Beverly Shaw
Master Gardener
Purdue University







Question and Answer

Q.  I have a small greenhouse that I use to winter over plants and to start new ones from seed in the spring. Each year I get whiteflies. I have bought commercial sprays from lawn and garden departments, but even with repeated applications, the whiteflies seem to persist. What is the best method to rid my greenhouse of these pests? Is there a prevention I should implement? Are there certain plants that attract whiteflies? -- Lisa Uhl, Corydon, Ind.

A.  Whiteflies remove plant fluids with their piercing-sucking mouthparts. They feed primarily on leaves, which may result in plant stunting and leaf distortion. Whiteflies produce a clear, sticky liquid called honeydew. Honeydew serves as a medium for growth of black, sooty mold fungi. These unsightly fungi can reduce photosynthesis and the plant's appearance.

Whiteflies come in through openings in the greenhouse, or on new plants that you bring into the greenhouse. In your case, you're probably bringing whiteflies in on your plants when you bring them in for winter. Inspect each plant for all whitefly life stages, including eggs. Look especially on the undersides of the leaves.

Apply contact insecticides when whitefly numbers are building up. Be sure to thoroughly cover leaf undersides. Appropriate insecticides, including insectidal soap, horticultural oils and others, are available at www.hort.purdue.edu/hort/ext/Pubs/HO/ID218.pdf.

Monitor with yellow sticky cards placed 1 to 2 inches above the plant canopy. These are available from some mail-order garden supply companies. Place two sticky cards per 1,000 square feet. Count the number of whiteflies on the sticky cards with a 10x hand lens. Record the number of whiteflies trapped on the cards before and after insecticide applications to determine efficacy. Make decisions about spraying by actually inspecting plants for pests, and spray only when necessary.

Reduce the introduction of whiteflies by putting up screens to exclude them. Growers who have installed screens report their use of pesticides declined by 50-90 percent.

Several species of parasitic wasps are quite effective against whiteflies. See www.biocontrol.ucr.edu/bemisia.html for more information.

Q. I have a lot of hydrangeas and the flowers are so pretty. How do I dry the blossoms? -- Carol Whitten, Lafayette, Ind.

To dry them naturally, allow the flowers to dry on the plant until the end of summer. Cut the blossoms, with as much stem as you desire, when the nights are cool but before the first frost. Remove the leaves and place the cuttings in vases without water. You can hang bunches of flowers upside down, but it's not necessary.

For nearly perfect blooms, consider drying them in silica gel. This process is more expensive and time-consuming. The instructions are available on the container of silica gel, available at craft stores, or in the publication "Preserving Plant Materials," HO 102 W, available the Purdue Extension office in your county or at www.hort.purdue.edu/ext/HO-102.pdf. This publication explains many other techniques, including dyeing, pressing and skeletonizing dried materials.

Working with the dried blossoms can cause a lot of breakage. If you're making a wreath, soak the blossoms in water to soften them. When they're pliable, begin your project. After it's done, allow it to dry again. This will take about a day.

Q.  How many different flowering crabapple trees are there? Can I start a tree from one of the apples off the tree? If so, how? How can I get a seed from each kind of tree? And will any flowering crabapple grow in my area? -- Theresa Murray, Hamilton, Ind.

A.  Many crabapple cultivars have been developed over the years, but many have fallen from favor due to a multitude of problems. The best crabapples are resistant to most insects and diseases and have attractive flowers, fruits and form. This rules out many cultivars. Currently, the International Ornamental Crabapple Society evaluates 67 crabs. For information about crabapples, get copies of "Crabapples Resistant to Apples Scabs and Japanese Beetle in Indiana," ID-217, and "Apple Scab of Indiana," BP-39, which are available from the Purdue Extension office in your county or at http://www.entm.purdue.edu/Entomology/ext/targets/ID/ID217/ID-217.htm and http://www.extension.purdue.edu/extmedia/BP/BP_39_W.pdf.

Most crabapples are grafted onto rootstocks of other crabapples so, unless you are interested in grafting, they cannot be reproduced from seed or simple cuttings.

Different crabapples have varying hardiness tolerances. Some will be hardy in your area but others may not. Research this information before you add them to your landscape.


Contact: B. Rosie Lerner
Editor: Olivia Maddox,