Downy Mildew on Hybridized Bushes

I have over 200 seed parents loaded with hips. I just discovered that after 10 days of rain I now have a serious case of downy mildew. Some large hips have already fallen others have yellow peduncles and purplish sooty looking blotches on the hips, canes, and foliage. Can anyone help me? I spayed Daconil 2787 and Rubigan on July 31st and again on August 7th because of all the rain. I didn’t notice any problems at that time. I was unable to be in the garden this past weekend and this is what I found today. What can I spray for downy that won’t kill the hips? And at what frequency and dilution should I spray it? Any help would be greatly appreciated. What was my best crop is in immediate danger of being totally wiped out.

Hi John:

I have used Subdue and Aliette along with Fore with good control, but don’t know what it would do to hips. Downy is devastating and hits hard almost before you know it. I don’t have info for dilutions, but I think that I got a web site from the forum that has all of the info (see below).

Good luck!



John, maybe you can call the companies that manufacture these products and see if they have the answers on the effect on hips? Other than that, what do the “big boys” use? Maybe Jackson and Perkins will share? Just a thought.

Thanks Jim and Judy, this hit so quick I was literally in shock. I read in an agricultural publication where captan is an effective control in grapes. I think I’ll spray that in the morning and then try to make some calls tomorrow. Really hurts considering they were doing great just a week ago.

Several things about pesticides:

Most of the older fungicides are surface preventatives. I.e. they will not stop or cure an existing infection (they would stop its spread). Some of the newer fungicides have a more systemic and curative action, but the downside of them is that they usually only target certain type(s) of fungus, rather than spectrum wide effect.

Also note that crop fungicides and ornamental fungicides may have the same active ingredient, but will often be marketed under different names.

Chris Mauchline


After losing about 10% of the crop in a period of three days, I sprayed with 3 Tablespoons of Captan per gallon. I follow that spray with another 3 days later. I haven’t sprayed again and the Hip drop has stopped. I not sure what I had but it does seem to have been stopped.

Do you have access to the scientific pub “Phytopathology”? An article in it last year discussed the Downey Mildew in the growing fields of Wasco and the problems with eliminating it.

Title: Control of downy mildews on miniature rose and snapdragon.

Authors: Daughtrey, M.; Tobiasz, M.

Authors Address: LIHREC, Dept. of Plant Pathology, Cornell University, Riverhead, NY, 11901, USA.

Published in: Phytopathology, volumn 91, 6 Supplement (2001). S194.

Abstract: " Two concurrent greenhouse experiments were conducted to evaluate new fungicides for downy mildew control on rose cultivars ‘Canyon Cupido’ and ‘Favorite Cupido’ and snapdragon ‘Rocket Mix’. Treatments (oz/100 gal; interval) were: trifloxystrobin (Compass 50WG 1.0; 7d and 2.0; 14d), trifloxystrobin+fludioxonil (Compass 1.0+Medallion 50W 1.0; 14d), azoxystrobin (Heritage 50WP 2.0; 14d), dimethomorph+mancozeb (Stature MZ 69WP 28.0; 7d) and copper hydroxide+mancozeb (Junction 61.1DF 56.0; 7d). Sprays were applied from 21 Mar to 19 Apr 2000. There were 5 replications of 3 plants of each cultivar in randomized complete blocks on plastic-tented greenhouse benches supplied with humidifiers. After the first spray, sporangia collected from infected commercial crops were sprayed onto their respective hosts. Symptoms occurred on all untreated plants. On roses, defoliation was best reduced by Stature MZ. All but the Heritage and the 1.0 oz; 7d Compass treatment reduced leaflet symptom incidence in ‘Favorite Cupido’. On snapdragons, all treatments reduced disease incidence. Snapdragons treated with Heritage or Stature MZ did not develop symptoms."

The following gives the abstracts of 2 papers by the same principle author.

(Fosetyl-Al is the active ingredient in Aliette.)

Title: Evaluation of fungicides against downy mildew (Peronospora sparsa) on rose.

Author: O’Neill, T M.

Author affiliation: ADAS Horticulture, Cambridge, UK.

Published in: Tests of Agrochemicals and Cultivars, volumn 15, pages 36-37, (1994).

Abstract: “Of several treatments tested, cymoxanil-mancozeb-oxadixyl mixt. (0.08+1.4+0.2 g/L) gave the best results. Fosetyl-Al gave good control when applied as a high-vol. spray, at 10-14 day intervals, but showed no control when applied as a drench.”

Title: The effect of fungicides, irrigation and plant density on the development of Peronospora sparsa, the cause of downy mildew in rose and blackberry.

Authors: O’Neill, T. M.; Pye, D.; Locke, T.

Authors affiliation: ADAS Arthur Rickwood, Cambridge, UK.

Published in: Annals of Applied Biology, volumn 140, pages 207-214, (2002).

Abstract: “Downy mildew of rose (Rosa spp.) and blackberry (Rubus fructicosus), caused by Peronospora sparsa, can cause significant losses in prodn. In a series of expts., fungicides with different modes of action to the commonly used phenylamide-based products were examd. for efficacy on both crops. Cymoxanil + mancozeb + oxadixyl and fluazinam gave good downy mildew control on both rose and blackberry. On outdoor, container-grown rose, high vol. sprays of fosetyl-aluminum were also effective, but on young micropropagated blackberry plants, application as a drench treatment was better than as a spray. Good control was also achieved on blackberry with chlorothalonil and with metalaxyl in formulation with either thiram or mancozeb. There was no evidence of loss of control with phenylamide fungicides due to resistance. Irrigation regimes were also examd. on blackberry and sub-irrigation of plants in propagation on a sand bed led to significantly lower disease levels than those found where plants had been irrigated by overhead sprinklers. Reducing the d. of container-grown rose plants had a measurable effect on the progress of downy mildew, though this was small and temporary when compared with the effect of fungicide treatment. Fungicide programs which gave season-long control of rose downy mildew resulted in significantly improved extension growth.”

Title: Detection and management of downy mildew in rose rootstock.

Authors: Aegerter, B. J.; Nunez, J. J.; Davis, R. M.

Authors Address: Department of Plant Pathology, University of California, Davis, CA, 95616, USA, USADepartment of Plant Pathology, University of California, Davis, CA, 95616, USA.

Published in: Plant Disease, volumn 86, pages 1363-1368, (2002).

Abstract: "A technique utilizing the polymerase chain reaction (PCR) was developed to investigate the occurrence and location of Peronospora sparsa in dormant, woody rose tissues. PCR primers were designed to amplify the internal transcribed spacer region of the ribosomal DNA of the pathogen. Inhibition of the reaction by plant compounds was minimized by optimizing the reagents used in the extraction of DNA from roses and in the amplification reaction. The PCR assay was capable of detecting as little as 2 pg of DNA from P. sparsa against a background of 4 ng of DNA from rose cane cortex. With this method, DNA of P. sparsa was detected in the cortex of stem and root tissues of symptomatic plants. Pathogen DNA also was detected in the cortex of crown tissues of asymptomatic mother plants used as a source of propagation materials. Epifluorescent and differential interference contrast microscopy were used to confirm the presence of abundant hyphae and oospores within the stem cortex of infected canes. Preplant treatments of dormant rootstock cuttings in fungicides or hot water were evaluated during natural outbreaks of the disease in commercial rose nurseries. In three trials conducted over 2 years, a 10-min preplant dip in the systemic fungicides metalaxyl or mefenoxam at rates of 100 to 10,000 mg a.i./liter reduced the area under the disease progress curve by 63 to 76% relative to nontreated plots. The evidence from PCR assays, microscopy, and fungicide trials all support the occurrence of perennating infections of P. sparsa within rose. "

In the following Peronospora sparsa (or just sparsa) is downy mildew.

Title: Chitosan in the control of rose diseases: 6-year-trials.

Author: Wojdyla, Adam T.

Author Address: The Research Institute of Pomology and Floriculture, Pomologiczna 18, 96-100, Skierniewice, Poland.

Published in: Bulletin of the Polish Academy of Sciences Biological Sciences, volumn 49, pages 243-252, (2001).

Abstract: " Effect of microcrystalline chitosan at concentrations from 0.025% to 0.2% on the spread of Sphaerotheca pannosa var. rosae, Peronospora sparsa and Botrytis cinerea on roses was investigated. After 2 and 4 spraying of diseased rose bushes the degree of shrub infection by S. pannosa var. rosae was evaluated. For P. sparsa the experiment was conducted on the plants grown under polytunnel and infection level was evaluated after 4 sprayings with chitosan. Activity of chitosan against B. cinerea was tested in the laboratory on the flower petals, which were scraped and inoculated with the pathogen. After 3, 5, and 7-day-incubation diameter of the necrosis was measured. Triforine 0.03% (for S. pannosa var. rosae), oxadixyl 0.016% (for P. sparsa), and vinclozolin 0.05% (for B. cinerea) were used as the standard fungicides. Depending on the observation date and concentration used, chitosan reduced development of powdery mildew from 43.5% to 85.4% and its effectiveness was similar to triforine. When applied against P. sparsa its effectiveness ranged from 50% to 73%. Increased of the compounds concentrations resulted in its lower antifungal activity. At concentrations of 0.0625% and 0.125% chitosan activity was comparable with oxadixyl. As a preventive treatment, chitosan at the concentration of 0.025%, similarly to oxadixyl, reduced disease occurrence by 72%. When used against B. cinerea, chitosan at concentrations of 0.1% and 0.2% reduced necrosis diameter respectively by 5% and 35% only. In concentration of 0.05% it had even stimulatory effect on the fungus growth."