Foliar Damage on Livin’ Easy Rose
Most rose varieties have some susceptibility to leaf damage from fungal pathogens; however, the damage does not necessarily kill the rose.
The Livin’ Easy old garden rose produces blooms most of the year in my gardens (except during the time period of frequent temperature drops below 32—usually from late November until early or mid-February).
Unfortunately, this rose is also somewhat susceptible to “downy mildew” infections — a plant disease caused by the fungus — that cause the plant to drop those infected leaves.
Disease Symptoms are prominent during rainy, cool periods of time, and symptoms generally disappear with low humidity. If humidity remains high or it continues to rain, the disease can continue to spread to infect leaves lower on the plant (rain will splash spores (fungal seeds) to lower leaves and the infection cycle renews.
With the recently cooler temperatures (50’s to low 90’s) and abundance of rain (about 5 1/2 inches over the last 3 weeks), I noticed that the irregular shaped, purplish to brownish regions appeared on the top side of some leaves (upper right side of picture to right).
Closer inspection of symptomatic leaves revealed the brown irregular regions on top of the leaf with the fungal growth evident on the bottom of the leaf (lower leaf shown in picture to right).
I generally do not treat this disease because we don’t have enough moisture for it to survive all year around and the Livin’ Easy rose has yet to defoliate (drop leaves) to the point that a fungicide needs to be applied. During rainy periods, remove fallen leaves to avoid reinfection by splashing rain (it is impossible to remove everything, but reducing the starting material for the fungus will help).
Interestingly, Downy Mildew is so prominent on grapes that the first “fungicide” —Bordeaux mixture — was developed in order to combat it. In 1882, Downy Mildew was so prominent in Europe that vineyards were threatened with complete destruction of the grapes. At that time, Millardet (a scientist) noticed that grape vines sprayed with a mixture of copper sulfate and lime did not have damaged leaves—Plant Pathology was borne!