SPECIALTY CUT FLOWER CORNER: For the beginning grower

Flowers and insects: A manageable combination, Part 2
Aphids, thrips, spidermites, leafhoppers, beetles and caterpillars--knowing your enemies, and how to handle them.

By Melanie DeVault

“With aphids, if I can be patient, nature often helps,” says Steve Bogash, regional Extension commercial horticulture educator in Central Pennsylvania. Photo used with permission from University of California Statewide IPM Program. J. K. Clark, photographer.

Lots of catalogs have magnifiers that let you see the tiny insects up close and personal, whether on plants or sticky traps (one is Gempler’s at www.gemplers.com). There are some good books out there with pictures of various stages in the insect’s life cycle, too. Our new favorite is The Ultimate Guide to Backyard Bugs, Garden Insects of North America by Whitney Cranshaw. Penn State College of Agricultural Sciences (as do many ag schools around the country) has a booklet entitled “Managing diseases, pests and plant growth in Greenhouses”. It's good outside the greenhouse, too, has good insect/disease descriptions (but no pictures) and you can ignore the heavy chemical info. (Available by calling, toll free, 877-345-0691; $9, plus $5 shipping/handling.)

So, without letting the following get you paranoid (because as we said above, flowers aren’t that difficult when managed well), here are some tips on . . .

The biggest problem insects

APHIDS -- Aphids can be winged or wingless. They develop wings as numbers in their colonies increase so they can move on to less populated areas and wreak further havoc on your flowers. They are generally small, according to Penn State’s booklet, 1 to 3 mm, and soft bodied. Caught on yellow sticky cards, their front wings usually have two parallel veins close to the outer edge which ends at a dark, thin part. Their legs and antennae are long. Their color varies and as they get bigger, they shed their exoskeleton which can be found on leaves or stuck in their sticky secretions. Penn State says the insects “feed by inserting their stylet-like mouthparts through plant tissue directly into the phloem and removing plant sap. Feeding can lead to plant stunting and deformities.” When you have a lot of them, they look like a yellow, sticky mess all over your flower stem, leaves, bud. The sticky secretion is called honeydew, which can be a growth base for sooty mold.

That’s not all. Aphids are responsible for transmitting some 60 percent of all plant viruses on ag crops worldwide. Why are they such a problem? Females give birth to live offspring, three to 10 a day, that immediately start to feed. They don’t need to mate, so each female gives birth to MORE females. Within a week, the offspring are ready to reproduce.

“With aphids, if I can be patient, nature often helps,” says Steve Bogash, regional Extension commercial horticulture educator in Central Pennsylvania -- if the problem isn’t too severe. “I was all set to get out the spray for an aphid problem at home and didn’t get around to it. Then I saw lots of lady bug larvae -- which generally will take care of the problem.”

Byczynski says she occasionally sees some aphids early
in the season -- greenhouse ranunculus seem especially susceptible. “They are easily controlled by insecticidal soap,” she says. Insecticidal soap kills by disrupting membranes. Horticultural oils can also be effective, killing by suffocation. Organic growers need to check each product with their certifying agency/OMRI manual, because not all organic pesticides are created equal and while some are allowed, others are restricted.

Critical to aphid control is sanitation. Keep an eye on flowers before problems develop. Start inspecting plants at the lower leaves upward. And get rid of weeds near any problem spots that develop. Biological controls can be very successful, especially in a greenhouse. Lady beetles (Hippodamia convergens) sold as adults can clean up bad problems. They also feed on other soft-bodied insects like thrips. Lacewings (Chrysoperla rufilabris), sold as eggs or larvae, also feed on thrips, spider mites, mealybugs and scales. Predatory Midges (Aphidoletes aphidimyza) sold as an adult for greenhouse release lay eggs near aphid colonies where the orange larvae can then feed on sticky insects. Aphelinus abdominalis, a type of wasp, parasitizes aphids--laying eggs on their bodies, killing them--and eats the ones left unparasitized. As Bogash says, most biological controls do better with a sanctuary in which to stick around. When released in the greenhouse, they’ll quickly go to work, putting on quite a show. But as the number of aphids diminish, the good guys may also disappear.

THRIPS -- Adults are found in blossoms, the larvae on leaves and deep in buds. Since they feed on all of the above, as leaves and flowers grow, they may look damaged, have a silver cast or appear streaked. Often black specks of excrement can be seen where the thrips fed. Thrips are tiny insects, just 1 to 2 mm in length with narrow bodies and fringed wings, and colors vary from straw-yellow to brown.

To find them hiding in flowers, try the old trick: tap blossoms over a sheet of white paper. This will dislodge them and, if you have a bunch, you’ll see what looks like black pepper on the paper. Penn State says the western flower thrip is the most likely to hit floral crops, particularly in a closed environment. And it doesn’t stay in the West, by any means.

Thrips are especially attracted to blue sticky traps, but they’ll also find the yellow traps. Look for the tiniest insect on the trap, and you'll see thrips with their wings folded over their abdomens sticking to the trap--they put up no struggle. (Don’t say ‘aw’ until you’ve seen the damage they can do.) They appear spindle shaped with protruding wings. Hairs line the edges of the wings and they sport V-shaped antennae. Thrips love marigolds and can hit lisianthus in a wet year.

The best controls are good sanitation and a weed-free zone. Early detection is important because they spread various diseases such as Tomato Spotted Wilt Virus. Dr. Stanton Gill, with Central Maryland Research and Education Center, Maryland Cooperative Extension recommends Amblyseius cucumeris, tan-orange predatory mites, as a good biological control. Each predatory mite can consume up to 10 thrips per day and will survive on spider mites should you run out of thrips (more on spider mites below). Orius insidiosus, minute predaceous pirate bugs, are good beneficials, too, Gill says.

SPIDER MITES -- Usually found on the undersides of leaves, especially near greenhouse heaters, vents and doors where it’s warmer and dry. Yep, they are a problem in hot and dry periods--they love water-stressed plants. Early sign of mite feeding is yellowish-white speckles on the upper side of the leaf as the chlorophyll is destroyed. Eventually, as populations increase, the whole leaf turns yellow.

Penn State says the mite, specifically the two-spotted spider mite, are minute arthropids with the largest adult female less than a millimeter in size. The body of the adult female and most immature stages is oval-shaped and usually appears light yellow to green with two large dark green spots on either side. All stages have eight legs except larval, which has six. Damage is caused by larvae nymphs and adults piercing the plant cells and sucking out the contents, leaving those tell-tale spots. Females lay eggs on the underside of leaves in fine webbing that the mites constantly produce. Now hear this: Each female can lay more than 100 eggs in a lifetime. Eggs can hatch in three days. Since they don’t have wings, sticky traps can’t catch them.

What to do? Don’t let weeds build up around your flowers and don’t let plants get water stressed. A good crop rotation helps, too. It’s harder in dry years, obviously. Bogash says spider mites can be a problem in low tunnels. He recommends using an insecticidal soap. Biological controls include Phytoseiulus persimilis, predatory mite; Feltiella acarisuga, Predatory Midge; Mesoseiulus longipes and Neoseiulus fallacis.

LEAFHOPPERS -- Are small wedge-shaped insects that hold their wings slightly out. They pierce plant tissue and suck sap, weakening the plant, and happen to carry viruses. The best protection is protective covering (Reemay or agribon fabric) over hoops. Aster leafhoppers, which cause the dreaded aster yellows disease, are green yellow with six black spots and they grow to about 1/8th of an inch so you can barely see them. Both insecticidal soap and hot pepper wax are said to control leafhoppers. Gill says neem will help control heavy infestations.

BEETLES -- Good sanitation and crop rotation are important steps in controlling beetles. We often just hand-pick them or squish them early in the season before they get to be a problem. Japanese beetles are slow to get up in the morning, so going out with a bucket of soapy water and flicking them in works wonders. Gill recommends neem for large problems. It represses the insects’ desire to feed. (And don’t forget the guineas! See Part 1 for more on using guineas.)

CATERPILLARS -- Caterpillars, immature butterflies and moths including armyworms, cutworms, leaftiers, leafrollers and loopers, have many natural enemies and are damaging only as larvae. The natural enemies include parasitic flies and wasps, damsel bugs, minute pirate bugs and more. Usually, caterpillars aren’t a major problem for flowers. If populations get out of control, and holes are being chewed in leaves (and large amounts of excrement are seen on foliage) there are three popular methods to fight back.

1. Find the buggers and pick 'em off.

2. Apply the microbial insecticide Bacillus thuringiensis (Bt) will paralyze and destroy the insect’s gut wall cells, but the insect must ingest the Bt, and it may take up to three days for it to die as it chews away. Bt is sold under several trade names. Again, check the OMRI listing for allowable organic brands.

3. Use the popular biological control, richogramma, an egg parasitoid. The tiny wasps lay their eggs in the eggs of caterpillars. A new wasp emerges from the parasitized egg rather than a new caterpillar.

Garlic sprays and hot pepper wax are getting a lot of press; garlic for repelling insects (Bogash says it can deter bigger pests like rabbits and groundhogs until they get used to the smell), and hot pepper wax for killing a number of insects from aphids and spider mites to thrips and leafminers. Garlic spray (garlic oil and water) is said to keep insects off plants and the key is to use it as a repellent spray on the plant before the bugs arrive, to keep insects from ever finding a home. A variety of hot pepper products are on the market. Or you can make your own (see sidebar for a common recipe).

Learn your beneficials

You probably knew lady beetles are your friends. But did you know other predators, like ants and wasps, collect insect prey to feed their developing young? Did you know fireflies do more than light up the night -- most are predators of slugs, snails and worms, according to Garden Insects of North America. The book even points out that some stink bugs are good. The Twospotted stink bug “specializes in beetle larvae such as the Colorado potato beetle” and the spined soldier bug primarily feeds on caterpillars.

Most ground beetles develop as predators. Soldier beetles can be important predators of aphids, mealybugs and other soft-bodied insects. Rove beetles are predators of insects found in soil. Even paper wasps feed their young on insects. (But, I can tell you first hand how aggressive they are in defending their nests, which they love to build inside high tunnels in places you don’t tend to see until it’s too late. Needless to say, they are no friends of mine!) There are many, many more. So know before you squish or you may be destroying a friend.

While there are pesticides and insecticides approved or allowable on a restricted basis by the Organic Materials Review Institute (OMRI) for certified organic growers, they should be used only as a last resort. Bogash advises keeping records of problems and scouting plants to discover pests before they take over.

All in all, if you use a reasonable crop rotation and have an awareness of insect problems that could occur, Bogash says growing cut flowers is nothing you can’t handle. I completely agree.

Next: Flower diseases--who, what, when, where and why.