Why Do My Grape Leaves Have Brown Spots? Causes by Symptom
As an Amazon Associate we earn from qualifying purchases.
Brown spots on grape leaves are a symptom, not a diagnosis. Several fungal diseases, and at least one nutrient problem, can produce them, and each looks a little different. Why do my grape leaves have brown spots? The answer starts with the spot itself: its color, its edges, anything growing on it, and where it sits on the leaf. Two university extension sources describe those features, and this guide sets them side by side.
Quick answer
- Start with the spot’s edges and center. Minnesota describes black rot as round tan spots with dark edges and tiny black pimples in the center.
- Turn the leaf over. Downy mildew produces cottony white growth on the underside, and that growth can disappear in hot, dry weather.
- Note where the spots sit. Phomopsis spots are most common on the lower leaves and along the veins.
- Consider non-fungal causes too. Nutrient deficiency and leafhopper feeding also change leaf color, and the sources describe how.
How we chose these sources
We limited the review to two non-retail extension publications. The first is a University of Minnesota Extension diagnostic page on grape leaf spots and discoloration, opened on 2026-10-27 and returned as HTTP 200. The second is a Michigan State University Extension bulletin, “Pest Control in Small Vineyards,” issued in April 1999. Its library copy carries a warning on the first page: “Archive copy of publication, do not use for current recommendations.” For that reason this article uses the Michigan bulletin only for descriptions of the diseases, and it gives no treatment advice from either source.
Black rot: tan spots with black dots
Minnesota’s page describes black rot this way: “Leaves have round tan spots with dark edges, tiny black pimples are often visible in the center of the spot.” The Michigan bulletin adds the cause and the leaf pattern. It calls black rot “a major fungus disease of grapevines in temperate climates” and says it “also requires water on the tissues for infection.” On the leaf, the lesions “appear as tan to orange spots” with “small, blackish fruiting bodies around the periphery of the lesions.”
The black dots are the feature that separates black rot from look-alikes. The bulletin puts it directly: “These small, black fruiting bodies confirm that the leaf spot was caused by black rot.” The same disease can reach the fruit. Minnesota says that “A red ring appears on berries, this grows quickly until the entire berry is brown,” and that infected berries “dry up, shrink and wrinkle into a bluish black ‘mummy’ that remains attached to the cluster.” Michigan describes the same sequence, noting that when black rot attacks grapes, “it first turns green berries a caramel color.”
When you find leaf spots with black dots, check the clusters as well. The fruit symptoms are the ones that cost a crop, and the two sources agree that they follow the leaf spots.
Downy mildew: yellow patches above, white growth below
Downy mildew is often easier to see from underneath. Minnesota describes “Yellow-green ‘greasy’ lesions develop on upper leaf surface” and says the lower surface “develops a dense, white cottony growth under humid conditions.” Michigan gives the same order of events: “On leaves, infection first appears as yellow, angular, blotchy areas on the upper surface (Fig. 3). Cottony white masses of spores soon develop on the lower surface of the leaf directly below the yellow spots (Fig. 4).”
Timing matters too. Michigan says the fungus “requires free water to infect vines. Therefore, it is especially prevalent during rainy periods and in the latter part of the growing season.” Late in the season, the bulletin adds, the spots “tend to be concentrated along the main veins of the leaf.” The bulletin also warns about dry weather: “During hot, dry weather, the cottony white masses of spores (Fig. 4) often dry up and disappear, thus making identification of this disease somewhat difficult.”
That warning changes how to read a clean underside. If the yellow patches appeared during a wet spell, the earlier pattern is still useful evidence even when the white growth has dried up.
Anthracnose and Botrytis: round spots and red-brown patches
Minnesota’s anthracnose entry, which it also calls bird’s eye rot on berries, describes leaves with “circular lesions with gray centers and brown or black margins.” The center of the spot “may fall out resulting in small ragged holes in the leaf.” On shoots, the page says these lesions can be confused with hail damage, but “unlike hail damage, the edges of the lesions are raised and black.” It also notes that “Infection is more prevalent in rainy years.”
Botrytis looks different on the leaf. Minnesota describes “large, red-brown patches” and says that “a gray mold may or may not be observed on the leaf.” The disease is better known for the fruit. Michigan says Botrytis bunch rot “most commonly occurs on tight-clustered varieties,” and that it “begins with the decay of individual berries, which take on a tan color and often have fuzzy, brown fruiting bodies protruding from the surface.” Minnesota says the infected berries can then shrivel and drop as hard mummies.
Phomopsis: spots low on the vine
Minnesota describes Phomopsis cane and leaf spot as “Dark brown spots with yellow edges” that “can also appear along leaf veins and petioles, the lower leaves are most commonly affected.” The Michigan bulletin says the disease “is easily identified by lesions on canes near their bases,” and that “pinpoint lesions on the first three or four leaves of shoots are also likely to occur.”
The same bulletin ranks its severity. “Severe infections can also cause fruit loss,” it says, but “In many vineyards, however, this disease is not nearly as damaging as powdery mildew, downy mildew and black rot.” That ranking helps when more than one disease could fit the spots you see.
Powdery mildew and non-fungal look-alikes
Powdery mildew usually shows as a coating rather than a distinct spot. Michigan says the disease “attacks all green tissues on the vine,” and that it “often appears as a grayish white film on the surface of infected tissues.” Minnesota says the upper leaf surface “develops white or grayish-white patches,” and that the disease “Can be more prevalent in drier conditions.”
Two common non-fungal causes can also darken or spot leaves. Minnesota’s nutrient deficiency entry says that “Leaves are purple, red, light green, or yellow, depending on the nutrient that is deficient,” and that the problem is “Prevalent in soils with high or low pH (below 6 or above 7).” Leafhopper feeding is the other. Minnesota says leafhoppers “feed on the underside of leaves” and leave “pale yellow to white blotches, mostly near leaf margins.” Michigan explains that “As they feed, they create a mottled pattern of dying leaf tissue,” and adds that “slight to moderate populations of this insect are usually only a nuisance and do not significantly influence vine performance.”
Minnesota also lists a virus-related pattern, Tomato/Tobacco Ringspot Virus Decline, where “Leaves exhibit a random pattern of yellows and greens.” That pattern is less likely to look like distinct brown spots, but it is worth ruling out when the discoloration is scattered.
Comparing the causes side by side
The table below puts the symptoms from both sources in one place. It does not replace reading the full entries, and it leaves out the details each source gives about timing and spread.
| Cause | What the leaf or fruit shows | Source |
|---|---|---|
| Black rot | Tan or orange spots with black dots; infected berries dry into mummies | Minnesota, Michigan |
| Downy mildew | Yellow angular patches on top; white growth underneath | Minnesota, Michigan |
| Anthracnose | Circular spots with gray centers and dark margins; centers may drop out | Minnesota |
| Botrytis | Large red-brown patches; gray mold may appear | Minnesota, Michigan |
| Phomopsis | Dark brown spots with yellow edges, mostly on lower leaves | Minnesota, Michigan |
| Powdery mildew | White or grayish-white patches or film on the upper surface | Minnesota, Michigan |
| Nutrient deficiency | Purple, red, light green or yellow leaves, depending on the nutrient | Minnesota |
| Leafhoppers | Pale yellow to white blotches; mottled dying tissue, seen from below | Minnesota, Michigan |
What we could not verify
Neither source says which cause is most likely in a particular yard. The Minnesota page works as a symptom guide and does not rank the causes by region, season or grape variety. The Michigan bulletin is dated April 1999, and its own first page says it should not be used for current recommendations. This article uses its descriptions only. Neither source offers a diagnosis from a photo or a sample, and neither covers every grape variety.
What the sources do not say
The sources do not say which pathogen is responsible for a given spot in a given climate, and they do not give a current management schedule. The Michigan bulletin names specific products in its tables, but those lists date from 1999, so this article does not repeat them. Minnesota’s page does not say how quickly any symptom spreads from leaf to leaf. Neither source describes spot development on grapes grown in containers.
Frequently asked questions
Are brown spots on grape leaves always a disease?
No. Minnesota lists nutrient deficiency and leafhopper feeding alongside the diseases on its page, and both change leaf color without being fungal infections. The spot’s edges, its center and whether anything grows on it are the features to compare first.
Where should I look first on the leaf?
Look at the underside first. Michigan says downy mildew’s “Cottony white masses of spores soon develop on the lower surface of the leaf directly below the yellow spots (Fig. 4).” Leafhopper feeding is also on the underside, since Minnesota says leafhoppers “feed on the underside of leaves.”
Do black rot spots mean the grapes will be lost?
Not necessarily, and the sources do not give a loss rate. Michigan says that when black rot directly attacks grapes, the berries shrivel “into dark, blackish mummies.” Minnesota describes the same outcome. Whether a given vine loses its crop depends on how much of the cluster is infected, and neither source quantifies that.
Is Phomopsis more serious than black rot?
The Michigan bulletin suggests it usually is not. It says Phomopsis “is not nearly as damaging as powdery mildew, downy mildew and black rot” in many vineyards, while also noting that severe infections can cause fruit loss. Minnesota does not rank the diseases by severity.
Can I tell the disease from a leaf photo alone?
The sources describe features you can see, but neither says a photo is enough. Michigan notes that downy mildew identification can be “somewhat difficult” in hot, dry weather. Minnesota’s page ends with a link to ask a gardening question, which is a sensible next step when the pattern is unclear.
For more on the biology behind plant disease, read how plants recognize pathogen molecules, and for the fungus that causes powdery mildew, see how powdery mildew fungi feed from plant cells.
Sources
- University of Minnesota Extension, “What’s wrong with my plant? Grape, Leaves, Spots/blotches/other discoloration,” https://apps.extension.umn.edu/garden/diagnose/plant/fruit/grape/leavesspots.html (opened 2026-10-27, HTTP 200)
- Michigan State University Extension, Thomas J. Zabadal, “Pest Control in Small Vineyards,” Extension Bulletin E-2698, April 1999 (archive copy), https://archive.lib.msu.edu/DMC/extension_publications/e2698/E2698-1999.PDF (opened 2026-10-27, HTTP 200)
