ASA Paper

November/December 2005

Garden Cleanup

Garden cleanup of “sanitation” at the end of the growing season is a way to reduce some of the plant disease potential for the following season – especially after a season in which diseases were so prevalent. The list of plant diseases is long, but those that can perhaps be reduced the following season by good fall clean up include rose black spot, hollyhock rust, Septoria leaf blight, bacterial blight, botrytis blight, bacterial leaf spot, canker and dieback, crabapple scab, and Septoria leaf spot, just to mention a few.

Disease management can include debris clean up, such as raking up infected leaves, flower heads, and other plant parts, and cutting infected stems back close to the ground. The debris can then be put in yard waste for collection or otherwise removed from the garden area. It can also include turning plant debris into the soil or adding it to a compost pile where it will degrade quickly. Plant pathogens are less likely to survive over winter if organic debris in the garden decomposes quickly.

Weed management can be important as well. Some weeds are hosts for the fungi that infect cultivated plants. For example, round-leaf mallow, a common lawn weed, also serves as a host to the hollyhock rust fungus and can serve as a source of spores (inoculum) the following season. Horse nettle, jimsonweed, and nightshade also serve as a host for the same pathogen that causes Septoria leaf spot on tomato. In addition, tomatoes are rotated out of a garden area for four years to avoid this disease.

Infected plant debris can also be fast composted, which involves raising the pile’s temperature so that debris decomposes quickly, killing the plant pathogens. Shredding or chopping plant debris allows more surface area for the decomposing organisms to work on, and will speed up the process. The internal pile temperature must reach and sustain 120 – 160 F for two to three weeks. Making fast compost involves a good mix of green and brown debris initially, turning the pile frequently, keeping it moist (50-60% moisture - moist, but not wet) and making sure enough nitrogen is in the pile to fuel the decomposition process among the microbes. Piling up debris and letting it sit unattended for several months will not kill plant disease organisms, and the compost pile may then actually become a source of inoculum for the following season.