When a fungicide is needed

Fungal leaf and root-rot diseases are usually most active in humid weather and in wet soil. Follow these guidelines to learn how to treat your plants and keep them healthy.

When a fungicide is needed

1. The basics

Fungal diseases can often be avoided by siting plants in an area with good air circulation, pruning plants to allow sun and air to reach inner branches, planting in soil that is naturally well drained, amending soil with compost to improve drainage or building shallow berms or raised beds so that plants can be set above the surrounding soil.

But, often in late summer when days are humid and nights are cool, spores of disfiguring leaf diseases like powdery and sooty mildew can erupt. Unfortunately, there is no one-size-fits-all fungicide to control all fungal plant diseases. Instead, you must check product labels to see if the affected plant is listed. You can do more harm than good to a plant by treating it with a fungicide that it cannot tolerate, or by mixing the concentrate at a stronger rate than is recommended on the label.

Also, be very careful when using fungicides near water, because many of them are toxic to fish and other aquatic animals. Warnings of any environmental dangers will be listed on all product labels.

For fungicides to work well, you must get excellent coverage with the spray. Many fungi colonize leaf undersides, so spraying from the bottom up as well as from the top down is always wise. Avoid spraying just before rain is expected, as the product may be washed off before it has a chance to work.

2. Gentle interventions

When you first notice a pest problem, simply removing and disposing of the affected plant part is sound practice, especially when the problem is a disease, most of which are caused by microscopic fungi. Yet this is impractical when the problem is more widespread, as when spider mites have colonized the leaf undersides of a large shrub.

Instead, spraying plants thoroughly and often with a strong spray of water from a hose will dislodge and disable these and other fragile, sucking insects like aphids.

3. The fall clean-up

When the first blasts of winter cold cause leaves to flutter down and perennials to die back and become dormant, you have an excellent opportunity to interrupt the life cycles of many pests and diseases by cleaning up your garden. Many fungal plant diseases overwinter in old fallen leaves and stems, and some insects find safe harbour in plant debris as well.

  • Before winter makes working outdoors uncomfortable, gather dead plant material that lies on the ground and pull up withered annuals, roots and all.
  • Gloved hands and a stiff rake will be your primary tools, though you may also need pruning shears to snip off the stems of perennials flush with the soil.
  • Before traces of their presence disappear, mark the locations of plants you intend to divide or move in spring.
  • After the first hard freeze, apply a thick, fluffy mulch of straw or evergreen boughs to insulate marginally hardy plants against damage from freezing and thawing. Then, when the new season begins, you will be ready to sail into it quickly.
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