Net Blotch
[Drechslera
dictyoides]
SYMPTOMS
Net
blotch is a disease that occurs on tall fescue during cool, wet, and cloudy periods
in the spring or early summer. Net blotch is a ‘Helminthosporium’ disease,
which is a complex of diseases caused by fungi that produce large, cigar-shaped
spores. Symptoms of net blotch appear as tiny, brown spots on the leaves. As
the lesions expand, they become oval or square and coalesce to form a net-like
pattern on the leaf. From a distance, net blotch appears as a general thinning
of the turf stand that is yellow or brown in color.
|
net blotch leaf spots
|
Characteristic
|
Description
|
|
Host
Grass Species
|
tall
fescue
|
|
Month(s)
with symptoms
|
March
to June, Sept to November
|
|
Stand
Symptoms
|
irregular
distribution across turf stand
|
|
Foliar
Symptoms - Location/Shape
|
angular
leaf spot or oval leaf spot
|
|
Foliar
Symptoms - Color
|
yellow,
brown
|
|
Root/Crown
Symptoms
|
none
|
|
Fungal
Signs
|
none
|
Note: Still not
sure if this is the right disease? The Turfgrass Disease
Identification program may be helpful. Or consult the experts at the Turf
Diagnostics Lab. Check the TurfFiles glossary for definitions
of unfamiliar terms.
FACTORS
AFFECTING DISEASE DEVELOPMENT
Net blotch is
one of several Helminthosporium diseases which survive in thatch during periods
that are unfavorable for disease development. These fungi are most active
during periods of cool (60 to 65°F) and wet weather, but some are able to cause
disease whenever temperatures are above freezing.
Net blotch is most severe on turf
that is growing slowly due to adverse weather conditions or improper management
practices. Shaded areas with little or no air movement result in weak turf and
extended periods of leaf wetness that favor disease development and plant
infection. Deficient or excessive nitrogen, excessive thatch, extended periods
of leaf wetness, drought stress, and low mowing heights are factors that
encourage the development of Helminthosporium diseases.
Certain cultivars of turfgrasses
are very susceptible to injury from Helminthosporium diseases while many of the
newly released cultivars have exhibited good resistance.
CULTURAL
CONTROL
Use
turfgrass cultivars with resistance to this disease when available. Use of
resistant cultivars is one of the best means of prevention. Select cultivars
based on regional trials and University recommendations. When planting
cool-season turfs, use blends and mixtures of multiple species and/or varieties
whenever possible.
Fertilize to meet the nutritional
needs of the turf but avoid over-stimulation and the development of lush,
succulent growth. Do not apply more than one pound of nitrogen per 1,000 square
feet in a single application. Tall fescue should be mowed to a height of 3 to
3.5 inches. Keep the mower blades sharp to prevent open wounds through which
the fungus can enter.
Reduce extended periods of leaf
wetness by watering deeply but infrequently to wet the entire root zone. Do not
irrigate just before or after sunrise, and ensure good surface and soil
drainage. Remove unwanted vegetation that impedes air movement and prune trees
to allow for light penetration. Power rake or dethatch to remove excessive
thatch and reduce the potential for pathogen survival.
CHEMICAL
CONTROL
Net blotch can be controlled on a
preventative or curative basis. Applications should be made in the early stages
of disease development for best results. Susceptible turfgrasses should be monitored
regularly for disease development during cool and wet weather conditions.
|
Fungicide
|
Efficacy (1)
|
Resistance Risk (2)
|
Class (3)
|
Products (4)
|
|
iprodione**
|
++++
|
4
|
dicarboxamide
|
26GT, Iprodione Pro
|
|
vinclozolin**
|
++++
|
4
|
dicarboxamide
|
Curalan, Touche
|
|
mancozeb**
|
++++
|
2
|
dithiocarbamate
|
Fore, Dithane, Protect
|
|
azoxystrobin
|
++++
|
6
|
QoI
|
Heritage
|
|
chlorothalonil**
|
+++
|
2
|
nitrile
|
Daconil, Chlorostar, Echo, Manicure
|
|
pyraclostrobin
|
+++
|
6
|
QoI
|
Insignia
|
|
propiconazole
|
++
|
4
|
DMI
|
Banner MAXX, Propiconazole G-Pro, Propiconazole Pro,
Quali-Pro Propiconazole, Savvi, Spectator
|
|
myclobutanil
|
+
|
4
|
DMI
|
Eagle
|
|
thiophanate-methyl
|
?
|
6
|
benzimidazole
|
3336, Fungo, T-Storm, Systec
|
|
maneb**
|
?
|
2
|
dithiocarbamate
|
Pentathlon
|
|
thiram**
|
?
|
2
|
dithiocarbamate
|
Spotrete
|
|
triticonazole
|
?
|
2
|
DMI
|
Trinity
|
|
fludioxonil
|
?
|
2
|
phenylpyrolle
|
Medallion
|
|
fluoxastrobin
|
?
|
6
|
QoI
|
Disarm
|
|
trifloxystrobin
|
?
|
6
|
QoI
|
Compass
|
|
** Not for application to
residential lawns.
|
|
Footnotes:
|
|
(1)
|
Efficacy Codes:
|
|
|
++++
|
excellent control when
conditions are highly favorable for disease development
|
|
|
+++
|
good control when disease
pressure is high, or excellent control when disease pressure is moderate
|
|
|
++
|
good control when disease
pressure is moderate, excellent control when disease pressure is low
|
|
|
+
|
good control when disease
pressure is low
|
|
|
0
|
does
not provide adequate control under any conditions
|
|
|
?
|
cannot be rated due to
insufficient data
|
|
(2)
|
Resistance Risk:
|
|
|
1
|
Rotating and tank-mixing not necessary,
but recommended to avoid potential side effects from continuous use of same
chemical class.
|
|
|
2
|
Rotate to different chemical
class after 3-4 applications; tank-mixing not necessary.
|
|
|
3
|
Rotate to different chemical class
after 2-3 applications; tank-mixing not necessary.
|
|
|
4
|
Rotate to different chemical
class after 1-2 applications; tank-mixing not necessary.
|
|
|
6
|
Rotate to different chemical
class after 1-2 applications; tank-mixing with low or moderate risk product
recommended.
|
|
|
9
|
Rotate to different chemical
class after EVERY application; tank-mix with low or moderate risk product for
EVERY application.
|
|
(3)
|
Continual use of fungicides
with similar control mechanisms (modes of action) can result in fungi that
are resistant to some chemicals. Poor or ineffective disease control can be
expected when this occurs. Managers can reduce the chances of this happening
by mixing or alternating fungicides belonging to different chemical classes.
|
|
(4)
|
Recommendations of specific
chemicals are based upon information on the manufacturer's label and
performance in a limited number of trials. Because environmental conditions
and methods of application may vary widely, performance of the chemical will
not always conform to the safety and pest control standards indicated by
experimental data. When more than one brand name exists for an agricultural
chemical, the name of brand that first came onto the market is listed first.
Otherwise, brand names are listed in alphabetical order. The order in which
brand names are given is not an indication of a recommendation or criticism.
|
|
|
Recommendations for the use of agricultural
chemicals are included in this publication as a convenience to the reader.
The use of brand names and any mention or listing of commercial products or
services does not imply endorsement by North Carolina State University or
discrimination against similar products or services not mentioned. Other
brand names may be labeled for use on turfgrasses. Individuals who use
agricultural chemicals are responsible for ensuring that the intended use
complies with current regulations and conforms to the product label. Be sure
to obtain current information about usage regulations and examine a current
product label before applying any chemical. For assistance, contact your
county's Cooperative Extension agent.
|
© North Carolina State University. This information sheet was prepared
by Lane P. Tredway, Gail G. Wilkerson, Bridget R. Lassiter, Jenifer J.
Reynolds, and Gregory S. Buol. Departments of Plant Pathology and Crop Science,
College of Agriculture & Life Sciences, North Carolina State University.
Prepared April 29, 2008. Available on-line at
www.turffiles.ncsu.edu. This publication was made possible through a grant
provided by the Center for Turfgrass Environmental Research & Education
(CENTERE) whose purpose is to support worthwhile projects that will benefit
both the private sector and the public, and protect the environment.