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 soilhttp://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

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Sample Submission• Accurate Diagnosis depends on a

good sample and symptom description

Enter sample information into PDIS (Plant Diagnostic Information System)

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Foliage diseases

Check for injuries, disease on the main stem/trunk

Keep most roots and soil intact if possible

Samples must contain the right material: an entire plant or several plants if practical

Diseases may show up on any part of the plant.

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Dead Plants Tell no Tales

Avoid dead plants Choose plants which show

a range of symptoms: moderate to severe

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Packaging & Shipping

Good Intentions

20Actual Results

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Packaging and Shipping blunders

Soil on foliage during shipping creates “diseases” that were not there when the sample was collected.

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Packaging and shipping blunders

Don’t add water or wrap in wet paper towels

Sample soup

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Good Packaging

Plastic bag to keep soil on roots

Dry paper towels to protect leaves from contact with plastic bag

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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.

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 Stunted plants, shortened internodesSwollen nodes 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 alfalfaNo 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 alfalfaNo 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 buntsBunt

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 (pl/3m)

Smutted 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 buntsBarley Wheat

Coveredsmut

Loose Smut

Dwarf bunt(TKC)

Common bunt

Charter + + - +

DBGreen + - - +

Dividend + - +Use high rate

+

Raxil + + - +

Vitavax + + - +

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 animals4 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 symptomsdepend 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/AgandNaturalResources/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

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Montana State UniversitySchutter 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

diagnostics@montana.edu

http://diagnostics.montana.edu/