The most serious insect pest on poinsettias is the white
fly. Mites, mealy bugs, thrips, and fungus gnats can also create problems. A
clean, weed-free greenhouse and a pest control program reduce insect problems.
Botrytis is a problem in the propagation area. Poinsettias are also very
susceptible to three major root rot diseases, Pythium, Rhizoctonia, and
Thielaviopsis. Well-timed fungicide applications reduce losses caused by fungi.
CHRYSANTHEMUM
Chrysanthemums (mums) have their origin in China, Japan, and Europe. There is evidence
that chrysanthemums were used in Chinese gardens around 550 BC. Mums were
brought to the United States and used only in the fall until the 1940s.
Then, it was found that chrysanthemums are photoperiodic and
thermoperiodic. Because flower buds set naturally from middle August to late
September, chrysanthemums are considered to be short-day plants. They are
lighted for vegetative growth and shaded between March and September to induce
flowering. By controlling light duration and temperatures, potted mum crops can
be produced throughout the year Easter and Mother's Day are two holidays that
see high sales of potted chrysanthemums.
Chrysanthemum varieties are very diverse. Mums come in many
colors and the flower forms differ There are also physiological differences
that influence production schedules. Mums are classified based on these
differences:
• Response group—One
grouping is based on the number of weeks it takes them to flower from the time
they begin receiving short days. For instance, a nine-week variety takes nine
weeks to flower once it is given short-day treatments. The response groups of
mums range from 6 weeks to 15 weeks. Garden mums include six-, seven-, and
eight-week varieties. The majority of potted chrysanthemums have a 9- or
10-week response.
• Flower forms—Mums
are also grouped by their flower forms, which include standard, spray, button,
spoon, decorative, daisy, spider, pompon, and anemone.
Propagation
As the popularity of chrysanthemums grew in the 1940s and
1950s, it was discovered that many of the plants were infected with viruses
that produced deformed growth. The Yoder Brothers Company began a crusade to
clean infected plants from the industry. They began producing cuttings free of
virus and other systemic diseases. Today, a few specialized companies provide
over percent of all the chrysanthemum
cuttings: The cuttings -are sold as rooted cuttings or as unrooted cuttings.
Cuttings are inches in length with three leaves. They are
rooted with bottom heat lit to maintain vegetative growth. Intermittent mist is
provided until roots form. Chrysanthemums are basal rooters. Fast-rooting
varieties root days.
Growing Procedures
The cuttings are graded or sorted before planting. This is
done according to the number of roots, diameter of the stem, and the length of
the stem. Failure to grade cuttings results in pots with lopsided growth. Some
cuttings in the pot may grow vigorously while others grow more slowly.
There are four main periods of growth and development in
producing a potted chrysanthemum crop. The first phase or vegetative phase
involves the promotion of root and leaf growth. The vegetative phase lasts
three to five weeks depending on the variety and the time of the year. Flower
bud initiation, flower bud development, and the finishing stages follow. Each
phase requires a different fertilizer rate and temperature.
Vegetative Phase
The vegetative phase is the most critical period of growth.
During this time, plants must build up reserves of sugar and produce a strong
root system. Begin feeding newly planted rooted cuttings immediately. Use a
starter fertilizer nitrogen at the first watering. Starter fertilizers are
typically high in phosphorous to encourage root growth. Thereafter, nitrogen
and potassium with each watering. Water when the growing medium approaches
drying.Long days must be provided to keep chrysanthemums in a vegetative stage
of growth. Interrupt the night darkness from December through February by
lighting the plants .From September through November and March through May,
light for three hours. In the summer months, light for one to two hours to be
sure plants stay vegetative.
PINCHING
Grow for 7 to 14 days or until roots appear at the
bottom of the pot before pinching the plants. Pinching is the removal of the
growing point of the stem. Pinching encourages breaks or branching of the
plants. Three to four strong breaks from a pinch are desired. Plants with good
lower leaf development produce more breaks than weaker plants. The results of
pinching include better-shaped plants that appear fuller and produce more
flowers. There are three methods of pinching:
The roll out pinch involves the removal of just the
meristematic tip of the stem. Care needs to be taken to remove the whole tip or
growth from the tip resumes. The roll out pinch is recommended in winter when
growth is sluggish.
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