What is sudden death syndrome? Sudden death syndrome (SDS) is one of the most important diseases of soybean in the Midwest. The disease was first observed in Arkansas in 1971, and has subsequently been reported throughout most soybean growing areas of the U.S. SDS was first documented in Wisconsin in 2005, and has become more common and severe since that time. The disease is most severe when soybeans are planted into cool, wet soils, and when midsummer rains saturate the soil. SDS often occurs in fields where soybean cyst nematode (SCN) is present.

What does sudden death syndrome look like? The first noticeable symptoms of SDS are chlorotic (i.e., yellow) blotches that form between the veins of soybean leaflets. These blotches expand into large, irregular, chlorotic patches (also between the veins), and this chlorotic tissue later dies and turns brown. Soon thereafter entire leaflets will die and shrivel. In severe cases, leaflets will drop off leaving the petioles attached. Taproots and below-ground portions of the stems of plants suffering from SDS, when split open, will exhibit a slightly tan to light brown discoloration of the vascular (i.e., water-conducting) tissue. The pith will remain white or cream-colored. In plants with advanced foliar symptoms of SDS, small, light blue patches will form on taproots and stems below the soil line. These patches are spore masses of the fungus that causes the disease.

Foliar symptoms of SDS can be confused with those of brown stem rot (see University of Wisconsin Farm Facts XGT1012, “Brown Stem Rot of Soybean”). However, in the case of brown stem rot (BSR), the pith of affected soybean plants will be brown. In addition, roots and lower stems of plants suffering from BSR will not have light blue spore masses.

Once symptoms of SDS are evident, yield losses are inevitable. Yield losses can range from slight to 100%, depending on the soybean variety being grown, the plant growth stage at the time of infection and whether or not SCN is present in a field. If SDS occurs after reproductive stages R5 or R6, impact on yield is usually minimal. If SDS occurs at flowering however, yield losses can be substantial. When SCN is present, the combined damage from both diseases can be substantially more than the sum of the damage expected from the individual diseases.

Where does sudden death syndrome come from? SDS is caused by the soilborne fungus, Fusarium virguliforme (synonym: F. solani f. sp. glycines).

F. virguliforme can overwinter freely in the soil, in crop residue, and in the cysts of SCN. The fungus infects soybean roots (by some reports as early as one week after crop emergence), and is generally restricted to roots as well as stems near the soil line. F. virguliforme does not invade leaves, flowers, pods or seeds, but does produce toxins in the roots that move to the leaves, causing SDS’s characteristic foliar symptoms.

How can I save a soybean crop with sudden death syndrome? SDS cannot be controlled once plants have been infected. Foliar fungicides and fungicide seed treatments have no effect on the disease.

How can I avoid problems with sudden death syndrome in the future? Use SDS-resistant varieties whenever possible in fields with a history of the disease; however, keep in mind that SDS-resistant varieties with maturity groups suitable for Wisconsin and other northern regions (groups I and II) are somewhat scarce at this time. If SDS and SCN are both problems in the same field, planting an SCN-resistant soybean variety may also be beneficial in managing SDS. Avoid planting too early. Wisconsin growers typically prefer to plant soybeans before May 10 to extend the length of the growing season and maximize yields. However, planting when soils are cool and wet makes plants more vulnerable to infection by F. virguliforme. Improve soil drainage by using tillage practices that reduce compaction problems. Rotation, while useful in managing other soybean diseases, does not appear to significantly reduce the severity of SDS. Even after several years of continuous production of corn, F. virguliforme populations typically are not reduced substantially. Research from Iowa State University has shown that corn (especially corn kernels) can harbor the SDS pathogen.

For more information on sudden death syndrome of soybean: Contact your county Extension agent.

What is soybean vein necrosis disease? Soybean vein necrosis disease (SVND) is a relatively recent discovery in soybean. SVND was first described in 2008 in Tennessee, but has since been confirmed in several other states including Arkansas, Delaware, Illinois, Iowa, Kentucky, Maryland, Michigan, Mississippi, Missouri, New York, Pennsylvania and Virginia. SVND was confirmed in Wisconsin in 2012. Researchers do not know if SVND can lead to significant yield reductions.

What does soybean vein necrosis disease look like? Soybean plants with SVND exhibit vein clearing (i.e., lightening of vein color) and chlorosis (i.e., yellowing), as well as mosaic patterns (i.e., blotchy light and dark areas) on affected leaves. Initially, symptoms develop around the veins of leaves and eventually expand outward. As the disease progresses, vein and leaf browning and necrosis (i.e., death) occur.

Where does soybean vein necrosis disease come from? SVND is caused by soybean vein necrosis virus (SVNV). SVNV is in the viral genus Tospovirus. This group of viruses includes common vegetable viruses (e.g., Tomato spotted wilt virus (TSWV) and Iris yellow spot virus (IYSV)) and ornamental viruses (e.g., Impatiens necrotic spot virus (INSV)) that can cause severe damage and substantial loss of yield and crop quality. Tospoviruses tend to have wide host ranges and are transmitted by several species of thrips. SVNV is also thought to be thrips-transmitted, but this has yet to be confirmed. SVNV may have been introduced to Wisconsin via thrips moving north on wind currents from the southern

How can I save a soybean crop with soybean vein necrosis disease? Currently very little is known about SVND. Thus there are no specific management practices recommended for SVND at this time.

How can I avoid problems with soybean vein necrosis disease in the future? Currently no specific control recommendations are in place. Researchers at universities across the country are attempting to determine what impact SVNV will have. Additional research is needed to determine how SVNV affects soybeans, how it is transmitted, how it overwinters, and what can be done to slow its spread.

For more information on soybean vein necrosis disease: Contact your county Extension agent.

What is soybean rust? Soybean rust is an extremely serious fungal disease of soybean that was first reported in the continental United States in November of 2004. Currently, soybean rust has been found in Alabama, Arkansas, Florida, Georgia, Hawaii, Louisiana, Mississippi, Missouri, South Carolina and Tennessee. Soybean rust had previously been reported in Asia, Australia, Africa and South America, where yield losses due to the disease have ranged from 10 to 80%. In addition to soybean (Glycine max), soybean rust affects approximately 90 other plant species in the legume family. In Wisconsin, other potential hosts include snap and kidney bean (Phaseolus vulgaris), American bird’s-foot trefoil (Lotus unifoliolatus), crimson clover (Trifolium incarnatum), Korean clover (Kummerowia stipulacea), white clover (Trifolium repens), purple crownvetch (Coronilla varia), Chinese lespedeza (Lespedeza cuneata), lupine (Lupinus spp.), pea (Pisum sativum), rattlebox (Crotalaria spp.), yellow sweetclover (Melilotus officinalis), ticktrefoil (Desmodium spp.), and winter vetch (Vicia villosa).

What does soybean rust look like? Initial symptoms of soybean rust include formation of small, gray spots on soybean leaves, particularly on the undersides of leaves. Spots are most likely to occur first on lower leaves where conditions are more favorable for spores to germinate and infect. Infections can also occur on petioles, stems and pods. Spots increase in size over time and change color from gray, to tan or reddish-brown. Tan lesions mature to form small pimple-like structures (called pustules) on the lower leaf surface. Pustules contain powdery tan spores that give the leaves the appearance that they have dandruff. Reddish-brown lesions are composed of primarily necrotic (i.e., dead) tissue and typically have only a limited number of pustules. As plant canopies close and pods begin to set, the soybean rust fungus can rapidly spread from lower to upper foliage of plants. Other diseases of soybean including brown spot, bacterial pustule and particularly downy mildew could potentially be confused with soybean rust.

Where does soybean rust come from? Soybean rust is caused by the fungi Phakopsora pachyrhizi and Phakopsora meibomiae. P. pachyrhizi is the more aggressive of the two species, and the fungus that was recently detected in the continental United States. P. pachyrhizi is thought to have been brought to the U.S. through hurricane activity in the late summer of 2004. Soybean rust fungi must overwinter on living plant tissue. Therefore, if soybean rust fungi ever reach Wisconsin, they are not likely to survive Wisconsin winters. In the South, however, plants such as kudzu (Pueraria montana var. lobata) can serve as overwintering hosts. Soybean rust spores produced on these plants could be moved north each year by prevailing winds, as is known to occur with other rust fungi (e.g., the corn rust pathogen). Soybean rust fungi may eventually reach Wisconsin via this route. This movement of spores via prevailing winds could occur each year, thus making soybean rust a recurring problem.

How do I save a soybean plants infected with soybean rust? If you suspect that your soybeans are suffering from soybean rust, proper diagnosis is crucial to document the presence of the disease in Wisconsin. See University of Wisconsin Pest Alert XG1001 (available at www.plantpath.wisc.edu/pddc) for details on submitting a sample for diagnosis. Keep in mind however that once soybean plants are infected and the soybean rust fungus has begun to produce spores, control of the disease is difficult and significant yield losses are likely. Fungicides with “curative” properties will likely be registered for use against soybean rust in Wisconsin by the 2005 growing season. However, curative fungicides have a very limited ability to eliminate existing disease and by the time soybean rust is observed, these products will likely not provide adequate control. Therefore, every attempt should be made to prevent infections (see below), rather than to attempt to control soybean rust after infections have occurred.

How do I prevent problems with soybean rust? Plant soybeans as early as possible, so that if soybean rust does occur, plants are as mature as possible when infection occurs, and yield loss can be minimized. Researchers throughout the soybean-producing regions in the United States will be monitoring for soybean rust in 2005. Watch for reports of the disease to the south of Wisconsin and consider preventative fungicide treatments as the rust fungus approaches the state. Currently products containing chlorothalonil (e.g., certain formulations of Bravo^® and Echo^®), azoxystrobin (e.g., Quadris^®) and pyraclostrobin (e.g., Headline^®) can used preventatively for control of soybean rust. Other preventative and “curative” fungicides will likely be registered for use in Wisconsin by the 2005 growing season. Both types of products will be most effective if used to prevent infections. If you decide to use fungicides for control, be sure to select a formulation that is labeled for use on soybeans, and be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

For more information on soybean rust or help in diagnosing this disease: Contact Craig Grau, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706-1598, [phone: (608) 262-6289, fax (608) 263-2626, email: cg6@plantpath.wisc.edu; or contact Brian Hudelson, Plant Disease Diagnostics Clinic, University of Wisconsin-Madison/Extension, 1630 Linden Drive, Madison, WI 53706-1598 [phone: (608) 262-2863, fax: (608) 263-2626, email: bdh@plantpath.wisc.edu]; or contact your county Extension agent.

 What is Sclerotinia stem rot? Sclerotinia stem rot (SSR), also known as white mold, is a serious and often lethal fungal disease that affects a wide range of agricultural crops in the U.S. including many broadleaf vegetable crops (e.g., carrots, cruciferous plants, peas, potatoes, snap beans) and field crops, especially soybean. SSR is most severe on soybeans in high-yielding environments that have dense, fast-growing canopies.

What does Sclerotinia stem rot look like? SSR causes sudden wilting of soybean leaves and rapid plant death. Lower stems of affected plants become bleached and under moist conditions (e.g., high humidity, frequent rain), become covered with a cottony white fungal growth. Small, black structures that look like rat or mouse droppings (called sclerotia) form on and inside the stems and pods of affected plants.

Where does Sclerotinia stem rot come from? Sclerotinia stem rot is caused by the fungus Sclerotinia sclerotiorum which survives as sclerotia in dead plant tissue. Sclerotia can survive for five years or more in soil. A cool, moist environment favors Sclerotinia stem rot development. Under these conditions, sclerotia germinate to produce small, mushroom-like structures (called apothecia) that produce spores. These spores can be spread by wind, insects, or rain splash. In soybeans, most infections occur via open or senescing (i.e., withering) flowers. Occasionally, the fungus will spread from plant-to-plant via direct contact of roots or other plant parts.

How can I save plants with Sclerotinia stem rot? SSR is difficult to control once the disease has occurred. If affected plants are limited to a small area in a field, removal and destruction of plants may help to limit production of sclerotia that can further contaminate and cause long-term problems in the field; however, this strategy usually is not feasible on a large scale. If affected plants are removed, they should be burned. DO NOT compost plants or till them into the soil.

How can I avoid problems with Sclerotinia stem rot in the future? To prevent introduction of the SSR fungus into soybean fields, be sure to plant sclerotia-free soybean seed. Also, harvest fields with SSR last to avoid spreading sclerotia of the SSR fungus from field to field on combines.

In fields with a history of SSR, grow soybean cultivars that have been bred for SSR resistance. This is the most economical and successful long-term strategy for SSR control. In addition, consider using no-till production for three to four years as this will reduce the number of viable sclerotia near the soil surface. Rotate soybeans with small grain crops that are not susceptible to SSR (e.g., wheat, barley, oats) to further reduce the number of viable sclerotia in the soil. Increase row spacing and reduce soybean seeding rates to promote a more open canopy that will have better air circulation and thus dry more rapidly. Also, make sure fields are well drained and avoid excessive irrigation especially during flowering. Remember that the SSR fungus prefers wetter conditions; under drier conditions the fungus is less likely to infect. Maintain good broadleaf weed control. Weeds not only decrease air circulation and promote wetter conditions, but can also be hosts for the SSR fungus.

Finally, there are fungicides and biological control products available for SSR management. Fungicides containing an active ingredient that is a succinate dehydrogenase inhibitor (SDHI), such as boscalid, are often effective in SSR control. The active ingredient picoxystrobin (a type of strobilurin fungicide) has also been shown to be effective in SSR control in university research trials. Timing of fungicide applications is critical. Fungicides should be applied during early flowering (R1) to early pod development (R3) growth stages. Fungicide applications made at the full pod (R4) growth stage or later will NOT be effective. In addition, applying fungicide treatments after symptoms are visible will not be effective. Several biocontrol agents (the most effective being one that contains a fungus called Coniothyrium minitans) have been shown to be effective in controlling SSR. Be sure to read and follow all label instructions of the fungicide/biological control product(s) that you select to ensure that you use the materials in the safest and most effective manner possible.

For more information on Sclerotinia stem rot: Contact your county Extension agent.

What is powdery mildew? Powdery mildew is a common fungal disease of wheat in Wisconsin. The disease interferes with photosynthesis, thereby reducing plant growth, heading, and grain fill. In extreme cases, powdery mildew can result in leaf, and even plant, death. When weather is favorable and the disease occurs at flag leaf emergence or during heading, yield losses of up to 40% can occur.

What does powdery mildew look like? Powdery mildew typically appears as white, cottony patches (masses of fungal threads and spores of the causal fungus) on the upper surfaces of leaves. Patches also can occur on lower leaf surfaces, as well as on stems, seed heads and awns. Fungal growth is confined primarily to the plant surface, with only limited penetration of the fungus into plant tissue. As the fungal growth ages, it turns from white to dull gray or light brown. When fully mature, the fungus forms reproductive structures called chasmothecia, which resemble small black dots or tiny seeds, among the fungal threads.

Where does powdery mildew come from? Powdery mildew is caused by the fungus Blumeria graminis which most commonly overwinters as ascospores (a type of spore) inside chasmothecia on wheat residue. During mild winters or when sufficient snow cover is present to provide good insulation, the fungus also survives on wheat residue as fungal threads or as conidia (a second type of spore). In the spring, both ascospores and conidia are blown onto actively growing wheat plants where infection occurs followed by development of typical cottony fungal threads. New conidia that form on infected plants can lead to additional infections throughout the wheat growing season. Once a wheat crop is harvested, volunteer wheat plants serve as a reservoir for the fungus until the next wheat crop is planted and begins to grow in the fall. The wheat powdery mildew fungus does not infect other small grains or weed grasses and these plants do not serve as a reservoir for the fungus. Similarly, fungi that cause powdery mildew on small grains other than wheat and weed grasses are unlikely to infect wheat. Moist, humid weather with widely fluctuating temperatures favors the development of powdery mildew. Long periods of excessive rain inhibit powdery mildew development by washing spores from plants before infection can occur.

How can I save wheat plants with powdery mildew? Careful, routine scouting of a wheat crop throughout the growing season is important to detect powdery mildew as early as possible. Frequent scouting allows for assessment of the likely impact of the disease on a wheat crop and helps to determine if and when fungicide applications are warranted. If you scout only once for powdery mildew, be sure to scout just prior to flag leaf emergence. Yield losses due to powdery mildew are greatest when the disease occurs prior to and at flag leaf emergence. Therefore, protecting the flag leaf is critical in preserving proper head development and grain fill. If powdery mildew is present at flag leaf emergence and weather is favorable for further disease development, consider applying a fungicide for control. While there are a wide variety of fungicides available labeled for control of wheat powdery mildew, products or premixes containing demethylation inhibitor group active ingredients (FRAC 3) have performed particularly well in university research trials. When using fungicides, be sure to read and follow all label instructions of the product that you select to ensure that you use it in the safest and most effective manner possible.

How can I avoid problems with powdery mildew in the future? Consider using wheat cultivars with powdery mildew resistance, but keep in mind that the level of powdery mildew resistance can vary widely from cultivar to cultivar. To reduce the amount of powdery mildew fungus in a field, use tillage practices (where feasible) to bury infested wheat residue, remove volunteer wheat plants, and routinely rotate wheat with other crops (e.g., corn, soybeans). Powdery mildew tends to be more severe in fields that have excess nutrients (particularly nitrogen). Therefore, fertilize (especially with nitrogen, potassium, and phosphorus) for optimal plant growth, but DO NOT overfertilize.

For more information on powdery mildew of wheat: Contact your county Extension agent.

What is Phytophthora root and stem rot? Phytophthora root and stem rot (PRSR) is a common disease of soybean that can ultimately cause death of soybeans at any stage of development. The disease can cause stand losses and severe yield reductions in susceptible soybean varieties. In Wisconsin, PRSR of soybean is becoming increasingly important due to expansion of soybean acreage, increased frequency of planting of soybeans in given fields, and substantial variability in the organism that causes the disease.

What does Phytophthora root and stem rot look like? Watch for symptoms of PRSR in fields or areas of fields with poor drainage (e.g., low-lying areas or areas with soil compaction problems). In addition, watch for the disease in well-drained fields when soils are saturated due to heavy rain or excessive irrigation. Symptomatic plants often occur in patches.

Symptoms of PRSR can vary depending on the age of affected plants. Early stages of PRSR can lead to seed rot or death of seedlings prior to emergence (called pre-emergence damping-off). Once plants emerge, PRSR can lead to yellowing, wilting, and death of seedlings (called post-emergence damping-off). Infected seedlings can be pulled easily from the ground because of damage to developing roots. Symptoms of PRSR in older plants (particularly those infected before flowering) include root decay, browning and water-soaking of stems extending 6 to 12 inches above the soil line, yellowing of leaves, wilting, and eventual death, with leaves on dead plants remaining attached. Stem lesions of PRSR are typically brown, long, narrow, and sunken. When infections remain confined primarily in roots, above-ground symptoms may be more subtle, and can include a lighter green color, stunting and uneven growth. Death due to PRSR tends to occur more rapidly in younger plants than older plants.

Symptoms of PRSR can be similar to symptoms of other soybean diseases, particularly Pythium root rot (PRR) and stem canker. PRR causes root symptoms similar to those caused by PRSR, but typically not the expansive stem lesions seen with PRSR. Stem canker, like PRSR, causes stem lesions, but stem canker lesions tend to be larger (eventually girdling stems), and become darker brown with age than those caused by PRSR. Also, older stem canker lesions will have numerous black, pimple-like spots (actually reproductive structures of the fungus that causes the disease). Such spots will not be present in lesions of plants suffering from PRSR.

Where does Phytophthora root and stem rot come from? PRSR is caused by the water mold Phytophthora sojae, a soilborne organism that survives via specialized spores called oospores. Oospores are produced in infected soybean plants, and can survive for many years in the soil after soybean residues decompose. Oospores germinate when soil moisture is high. P. sojae tends to be most active when temperatures are between 58°F and 77°F, in contrast to Pythium species (the causes of Pythium root rot) which tend to be active over a wider temperature range (50°F to 95°F).

How can I save a soybean crop with Phytophthora root and stem rot? Once soybean plants become infected by P. sojae, there is no cure. Therefore, management of PRSR relies on preventing infections from occurring.

How can I avoid problems with Phytophthora root and stem rot in the future? Use PRSR-resistant varieties as a primary means of disease management. Both race-specific resistance [complete resistance to a specific variant of the pathogen (called a race)] and field resistance (partial resistance to many races) are available in soybean varieties marketed in Wisconsin. When choosing a race-specific variety, be sure to know which race(s) of the pathogen is/are prevalent in your area and match race-specific resistance genes with the predominant race(s). The performance of race-specific resistant varieties can change over time. Therefore, monitor the performance of race-specific resistant varieties very closely, and base future selection of race-specific resistant varieties on the performance (or lack thereof) of recently planted varieties. Field (partial) resistance to PRSR is present at differing levels in most soybean varieties marketed in Wisconsin. While field resistance can be useful in managing PRSR, this type of resistance is not particularly effective during early growth stages or under high disease pressure (e.g., when P. sojae levels are high in soil, or when soil conditions are excessively wet). In addition to using resistant varieties, consider using seed treatments containing metalaxyl or mefenoxam. These active ingredients have been shown to be effective in providing early protection of soybean seeds and seedlings against P. sojae. Also, improve soil drainage to promote drier soils that are less favorable for P. sojae growth and reproduction. Crop rotation will not eliminate PRSR or eradicate P. sojae, but should be used to prevent the rapid build-up of high levels of the pathogen that can reduce the effectiveness of field resistance.

For more information on Phytophthora root and stem rot of soybean: Contact your county Extension agent.

What is leaf and glume blotch? Leaf and glume blotch is a common disease of wheat, and to a lesser extent barley and rye. While the impact of the disease is typically relatively minor (usually 5% or less of a wheat crop is affected), under favorable environmental conditions, leaf and glume blotch can destroy upwards of 20% of a wheat crop.

What does leaf and glume blotch look like? Leaf and glume blotch on leaves appears initially as small yellow flecks that enlarge to form brown, lens-shaped lesions, often surrounded by yellow halos. These regions can merge, leading to large necrotic (i.e., dead) areas on leaves. The disease can also affect stems and grain heads resulting in smaller brown to purple lesions on tillers and botchy brown to purple areas on glumes (i.e., the leafy, husk tissue that surrounds developing seeds). As the disease develops, small, dark, pimple-like dots (reproductive structures of the fungus that causes the disease) form in the discolored tissue. When the humidity is high, gelatinous masses of fungal spores are exuded from these tiny dots giving leaves, stems and grain heads a shiny, wet appearance.

Where does leaf and glume blotch come from? Leaf and glume blotch is caused by the fungus Stagonospora nodorum which can survive in wheat debris, as well as in wheat seed. Spores of the fungus are produced on wheat debris and on infected plants during periods of high humidity and moderate temperatures (optimally around 68°F), and are easily moved within a wheat planting by splashing due to heavy rains.

How can I save plants with leaf and glume blotch? Once plants are infected with the leaf and glume blotch fungus, curative treatments are not available. Luckily, under weather conditions typical for small grain production in Wisconsin, damage due to leaf and glume blotch is not severe (at most perhaps 5% of an overall wheat crop in a typical growing season). However, under weather conditions favorable for leaf and glume blotch to develop, early detection of the disease is important to provide greater flexibility in applying fungicide treatments that can limit disease development (see details below). In particular, fungicide treatments that protect the flag leaves of wheat plants (i.e., the leaves just under the grain heads) can be important in preventing significant losses due to leaf and glume blotch.

How can I avoid problems with leaf and glume blotch in the future? The best method for managing leaf and glume blotch is through the use of appropriate crop rotation. Rotate wheat and other small grains with nonsusceptible crops (e.g., soybeans, corn, or vegetable crops) for at least one year. Where feasible, also consider using tillage practices that partially or fully bury wheat debris, and avoid planting wheat excessively early. Rotation, proper tillage and delayed planting all provide time for wheat debris to decay which in turn eliminates the primary source of spores of the leaf and glume blotch pathogen. Also, use wheat seed that was produced in leaf and glume blotch-free fields to avoid introducing the fungus on contaminated seed.

Where leaf and glume blotch has been a chronic problem, use leaf and glume blotch-resistant wheat cultivars and reduce seeding rates to allow better air penetration and more rapid drying of plants. Avoid overuse of nitrogen fertilizers as this will promote excessive leaf growth that will slow leaf drying. Finally scout wheat fields routinely and consider using preventative fungicide treatments at the emerging flag leaf stage of development (Feekes 8). Many strobilurin fungicides (FRAC group 11) and demethylation inhibitor fungicides (FRAC group 3), as well as mixes of active ingredients with these modes of action provide very good control of leaf and glume blotch. Use fungicides containing a strobilurin only prior to heading; avoid using these products after wheat has flowered. Demythylation inhibitor fungicides can be applied both before and after wheat has flowered. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the material(s) in the safest and most effective manner possible.

For more information on leaf and glume blotch: Contact your county Extension agent.

What is leaf blotch? Leaf blotch is a complex of common fungal diseases of small grains (e.g., wheat, barley, oats and rye), and many grasses. In Wisconsin, winter wheat is the most important commercial crop affected by these diseases with potential yield losses of up to a 30%. Leaf blotch diseases are generally favored by cool, wet, windy weather.

What does leaf blotch look like? Symptoms of leaf blotch diseases usually first appear between the veins of lower leaves as chlorotic (i.e, yellow), water-soaked flecks that enlarge to become dry, yellow (eventually red-brown), blocky- to oval-shaped lesions, sometimes surrounded by yellow haloes. Some leaf blotch fungi can infect glumes in seed heads as well as leaves, causing a disease known as glume blotch. Glume blotch symptoms include small brown to purple lesions on heads and stems. Rows of tiny black specks (reproductive structures of leaf blotch fungi) are often visible in mature leaf and glume blotch lesions.

Where does leaf blotch come from? Several species of fungi can cause leaf blotch. These include Septoria tritici, Stagnospora nodorum and Stagnospora avenae f. sp. triticae. S. tritici is the primary cause of leaf blotch of wheat. S. nodorum can cause both leaf and glume blotch. These fungi are quite variable, and variants that infect wheat tend not to cause severe disease on other leaf blotch susceptible hosts and vice versa. Wheat leaf blotch fungi survive in infested wheat residues, wheat seeds, and volunteer wheat plants. Initial infections typically occur in the fall as seedlings emerge, and are caused by spores (called ascospores) that are produced on wheat residue from a previous wheat crop. Infested seed can also be a source spores that cause initial infections. Additional infections can occur the following spring and are due to spores (called conidia) that are produced in lesions on infected wheat plants.

How can I save a wheat crop with leaf blotch? In areas with a history of severe leaf blotch diseases, and on wheat varieties susceptible to leaf blotch, preventative applications of fungicide to protect the flag leaf (Feekes 8 and 9 growth stages) may be necessary. However, any decision to apply fungicides should be based on regular, careful scouting. Because heavy rainfall favors leaf blotch development, rain patterns should be considered when determining the frequency of monitoring for disease development. To assess the need for treatments, scout five locations within a given wheat field. Once two of the five areas have 25% or more of leaves showing symptoms of leaf blotch, scouting should be repeated approximately every 4 days. Once three of five areas have 25% or more of leaves exhibiting symptoms, then fungicide applications should be considered.

How can I avoid problems with leaf blotch in the future? Successful management of leaf blotch can be accomplished through an integrated approach that combines use of resistant varieties, pathogen-free seed, crop rotation, proper crop debris management, volunteer wheat eradication, and fungicide treatments. Several sources of complete resistance to specific variants (called races) of leaf blotch fungi are available in commercial wheat varieties. Some partial resistance to many races is also available. These forms of resistance are limited so it is important to use resistance in combination with other management techniques. Use crop rotations that include non-cereal crops for at least a year between successive wheat crops. When possible, deeply incorporate wheat residues by tillage prior to planting to promote more rapid decay of these residues. Note that residues include not only materials left over from a previous wheat crop, but also wheat straw that has been used as animal bedding and then subsequently disposed of by spreading it onto a field. Deep incorporation of residues will help reduce the levels of leaf blotch pathogens in the soil and will assist in managing volunteer wheat. Use of host resistance and cultural techniques such as tillage can help reduce the need for fungicide applications (as described above).

For more information on leaf blotch diseases of wheat: Contact your county Extension agent.

Freezing rains and ice accumulation in Wisconsin during the winter often lead to questions about potential ice damage to alfalfa stands.

How does ice cause damage to alfalfa?  The freezing temperatures of ice often do little damage directly to alfalfa.  Temperatures significantly below freezing (less than 15°F when plants have hardened off well) are required to cause damage in alfalfa crowns, one to four inches into the soil.

 Ice primarily damages alfalfa because alfalfa roots require oxygen during the winter.  This oxygen diffuses into the soil from air above ground.  A solid layer of ice restricts air diffusion and suffocates the alfalfa.  Lack of oxygen is a common reason for loss of alfalfa in low spots in fields.  Alfalfa covered by ice for three to four weeks will likely suffer injury or death.

How can I assess potential ice damage to my alfalfa?  If plants have been fertilized according to soil test recommendations, allowed to accumulate good root carbohydrate levels during the fall period, and have hardened properly in the fall, cold injury due to ice is less likely.  When determining whether or not ice sheets will cause suffocation damage to alfalfa stands, one must consider whether the ice is in a solid sheet.  If the ice is non-uniform, cracked, or has holes, it will not completely restrict air movement into the soil and as a consequence, less damage will result.  In addition, alfalfa stems sticking up through the ice will help create holes that will aid in the diffusion of oxygen. 

What can I do about ice on my alfalfa?  The short answer is nothing.  Some growers have used a large tractor and disc in an attempt to break the ice.  This technique generally will not break the ice unless there is a layer of snow in between the ice and ground.  Other growers have applied fertilizer to ice with the idea that salts in the fertilizer will melt through the ice and create holes, allowing for air movement.  Often, however, fertilizer particles will not melt totally through the ice and thus, fertilizer applications are not effective.  In addition, subsequent rainfalls or even melting of the ice can lead to substantial runoff problems, particularly if the fertilizer contains nitrogen or phosphorus.  Because of runoff issues, current nutrient management standards prohibit most nitrogen and phosphorus fertilizer applications on frozen or snow-covered soils, except when an application is made to winter grains.  Even broadcast applications of potassium fertilizers on an ice cover are problematic.  If runoff occurs, distribution of the fertilizer can be quite variable and off-site losses could represent an economic loss to growers. 

While growers may be concerned about ice on alfalfa, their best course of action is to wait and see how long the ice lasts and afterward assess what damage, if any, occurs.  In the recent past, ice sheeting has occurred across central Wisconsin for at least eight weeks with very little resulting winterkill or injury.

For more information on ice damage to alfalfa:  Contact your county Extension agent.