Unit 4: Plant Disease Management for Field Crops

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

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

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

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?

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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!