Diseases 2012 – issue 1
Wendland ag agronomy
Diseases 2012 – Issue 1
WEndland WEndland Ag Ag Agronomy Agronomy
FOOD FOR THOUGHT Why the buzz about plant diseases?
S
o, why all of sudden these All of these types of fungi are last few years do we have called Pathogenic fungi. There so many diseases? If we are a lot of other fungi on and think about the disease triangle around plants that will not cause we need a pathogen (disease), any harm. Pathogenic fungi are Bennie favourable weather conditions spread by wind, water, soil, seed Dunhin and a susceptible host for disborne and contact with infected ease to form. We have the host tissues. All that is needed for inplants which are the crops we fection is a spore (reproductive grow, and the last several years’ weather con- part) to fall on a susceptible host leaf and when ditions were optimum for disease develop- the climate is perfect the spores will germinate ment. Spores are blown in from the south in and infect the plant. air currents and some pathogens overwinter in For Bacteria to infect it typically needs our fields which cause a build up of inoculum some sort of mechanical injury such as hail, (disease spores) in our soils and stubble. We frost, injury due to feeding (insects or animals) are heading for our third wet season; there- or equipment. It grows within the plant and fore, we can expect another big disease year. secretes enzymes that destroy plant cells. BacTo understand diseases and why we need teria are typically less destructive than fungi. to control them, we need to understand what Because of bacteria’s nature of infection, it is diseases are and how the infection process very difficult to control and not a lot of prodworks. There are 3 major types of diseases: ucts are available to control it. Therefore, after Fungi, bacteria and viruses. mechanical injury we always recommend a foFungi are responsible for most of the plant liar nutrition product to try to keep the plant as diseases we deal with in agriculture and are healthy as possible so that the plant’s natural mostly the only type that we can control suc- resistance mechanisms can work as optimal as cessfully. It infects living plant tissue, destroys possible. it and then lives off of it. Because of this, photoViruses, along with bacteria, also need synthesis is reduced dramatically which means some kind of mechanical injury present (feedthat the plant doesn’t have enough energy to ing, hail, frost, etc.) to infect the plant. Due to grow. Some fungi will attack the stems of the the small size of viruses, they can often infect plants which (like Sclerotinia) will cause the through microscopic wounds/cracks and need whole plant to die. Others will reduce the leaf to live off the plant cells. Therefore viruses surface (leaf diseases) that will reduce yield. don’t normally kill plant tissue, but because
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Food for thought
of its parasitic nature, it limits growth of the host plant dramatically. Viruses don’t live on dead plant tissue. They can spread from plant to plant, but they normally spread through a vector like insects. Therefore the only control we can provide for diseases caused by viruses is to control the vectors (insects). We need to change the way we think about fungicides. With herbicides you see the weed that is going to influence yield in your crop so you spray a herbicide to kill it. With fungicides this is not the case. When we see symptoms on the leaves it is already too late to prevent yield loss. When fungi infect a plant it happens as follows: spores fall on the leaves, it germinates with favourable weather conditions, hyphae (germination tubes) grow towards a stoma where it can enter the plants cell, and then it grows inside the cells where it forms its reproductive stage (see diagram belowsource BASF). It is only in these last 2 stages where symptoms become visible on the leaves; six days after the spores germinated. By then it is too late to prevent the pathogen to cause plant injury. Therefore we need to spray fungicides preventatively and not curatively like herbicides. We have to stop the disease from
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Diseases 2012 – issue 1
infecting the leaves. Also, some diseases are polycyclic (multiple cycles in one season –e.g rusts) and some are monocyclic (only one cycle per season – e.g Fusarium). Not all fungicides are created equally! The different active ingredients have different modes of action. Make sure you are aware of what you are applying so that the timing of application can be optimal for the fungicide. Some fungicides prevent the spores from germinating, others prevent hyphae formation and some prevent the pathogen’s hyphae from entering the plant cells. This is the reason why we need to apply fungicides at different timings for different diseases. Please also remember that some fungicides have a systemic and others have a contact mode of action. We normally use fungicides with a contact mode of action when disease symptoms are already visible on the plant. Make sure you know what disease you’re trying to control and what fungicide you are going to use. Be prepared as disease can be destructive to our crops this year. Please contact a Wendland Ag agronomist if you need more information on diseases.
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Diseases 2012 – issue 1
Wendland ag agronomy
Disease Identification & Fungicides 101
P
lant disease is a very seriplant. It is so important to not let ous issue that can lead to the disease spread to the upperlosses in both crop yield most leaves. Again, the goal is to and quality. When it comes to ensure the flag leaf stays as green plant disease, a proactive apas possible throughout the season Bethany proach is essential. Proper crop to ensure the plant reaches its full wyatt rotation, weather conditions, the potential. The glume blotch in crop’s potential, crop prices and wheat will be brown marks startproper timing must all be taken ing on the tips of the glumes that into consideration when it comes to disease. will work its way down and then may have black Disease can appear suddenly and then spread pepper like dots present on it. very quickly, so you don’t want to be caught off Defense: Apply any of the following fungiguard. With the weather conditions we’ve had cides at flag leaf timing (Check labels for regislately, it is a good idea to plan for a fungicide tration): Tilt, Stratego 250 EC, Quilt, Caramba, application on all of your crops this year. Be- Headline, Folicur, Prosaro, Acapela and Bravo. low is a brief overview of plant diseases by crop type and recommended fungicides that are registered for their control/prevention.
Cereal Crops Cereals have a long list of both leaf and head diseases that they are susceptible to. Many of the leaf diseases can look similar to each other, but at the same time most are treated similar. It is important to start monitoring cereal crops near the end of June. The goal is to protect the flag leaf, which is responsible for 60-65% of the final yield. This illustrates just how important that one leaf really is! Of course disease can start showing up earlier in the season. If this is the case, it may be a good idea to add a half rate of a fungicide with your herbicide application in order to help the plant make it through to the flag leaf timing application. In this case, a product such as Tilt is a great option. Septoria Septoria is commonly called Septoria Complex because it can cause leaf blotch or glume blotch. Septoria leaf blotch can affect all of the small grains (wheat, barley and oats), but glume blotch most commonly occurs in wheat. This disease favors wet, humid and windy conditions, with temperatures between 15 and 25 degrees C. Symptoms: Septoria will start out as small yellow/green specks between the leaf veins. These specks will eventually expand, join up and turn yellow. They will then turn reddish brown and ultimately greyish brown as the leaf material dies. The disease starts out on the lower leaves and will eventually work its way up the
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Leaf Blotch
Glume Blotch
Tan Spot Tan spot is found in wheat and will thrive under wet and humid conditions. Seeding wheat on wheat stubble can increase disease incidence and severity. Symptoms: Tan spot will start out as tan or yellow specks on the older leaves. These specks will grow, turn oval in shape and develop a yellow border with a tan center (hence the name Tan Spot!). There is also usually a small brown spot in the center of the lesion. These lesions can eventually join together as they increase in size. Seeds of infected plants may have pink/reddish or black tips. Defense: Apply fungicide at flag leaf timing, or when necessary with: Tilt, Bravo, Caramba, Folicur, Headline, Prosaro, Quilt, Acapela or Stratego. Tan Spot Page 3
Food for thought
Diseases 2012 – issue 1
streaks with lines running across them, leaving a “netted” appearance. The disease can also take on a spot form, known as Spot Blotch, which looks like dark brown spots. Heads that are affected can have shriveled seeds. Defense: Apply any of the following fungicides at flag leaf timing: Tilt, Caramba, Folicur, Headline, Prosaro, Quilt or Stratego.
Scald
Net Blotch
Scald Scald is found in barley and favors high humidity, lots of rain and cooler temperatures (1214 degrees C). Symptoms: The disease starts on the older leaves as “oil or water soaked” spots that are oval in shape. They can be very visible when the leaf is held up to the sun (as with most leaf diseases in cereals). These spots start out as grey/green, but then will turn tan or grey. These spots will soon dry out. The margins of these spots will be dark brown. Under heavy infection, the entire leaf can become covered as all of the lesions join up. The glumes can be affected and the seeds will then be shriveled. Defense: Apply any of the following fungicides at flag leaf timing: Tilt, Caramba, Folicur, Headline, Prosaro, Quilt or Stratego. Net Blotch Net blotch is another disease found in barley. The disease favors high humidity, high rainfall and temperatures around 15-25 degrees C, but can occur anywhere from 8-30 degrees C. Symptoms: Net blotch will start out as light green or brown spots on the leaves and possibly the glumes. These spots will then turn into
Spot Form of Net Blotch Page 4
Leaf Rust
Stripe Rust
Stem Rust
Rust This disease can be present as leaf, stem or stripe rust. Oats can get Crown Rust. Rust favors humid, windy conditions with temperatures around 11-22 degrees C. It is humid, windy weather that will spread the spores. Symptoms: Small pustules present on leaves, heads or stems that can be yellow/orange or reddish in color. The pustules will rub off on your skin or clothes, leaving evident orange/reddish color. Later on, leaves can turn brown and die. Defense: Apply fungicide at flag leaf timing, or when necessary: Tilt, Folicur, Stratego, Acapela and Quilt. Check labels for registrations for type of rust, as this can vary.
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Wendland ag agronomy
Diseases 2012 – issue 1
Fusarium Head Blight Fusarium Head Blight (FHB) has traditionally been found mostly in Manitoba and Eastern Saskatchewan, but recently it has been moving west. It mostly affects wheat and barley. FHB is an issue as it results in downgrading as the diseased kernels will contain DON, or deoxynivalenol. DON is a concern because it is toxic to livestock when the grain is fed to them, and it causes issues with baking quality in wheat and malting qualities in barley. Warm, wet weather during flowering can lead to FHB. Symptoms: Fusarium Head Blight will start out as orange to pink coloring at the bottom of the spikelet. Once the disease it more advanced, it leads to premature bleaching of all or part of the heads. The kernels will shrivel and discolor. Defense: Applying a fungicide at the start of flowering: Prosaro, Caramba or Folicur. Ergot Ergot is has the biggest impact on open pollinated crops such as rye, but self- pollinated crops like wheat and barley are also susceptible. Rye is open-pollinated which allows the fungus easy access into the head while flowering. However, certain conditions will allow the fungus access into wheat and barley heads during flowering too. First of all, a wet spring is needed to allow the ergot bodies to germinate. Cool, cloudy and wet conditions extend the flowering period, which allows the period for infection to occur to be lengthened. But, it has been argued that a copper deficiency is what causes ergot. This is because when you have a copper deficiency, flowering is delayed and it triggers male sterility, and as a result makes the floret stay open
Fusarium Head Blight on Wheat
Ergot in Barley
longer. Ergot doesn’t generally cause much yield loss, but downgrading can occur. Symptoms: Developing kernels that are infected with turn into large, black fungal bodies, which can be as big as 2cm. Defense: Plant clean seed, rotate crop and ensure proper fertility (but this is all just part of good agronomics!)
Canola Canola diseases have been receiving a lot of attention lately. With the increase in disease pressures and good canola prices, it makes it easier to justify a fungicide application. Sclerotinia Sclerotinia affects the most canola acres and in extreme cases, yield losses can reach up to 20%. Heavy dews and moist humid weather will increase the incidence of infection. Tempera-
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Sclerotinia Lesion
tures of 15-25 degrees C mixed with dews, humidity and moisture for at least 10 days is the ideal situation for Sclerotinia. Sclerotinia symptoms show up later in the season and by this time, it is too late to apply a fungicide. Spraying for Sclerotinia is a 100% preventative application. The Canola Council has a checklist that can help justify making the decision of whether to apply a fungicide or not. But in the last few years, the conditions have been perfect and Page 5
Food for thought
Diseases 2012 – issue 1
the payback has 10 days is the been huge. ideal situation for Symptoms: Sclerotinia. ScleWatery lesions rotinia sympwill begin to aptoms show up pear on leaves later in the seaand stem, espeson and by this cially in the leaf time, it is too late and stem axils. to apply a funThis is because gicide. Spraying the infected for Sclerotinia is flower petal will a 100% prevenfall into the axtative applicails and start the tion. The Canola infection there. Council has a Eventually these checklist that lesions will turn can help justify white/grey and making the deciBlackleg Infected Stems/Roots will result in sion of whether the plant ripento apply a funing prematuregicide or not. ly. Hard, black But in the last fungal bodies few years, the known as Scleconditions have rotia will develop been perfect and inside the infectthe payback has ed stems. These been huge. then fall into the Symptoms: soil and will gerWatery lesions minate the folwill begin to aplowing year, repear on leaves leasing spores, and stem, espethus starting the cially in the leaf cycle all over and stem axils. again. Crop rotaThis is because tion is important, the infected Blackleg Lesion on Leaf and one must reflower petal will member pulses fall into the axils are a host for Sclerotinia as well. These dis- and start the infection there. Eventually these ease plants ripen prematurely which not only lesions will turn white/grey and will result in results in yield loss, but it also makes swath- the plant ripening prematurely. Hard, black ing difficult. fungal bodies known as Sclerotia will develDefense: Applying at fungicide at 20-50% op inside the infected stems. These then fall bloom (20-30% is optimal). It is also better to into the soil and will germinate the following go too early than too late, but timing is critical. year, releasing spores, thus starting the cycle There are many registered products including: all over again. Crop rotation is important, and Proline, Lance, Serenade, Astound, Vertisan, one must remember pulses are a host for ScleQuadris and Rovral. rotinia as well. These disease plants ripen prematurely which not only results in yield loss, Blackleg but it also makes swathing difficult. Sclerotinia affects the most canola acres Defense: Applying at fungicide at 20-50% and in extreme cases, yield losses can reach bloom (20-30% is optimal). It is also better to up to 20%. Heavy dews and moist humid go too early than too late, but timing is critical. weather will increase the incidence of infec- There are many registered products including: tion. Temperatures of 15-25 degrees C mixed Proline, Lance, Serenade, Astound, Vertisan, with dews, humidity and moisture for at least Quadris and Rovral. Page 6
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Wendland ag agronomy
Diseases 2012 – issue 1
Pulses Ascochyta Ascochyta occurs in peas and lentils. Wet weather and dense canopies increase the incidence of disease. In lentils it is commonly referred to as Ascochyta blight, but in peas it is known as Ascochyta leaf and pod spot. Symptoms: In lentils, the lesions start out as grey, but will become tan in color accompanied by a dark brown margin. They will eventually become covered in pycnidia and can develop anywhere on the plant. In peas, the lesions also become covered in pycnidia, but begin as little brown spots on the lower leaves. These lesions with then move up the plant onto pods and the newer leaves. Defense: Apply foliar fungicide at early flowering, or earlier if necessary. Lentils- Bravo, Headline Duo, Headline, Lance and Quadris. PeasHeadline Duo, Lance and Quadris. Headline EC will be effective against Ascochyta on Peas the disease.
Ascochyta on Lentils
Mycosphaerella Blight and Foot Rot Mycosphaerella is an aggressive disease in peas that thrives in cool, wet weather. It is very common and can infect the leaves, stems, flowers and pods. The foot rot occurs at the base of the stem. Symptoms: Early on, the lesions will appear as purple spots with irregular margins on the leaves. On the petals, the spots are small but can cause the blossoms to fall off. The stems get purple/black and sunken lesions, whereas the pods
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Mycosphaerella in Peas
will get light lesions that eventually turn purple/ brown. Defense: Apply one of the fungicides at early flowering or early if necessary. Bravo, Headline, Headline Duo, Lance, Acapella and Quadris. If disease conditions continue, as second application of a fungicide with a different mode of action can be applied 10-14 days later. Anthracnose Anthracnose is a very serious lentil disease. It thrives under warm and wet conditions, especially when crop rotations are shortened. Symptoms: The lower leaflets will first get lesions that are grey/white in color and appear “water-soaked” in appearance. The lesions will become darker over time and cause the leaflets to drop. Lesions on the stem will appear tan/ brown and sunken. They can eventually girdle the stem. Overall, large yellow patches can appear in the field, which will eventually turn brown. Defense: Apply fungicide at early flowering or earlier if necessary: Bravo, Headline Duo, Headline, Quadris and Quilt.
Anthracnose in Lentils Page 7
Food for thought
Diseases 2012 – issue 1
Disease Summary... There are many more diseases that can be an issue in our crops: Downy and Powdery Mildew, Alternaria Black Spot, Botrytis, Smut, Bacterial Blight, etc. But listed above is an overview of the main diseases we need to be aware of so that we can be proactive in managing them. There are also many other fungicides that can be used for some of these diseases, but again those are the main ones we would use. Managing disease is about a lot more than choosing the best fungicide at the optimum time; it also includes a proper
Saskatoon Blaine Lake Cut Knife Delmas
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crop rotation, using clean, disease free seed and treating seed with a registered seed treatment. Lastly, it is important to rotate fungicide groups to prevent disease resistance, just as you would with herbicides. When any mechanical injury occurs, such as hail, the plant will have a lot of open “wounds” that is the perfect infection point for diseases. Make sure you apply fungicides to prevent these kind of infections. It is also a good practice to add a foliar nutrient to help the plants through the stress.
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Domremy Rosthern Waldheim
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