February 2025 - 32

PLANT HEALTH
Since pythium
root rot is difficult to
control once it takes
hold, prevention
is essential.
cleaned and disinfected. Always use high-quality, diseasefree
cuttings and immediately remove any plants showing
signs of infection. The presence of algae is a great indicator
of water, fertilizer and sanitation issues and serves as a
warning for potential pythium problems (Figure 4).
Chemical controls
Since pythium root rot is difficult to control once it takes
hold, prevention is essential. Pythium often enters the
greenhouse on infected liners or cuttings, so it's important
to inspect all incoming plants for signs of disease and seek
a laboratory diagnosis for any suspicious cases. A proactive
fungicide program is vital for controlling the spread of
pythium and minimizing losses.
Developing an effective fungicide program is challenging
because of the risk of resistance, particularly since some
pythium species are highly adaptable. To minimize the risk
of fungicide resistance, rotate fungicides with different FRAC
codes. Fungicides should be applied preventatively, as once
the infection is established, control is much more difficult
(Table 1).
Fungicide application
Begin with a Banol (FRAC 28) drench at the rooted
cutting or plug stage to protect against early infection.
Apply the recommended rate of 2 ounces per 10 gallons,
drenched onto the cutting bed at a rate of two gallons per
10 ft² before setting the cuttings. Banol can also be used
as a dip for bare root plants before potting. After potting,
drench each pot with 3.5 ounces of solution per 4-inch
pot. While some growers may be concerned that applying
fungicides at this stage might inhibit rooting, there is little
evidence to support this concern for most fungicides.
Two to three weeks after pinch, apply either Terrazole L
(FRAC 14) at a rate of 4-6 ounces or Terrazole WP at
4-6 ounces. Terrazole efficacy can be affected by pH, so
32 FEBRUARY 2025 GPNMAG.COM
Figure 4. The presence of
algae is a great indicator of
water, fertilizer and sanitation
issues, and a warning sign for
potential pythium problems.
TRADE NAME
COMMON
NAME
Aliette fosetyl-Al
Banol propamocarb
Segway cyazofamid
Subdue Maxx mefenoxam
Terrazole L or WP etridiazole
FRAC
CODE
P07/33
28
21
4
14
RATE
6.4-12.8 ounces/
100 gallons
2 ounces/10 gallons
2-3 ounces/
100 gallons
1 ounce/100 gallons
4-6 ounces/
100 gallons
Table 1. Fungicides should be applied preventatively. To minimize
the risk of fungicide resistance, rotate fungicides with different
FRAC codes.
adjusting the acidity of the irrigation or ebb flow water may
improve performance. Alternatively, Subdue Maxx (FRAC 4)
can be used at 1 ounce per 100 gallons if resistance is not
an issue. Two to three weeks later, apply Segway (FRAC 21)
at 2-3 ounces per 100 gallons. If disease pressure is
high, consider adding Aliette (FRAC P07/33) or another
phosphorous acid fungicide (FRAC 33) to the rotation. It's
important to note that Segway should not be used more
than twice per cropping cycle.
To improve fungicide distribution and uptake, always
follow drenches with additional water - at least half the
volume of the fungicide solution - within 24 hours. This
improves distribution of the fungicides and ensures better
efficacy. By rotating fungicides with different FRAC codes,
you can help reduce the risk of resistance developing in
your greenhouse operation.
Janna Beckerman is ornamentals technical specialist for Envu. She is
also a former professor and Extension specialist at Purdue University
of 20 years and can be reached at janna.beckerman@envu.com.
http://www.GPNMAG.COM
February 2025

Table of Contents for the Digital Edition of February 2025
