It’s late November and garden ghosts from last summer’s bounty may still linger in standing dead stalks of flowers long gone. Unfortunately, some of this left-over plant material may be infected with fungal or bacterial diseases. Roses may keep their foliage until well into winter, even if it’s infected with black spot or powdery mildew. Pear leaves infested with blister mites will come back to haunt you if you don’t rake them up. And all those tomato vines that succumbed to late blight last summer will cause you problems next year unless you get rid of them.
Getting infected plant material out of your garden is called sanitizing and it’s one of the basic tools for managing plant disease or infestations by insects or mites. Sanitizing disrupts the life cycle of these organisms. The bacteria and fungi inside dead infected plant material are still alive and waiting for the opportunity to reproduce. Insects, mites, and eggs are also not dead but merely dormant, waiting for winter to be over. The bacteria, fungi, insects, and mites will all begin to reproduce and create a new generation to infect your garden again next spring as soon as the weather permits. When you seek and destroy these critters while they are dormant you have drastically decreased the numbers that will survive to give you headaches next year. If you can gather all the infected and/or infested material up and get it out of your garden you have reduced the inoculum load significantly. The result is less disease and fewer pests. Sanitizing won’t eradicate these problems but it will give you a fighting chance to manage your garden more effectively.
One important technique of sanitizing is simply plucking infected leaves or pruning infected stems off your plants. Pull or prune them away and put them in a bag, then dispose of them in the trash. NOT THE COMPOST.
For leaves, look for ones with abnormal spots or blotches on them. The discolored areas may be virtually any color from yellow, brown, black, orange, red, or purple to gray or white. Leaves with discolored spots or blotches are almost certainly infected with fungal or bacterial diseases. Also look for leaves that are rolled into a tube or that have strange growths on them because they usually harbor insects or mites. Leaves that have fallen to the ground should be raked up and hauled away if they were diseased or infested.
Black spot of roses, for example, is a fungus that lives inside dead rose leaves and in the soil under rose bushes. The fungus will produce spores that will re-infect your rose bushes next spring. If you rake up all the dead rose leaves and pluck off all the infected ones from your roses you will eliminate a huge source of spores and reduce the incidence of infection next year. It also helps to mulch your roses to avoid splash-up of spores from the soil to the bottom leaves of your roses.
For stems, look for those that are spotted and discolored. Like leaves, these should be pruned away and discarded. Check for sunken, discolored patches (cankers) on stems and prune them away. Stems that have holes in them are infested with borers, insects that live inside the stem. Prune these away before the insects inside have a chance to mature, mate, and lay eggs.
Do not compost any infected or infested material. Some disease organisms, such as late blight of tomatoes and potatoes, can live in the soil so plant material infected with late blight should never be composted. If your compost becomes infected you will spread disease throughout your garden as you use your compost. (Yikes!)
Gather up all the infected plant material and dispose of it in the trash. If you live in an area where you are allowed to burn it, burning is also a very effective way to kill these organisms. In any event, get them out of your garden and out of your life. You’ll be glad you did.