1. Unit 4: Plant Disease Management for Field Crops

2. Unit 4: Plant Disease Management for Field Crops
Unit 4 Objectives:
Discuss some common plant disease problems of common field crops in IL
Awareness of possible prevention/treatment methods
Understanding of the types of chemicals or treatments necessary for control

3. Unit 4: Plant Disease Management for Field Crops
Crop yield and quality is affected by disease each year in IL
Disease management strategies should be part of your IPM plan
Resistant or tolerant varieties of crop
Crop rotations
Fungicides
Use in conjunction w/ other practices or as a last resort
Appropriate agronomic practices

4. Unit 4: Plant Disease Management for Field Crops
Success often depends on amount of scouting, stage of identification, and accuracy of diagnosis
Proper scouting will ensure that controls/treatments are used at the most effective times
Can help prevent an economic loss

5. Unit 4: Plant Disease Management for Field Crops
Disease Diagnosis
Accurate diagnosis is critical first step for control
Many diseases or nutrient deficiencies can cause the same symptoms
Must correctly diagnose in order to prevent unnecessary applications
Plants should be collected for identification as soon as disease is suspected
Is this always realistic?

6. Unit 4: Plant Disease Management for Field Crops
Best to try to identify the disease while the plant is still alive
Samples can either be sent to the Plant Clinic at U of I or be taken to the local Extension Office
Read the Label
Make sure you understand all restrictions associated w/ each chemical
These chemicals may not be used as frequently as herbicides or insecticides, so you may not be as up to date w/ them

7. Unit 4: Plant Disease Management for Field Crops
Must be purchased and applied by a licensed applicator
Fungicide Guidelines
Seed Treatments
Greatest benefits found when:
Seed is low quality due to damage or fungal infestation
Seedbed is cool and wet delaying germination and emergence
Low seeding rates
Should not be used as a substitute for good quality seed

8. Unit 4: Plant Disease Management for Field Crops
Low yields and economic losses will still be realized w/ low quality or damaged seed
Selection is crucial
Some treatments may only control specific pathogens
Foliar Treatments
May reduce losses in corn, soybeans, and small grains
Should only be used on fields w/ an expected disease severity
If the disease is diagnosed early, and fungicide applied correctly, should have maximum benefit

9. Unit 4: Plant Disease Management for Field Crops
Fungicides applied to corn usually reserved for seed-production fields
Leaf blights
Gray leaf spot
Rust diseases
Generally justified only when disease is prevalent within 1-2 weeks of tasseling
Infections occurring 1-2 weeks or later after tasseling usually not economically controlled
Foliar fungicides applied to small grains
Rusts
Septoria

10. Unit 4: Plant Disease Management for Field Crops
Leaf blights
Tan spot
These tend to occur after inadequate rotations and during damp weather
Most damage occurs from emergence to flag leaf/early milk stage
Fungicides can increase yields, seed weight, and quality
Decisions to spray should be based on the amount of disease at flag leaf emergence
Use of adjuvants is recommended (especially for corn and small grains)

11. Unit 4: Plant Disease Management for Field Crops
Nematicide Applications
Granular forms for corn and sorghum should be applied as band treatments
Should only be used when soil analysis shows high numbers of parasitic nematodes
Not designed to replace crop rotation or use of resistant varieties

12. Unit 4: Plant Disease Management for Field Crops
Alfalfa Seedling Blight
Caused by soil-borne fungi
Often occurs under wet conditions
Usually the first disease stress alfalfa may encounter
Often leads to poor or stunted stands
May survive, but yields will be reduced

13. Unit 4: Plant Disease Management for Field Crops
Easy way to suspect is if alfalfa stand emerges, but weeds grow quicker
Alfalfa usually grows very aggressively and crowds out weeds

15. Unit 4: Plant Disease Management for Field Crops
Alfalfa Root rots
Phytophthora, Fusarium wilt, Aphanomyces
Causes poor seedling stands, as well as, root damage
Identified by lesions on the taproot, subsequent disintegration of root tissue, and death
Control w/ resistant varieties

17. Unit 4: Plant Disease Management for Field Crops
Corn Gray Leaf Spot
Early symptoms are signified by 1/16” olive spots on the leaves w/ a yellow halo
At two weeks the spots are their signature gray or tan color
¾ to 2 ½” long
Run parallel to leaf veins
Begins on lower leaves and can spread upward
Entire leaf may appear gray under extreme conditions
Moist conditions and degrees are ideal

19. Unit 4: Plant Disease Management for Field Crops
Corn Stalk Rot
Fusarium
Leaves turn from healthy green to dull green
Lower stalk yellows
Stalk easily collapses and will cause lodging
Inside of the stalk may be pink
Favorable conditions
Dry early
Above avg. rain midseason
Temps degrees
Many other types of stalk rot are known

21. Unit 4: Plant Disease Management for Field Crops
Soybean Brown Stem Rot
Soil borne disease that becomes visible late in the season
Survives on plant material that may be buried >1’ deep
Infects the roots and stem early in life
Grows w/ the plant
Often infects the xylem tissue and restricts nutrient and water passage as the plant matures

22. Unit 4: Plant Disease Management for Field Crops
Symptoms
Typically not visible until late reproductive stages
May not be visible at all
Internal browning of vascular tissue in stem and/or leaves
Leaves may have appearance similar to high temperature scorching
May occur in circular patterns
Favorable weather conditions
Cool wet conditions either in early development or at reproductive stages
Development inhibited above 80º

26. Unit 4: Plant Disease Management for Field Crops
Soybean Phytophthora Root Rot
Spores reside in the soil
Germinate under wet conditions to form more spores
Mobile w/ soil water
Encysts on soybean roots
Symptoms
Stand reduction either pre or postemergence
Leaves may wilt
Water soaked lesions on stem and/or roots

27. Unit 4: Plant Disease Management for Field Crops
Favorable Conditions
>60º temps
Very wet soils
Poorly drained
Low areas
Compacted soils
High clay soils
Not restricted to these areas only

30. Unit 4: Plant Disease Management for Field Crops
Soybean Cyst Nematode
Very similar symptoms to many other diseases
Can go undetected as the cause of economic loss for many years
Will often occur in circular/oval shaped patterns
Infected plants will be less vigorous and somewhat yellow
May be slow to fill foliage

31. Unit 4: Plant Disease Management for Field Crops
Severity of symptoms can vary greatly from nonexistent to very visible
Infections cause dwarfed and stunted root systems
Can reduce the number of nitrogen-fixing nodes
Roots may be susceptible to other diseases
True identification can only be done by root examination
White/yellow oval shaped eggs on the roots
Nodes are much smaller than the nitrogen nodes

36. Unit 4: Plant Disease Management for Field Crops
Asian Soybean Rust
Severe foliar damage
Destroys photosynthetic tissue
Early defoliation
Early maturation
Yield losses can be 10-80%
6 hours of wet conditions and temps 59-82º ideal for germination
Dry conditions will restrict it

37. Unit 4: Plant Disease Management for Field Crops
Spores penetrate cells directly instead of wait for another opening in the leaf
9-10d from initial infection to next stage of spore production
Common hosts include kudzu, vetch, yellow sweet clover
Spreads w/ wind patterns

41. Unit 4: Plant Disease Management for Field Crops
Wheat Septoria Leaf Blotch
Recognized by oval shaped lesions on the leaves
Centers of the lesions may be grayish
May ooze when squeezed under high humidity conditions
Spores only mobile by splashing raindrops
Also infect stems and head
Head become purple-streaked

42. Unit 4: Plant Disease Management for Field Crops
Can result in low test weight and shriveled seeds
Usually survives on straw and inoculates the following crop year
Favorable conditions:
Splashing rains
Temps between 68-82º

45. Unit 4: Plant Disease Management for Field Crops
Wheat Fusarium Head Blight (Scab)
Caused reduced yield and grain quality
May also contaminate grain w/ mycotoxins
Vomitoxin – not extremely toxic when fed, but will decrease consumption and feed efficiency (non ruminants most sensitive)
Favorable conditions:
Humid during flowering
Identified by bleached spikelets of the head
May even kill the developing seed in the dough stage

48. Unit 4: Plant Disease Management for Field Crops
Unit 4 Assignment:
Create a treatment protocol for each of the discussed diseases
Product and active ingredient
Application rate
Application methods
Time of application
Bring an article on a plant disease
One page written summary
20 points -- Due next time!