Dr. Eldon W. Lyle

Here is some down to earth advice from Dr. Eldon W. Lyle, Past President of the ARS and Plant Pathologist at the Texas Rose Research Foundation, which was first published in 1979 and just as good today. "It is a waste of time to pick off black-spotted leaves except to make the plants more tidy.Unseen infection can quickly take over and supply enough spores of the fungus to create a fast spread of the disease.While the infected leaves remain attached to the rose stems or canes, they put substance and food into the bushes." "Defoliation, whether from blackspot or from hand picking of leaves, will lessen the vitality of the bushes in proportion to the amount of leaves removed.If only 10 percent of the leaves are shed, there would not be much harm to the bushes.Anything over 50 percent defoliation is very weakening.
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Dr. Lyle continued, "The main thing is to get a good spray program once a week (every seven days) and use materials such as Benlate and Manzate or Benlate and Phaltan.The spray should contain one tablespoon of Benlate per two gallons of water.Add either Manzate or Phaltan to this at the same rate.Use enough spray to reach the dripping stage from the leaves." "Also, next season, start such a spray program the same week as pruning back the bushes in the spring.The spores coming from cane infections where the spores overwinter may be killed before spreading to tender new leaves as they start to form." Dr. Lyle also reported very favorably on Funginex (one tablespoon per gallon) or Triforine (an 18 percent formulation used at one teaspoon per gallon) as very effective in control of mildew and blackspot when used weekly. Fallen leaves.Dr. Lyle concluded, "Fallen leaves on the ground or top of the mulch are not a source of carryover of the disease, even though this is a frequent belief.As soon as the diseased leaves fall and start to rot, the blackspot disease also decays.There is no need for removing the mulch that remains from season to season.Just add more to it as needed." return to top

The Foundation hired as its director Dr. Eldon W. Lyle, a plant pathologist from Cornell University and one of the nation's foremost specialists in rose research.The East Texas rose growers who sponsored the Foundation had a goal of producing the highest quality roses in the industry.Dr. Lyle proceeded to conduct intensive research on rose diseases and utilized local rose fields to test treatments for black spot fungus.As a result, his discoveries benefited the rose industry and rosarians nationwide.

According to Dr. Eldon W. Lyle, longtime plant pathologist with the Texas Rose Research Foundation in Tyler, it's a waste of time to pick off infected leaflets, no matter how gruesome they may look.The chief source of black spot spores, he found, is in lesions on the canes.And leaflets that are clinging to the plant are still manufacturing food for the roses.

Dr. Lyle also insists that fallen leaflets on the ground are not a carry-over source for the disease, even though many believe them to be."As soon as the diseased leaflets fall and start to rot," he says, "the black spot fungus also decays."

So, remove infected leaflets only to tidy up and if it makes you feel better.But, when you spray for black spot, be sure to wet all the woody parts of your plants and not only the foliage.

Old rule: Some types of roses do quite well in the shade.

Of course, "quite well" is relative, and some types of roses do require less direct sunlight than do others.