Rust On Snow On The Mountain - Knowledgebase Question

Nashwauk, MN
Question by joeysbait
May 21, 2000
We have a large amount of Snow on the Mt planted at our cabin (same area about 10 mi away). It is on the Northeast side, gets a lot of morning and afternoon sun but last year it developed rust after early July. It looked like the rust you get on old head lettuce from the grocery. and was very unsightly. We had a lot of rain in July (11 inches on the 4th) What can we do to prevent this again. Could it be a fungus and if so how do we treat it?

Answer from NGA
May 21, 2000


Rust can attack a number of plants, and the control measures would be similar to those for hollyhocks (see below), although you might want to test any spray on a sample of the planting a few days prior to treating the entire area.

It is also possible that it is a different fungal infection, but the controls would still include the same general idea of cleaning up infected foliage to prevent reinfection, increasing air circulation if possible, and avoiding wetting the leaves, especially in the evening. In some cases it is also effective to simply mow off the foliage and allow it to regrow a fresh set of leaves. Bishop's weed (Aegopodium) is tough enough to withstand this treatment and bounce back.

Hollyhock rust is a very common furngal disease. It
begins with yellow spots or orange spots with red centers on
the top side of the leaf, along with brown pin-head sized dots
on the underside of the leaf. Eventually gray pustules form on
the underside of the leaf, and all the spots run together, killing
big areas of leaf tissue.

Hollyhock rust overwinters on the basal leaves and old stems
of the plant. In the fall, after killing frosts, remove and destroy
the old leaves and stems. During the growing season you can
remove and destroy infected leaves. Disturbing plants while
the leaves are wet spreads the disease, so allow plants to dry
before working around them. You might also use a fungicide
labeled for hollyhock rust, or try a product containing neem
such as Neem-Away (sold by Gardens Alive, 5100 Schenley
Rd., Lawrenceburg IN 47025; 812/537-8650; Be sure to follow the
application instructions carefully.

Other cultural practices that keep hollyhocks healthy include
growing them in full sun, in rich moist soil and making sure
they have good air circulation.

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