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A.
Good news!
You are in better shape than you think. Your mulch is hard at work doing all the wonderful things that mulch does: moderating soil temperatures,
conserving moisture, reducing erosion, discouraging weeds, reducing soil compaction, and minimizing certain soil-born diseases; AND it is conditioning and enriching the
soil as it decays.
That is where the white fungus comes in. Unlike black spot or powdery mildew which are parasitic fungi feeding on your bushes, your white fungus is a saprophyte.
It works together with assorted other microorganisms to break down organic matter (your mulch) into vital elements your plants can absorb.
There are many types of bacteria and fungi involved in this process and even combination organisms
- part bacteria, part fungi -called actinomycetes which are the grey-ish, cobwebby strands that you may have spotted.
Given time, this army of organisms will break down your mulch into healthy, dark, crumbly soil.
However, there may be two short-term problems. In wet weather, the fungus can appear on top of the mulch, looking rather unsightly.
Simply turn it under. It won't harm your plants or the decomposition process.
Of more concern is the fact that rapid decay may draw nitrogen from your soil, resulting in temporary nitrogen deficiency (weak growth) for your plants.
Assuming you followed the rose bed basics: nearly full sun, good drainage, incorporation of organic material into the soil, and proper planting depth, this nitrogen deficiency may be your problem.
First, contact your county extension agent for instructions on submitting a soil sample.
It always pays to know what you're dealing with. For example, nitrogen is easily depleted from your soil, but phosphorus, which is not very mobile, can build up to unacceptable levels if applied too zealously.
By following the recommendations from the soil analysis, you can tailor your monthly feedings during the growing season to fit the specific needs of your plants.
If supplemental nitrogen in the form of blood meal or cottonseed meal is required to counteract the leaching effects of the decaying mulch, you'll
know how much to add with confidence.
Then you can go back to the important business of admiring your roses, and standing guard against those pesky parasitic
fungi.