Regal geraniums are a group of plants referred to as Pelagonium domesticum. Regal geraniums are also called Martha Washington geraniums. The plants grow to a mature height of 1 to 4 feet and bloom with single or double flowers clusters in solid or mixed colors. The scented foliage is rounded, lobed or toothed. Regal geraniums are hardy in U.S. Department of Agriculture plant hardiness zones 10 and 11 and are susceptible to a number of problems and diseases common to pelargonium varieties.
Bacterial blight is a common problem with geraniums, including regal geraniums, according to University of California’s Integrated Pest Management Program. The bacterial disease is caused by Erwinia, Pseudomonas or Xanthomonas spp. The disease is characterized by the rotting and browning of infected plant tissues accompanied by an unpleasant odor. The deterioration is most evident near the soil line. Infected plants are also stunted. As disease progresses, dead plant tissue falls out giving the plants a jagged look. Management includes using plants from reliable sources. Plant in well-drained soil and do not used overhead irrigation.
Regal geraniums, and other pelargonium, may be affected by crown gall. The bacterial disease is caused by Agrobacterium tumefaciens and is characterized with the appearance of distorted growths on the roots just below the soil line. In severe cases, the galls also appear on the limbs, trunks and foliage. Infected plants lose vigor and become susceptible to other diseases. Use clean pruning tools, good quality plants, and avoid unnecessarily injuring plants to prevent crown gall. Chemical control options includes the use of Agrobacterium tumefaciens K-84, a biological agent.
Too much or too little water is cited as a common problem with pelargonium varieties. When plants get too little water, it leads to wilting and discolored foliage with premature leaf drop. Too much water also causes poor plant growth and is especially damaging to the roots because a majority of bacteria and fungi thrive in excessively moist soil. Management includes planting in well-drained soil and watering according to plant requirements. Avoid overhead irrigation and drip irrigation methods.