Unit 4: Plant Disease Management for Field Crops

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 70-85 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 80-100 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!