pile might actually become a source of infecting organisms for the next season.
If you are unsure whether your compost pile reaches these temperature and moisture levels, you might want to get ride of diseased plants as part of yard-waste collection.

Weed management is important as well because some weeds are hosts for the fungi that infect cultivated plants.

Remove suspicious weeds and either hot-compost them, especially if they bear seeds, or send them off in yard-waste collection.

One last thing is to cut down the stems of coneflowers, daisies, sunflowers and related plants to remove insects and mites that use the old stalks as wintering sites.

The four-lined plant bug, a common pest in perennial gardens, spends the winter in the egg stage; eggs were inserted into stems earlier in the season. Stem-boring beetles also spend the winter in stems. Stems can be chipped or shredded to add to the compost pile.

But if you aren't a hot composter, chances are these pests will survive to infest the garden next season. If that's the case, put the stems out for yard-waste collection.

Master gardener program
When I worked with the Ohio State University Extension, one of the most popular programs was the master gardener volunteers. The program offers 50 hours of training in horticultural topics by experts in exchange for 50 volunteer hours. The OSU Extension-Franklin County will offer the program this winter. Informational sessions to introduce volunteers to the program and its application and selection process will take place from 7 to 9 p.m. Tuesday and Thursday at the Nationwide/Ohio Farm Bureau 4-H Center, 2201 Fred Taylor Dr. Attendance at one of the sessions is mandatory. To register, call 614-247-6046 or send an e-mail to skurdal.1 @osu.edu. To learn more about the program, visit franklin.osu.edu/horticulture.

Jane C. Martin is a horticulturist. Gardeners may find answers to their questions at plantfacts.osu.edu/faq.

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