May 2019 - 36

PLANT HEALTH
It's Whitefly Time:
How to Update Your Rotation Program
Battling whiteflies is a constant challenge for growers. Selecting the right products with different
modes of action is the first step in winning the battle.
BY ANNA V. CHAPMAN
S
pring is here. One of the most challenging pests to be on the
lookout for this time of year is whiteflies, with sweet potato
whitefly (Bemisia tabaci) being the most financially destructive in
greenhouse and nursery production. Complicating the efforts to combat
sweet potato whitefly is the complexity of biotypes you may encounter
and the susceptibility differences of these biotypes to chemical control.
Sweet potato whiteflies frequently travel into greenhouses on infested
propagation material or fly in from neighboring agricultural fields and
once they have found their way into your ornamental production, there
are a number of plant hosts they will infest. Whiteflies feed directly on
the phloem or sap of the plant, removing valuable nutrients and water
while reducing plant quality and vigor.
Additionally, whiteflies excrete sugary rich honeydew which coats
leaves and promotes the growth of sooty mold which further damages
the quality of the plant. Both direct feeding damage and sooty mold
are exacerbated by the sweet potato whitefly's potential to reproduce
rapidly, which intensifies plant injury.
BATTLING B AND Q BIOTYPES
Most growers are familiar with the two biotypes of sweet potato
whitefly; the B and Q biotypes. Although these biotypes look exactly
alike, they are distinguishable, most notably to growers, by their
response to certain pesticides. Both biotypes were introduced to the
Unites States and quickly became serious pests in both agricultural
crops and ornamentals.
The B biotype introduced to the United States in the 1980s is the
most commonly encountered type with several effective insecticide tools
available for control. However, this species overall does have a tendency
for resistance. Rotating the use of effective products will help prevent
resistance development in the B biotype and keep chemical tools
effective for longer.
The Q biotype introduced in the early 2000s has spread across the
country with at least 26 states reporting occurrences, largely within
greenhouses. Managing the Q biotype is a greater challenge due to
known resistance to several chemical classes which limits the number
of insecticides available for treatment. This includes some insect
growth regulators, pyrethroids, pymetrozine and the neonicotinoid
imidacloprid. The recent pressure on growers to stop the use of
neonicotinoid insecticides has resulted in many domestic and overseas
growers moving away from effective insecticides to older chemistries.
This undoubtedly has contributed to the sweet potato whitefly problem
overall and reported failures coming from greenhouses and nurseries
across the U.S. and in Canada.
CREATING THE RIGHT ROTATION
For managing both B and Q biotype, the name of the game is keeping
population numbers low and breaking the life cycle and reproduction
potential of the insect. In a good management program, monitoring and
sending off whitefly samples for identification is a great step to help
guide your selection of products for rotation and hopefully decrease
the number of needed applications to keep sweet potato whitefly under
Bemisia tabaci male and female mating pair.
36 MAY 2019 GPNMAG.COM

http://www.GPNMAG.COM

May 2019

Table of Contents for the Digital Edition of May 2019