Downy mildew
Downy mildew | |
---|---|
Causal agents | oomycetes |
Hosts | plants |
Downy mildew refers to any of several types of
Symptoms
Initial symptoms include large, angular or blocky, yellow areas visible on the upper surface.[3] They can also be distinguished by their sporadic yellow patch appearance. As lesions mature, they expand rapidly and turn brown. The under surface of infected leaves appears watersoaked. Upon closer inspection, a purple-brown mold (see arrow) becomes apparent. Small spores shaped like footballs can be observed among the mold with a 10x hand lens. As a result of numerous infectious sites, leaves might show a blighted appearance if the disease continues to spread. In disease-favorable conditions (cool nights with long dew periods), downy mildew will spread rapidly, destroying leaf tissue without affecting stems or petioles.[4]
Treatment and management
Cultural options
Because the downy mildew pathogen does not overwinter in midwestern fields, crop rotations and tillage practices do not affect disease development. The pathogen tends to become established in late summer. Therefore, planting early season varieties may further reduce the already minor threat posed by downy mildew.[4] When downy mildew does pose a threat, the removal and destruction of plants displaying symptoms is good practice.
Chemical control
Fungicides applied specifically for downy mildew control may be unnecessary. Broad spectrum protectant fungicides such as
Organic control
One way to control downy mildew is to eliminate moisture and humidity around the impacted plants. Watering from below, such as with a drip system, and improve air circulation through selective pruning. In enclosed environments, like in the house or in a greenhouse, reducing the humidity will help as well.
Resistant cultivars
Recent breeding efforts have produced resistant basil cultivars. Choosing resistant cultivars, in combination with other prevention and control measures, can help growers with high downy mildew pressure still produce a viable crop.[7]
Plant-specific mildews
Basil
Downy mildew of basil caused by Peronospora belbahrii has been a huge problem for both commercial producers and home growers. The disease was first reported in Italy in 2004,[8] was reported in the U.S. in 2007 and 2008[9][10] and has been steadily increasing in prevalence, distribution, and economic importance since then. The highest disease occurrence in basil leaves occurs at temperatures around 68°F.
Cucurbitaceae
Grapes
Plasmopara viticola is the causal agent of grapevine downy mildew.
Hops
Hop Downy Mildew (caused by
Ornamentals
A new and particularly aggressive form of
Peronospora sparsa attacks rose bushes (including Rosa canina) and Rubus species.[11]
Soybeans
Peronospora manshurica infects soybeans, reducing photosynthetic activity, yield, and quality.[12] The fungus spreads by oospores on diseased leaves and/or on infected seed. The disease spreads in environments with high humidity and favors temperatures between 20-22 °C. Tufts of grayish to pale-colored sporangiophores on the underside of leaves easily distinguish the infection from other foliar diseases.[13] The disease is often controlled using the fungicides mancozeb, maneb, or zineb.[12]
Spinach
Downy mildew on spinach is caused by Peronospora effusa, an oomycete pathogen that poses a challenge to spinach production worldwide, especially in organic production.[14]
Sunflowers
See also
- Blue mold(of tobacco plants)
- Peronosporaceae (with a list of the downy mildew genera)
References
- ^ NCBI-Taxonomy – ncbi.nlm.nih.gov
- ^ HYP3 – ncbi.nlm.nih.gov
- ^ Schilder, Annemiek. Downy mildew - Plasmopara viticola. Archived June 11, 2010, at the Wayback Machine MSU Plant Pathology.
- ^ a b c Richard Latin, Karen Rane, "Pumpkin Diseases" (PDF), Department of Botany and Plant Pathology, purdue.edu
- ^ "Oxathiapiprolin" (PDF). New Active Ingredient Review. Minnesota Department of Agriculture. October 2015. Archived from the original (PDF) on 2017-11-07. Retrieved 2017-11-09.
- ^ grainews.ca: "Gowan buys Dow’s Gavel potato fungicide", 18 Jul 2008
- ^ https://www.johnnyseeds.com/on/demandware.static/-/Library-Sites-JSSSharedLibrary/default/dwc8916fa0/assets/information/7648-basil-downy-mildew-prevention.pdf [bare URL PDF]
- ^ Garibaldi, A., Minuto, A., Minuto, G., Gullino, M.L., 2004. First Report of Downy Mildew on Basil (Ocimum basilicum) in Italy. Plant Disease 88, 312-312.
- ^ Roberts, P.D., Raid, R.N., Harmon, P.F., Jordan, S.A., Palmateer, A.J., 2009. First Report of Downy Mildew Caused by a Peronospora sp. on Basil in Florida and the United States. Plant Disease 93, 199-199.
- ^ Wick, R.L., Brazee, N.J., 2009. First Report of Downy Mildew Caused by a Peronospora Species on Sweet Basil (Ocimum basilicum) in Massachusetts. Plant Disease 93, 318-318.
- .
- ^ ISBN 9789290580478. Retrieved 6 February 2016.
- ISBN 9780890540930.
- PMID 30939071.
- ^ Friskop, Andrew; Markell, Sam; Gulya, Tom (2009). "Downy Mildew of Sunflower" (PDF). Sunflower Publications. Fargo, North Dakota: North Dakota State University Extension Service. Retrieved 4 March 2016.
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