March 2023 - 8A

CULTIVATION
cultivars were able to take high levels of fertilizer (over
2,000 ppm) while others appeared to max out at lower
levels (approximately 1,500 ppm or less).
in storage. This pathogen leads to fruit/stem rots,
with a white/gray or light brown moldy growth. The
disease develops as it overwinters in the soil as
mycelium, in plant debris or as sclerotia (hardened
survival structure). It requires cool, damp weather for
best germination.
Disease can be expected when nighttime
temperatures fall below 60° F with relative humidity
at 90% or higher. Southern blight can be a destructive
disease to numerous vegetables and fruit crops,
especially in tomato, pepper, melon, and watermelon.
Plants are attacked just below the soil and end up
girdled. This results in infected plants wilting then
desiccating completely in a brief time period. The
pathogen grows mycelium over infected tissue and the
soil surface, resulting in a white mat with tan/brown,
mustard-seed-size sclerotia. Environmental conditions
that are favorable for Southern blight disease
development are high temperatures (80 to 95° F),
humid conditions and an acidic soil. Sclerotia germinate
at pH 3 to 7, but is inhibited at pH levels above 7. These
two pathogens were confirmed with a lab analysis
after their discovery during routine scouting for pests
and diseases.
Both cultivars were planted on the same date and
Image 2. Southern blight, with white mycelium growing at
the base with mustard seed-size sclerotia. Photo: University of
Florida plant pathology department.
Insects & Pests
Another observation in
growing different genetics
in side by side trials has
been in susceptibility or
tolerance to insect pests
and diseases. A clear
example was in a field
trial with what we will call
Cultivar A and Cultivar B.
The farmer had many years
of experience growing a
wide variety of crops. This
hemp crop was grown
in the field, using raised
beds with plastic mulch
and drip tape. The two
diseases observed in the
field were Botrytis bud rot
(Botrytis) and Southern
blight (Sclerotium rolfsii).
Botrytis is a very common, widely distributed disease
on a wide variety of crops grown in the field, in
greenhouses, during the drying/curing phase and
8A | 2023 GUIDE TO HEMP PRODUCTION
Having some
sort of on-site trials is
important as farmers and
growers learn to grow this
new crop.
roughly the same size. They were fertilized based on soil
and tissue analysis. Cultivar A was stockier, with denser
flower and appeared more susceptible to Botrytis
(Image 1). There was very little to no Southern blight
observed in Cultivar A. Cultivar B had very little Botrytis
observed but much more Southern blight (Images 2
and 3). There was a clear distinction here, side by side,
where A was more susceptible to Botrytis but appeared
to be less susceptible to Southern blight, whereas
B was the opposite (less susceptible to Botrytis but
more susceptible
to Southern blight).
This susceptibility
or tolerance to the
two diseases can
be attributed to the
difference in genetics,
as all the other
variables such as
planting date, size/age
at planting, irrigation
schedule, fertilizer
regime, exposure
to environmental
conditions and
IPM program were
the same.
Need for Trialing
In conclusion,
having some sort of on-site trials is important as
farmers and growers learn to grow this new crop.
One of the main pieces of advice we give to new
March 2023

Table of Contents for the Digital Edition of March 2023
