Tall and colorful hollyhocks (Alcea rosea) add dimension and a pop of pink, purple, red and white to gardens. But pests can present a problem, feasting on both leaves and flowers. Hollyhock's enemies include the hollyhock weevil, Japanese beetle, spider mite and hollyhock sawfly. As you formulate your plan of attack on these bugs, start with sprays that are least toxic to kids, pets and the environment. First see if insecticidal soaps and horticultural oils will rid your hollyhocks of intruders. If not, then consider moving on to chemical sprays.
1. Insecticidal Soap
Insecticidal soaps don't wash weevils and other pests from hollyhocks. Instead, they wash off an insect's protective coating, penetrating its inner membranes. But to be effective, insecticidal soap must be aimed directly at bugs rather than just coming in contact with the hollyhock's blossoms, leaves and stem. While these soaps have a low toxicity level, keep your children away from the flowers immediately after spraying to ensure the spray clings to the pests.
2. Horticultural Oil
Generally comprised of highly refined petroleum oils combined with an emulsifiying agent, horticultural oils can be an effective tool in your bug-fighting arsenal, particularly against spider mights and sawtail flies. Oil from the seeds of the neem tree can also help rid your hollyhocks of pests. The oils kill insects in various ways. In some, it interferes with breathing mechanisms, while in others it can shut down metabolism. The oils evaporate quickly once on the plant and should not be harmful to pets or children. But take care in spraying because some oils can stain decks and the siding on houses. Also, some trees, including black walnuts and Japanese maples, are sensitive to oils.
3. Pyrethrins and Pyrethroids
There are more than 3,000 pyrethrin and pyrethroid registered pesticides. Pyrethrins are derived from chrysanthemum flowers and attack insects' nervous systems, paralyzing the bugs. Pyrethroids are synthetic forms of pyrethrins. While these control agents may sound natural, caution must be used when spraying them on hollyhocks and other plants. Inhaling large amounts of the pesticides can trigger asthma attacks, sneezing, headaches and even convulsions. As with many other pesticides, it takes less of this chemical to cause a reaction in children than in adults. Keep these pesticides under lock and key.
4. Other Chemical Insecticides
If insects continue to plague your hollyhocks, and less toxic methods have proved fruitless, you could call in the big gun chemicals, including insecticides that include sevin, orthene or malathion, as a last resort. These pesticides work by disrupting an insect's nervous system. For best results, spray these chemicals in the evening, taking care not to spray them into a breeze that blows back to you. Use gloves. Signs of excessive exposure include headaches, nausea and shortness of breath. Keep children away from sprayed hollyhocks, and don't allow pets near them. Some of these chemicals are potentially carcinogenic. For example, the EPA has determined there is "suggestive evidence of carcinogenicity" with malathion.
- Utah State University Cooperative Extension: Hollyhock Weevils
- Ohio State University: Hollyhocks Under Siege
- University of Illionis Extentsion: Hollyhocks
- Washington State University Extension: Guidelines for Insecticidal Soap
- Colorado State University: Insect Control: Horticultural Oils
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