Can Rust Spread From a Geranium to Vegetable Plants?

Rust Fungi

• Thousands of known species of rust fungi belonging to the order Pucciniales exist, all with brightly colored fungal fruiting bodies -- many are rust colored, but a few are yellow, purple, reddish or orange. Although the rust on your geranium may look a lot like the rust on soybeans or corn, rust species require very specific hosts in order to reproduce. Rusts require a compatible living host to successfully reproduce; they rarely kill their hosts, but can affect growth and yield considerably.

Flower and Vegetable Hosts

• Many rusts alternate between two different hosts in order to complete their life cycles, but geranium rust is a special case. Although geranium rust can live on many different members of the genus Pelargonium, it can only survive on the plants in this family. Since no closely related vegetables exist, your sick geraniums can't pass their rust to them. However, if rust is active elsewhere in your garden, it may coincidentally appear at the same time as geranium rust since all of these fungi require similar conditions to thrive.

Cultural Controls for Rust

• Good circulation and proper watering are keys to preventing the spread of rust in any garden. Rust spores germinate when temperatures are between 60 and 70 degrees Fahrenheit, where standing water is abundant. In under six hours, rust spores can germinate in the small beads of water on the leaves of compatible host plants.

  Watering at the base of plants is vital to preventing further rust spread between compatible species. If your garden is starting to erupt with a variety of rusts, try watering in the morning and thinning plants to increase air circulation. Sometimes it's easier to simply remove diseased plants and replace them, especially early in the season.

Treating Rust Chemically

• If rust is a serious problem in your garden, and both your geraniums and your vegetable plants are suffering, consider treating all your troubled plants at once. Although the rusts on your plants will be different, all rust species can be treated with neem oil mixed in a hand-held sprayer at a rate of 2 tablespoons per gallon of water.
  Coat the leaves of your plants until they're wet, but not dripping, making sure to get both the top and underside. Repeat your neem treatment weekly until all signs of rust have gone. Neem can also be used as a preventative against a spreading rust problem when applied every two weeks to plants at risk. Remember that neem is a garden chemical and be sure to read the entire label before using it.