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Gray leaf spot/blight of Hakone Grass

Hakone grass (Hakonechloa macra), also known as Japanese forest grass, is often used for massing in beds in where a low maintenance ground cover is needed in semi-shaded areas. The graceful arching stems along with the availability of gold or white striped variegated cultivars make it an attractive option. There are few reports of disease problems on Hakone grass but one problem seems to show up with some regularity in both nurseries and landscape beds:  gray leaf spot and blight, caused by the fungus Magnaporthe (= Pyricularia).

Fig 1 and 2: Hakone grass in a landscape bed with gray leaf spot.

Figure 3

Reports of this problem from studies done in Ohio indicate that blight found on hakone grass is caused by the same fungus that causes gray leaf spot on perennial ryegrass and fescue.  Gray leaf spot on perennial ryegrass is a widespread problem in the Midwest, especially on golf course fairways and athletic fields during periods of warm humid weather with frequent rainfall or irrigation. The fungus survives the winter as dormant mycelium on infested plant debris.

 

Fig 3: Perennial ryegrass fairway heavily damaged during an outbreak of gray leaf spot.

 

 

 

Figs 4 and 5: Spores of the gray leaf spot pathogen on a blade of perennial ryegrass

In nurseries using overhead irrigation the disease can quickly become established and, although plants are not killed, they may become unsuitable for sale. Plants that are grown with high nitrogen fertilizers and spaced close together are more likely to be damaged. Spores from infected ryegrass in the landscape can easily spread to landscape beds, leading to spots and blighting when conditions conducive to infection. Preventive fungicide applications of the following fungicides may be needed: Compass®, Disarm®, Heritage®, Pageant®, Broadform®, Mural® and thiophanate-methyl (Cleary 3336® and other generic fungicides with the same active ingredient). In landscape beds you can reduce impact from this disease by starting with healthy plants and by making sure plants are properly spaced, mulched and are not drought stressed. Also, avoid sprinkler irrigation and high nitrogen fertilizers.

Figs 6, 7, 8: Hakone grass, cultivar ‘All Gold’ showing leaf spots and blighting of lower leaves caused by gray leaf spot.

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