By: Bonnie L. Grant, Certified Urban Agriculturist
Fungal diseases in grain crops are all too common,and barley is no exception. Barley spot blotch disease can affect any part of the plant at any time. Seedlings are most commonly infected but, if they escape, the disease may show up in developing shoots. There are several steps to preventing and treating barley spot blotch.
Barley spot blotch disease is found in many wild and cultivated grasses. Spot blotch of barley is caused by the fungus Bipolaris sorokiniana. The fungus is known to reduce yields by 1 to 3 percent. When barley kernels are produced,they often have black point, a discoloring on the tips of the kernels.
In seedlings, look at the soil line for chocolate brown streaks. The infection progresses to turn shoots yellow, and they may die. If they survive, the shoots and roots are weak and deformed, and seed heads may not completely emerge.
Mature plants can develop oblong dark brown lesions. Where many lesions are present, the leaves dry out and may die. Kernels on barley with spot blotch are shriveled and underweight. Presence of the disease diminishes yield and weight of grain.
Once barley spot blotch symptoms are evident, the field is already infected. The fungus overwinters in wild or cultivated grasses and grains. The disease moves quickly when temperatures are between 60 to 80 degrees Fahrenheit (16 to 27 C.) and conditions are wet and windy. Spores will travel on wind and rain splash.
The barley spot blotch disease can also be seed borne and causes seedling blight, crown rot, and root rot. Injury caused by insects allows a pathway for introduction in mature plants. No-till fields are at greatest risk of barley spot blotch fungus.
Timed fungicide applications can reduce the damage and incidence of the disease. There are also cultural steps to take to prevent the occurrence of the fungus. Barley with spot blotch should be treated with registered fungicides at the first sign of the disease. Studies show that four applications of fungicide during the season will help control spot blotch and reduce grain loss.
Watch seedlings carefully. Prevention is possible with certified treated, disease free seed. Do not save seed from fields that have shown signs of the disease. Rotate barley with non-host plants such as oats, rye and broadleaf grasses. Cleanup discarded plant material. The 6-rowed barley varieties have greater resistance than two-row cultivars.
Spot blotch of barley also mutates, causing new races, which makes creating effective resistant cultivars difficult.
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Developed by Steven B. Johnson, Extension Crops Specialist
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Ergot is a disease of cereal crops and grasses caused by the fungus Claviceps purpurea, which infects developing grains. Claviceps purpurea has a very broad host range of more than 300 species in over 50 genera of grasses, including wheat, rye, barley, and all of the cool-season forage grasses. Rye and triticale are very susceptible to the pathogen, wheat, and barley less so, and oats very rarely. Many common weed grasses are common hosts of the pathogen and serve as a pathogen reservoir.
The greatest concern regarding ergot is the alkaloid toxins produced by the fungus and their effect on humans and animals. “Ergotism” develops after ingesting ergot-contaminated grain, or grain products (like bread), processed from ergot-contaminated grain. Convulsions, severe pain, hallucinations, gangrenous limbs, and more, have been reported as symptoms in severe cases. In the Middle Ages, regular outbreaks of ergotism occurred in which many people died. Ergotism was later known as “St. Anthony’s Fire,” as monks of the newly formed order of St. Anthony built hospitals for ergotism treatment. Claviceps purpurea has been used during childbirth and for migraine treatment and was the source for the first isolation of the alkaloid LSD.
Barley and other small grains represent important rotation crops for Maine potato producers. Such crops are grown for livestock feed, malt production, and other uses. Owing to the toxicity of the Claviceps purpurea fungus, ergot infection results in crop loss and crop rejection. The presence of ergot could render a farmer’s entire grain crop worthless.
The ergot pathogen overwinters as black ergot bodies that are actually sclerotia (rough black masses of hardened fungal mycelium) of Claviceps purpurea. Ergot bodies may be introduced from planted seed or neighboring grasses or may remain from a previous cereal crop. Moist soil is required for germination of sclerotia, which generally begins in spring. Once sclerotia germinate, dry conditions may interrupt the process, but germination will continue when wet conditions resume. As the ergot bodies germinate, they form tiny spore-producing, mushroom-like structures. These structures produce wind-dispersed spores that infect grass or grain flowers. Grain and grass are most susceptible just before the flowers are fully open.
Ergot bodies in grain heads. Photo by Steven Johnson.
Within 5 days, infected flowers produce “honeydew,” the secondary phase of the disease. The honeydew is a sticky asexual spore-filled liquid that oozes from infected flowers and contains a large number of ergot spores. Rain splash, visiting insects, and direct contact all spread the infective spores for as long as flowering continues. Cool weather favors increased disease levels by extending the flowering period and thereby increasing the period of infection. Moisture is not required for pathogen transmission during the honeydew phase of the disease.
Within 10 days of flower infection, sclerotia begin to form and the infected seed ovary is replaced with a hardened dark ergot body. Grain heads may have more than one ergot body. At this point, the typical ergot symptoms are evident, including the presence of an elongated ergot body, frequently sticking out farther than the unaffected grain in the head.
The easily recognizable sign of the disease is the presence of dark sclerotia or ergot bodies. These replace the grain in cereal and grass heads and can be readily identified at harvest and in infested grain seed. There are tolerances for ergot levels and they vary from crop species to crop species. Grain lots above the ergot tolerance are described as “ergoty” and may be rejected.
Little can be done to control ergot once it is present in the crop. Prevention is the best management, but it must be done before ergot symptoms have been observed. No barley varieties are resistant to Claviceps purpurea and there are no fungicides to control the disease. Planting ergot-free seed from reputable sources will prevent introduction or re-introduction of the fungus into the field. Sclerotia of Claviceps purpurea can be cleaned from seed, but broken pieces of sclerotia still contain toxic alkaloids.
Tillage that buries residue at least 4 inches below the soil surface keeps the sclerotia from germinating. Since sclerotia don’t survive for more than a year, crop rotation with a nonsusceptible host will help control ergot. Broadleaf plants are not affected by the pathogen and make a good rotation crop.
Weed grasses in or near fields are can be a source of inoculum. Mow or otherwise destroy stands of grasses adjacent to cereal fields. This is most effective if done before grasses flower. If ergot is higher on field edges, these areas could be harvested separately and the grain destroyed.
Recent efforts have correlated ergot with copper-deficient soils. In such soils, the addition of copper may help control ergot infection. The addition of copper is far more effective with wheat or barley than with rye.
Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.
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SMALL GRAINS DISEASE UPDATE
Cool to cold temperatures persist, which has squashed most disease progress in small grains. Most wheat is around Feekes 6-7 in many parts of the Delaware, and some barley is at boot or early head emergence. In wheat, diseases are scarce or nearly absent in many fields. Powdery mildew is still observed in some fields, mostly at low levels, and recent freezes should significantly push back the disease. Some subtle virus symptoms are out there at very low levels in some fields.
In barley you will see net blotch or the spot form of net blotch to some degree (Figure 1). Without using molecular tools, there is no way of distinguishing the two, but for our purposes we can treat them the same. Symptoms are jet black circular blotches to elongated, cross-hatched blotches. This is another disease that can be residue-borne, persisting in residues of barley and volunteer barley. No till fields with high levels of residue therefore, will show greater symptoms. Contaminated seed is another source of the disease. Disease progresses when it is very wet and temperatures fall in-between 60-80 F. Planting barley early can exacerbate the disease in young plants as it allows the pathogen to establish and damage germinating seedlings. Rotation, encouraging residue decomposition via disking and planting clean seed are the best means of managing this disease. In areas where continuous small grain production is used (Western US, UK) this disease can cause some significant damage. Here it is more of an annoyance. However, if anyone is considering looking into malting winter barley in the future this disease should be on your radar. We also will need to be able to distinguish the spot from net blotch forms as there is no good resistance for the spot blotch form, but some good resistance sources for the net blotch form. We are working on generating some of that preliminary data this season.
Also, you may see some frost damage in barley as heads emerge, particularly in fields that were far along. Time will tell.
Figure 1. Net blotch of barley.
As far as scouting wheat, make sure to see where you are at disease-wise in wheat at flag leaf emergence (Feekes 8-9). There are reports of stripe rust and common leaf rust in North Carolina and Tennessee, and recent weather patterns may have started to move spores closer to areas of MD and DE. Stripe rust is a beast at cooler temperatures, whereas leaf rust tends to be more of a warm weather disease. Stripe rust does not always form stripes (Figure 2). However, the spore color is significantly different from common rust. Common rust pustules are brown to red brown, whereas stripe rust pustules are yellow to orange. Make sure you are scouting your fields, because you do not want to be stuck playing catch up to stripe rust in a susceptible variety.
Figure 2. Typical stripe rust symptoms on wheat foliage.
Expect to see symptoms of barley yellow dwarf in some barley and wheat fields. We have observed putative BYDV symptoms indicative of Fall infection at very low levels in some fields. Typically, characteristic symptoms appear after the flag leaf emerges, particularly if temperatures are cool and sunny. In barley you may see bright yellow flag leaves, that can become puckered to necrotic, and in wheat flag leaves may have a purplish to orange appearance. BYDV follows patterns of infected aphids, so it often occurs in small patches or areas of the field. Plants can also be stunted, particularly at the center of these patches. Seldom are severe BYDV issues detected in Delaware and Maryland, but issues can occur from time to time. This virus is a big deal in southern areas where temperatures remain warmer for longer and out west where large areas of pasture exist for grazing by cattle, etc. The result is greater populations of aphids coupled with more potential sources of overwintering virus. The other piece is that we historically see the moderate/mild strains of the virus, so even if you see symptoms, the likelihood for any significant yield hit is low. Bottom line: know that the infection occurred long ago, and that you cannot fix infected plants. If you have areas that tend to seem to be hot spots for BYDV, avoid planting early and select varieties rated excellent for BYDV in the Virginia Tech small grains guide.
Bobby L. Tyson and W. Cecil Hammond
Wheat must be harvested with minimum losses to realize the maximum return from all production practices. Minimum losses are achieved by harvesting on time with proper combine adjustments and operation. If the grain contains excess moisture, it must also be dried for safe storage.
A thorough understanding of the combine components is required to make the proper adjustments for satisfactory operation (Figure 22). By studying this diagram, you should be able to understand the general functions of the combine and why adjustments must be made for various conditions.
The header gathers, cuts and conveys the grain and straw into the combine, then into the cylinder. All the grain and straw must then pass between the cylinder and concave, where the grain is threshed from the heads. Some of the threshed grain will fall through the concave onto the cleaning shoe, which is made up of a chaffer (coarse sieve) and a sieve (fine sieve).
The straw and the grain that remains in the straw then move to the straw walker (rack). The reciprocating motion of the straw walker causes the straw to move across the straw walker and out the back of the combine. As the straw moves over the straw walker, the threshed grain is vibrated out of the straw and conveyed to the chaffer where it joins the threshed grain coming directly from the cylinder and concave.
The grain contains a lot of trash and broken straw when it reaches the chaffer. The chaffer is a coarse sieve that is usually adjustable. The chaffer shakes in a back-and-forth motion, which moves the material riding on the chaffer out the back of the combine. Grain and heavy small trash fall through the chaffer onto a sieve that is finer than the chaffer. The sieve also shakes, causing the material on the sieve to move to the rear. The material passing over the sieve is called "tailings" and is returned by an auger and elevator to the cylinder for additional threshing.
A fan blows air up through the sieve and chaffer to remove light trash and to aid the rearward movement of the material on the chaffer and sieve. Excess cleaning air will blow grain out the rear of the combine, and too little air may cause the cleaning chaffer to clog and pass grain out the back of the combine (Figure 23).
Another method of threshing is to place one or two rotors (rotating cylinders) parallel or transverse to the flow of the crop through the threshing area. Threshing takes place as the material moves towards the rear in a spiraling cylindrical mass between the rotor and the rotor cage.
The crop makes several revolutions around the chamber while passing through the machine but at a slower speed than the rotor. As a result, the rasp bars make several contacts as the crop is moved past the concaves. Thus, the rotor uses a rubbing, rolling action in threshing. Separation of the grain from the straw is aided by the centrifugal force set up by the rotors. Nearly 85 percent of the threshed grain falls through the concave grate. The remainder of the grain, along with the straw, continues the rearward spiraling motion into the separation area of the rotor cage.
It is evident that one adjustment can affect grain losses in several ways. The main combine adjustments are the reel position and speed, the cutter bar height, the cylinder speed, the concave clearance, the chaffer and sieve openings, and the fan and windboard settings. The owner?s manual will give the initial settings for all grain however, the following adjustments are for small grain in average conditions.
The final adjustments must be made in the field because they will be affected by such things as grain moisture, the condition of the straw, the quantity of weeds or green material, the kind of grain and yield.
The reel shaft should be 8 to 12 inches forward of the cutter bar with the top of the reel slats (boards) at a height just below the grain head. The reel tip speed should be 25 percent faster than the ground speed. For lodged wheat, a pickup reel should be used its height should just clear the cutter bar.
Tip speed of 5,700 to 6,500 feet per minute is recommended for wheat. The cylinder revolutions per minute (rpm) will vary with its diameter as follows:
|12 x tip speed (ft/min) |
3.14 x diameter (in)
|=||3.82 x tip speed (ft/min) |
Cylinder diameter (in)
The cylinder speeds required for an initial cylinder tip speed of 6,000 feet per minute with various cylinder diameters used in new combines are shown in Table 20.
|Cylinder diameter (in)||Cylinder speed (rpm)|
Concave clearance should be ¼ to ½ inch with an initial setting of 3 /8 being suggested (Figure 24). Consult your owner?s manual for rotor speeds in rotary combines.
Set chaffer opening to 5 /8 inch (adjustable type) measured perpendicular to the tip of the movable finger (Figure 25).
Set sieve opening at ¼-inch (adjustable type) measured perpendicular to the tip of the movable finger (Figure 25).
Inlet 75 percent open with windboard directing air to the front half of the chaffer and sieve. Note: On models with an adjustable speed fan, start with an initial fan speed of approximately 65 percent full speed.
Three miles per hour maximum.
The grain tank should be checked periodically, along with the combine losses on the ground, to make sure the combine is adjusted properly. Excess trash in the grain tank means improper fan, chaffer and/or sieve adjustment. If you try to get the grain too clean, you will increase losses by blowing grain out the back of the combine. Also, check the tailings elevator for the quantity of grain being returned to the cylinder. Excess tailings can result in cracked grain.
Field losses may be divided into two categories: preharvest and harvest (machine). Preharvest losses are defined as those shatter losses on the ground and the loss of dry matter due to birds, wildlife, weather, and natural respiration. Figure 26 illustrates the effect of time on these preharvest losses.
Harvesting losses are those losses caused by the combine. Some harvesting losses are unavoidable, but excessive losses are due to improper combine operations and/or adjustments. Modern combines are capable of harvesting 97 percent to 98 percent of the small grain.
The harvesting machine losses can be divided into the following categories:
The grain lost by rough handling by the cutter bar and the reel, and grain not cut by the cutter bar because of excessive cutting height or lodged grain.
Cylinder Losses (threshing loss)
The grain lost over the straw walker because of unthreshed heads and/or cracked grain from high cylinder speeds and/or insufficient concave clearance.
Combine Leakage Losses
Grain lost through cracks and clean-out doors in the bottom of the combine.
Straw Walker Losses (rack or separating losses)
Threshed grain lost over the straw walker because of excessive straw feed rate caused by excessive ground speed and/or low cutter bar height.
Chaffer and Sieve Losses (shoe or cleaning losses)
Grain lost over the chaffer and sieve because of excess fan air (grain blown over), excess material on the chaffer (straw broken up too much by the cylinder because of excessive speed and/or too little concave clearance), or because the chaffer and sieve are closed too much (material riding over the chaffer out the rear of the combine and excessive amount of tailings returned to the cylinder).
Field losses can be determined by counting the kernels of grain on the ground for a given area (Table 21). The number of kernels per square foot should be counted in several places and averaged for more accuracy. There are usually more kernels directly behind the combine than across the rest of the swath therefore, when determining threshing losses, the kernels counted behind the combine must be taken across the entire swath width (Figure 27).
Table 21. Small grain loss chart
Combine losses can be checked by the following procedure:
The cylinder loss (cut but unthreshed heads, Table 22, Column 5, Line C) should not exceed 0.5 percent of the yield, and the total machine loss should not exceed 3 percent of the yield. If the total machine losses are over 3 percent, the appropriate adjustments should be made and the losses remeasured.
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