October 2020 - 20
PLANT HEALTH
Protecting Poinsettias
Through Shipping and Finishing Strong
BY NANCY RECHCIGL
W
ith fall now upon us, poinsettia production is in full swing.
From mid-season to finish, it is important to continue
watching for common pest and disease problems, such
as whiteflies and foliar diseases. Closely monitoring plants and
recognizing problems early allows you to make corrective actions
sooner, so crop quality is not put at risk.
GAIN CONTROL OF COMMON DISEASES
The most common diseases you may encounter when growing
poinsettias are:
Alternaria and Xanthomonas leaf spots. Alternaria leaf spots
begin as small lesions with a tan center and dark margins. They are
somewhat rounded and usually surrounded by a chlorotic tissue.
As the infection spreads, the leaf will become more chlorotic
and drop from the plant. These spots can easily be mistaken for
bacterial leaf spot caused by Xanthomonas axonopodis.
Infections by Xanthomonas spp. cause small, angular-shaped
spots with dark, brown margins. If you hold the leaf up toward the
light, you may notice water-soaked tissue around the margin of the
lesion. These lesions may also be surrounded by chlorotic tissue.
Keeping water off the foliage will help reduce the spread and
Fall is here, and poinsettia production is in
full swing. Planning ahead and recognizing
problems early will help growers finish the
season strong with high-quality crops.
severity of fungal and bacterial leaf spot diseases. Many of the
fungicides used in poinsettia production have good activity against
Alternaria sp. Products containing copper, such as Phyton 27,
Camelot and Kalmor fungicides, and biologicals such as Triathlon
BA and Cease biofungicides, may help minimize the spread of
bacterial diseases.
Botrytis. Botrytis thrives in cool, humid environments and can be
particularly problematic in the later part of poinsettia production.
Initial infections cause water-soaked, V-shaped lesions on the
foliage and bracts. Once established, the mold can quickly spread
throughout the crop and production area.
Powdery mildew. Powdery mildew can be a problem on
poinsettias produced in cooler regions of the country. Infections
initially appear as small, chlorotic spots on the foliage that are
soon covered with white, fluffy colonies of the fungus. Over time,
they increase in size and number to cover the plants' surface,
reducing growth and causing leaves to turn yellow, brown and
then drop.
KEEP WHITEFLIES AWAY
By far, the most significant and damaging pest on poinsettias is
the whitefly. Adult and immature whiteflies have piercing-sucking
mouthparts that are inserted into the phloem and extract plant
sap, which affects plant vigor. Indications of whitefly activity
include:
* Reduced leaf expansion
* Yellowing of foliage
* Sticky honeydew secretions and black sooty mold growth on
the upper surface of leaves
20 OCTOBER 2020 GPNMAG.COM
http://www.GPNMAG.COM
October 2020
Table of Contents for the Digital Edition of October 2020
October 2020 - 1
October 2020 - 2
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