Rose diseases can be heartbreaking. After months of nurturing care, you've grown beautiful plants with gorgeous, velvety blossoms, bursting with color and fragrance. Then along comes one of these nasties, and you find your gorgeous plants stricken with an ugly, creeping disease that renders your beautiful plants wilted or buds debilitated. Depending on what rose diseases a plant contracts, they can be quite devastating to the health of your plant and even fatal. You'll want to keep an eye out in order to catch any of these ailments early one, when treatment is simple.
Besides rose diseases, environmental factors can effect your plants too, and they should be watched for an remedied when found. To keep most rose diseases under control, a commercial fungicide will take care of it. In other cases, proper pruning techniques and the maintenance of clean garden implements goes a long way in preventing such conditions from occurring in the first place.
One thing you can do is plant disease resistant roses to help curtail some of these issues. In most cases though, some preventative maintenance is all you need.
In 20+ years of rose gardening, I have found that only two sprays are needed to keep your plants healthy. The first is sulpher. This will work for most of the diseases. But not for blackspot: for this you need Capstan. A regular spraying program with both of these, and a little care to burn infected plant material (do not compost diseased material!) will go a long way to keeping your roses healthy.
If you suspect a problem with your plants, take a look at the table below to see if any of these rose diseases could be your problem.
If you've ever needed a good reason to water in the morning, Black Spot is it. Spread by splashing water, this fungus disease causes round black spots on leaves; leaves turn yellow and eventually fall off. The spots are generally circular with an irregular edge and occasionally a yellow halo. Continual defolation will cause dieback or death of the plant. Use a fungicide to handle.
Cankers enters a plant through wounds. It causes canes to turn brown, purple or white. Cankers may circle the stem, but begin as a small yellow/red spot on the bark and start getting larger. If it surrounds the entire stem, the stem will die, but if it infects only part of the stem, the growth above the canker will continue. Handle by pruning to below the canker in early spring, then apply a spray of dormant oil.
Rose Rust causes orange spots to appear on the undersides of leaves in wet and mild weather. They enlarge into thick, powdery masses of orange spots. Yellow blotches appear on leaf surfaces. If it goes too far, it can defoliate your plant. The fungus is spread by wind.
This is actually a bacterial disease underground.
An underground problem; a bacterial disease that causes rough, round growth on the roots or bud union. Sorry, but remove the plant.
While leaves are not as effected by Grey Mould the flowers and buds. Buds will rot on their stems and move down the stems. It causes pink rings.
If you find chimney soot on your leaves, it is probably sooty mould. It usually caused by sap sucking insects like scales and aphids. It covers the plants leaves and does not look good.
Another leaf-yellowing factor is Rose Mosaic. The yellow patches can be all over blotches or patterns of lines in waves. This can occur on a few or many leaves. It is caused by a virus.
Crown Gall Rot
If your plant is wounded, it could contract Crown Gall Rot. These are large lumps at the base of the stem or on roots and galls are softer than the surrounding area. If your plant is young, this disease may prevent it from blooming. Your plant will also wilt easily and won't grow the way it should.
This fungus occurs where leaves are water soaked. At first it may not be noticeable, but they eventually turn black with a distinct defined edge. As the spot expands, the center turns grey and may fall out, making holes in the leaves. Defoliation may occur.
If you live in a place where days are warm and nights are cool, watch out for Mildew. If you have it, you will see a gray to white furry powder-like coating covering new leaves, stems and flower buds. Your leaves may curl, or look crumpled and distorted. You'll need insecticide to handle Powdery Mildew.
This Mildew is spread by wind. It causes purple-red to dark-brown spots on leaves that often angular in appearance. Purple marks can appear on split stems, petioles and flower stalks, and the purple marks can turn up on other parts of your plant. New growth will be deformed. Use insecticide.
Frost is pretty much a no-brainer. It will kill new growth and cause stems and leaves to wilt, then turn black and fall off. Make sure to time your pruning so growth occurs after threat of frost is over.
Got limp and light-brown leaves? Try testing your soil for salinity. If it's greater than 1200 ppm, you will start having trouble.
Watch it with the herbicide. Too much over too long a period can cause your leaves to appear yellow and elongated. You can get twisted leaves and distorted buds. Plants may even die as a result. Soil borne herbicide will contact a plant's root system and can take several years to clear up.
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