Document Type : Research Article
Iranian research institute of plant protection
Golestan Agricultural and Natural Resources Research Center
Hamadan agricultural and natural resources research and education center
Downy mildew disease caused by Plasmopara viticola (Berk. & Curt.) Berl. & Toni is one of the most important diseases of vine. Especially in wet areas, it causes qualitative and quantitative damage to the crop. Although all green parts of the grapevine are susceptible, the first symptoms of downy mildew of grapes are usually seen on the leaves as soon as 5 to 7 days after infection. Foliar symptoms appear as yellow circular spots with an oily appearance (oilspots). Young oilspots on young leaves are surrounded by a brownish-yellow halo. This halo fades as the oilspot matures. The spots are yellow in white grape varieties and red in some red grape varieties (e.g., Ruby Red). Under favorable weather conditions, large numbers of oilspots may develop and coalesce to cover most of the leaf surface. After suitably warm, humid nights, a white downy fungal growth (sporangia) will appear on the underside of the leaves and other infected plant parts. The disease gets its name "downy mildew" from the presence of this downy growth. In late summer and early fall, the diseased leaves take on a tapestry-like appearance when the growth of the pathogen is restricted by the veinlets. Confirmation of active downy mildew is made by the "bag test." To do this test, seal suspect diseased leaves and/or fruit bunches in a moistened (not wet) plastic bag and incubate in a warm (13-28ºC), dark place overnight. Look for fresh, white downy sporulation beneath suspect oilspots or on shoots or fruit bunches. Note that mature berries, although they may be symptomatic and harbor the pathogen, may not support sporulation even when provided with ideal conditions. Infected parts of young fruit bunches turn brown, wither, and die rapidly. If infections occur on the young bunch stalk, the entire inflorescence may die. Developing young berries will either die or, if between 3 and 5 mm in diameter, become discolored. Berries become resistant to infection within 2-3 week after bloom, although all parts of the rachis may remain susceptible 2 months after bloom. The pathogen survives the winter period as oospores embedded in dead leaves and other host tissue on the vineyard floor. Oospores may be released from the decaying plant material on the soil surface. Oospores typically produce sporangia. These sporangia, in turn, produce zoospores. Sporangia and zoospores are splashed by rain or carried by wind to the lower leaves and tissues of the grapevines. The conditions necessary for oospore germination are wet soils with temperatures above 10ºC. Sporangia for secondary infections are produced on sporangiophores that emerge through stomata of infected leaves and other grapevine tissues. Sexual reproduction occurs towards the end of the season. The resulting oospores are thick-walled and serve as survival spores.
Materials and Methods
The experiment was conducted in grape orchards located in Hamadan, Bojnourd, and Faruj, which had a history of Downey mildew. Different cultivars of grapes were selected for the experiment. The experimental design used was a randomized complete block design (RCBD) with 8 treatments and 4 replications.The control treatments included plots without any spraying and plots sprayed with water. The remaining treatments involved the application of specific treatments at three different stages. The first spraying was done before flowering, the second spraying after fall petals, and the third spraying 10 days after the second spray. Ten days after the final spraying, samples were collected from the grape leaves, and the percentage of disease incidence and disease severity were calculated. The data obtained for disease incidence and severity were analyzed using statistical software, such as SAS, and the means of these traits were compared using Duncan's multiple range test at a significance level of one percent. This test helps determine significant differences between the treatment means.
Results and Discussion
The analysis of variance conducted on the data obtained from the evaluation of treated grape leaves revealed a statistically significant effect of the treatments on reducing the percentage of disease severity and disease incidence. Among the treatments, Profiler® at concentrations of 3 ml L-1, 2.5 ml L-1, and 1 ml L-1, Mishocap® at 3 ml L-1, and Captan at 3 ml L-1 demonstrated high efficiency in controlling grape Downey mildew disease. The new fungicide Profiler® at a concentration of 3 ml L-1 exhibited an efficacy of 94% in Hamadan, 67% in Bojnourd, and 47% in Faruj. Profiler® at a concentration of 2.5 ml L-1 had slightly lower efficacy, but the difference was not statistically significant compared to Profiler® at 3 ml L-1. Interestingly, the control treatments, including water spraying and no spraying, did not show a significant difference in disease control compared to the treated plots. These results indicate that Profiler® at appropriate concentrations and Mishocap® and Captan at their recommended concentrations can be effective options for controlling grape Downey mildew disease.
Because both Profiler® 3 and 2.5 ml L-1concentrations are effective in controlling the disease, therefore in order to protect the health of the consumer and the environment as well as reduction in costs, the preferred dose is 2.5 ml L-1.
Send comment about this article