RUST FUNGUS CONTROL
By Dr. Peter Baye
From “Some Low-Tech Horticultural Tips for Growing Fuchsias”
A Program for Vallejo Branch,
March 2002
Nothing will make existing infections (rust spots) disappear. Leaves already infected have to come off. Sprays are used to prevent the spread of fungi to young, uninfected leaves, not cure infected ones. To minimize risk of injuring foliage, spray only in cool, moist, shaded conditions, never in sun or high temperatures.
Lime-sulfur spray: Very dilute applications of lime-sulfur liquid spray (calcium polysulfide) applied repeatedly during the time infections appear, can stop the spread and growth of leaf rust fungi. Lime-sulfur stinks, however, like rotten eggs. It is relatively non-toxic, though. Full strength solutions for spraying when woody plants are dormant can burn foliage on growing plants, so use very dilute solutions. I usually start with 1/2 the weakest concentration recommended, and step it up to more concentrated levels based on results. Add a spreader-sticker (surfactant) or a drop of liquid soap. Frequency of spraying should be slightly more often than you observe new orange spots on leaves.
Baking soda: Baking soda (sodium bicarbonate) has been tested as an effective inhibitor of rust fungi on hybrid tea roses. It is quite non-toxic, and has limited potential to burn foliage. For fuchsias, adjust the concentrations to your local conditions and plants, starting with about 1/2 teaspoon per quart of water, with a drop or two of soap to act as a spreader. Increase the concentration if repeated sprays do not slow the spread. Watch for leaf tip burn—a sign that injury occurs from concentrations of baking soda too high for your temperatures.
Simple Green: Dilute solutions of the nontoxic household cleaner appear to have some ability to inhibit rust fungi, as well as insects. For fuchsias, adjust the concentrations to your local conditions and plants, starting with about 1/2 teaspoon per quart of water, with a drop or two of soap to act as a spreader. Increase the concentration if repeated sprays do not slow the spread of rust. Watch for leaf tip burn—a sign that in-jury occurs from concentrations of Simple Green too high for your temperatures.
Eucalvotus/menthol oil mouthwash: The active ingredients in eucalyptus/menthol mouthwash are ethyl alcohol (about 35%) and aromatic oils. Eucalyptus and menthol both are biochemically active, and inhibit the growth of bacteria and fungi. This is the basis for the “folk remedy” of mouthwash as an all purpose insecticide/fungicide. As long as it is applied at a reasonable dilution and at low temperature and in shade, it may be effective at preventing and treating infections and infestations. If your plants are sticky or too fragrant after spraying, wash off the plants with clear tap water. Begin with dilute solutions (e.g. 1/4 mouthwash, 3/4 water) and increase as needed.
Synthetic fungicides: A last resort. Synthetic fungicides are highly toxic to mammals, such as humans. As their labels warn, they also are a hazard to wildlife, such as hummingbirds that are attracted to fuchsias.