Rust - rusty looking spots, plant turns yellow Treat with fungicidal spray.

Dropsy - mostly a problem with indoor plants that show lesions Don’t water plant so much and put it in sunniest spot you can find.

3. Look for pests such as caterpillars, flys, mites,termites and slugs are garden pests that might like to make a meal of your geraniums. You can control most of these pests with special sprays that you can get at your garden supply store. Aphids are another problem that may be controlled with ladybugs. Slugs can be captured simply by putting out a saucer of beer.

4. Make sure you fertilize properly. Geraniums like a soil that has plenty of nitrogen and lack of it can cause plant to turn yellow. If you suspect this could be problem, then you might try fertilizing with a fertilizer that has a high concentration of nitrogen.

Disease

Geraniums are hardy, but like any plant can be susceptible to disease. Some common disease are Black Leg where stem becomes blackened and leaves fall off, Leaf Spot where leaves become spotted and drop off, Gray Mold where plant has gray moldy spots, Rust where plant gets rusty looking spots and leaves turn yellow and drop off, Root Knot nematodes -swelled roots and stunted growth and Dropsy which produces lesions on plants.

To combat most disease, remove all leaves that are infected, make sure you do not take cuttings from any plant with disease. When watering make sure you do not splash leaves.

Pests

Some common geranium pests include:

Caterpillars - some caterpillars like to much on geraniums (perhaps they have heard of it’s medicinal properties?). These can be controlled with sprays.

Aphids - try controlling aphids with ladybugs or a special spray.

Whitefly - usually starts in greenhouse but can spread to garden on infested plants. Small white flys and black sooty goop can be seen on leaves which will fall off after turning yellow. Can be controlled with sprays.

Mites - Causes leaves to curl and drop off – control with sprays.

Termites - Subterranean termites tunnel through stems of geraniums causing them to turn yellow and die. Treat soil with appropriate termite treatment. Don’t let them get to your house!

Slugs - slugs love gardens but they also love beer. Leave a saucer out and you will catch more than your fair share of slugs!