Buckeye Yard and Garden onLine

The season for sanitation practices in our gardens and landscapes is already upon us - but it is never too late to start.  Eliminating a plant pathogen or pest is a time-honored cultural practice that pays big dividends, from removing black-spotted rose leaves and canes to pruning out infestations of oystershell scale.  There is a storied history to this aspect of natural control.  We have an advantage today with our understanding of the importance of  pest and pathogen life cycles, with our knowledge that tiny, sometimes invisible to the naked eye entities may cause plant problems, with our understanding of the infection process.

Think of how much more difficult it was when these ideas emerged, when for example late blight of potato was ravaging the fields of Ireland during the Irish potato famine in the 1840s.  There was not even a germ theory of disease.  Once people understood that the Phytophthora infestans fungus was involved and worked out the life cycle of the fungus and the disease cycle for late blight, they realized that leaving cull piles of diseased potatoes in the fields till the next season was a clearly bad idea.  It helped reintroduce the pathogen to the next potato crop.  A simple revolution - clean it up.

So too it goes with ornamental disease control today.  It is very important to understand both the life cycle of a disease-causing fungus, and the resulting disease cycle.  For example, Diplocarpon rosae, the fungus that causes rose black spot, overwinters in black-spotted leaves from the previous season's infestations and on infected rose canes.  Removing infected plant tissue from the planting will limit re-infections the next season.  If the disease does develop from fungal spores blown in from nearby plantings, remove newly infected black-spotted leaves during the season.

This sanitation protocol is a critical approach to managing black spot on susceptible roses, even if fungicide programs are also used.  In wet years total or even acceptable control of this disease even with fungicides is often not enough.  There are many other diseases where this type of sanitation is critical, from cleaning up leaves and stems of hollyhock with hollyhock rust to not reusing pots with soil contaminated with soil borne pathogens.

Sanitation is also one of the sometimes unrecognized results of other common horticultural practices.  When possible, deadheading of geraniums is often recommended in order to make the planting more attractive and to encourage better bloom production.  An important additional benefit often accrues when Botrytis gray mold is part of the package. The Botrytis fungus thrives on senescing, declining plant tissue.  Think of a healthy florist's geranium (Pelargonium x hortorum) without any disease problems.  No matter how healthy, it will develop senescing tissue during the season, namely on blossoms as they age. These dying blossoms are a real treat for the Botrytis fungus which colonizes the petals, which fall on healthy leaf tissue below, where the fungus proliferates and, especially on the now moistened and shaded leaf tissue, the result is Botrytis infections of the leaves.  Unless you deadhead.