Transcript Biotic and Abiotic Disorders of Forage Crops

Biotic and abiotic disorders of
forage crops
Dr. Mary Burrows
Montana State University
Bozeman, MT
Overview
• How do I tell if my forage crop has a
nutrient deficiency?
• How do I recognize and manage
common plant diseases in alfalfa and
hay barley?
Nutrient deficiency
• Macronutrients are nutrients required in relatively large amounts
– Nitrogen (N)
– Phosphorous (P)
– Potassium (K)
– Sulfur (S)
• Micronutrients are needed in small or trace amounts for plant
survival and adequate production
– Calcium (Ca)
– Magnesium (Mg)
– Iron (Fe)
• A balance of nutrients is required for optimum growth
• Nutrient deficiency can be easily confused with disease:
– PATTERNS & testing
The most common nutrient
deficiencies
• Cereals: Nitrogen, Phosphorous
• Alfalfa: Phosphorous, Potassium, Sulfur
Nitrogen fertilization
• Not necessary for alfalfa except small
amounts at the time of establishment;
adding nitrogen to mature alfalfa can
reduce N-fixing bacterial activity
• Manage N in cereals for yield and
protein
What does nitrogen deficiency look like?
Reduced tillering, stunting, poor kernel fill, and low grain protein
Nitrogen deficiency in cereals
• In the spring, often associated with cool
wet weather: if there is sufficient soil
nitrogen plants will green up when it
gets warmer
• Foliar symptoms of nitrogen deficiency
can be similar to root rots
Phosphorous deficiency symptoms
• Cereals: lack of vigor and poor tillering;
purpling less common
• Alfalfa: plants are stunted and unthrifty,
purpling of stems and leaves, root
development is impeded and they
develop a light brown color. Growth is
abnormally stiff and upright. Yellowing
and death of older leaves occur with
severe deficiency
Phosphorous deficiency
Potassium deficiency symptoms
• Cereals: Growth short and uneven and few heads
form; leaves bluish green and dying off of older
leaves beginning near tips and margins. White
blotchy lesions develop when deficiency is very
acute. More susceptible to powdery mildew.
• Alfalfa: small white spots on the older leaves, often
on leaf margins. Leaf tissue between the spots
yellows and dies. Often symptoms are more
pronounced on regrowth after first or second cutting.
Potassium deficient plants are more susceptible to
winter injury.
Potassium deficiency
Sulfur deficiency symptoms
• Cereals: overall yellowing and stunting
of the plant. It is difficult to distinguish
sulfur from nitrogen deficiency
• Alfalfa: stunting of plants and yellowing
of youngest leaves and veins
Sulfur deficiency
How do I manage nutrient
deficiencies?
• Get your soil tested
– Alfalfa: every 3 years
– Grass: nitrate every year; P & K every 3 yr
• Get a tissue test if necessary
• Amend soil
http://landresources.montana.edu/soilfertility/
How do I tell if it’s a nutrient
deficiency or a disease?
•
•
•
•
Symptoms
Patterns
Soil test
Send in a sample
Sample Submission
• Accurate Diagnosis depends on a
good sample and symptom
description
Enter sample
information into
PDIS (Plant
Diagnostic
Information
System)
16
Samples must contain the right material:
an entire plant or several plants if practical
Foliage diseases
Keep most roots and
soil intact if possible
Diseases may
show up on any
part of the
plant.
Check for injuries, disease
on the main stem/trunk
17
Dead Plants Tell no Tales
 Avoid dead plants
 Choose plants which show
a range of symptoms:
moderate to severe
18
Packaging & Shipping
Good
Intentions
19
Actual Results
20
Packaging and Shipping blunders
Soil on foliage during
shipping creates
“diseases” that were
not there when the
sample was collected.
21
Packaging and shipping blunders
Sample
soup
Don’t add water or wrap in wet paper towels
22
Good Packaging
 Plastic bag to keep soil
on roots
 Dry paper towels to
protect leaves from
contact with plastic bag23
Sample Submission
• Try to keep sample as fresh as possible until
you can get it to the county agent: refrigerate
if possible.
• Include photographs illustrating the problem
if possible.
24
Overview
• How do I tell if my forage crop has a
nutrient deficiency?
• How do I recognize and manage
common plant diseases in alfalfa and
hay barley?
Crown rot symptoms in alfalfa
Verticillium, Fusarium,
Rhizoctonia, Phytophthora,
Pythium, Phoma,
Mycoleptodiscus, Stagonospora,
and Macrophomina
Brown root rot of alfalfa
• Phoma sclerotioides
• Most active in late winter and early
spring
• Very broad host range, including
grasses
2006 Survey
Crown rot control
• Variety selection
• Promote vigorous growth with proper fertility and
irrigation practices.
• Control foliar diseases and insect problems. Crown rot
fungi often enter through wounds.
• Avoid cutting hay when soils are wet.
• Avoid heavy grazing.
• Control weeds with herbicides and avoid cultivation
practices which damage crowns.
• Avoid field sites with heavy or poorly-drained soils.
• Rotate out of alfalfa for 2-3 years.
• Heavy watering in the fall will delay dormancy
– Stop watering end of September
Stem nematode in alfalfa
• Ditylenchus dipsaci
White flagging
Swollen nodes
Stunted plants, shortened internodes
Crinkled leaves (between veins)
2009, Yellowstone Co.
Stem nematode on alfalfa
• Spread by surface water runoff, irrigation,
wind-blown crop debris, infested hay, soil and
crop debris clinging to equipment, humans and
livestock, and with seed
• Prevent introduction of nematodes into a field
• Rotate with a non-host (not alfalfa or sainfoin)
and control alfalfa volunteers 2-4 years
• Some resistant varieties
• Cut infected fields slightly higher and when dry
to reduce spread
Foliar diseases of alfalfa
No fungicides are labeled for forage alfalfa
Spring black stem
• Phoma medicaginis
• Residue-borne
• Primarily moves via
water; also via
equipment, insects, and
wind
• The first cutting is often
the most damaged
• Control by early cutting,
variety resistance
Foliar diseases of alfalfa
No fungicides are labeled for forage alfalfa
Stemphylium leaf spot
• Stemphylium botryosum
• Residue-borne
• Primarily moves via
water; also via
equipment, insects, and
wind
• Control by early cutting
and variety resistance
Spot and net blotch of barley
• Primarily important under irrigation
• Residue borne
How do you control?
Smuts and bunts
Bunt
Smut
• Favored by a cool, wet spring
• Soilborne and in contaminated seed
• Seed treatments are effective
Seed treatment effects on covered smut of
spring barley, 2005, Bozeman
Treatment
Emergence Smutted
(pl/3m)
heads/6m
Yield
(kg/ha)
No treatment
144
62
57.3
Allegiance
145
49
59.4
Charter+Allegiance
147
0
64.7
BAS 500XBF +
Allegiance
145
2
62.9
BAS + Charter +
Allegiance
144
0.3
63.1
Raxil MD
146
0
63.4
Dividend XL RTA
140
0
63.3
Similar story for loose smut of barley, common bunt of wheat
Dwarf bunt
Dwarf bunt
• Tilletia controversa Koch (TCK)
• Winter wheat
• Occurs when plants are exposed to
prolonged snow cover
• Soilborne spores germinate under the
snow and infect young plants
• Control with seed treatment (Dividend)
Seed treatments for smuts and bunts
Barley
Covered
Loose
smut
Smut
Wheat
Dwarf bunt Common
(TKC)
bunt
Charter
+
+
-
+
DBGreen
+
-
-
+
Dividend
+
-
+
+
Raxil
+
+
-
+
Vitavax
+
+
-
+
Use high rate
Reasons for seed treatment
From: McMullen and Lamey. 2000. Seed treatment for disease control. NDSU extension publication PP-447
Why do we need to treat seed??
• Give crop the best possible chance to
emerge and establish
• Improve the general health of the grain
crop.
In 1972, 30% of the Montana wheat
crop carried smut spores
Release of Carboxin followed by other systemic fungicides
In 1997, < 2% of the Montana wheat
crop carried smut spores
Survey of Canada, 2005
32% of wheat fields had smut
57% of barley fields had smut
Smut spores are readily available
We cannot predict when this disease will
become an urgent issue
Varieties, cultural practices, and the weather
change from year to year
Ergot in grasses used for
feed/forage
• Calviceps purpurea
• Sclerotia contaminate seed
• Soilborne sclerotia overwinter;
viable approximately 3 yr in soil or
longer in stored grain
• Ascospores dispersed by wind and rain infect
florets; conidia formed on ovary surface serve
as secondary inoculum
• Grain converted into sclerotia
• More abundant during moist growing seasons
Ergot history (rye)
• 400 B.C. Hippocrates prescribed ergoty
grain to “further childbirth”
• 1039 St. Anthony’s fire
• 1692 Salem witch trials
• 1935 LSD was synthesized during
research on the active ingredients in
ergot
– Ergot contains Lysergic acid
Ergoty grain is toxic to animals
4 forms of toxicity
• Convulsions
• Gangrene
• Hyperthermia (increased body temperature)
in cattle
• Agalactia (no milk) and lack of mammary
gland development, prolonged gestations,
and early foal deaths in mares fed heavily
contaminated feed
Ergot toxicity symptoms
depend on:
• Type of ergot consumed
• Ratio of major toxic alkaloids present in the ergot:
ergotamine, ergotoxine, and ergometrine
• Frequency and quantity of ingestion
• Climactic conditions when ergot was growing
• Species of ergot
• Other impurities in the grain such as histamine and
acetylcholine
• Claviceps purpurea is usually associated with
gangrenous ergotism
Ergot control
•
•
•
•
•
•
Harvest before the heads are mature
Rotate out of grains at least 1 yr
Deep plowing
Plant only ergot-free seed
Control grassy weeds
Seed treatments not effective
There are a wide array of seed
treatment options available
• http://msuextension.org/publications/AgandN
aturalResources/MT199608AG.pdf
• http://www.ag.ndsu.edu/pubs/plantsci/
pests/pp622w.htm
• http://www. greenbook.net
• http://www.cdms.net
Be a First Detector
First Detectors are the front line for early
discovery of new invasive pests.
Your role as a First Detector
• Receive NPDN First Detector training
• Take online modules (http://cbc.at.ufl.edu)
• Attend classes like this one
• Be alert to the unusual or different
• Be placed on a national notification
registry of First Detectors
• Receive pest alerts and other
relevant updates
MODULE 1 – Mission of the NPDN
Importance of Early Detection
critical control point
amount of disease (%)
100
80
pathogen
detection
60
40
20
0
high
impact
economic
threshold
low
impact
0 2 4 6 8 10 12 14 16 18 20 22 24
time (weeks)
Montana State University
Schutter Diagnostic Lab
Physical address
121 Plant BioScience Bldg. (PBB)
Mailing Address
119 Plant BioScience Bldg.
P.O. Box 173150
Bozeman, MT 59717-3150
(406) 994-5150 or -5690
[email protected]
http://diagnostics.montana.edu/