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Some insect pests are very
specialized—usually feasting on one crop. Many are named after that one
particular crop that they ingest most—like pickleworms, melonworms, and
sweetpotato weevils. Unfortunately for growers of ornamentals, soybean,
maize, fruit, and vegetables, the Japanese beetle is not a picky eater. It
feeds on nearly 300 plant species in almost 80 plant families. The beetle, Popillia japonica,
is by far the most destructive pest of ornamental and turf plants in the
eastern United States, with more than $450 million spent each year to
control it and replace damaged plants. But there is hope, since there is one
plant that the hungry little critter may want to avoid—the geranium, Pelargonium
zonale. Though its lovely, colorful flowers are very attractive for
all and profitable for growers, the flowers are deadly to the beetles.
Within 30 minutes of consuming the petals, the beetle rolls over on its
back, its legs and antennae slowly twitch, and it remains paralyzed for
several hours. When paralyzed under laboratory conditions, the beetles
typically recover within 24 hours, but they often die under field
conditions because predators spot and devour them. The poisoning effect of geranium
flowers on beetles is not a new discovery; it has been reported in
scientific papers dating back to the 1920s. But the phenomenon has not
been studied in depth—how or why it happens—until recently, when Agricultural
Research Service scientists in Ohio picked up where scientists left
off more than half a century ago. Currently, Chris Ranger, an
entomologist in the ARS Application Technology Research Unit in Wooster,
is working on a natural, botanical formulation for controlling the beetles
based on paralytic compounds isolated from geraniums. Patent rights are
being pursued. Ranger is collaborating with Ajay Singh, a natural products
chemist from Rutgers, The State University of New Jersey. Also at Wooster, agricultural engineer
Heping Zhu is working on pesticidal droplet reactions on hairy and glassy
(waxy) geranium species that could help leaves retain and hold on to the
pesticides that are sprayed on them—which, in turn, could help reduce
pesticide use. Meanwhile, at ARS in Toledo,
horticulturist Jonathan Frantz is collaborating with Susan Stieve, curator
of Ohio State University’s Ornamental Plant Germplasm Center in
Columbus, in studies of begonias. Begonias are considered to be sensitive
to high light and perform best under low-light conditions found in shade
gardens or along the north side of houses. If varieties are found that
grow equally well in high light, they could be used in breeding programs
or grown commercially. This fits commercial growers’ systems well
because they have gone to great effort to maximize the light inside
greenhouses.
The team found that two varieties—Begonia
cubensis and B. echinosepala var. elongatifolia—performed
well in either light environment. “Their leaf area, plant weight, and
flower development did not appear to be negatively affected by the higher
light levels,” says Frantz. “Lower light environments still result in
less bleaching in other begonia species, but all species we tested had
similar sizes and developmental rates in either light level.” Frantz and Stieve are also studying
whether a specialized breed of begonia can tolerate colder temperatures. Ohio and neighboring Michigan are some
of the largest producers of horticultural plants, most of them grown in
greenhouses. The scientists are screening the begonias at two production
temperatures—5˚F colder than normal and 10˚F colder than
normal. Begonias are found naturally in a wide variety of climates and
altitudes—ecological clues that can be used to identify promising
germplasm. “For every one degree cooler, growers
can reduce heating bills by 3 percent in northern climates,” said
Frantz. “And with the way energy costs are rising, that can make a huge
difference in operating expenses. But the tradeoff is that cooler
temperatures can greatly delay flower development.” The trick is to find
varieties or species with acceptable growth and with flowers that are not
delayed significantly by cooler temperatures.—By Alfredo
Flores, Agricultural Research Service Information Staff.
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