I have a green fungus or algae in my rose bed soil. I scraped off the top layer of crust and then put Pennington ultragreen plant food down. 15-10-10. Is this green stuff harmful? What should I do to control it? I've been fighting black spot on my hybrid tea roses. The soil is very moist in this bed due to no gutters. Help! See Photo
Garden Soil in Rose Bed.
It looks like the conditions are just right for the algae to grow there. The only thing you can really do is to periodically keep the soils lightly tilled to help disrupt the appearance of it. Even scraping it off will not help as the spores just spread. There are some algae killing products on the market that are safe around plants that could be used as well but are only somewhat effective (algae-sides). Lightly working up the soils and adding some garden soils to make more of a drainage grade in the rose beds will help too. Use some bagged or other good garden soils added to the rose beds to improve drainage out of them. The standing water in flat areas helps the algae to take hold.
Fighting black spot can be a serious battle, add high humidity to it and you have a serious war on your hands. The only fungicide I have found to stop black spot in its tracks is called Mancozeb. It can be purchased at Amazon.com. Mix it up and apray it on the rosebushes every 7 to 10 days if black spot is present. Do this for four to five sprayings. It will leave a yellowish powdery residue on the foliage, that is part of how it works. Keep in mind that the black spot marks will not go away. However the new foliage coming on should be free from the black spot if it has been killed.