Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 15, No. 16 August 26, 2005 Corn Stalk Rots By Laura Sweets Any factors which stress corn during the growing season, including drought stress, may contribute to an increase in stalk rots that season. This is certainly a year in which it would be wise to scout fields for corn stalk rots and to harvest fields with stalk rot problems as quickly as possible. A number of different fungi and bacteria cause stalk rots of corn. Although many of these pathogens cause distinctive symptoms, there are also general symptoms which are common to all stalk rot diseases. Early symptoms, which occur a few weeks after pollination, usually start with premature dying of bottom leaves. Eventually, the entire plant may die and appear light green to gray. Diseased stalks usually begin losing firmness during August. The cells in the interior of the stalk are dissolved, resulting in a loss of stalk firmness and strength. Stalks may then lodge, particularly if harvest is delayed or wind storms occur. Fusarium stalk rot and Gibberella stalk rot can be difficult to distinguish in the field. Both can cause a pink to reddish discoloration of diseased stalk tissue. Tufts of white mycelium may be evident at the nodes of diseased stalks. When stalks are split open the pith is usually shredded and discolored. Anthracnose stalk rot, caused by the fungus Colletotrichum graminicola, may be most evident at the nodes. Initially lesions are tan to reddish-brown but they become shiny black later in the season. These shiny black lesions may begin at a node and extend out from that node. The lesions may merge to discolor much of the lower stalk tissue. Internal pith tissues may also be discolored and may disintegrate as disease progresses. Diplodia stalk rot may begin as a brown to tan discoloration of the lower internodes. Stalks become spongy. The pith disintegrates leaving only the vascular bundles. Mats of white fungal growth of Diplodia maydis may be evident on affected tissues. Diplodia also produces fruiting bodies which may be seen as small black specks embedded in the white fungal mat. Charcoal rot may begin as a root rot and move into the lower internodes of the stalks. Pith tissues will be shredded and plants may break at the crown. The charcoal rot fungus, Macrophomina phaseolina, produces very small survival structures called microsclerotia which may be visible as very small, black flecks just beneath the stalk surface or on the vascular strands remaining in the interior of the shredded stalks. Stalk rots are caused by several different fungi and bacteria which are part of the complex of microorganisms that decompose dead plant material in the soil. They survive from one growing season to the next in soil, in infested corn residues or on seed. Stalk rot pathogens enter the corn plant in a variety of ways. The spores may be blown into the base of the leaf sheath where they may germinate and grow into the stalk. Spores may enter directly into a plant through wounds made by corn borers, hail or mechanical injury. When fungi are present in soil or infested residue as either spores or mycelium, they may infect the root system causing root rot early in the growing season and later grow up into the stalk causing stalk rot. Stalk rot becomes a problem when plants are stressed during the grain filling stage of development. Water shortage, extended periods of cloudy weather, hail damage, corn borer infestation, low potassium in relation to nitrogen, leaf diseases and other stresses that occur in August and September may be associated with an increase in stalk rot. Losses from stalk rots vary from season to season and from region to region. Yield losses of 10 to 20% may occur on susceptible hybrids. Tolls greater than 50% have been reported in localized areas. Losses may be direct losses due to poor filling of the ears or lightweight and poorly finished ears or indirect through harvest losses because of stalk breakage or lodging. Harvest losses may be reduced if fields are scouted 40-60 days after pollination to check for symptoms of stalk rot. Stalk rot can be detected by either pinching stalks or pushing on stalks. If more than 10-15 percent of the stalks are rotted, the field should be harvested as soon as possible. Management of stalk rots of corn should include the following: * Select hybrids with good stalk strength and lodging characteristics. * Plant at recommended plant populations for that hybrid. * Follow proper fertility practices. * Avoid or minimize stress to corn (especially during pollination and grain fill). * Harvest in a timely manner. Laura Sweets, Plant Pathology 573-884-7307 Late Season Soybean Diseases By Laura Sweets This has been an unusual year for soybean diseases. Septoria brown spot was very prevalent early in the season and is still causing yellowing or browning of leaves and premature leaf drop in some fields. Frogeye leaf spot has not been widespread this year. Cercospora kikuchii and Colletotrichum spp. have shown up in some fields causing leaf spot, yellowing and shoot dieback. Downy mildew has been evident in the upper canopy of some fields. Sudden death syndrome has not been nearly as widespread or severe as it was during the 2004 season. And losses from soybean cyst nematode are always likely in Missouri soybean fields. Although yield loss from moisture stress may be greater than yield losses from late season soybean diseases in much of the state this season, yield losses from these various late season diseases can still occur. Yield losses from late season soybean diseases will vary depending on when symptoms began to occur, number of plants infected, severity of disease in infected plants and weather conditions from now to harvest. Septoria Brown Spot Septoria brown spot causes small brown spots on the unifoliolate and lower trifoliolate leaves. The individual spots may run together forming irregularly shaped brown blotches on the leaves. Infected leaves may yellow and drop prematurely. Brown spot usually starts on the lower portion of the plant. Under favorable weather conditions (warm, wet weather), the disease may move up through the plant. Brown spot was evident in many Missouri soybean fields earlier this season. With the hot, dry conditions for much of the growing season, Septoria brown spot has not been active through the entire season. However, in fields which haven’t canopied fully, the symptoms from earlier in the season may still be evident. Distinct small brown spots may be found on leaves in the midcanopy of many plants. Lower leaves may show more extensive spotting or larger blotches or may have yellowed and even dropped prematurely. Symptoms can move up through the canopy to the upper leaves of soybean plants. Upper leaves may also show spotting and yellowing. The fungus which causes this disease, Septoria glycines, survives in infested residues left on the soil surface. Fields with continuous soybean production are more likely to show damage. Planting disease-free, good quality seed of resistant varieties, rotating crops with at least one year between soybean crops and maintaining good plant vigor should reduce losses from Septoria brown spot. Frogeye Leaf Spot Frogeye leaf spot is occurring in some fields in the state but has not been particularly widespread or severe this year. Frogeye leaf spot begins as small, reddish brown circular lesions on soybean leaves. The individual lesions do not increase greatly in size but as they mature the center of the lesion turns light tan to gray. The mature lesions have a light center with a dark purple or brown border. On severely infected leaves the lesions may merge killing larger areas of leaf tissue. These areas may drop out giving the leaves a very tattered or lacy appearance. From a distance fields with high levels of frogeye leaf spot may have a dry, brown cast. The fungus which causes this disease, Cercospora sojina, can survive in infested residues left on the soil surface. Fields with continuous soybean production are more likely to show damage. The disease is favored by warm, wet weather, high humidity and conditions which increase moisture levels in the canopy. Shaded fields, fields with heavy tree growth along the edges and river bottom fields have been more likely to have severe frogeye leaf spot this season. Planting disease-free, good quality seed of resistant varieties, rotating crops with at least one year between soybean crops and maintaining good plant vigor should reduce losses from frogeye leaf spot. Cercospora Leaf Spot and Purple Seed Stain Cercospora kikuchii can infect soybean seeds, pods, stems and leaves but is most commonly found on the seed. However, this year we are seeing some cases of leaf spot or leaf blight caused by this fungus. Infection is primarily occurring on the uppermost leaves and begins as reddish purple to reddish brown, angular to somewhat circular lesions on the soybean leaves. These lesions may coalesce to kill larger areas of leaf tissue. The uppermost trifoliolate leaf and petiole may be blighted and brown. One striking symptom of this disease may be the premature yellowing and then blighting of the youngest, upper leaves over large areas of affected fields. In most fields, the symptoms have not progressed down the plants more than one to two nodes. Pods at the uppermost node may develop round, reddish purple to reddish brown lesions. This pathogen may also infect seed causing purple seed stain. Infected seed show a conspicuous discoloration ranging in color from pink to pale purple to dark purple. The discoloration may range from small specks to large blotches which cover the entire surface of the seed coat. Temperatures of 82- 86EF with extended periods of high humidity favor disease development. At this point in the season control of Cercospora leaf spot and purple seed stain is not feasible. It is important to remember that since this fungus can infect the seed, seed from heavily infected fields should not be used for seed. If infected seed must be planted, seed lots should be thoroughly cleaned and an appropriate seed treatment fungicide used. Rotating soybean with crops other than legumes will also help reduce Cercospora leaf spot and blight in future soybean crops. Colletotrichum species Colletotrichum truncatum and several other Colletotrichum species cause anthracnose of soybean. Typically, anthracnose is a late season stem and pod disease of soybean. Symptoms occur on stems, pods and petioles as irregularly shaped, light to dark brown spots, streaks or lesions. Eventually black fungal structures may be evident in these lesions. Anthracnose may also cause a tipblight. The tipblight phase of anthracnose causes a yellowing or browning of the uppermost leaves and pods. The blighted tips may dry up and die prematurely. Anthracnose is favored by warm, wet weather, and the tipblight phase of anthracnose is most likely to occur after a rainy period. Again, at this point in the season control of anthracnose is not feasible. This fungus may also infect seed so seed from heavily infected fields should not be used for seed. If infected seed must be planted, seed lots should be thoroughly cleaned and an appropriate seed treatment fungicide used. Rotating crops with at least one year out of soybean will also help reduce anthracnose. Sudden Death Syndrome Symptoms of sudden death syndrome (SDS) may appear several weeks before flowering but are more pronounced after flowering. Foliage symptoms begin as scattered yellow blotches in the interveinal leaf tissue. These yellow blotches may increase in size and merger to affect larger areas of leaf tissue. Yellow areas may turn brown but veins remain green giving the leaves a striking appearance. Infected plants may wilt and die prematurely. Severely affected leaflets may drop off the plant leaving the petiole attached or may curl upward and remain attached to the plant. Root systems may show deterioration and discoloration of lateral roots and taproot. When split open, internal tissues of the taproot and stem may show a light gray to light brown discoloration. Management options for SDS are somewhat limited but should include planting varieties which have performed well where SDS has been a problem, improving drainage in poorly drained fields, avoiding compaction, staggering planting dates, delaying planting until soils are warm and dry, avoiding continuous crop soybean, maintaining good crop vigor, avoiding crop stress including stress from soybean cyst nematode and harvesting fields with SDS in a timely fashion. Laura Sweets, Plant Pathology 573-884-7307 Sericea Lespedeza: Eliminate Small Infestations Now or Deal With Bigger Problems Later By Kevin Bradley In spite of the dry weather we are experiencing throughout most of the state, one species that you may have noticed remaining distinctly green among our drought-stricken pastures and hay fields is sericea lespedeza (Lespedeza cuneata). Why is this? Well ironically enough, sericea lespedeza just happens to be a plant that is extremely drought hardy. And this is just one of the characteristics of sericea lespedeza that make it a competitive, invasive species that you don’t want on your property. In case you aren’t familiar with sericea lespedeza, it is a non-native perennial legume that was introduced into the United States in 1896 as a forage crop. It resembles many other annual lespedezas utilized for forage but has erect stems that may reach as much as 5 feet in height (Figure 1). Sericea has trifoliate leaves with conspicuous points at the leaf tips. Individual leaves are rarely longer than 1 inch in length and have hairs on the leaf undersides only. Sericea plants are usually highly branched in the upper canopy and plants can occur as a single stem or as several stems that originate from the same perennial base. In the early 1930’s, sericea was often planted in Kansas and Missouri for erosion control, wildlife habitat, and occasionally for use as a forage. Over the last several decades, however, sericea has developed into a significant problem weed of pastures, hay fields, and roadside rights-of-way. It can tolerate a variety of soil conditions and competes with native vegetation for moisture, nutrients, and sunlight. It has the ability to emit chemicals that inhibit the germination and development of nearby plants (called allelopathy), and it is also a prolific seed producer (Figure 2). In 1970, some researchers found that established sericea plants could produce as much as 600 pounds of seed per acre annually. Sericea can become a damaging invader in pastures, hay fields, and partially wooded sites. In these areas, grazing by cattle is limited to young, tender growth because these plants become unpalatable as the plants mature. For example, some research conducted in the early 1940’s revealed that tannin levels increased from 6 to 21 percent as sericea increased from 4 to 36 inches in height. Because of this, cattle tend to selectively graze around the stiff stems during the latter part of the summer resulting in the production of additional seed for the following year. Because of its highly competitive nature, sericea lespedeza was declared a statewide noxious weed in Kansas in 2000. Sericea appears to be spreading northward into Nebraska and eastward throughout Missouri. It is not currently declared a noxious weed in Missouri, although it now occurs in most of the counties in this state. In most areas of Missouri, sericea will soon be approaching the bloom stage of growth. Sericea’s flowers are not as noticeable as many other species but upon closer examination of these plants you will find white to yellow flowers with purple tinges located in the upper leaf axils of the stems. This stage is important because several studies have shown that the herbicide metsulfuron is particularly effective on sericea when applied during the bloom stage of growth. Metsulfuron is the active ingredient in Cimarron (which used to be sold as Ally) and Escort, and is also included with 2, 4-D and dicamba in a prepackaged herbicide mix sold as Cimarron Max. Either of these products should provide good control of sericea when applied in the bloom stage of growth. Another option is to apply triclopyr or herbicides that contain triclopyr when sericea is in the vegetative stage of growth and usually no taller than knee-high in height. In our research studies, this has corresponded to a late-May to mid-June timeframe. Triclopyr is the active ingredient in Remedy and is also one of the components of Crossbow and PastureGard. PastureGard is a new herbicide that just became available for use in Missouri this season, and our evaluations of this herbicide on sericea have been promising. Although we have only collected one year of data thus far, our initial results indicate that we achieved greater than 95% control of sericea lespedeza when we applied 2 pints of PastureGard per acre in mid-June. Similar or higher levels of control were achieved with Remedy applications made during the same timeframe. One non-chemical option for controlling sericea lespedeza is to graze heavily infested areas with goats, which will eat the sericea regardless of tannin content. Stocking rates must be adjusted to levels that will keep the sericea below a 3 or 4 inch height. This method should prevent seed production and may eliminate sericea lespedeza infestations altogether after several years. Another way to reduce seed production is to mow plants consecutively throughout the growing season, which will deplete the perennial rootstocks significantly but it is unlikely that mowing alone will eliminate sericea lespedeza infestations. If you’ve had sericea lespedeza on your property for several years, you certainly can get good control of existing infestations with the herbicidal options discussed above (metsulfuron in the bloom stage and triclopyr in the vegetative stage). However, it’s still unlikely that you will be able to "close the book" on the sericea lespedeza chapter forever. Why? Because unfortunately another characteristic of sericea is its ability to produce seed that can remain viable in the soil for as many as 20 years. With plants that are able to produce several thousand seed each, you can see that new sericea seedlings may be a problem for years to come. In other words, eradicating existing stands that have been established for several years is rarely a one time event. This is why early detection and elimination of small sericea infestations now will save you lots of money in the longrun. Kevin Bradley, Weed Science 573-882-4039 Channeling Grain from Corn Hybrids with Some Biotech Traits By Bill Wiebold Marketing corn grain can be complicated if the grain is produced by hybrids that carry one or more biotech traits. Seed companies must provide US and foreign government agencies with large amounts of data on each biotech trait and any combination (stacked) of biotech traits before grain is approved for feed (animal) and food (human) purposes. The three most important government entities for US grain marketing are the US, European Union (EU), and Japan. Because it has been nearly impossible to gain biotech approval in the EU, seed companies will usually market hybrids if the biotech event (or stacked events) is approved in the US and Japan. It is highly recommended that corn grain containing biotech events that are not approved in all three markets be carefully channeled to prevent disruption in the export market. This means that grain not approved for export to the EU should be used for on-farm livestock rations, sold to domestic livestock feeding channels, or delivered to elevators accepting grain not yet approved for EU export. The American Seed Trade Association ( http://asta.farmprogress.com/) web site provides information about the grain facilities accepting such hybrids. Remember that these web sites rely on data collected from surveys and corn producers should reread their grower agreements carefully and comply with their requirements. There are signs that the logjam for biotech trait approval in the European Union is starting to be relieved. However, these approvals may actually complicate grain marketing this fall and winter. Producers should be aware that single biotech traits and stacked biotech traits require separate approval. So, a trait such as Mon863 (Roundup Ready 2), has been approved for both food and feed uses in the EU, but it may not have been approved for both uses if stacked with another biotech trait even if the other trait had also been approved. Also, the EU is approving biotech corn traits separately for food uses and processed feed uses. So it is possible that traits could be approved for gluten feed or DDGS, but not approved for import as whole kernels. Smart channeling of corn grain is essential to the well-being of all US corn producers. The web site www. MarketChoices.info provides a listing of the approval status of biotech corn events for each of these three markets. Producers should understand clearly which trait or traits are in their grain and market accordingly. Biotech traits are useful weapons in controlling problem weeds and insect pests. But, they should be part of an integrated pest management plan that limits the development of resistant weeds and insects. And, knowledge about which biotech event is present and if it is stacked with other biotech events is essential to smart marketing. Bill Wiebold, Ag Ext.-Plant Sciences 573-882-0621 Pick and Choose: Choose and Pick By Bill Casady No nice uniform fields to harvest this year. Some have experienced non-uniform weather that has caused extreme variability both in crop conditions and more recently in field conditions. Poor moisture availability while the crop was made followed by excesses late in the growing season will leave areas of some fields with nearly too little to pick next to areas with nearly too little traction to pick. When soils stay too wet to harvest, we eventually have to go in and harvest even if conditions do not improve. It is not even a logical or financially sound choice to leave a crop in the field in most cases. Compaction is a fundamental problem and fact of life with large machinery anyway. Yet in a year where moisture shortages may have caused a yield deficit, the decision becomes a closer call. Moreover, some grain will be of only fair to poor quality and should be moved immediately into the market and not into storage on the farm. Scout fields this fall to map out harvest plans before heading to the field. Note areas that produced good ears and good quality grain as well as those with both inferior production and poor quality. Drainage maps will also help identify areas that will remain wet due to recent excesses. Hold off on these if possible. In some cases these will be some of the higher producing areas, but in most cases, poor drainage translates directly into poor root development and poor production due to drought stress. No-till fields are expected to solidly outperform any so-called conventional tillage in a year like 2005. Root development in no-till is often superior and results in greater resiliency to drought conditions such as those in July of this growing season. The superior structure of no-till soils will also resist the tendency to compact these now wetter soils this fall. Pick and choose what to harvest first this year. Don’t let good grain fall victim to lodging due to poor stalk strength before getting this grain into storage. Take poorer quality grain straight to market or commercial storage to avoid on-farm storage problems with that grain. Finally keep compaction in check by staying in existing tracks with grain carts and combines, by making multiple trips into the field as opposed to a few mammoth trips, and choosing what to harvest before getting ready to pick. Stay safe. Bill Casady, Ag Ext.-Food Science & Nutrition 573-882-4370 Now is the time for fall nitrogen on fescue pastures By John Lory Fall nitrogen on fescue pastures should be applied no later than mid September and is best applied in mid August. Most fall fescue growth is completed by October 15th. Recommended fall nitrogen rate is 50 to 80 pounds nitrogen per acre. Yield increases from fall nitrogen are less dependable than spring applied nitrogen because adequate rainfall is less dependable in the fall. Yield potential is also less in the fall. But your ability to manage animals to fully utilize fall growth is much greater in fall making fall forage quite valuable. Fescue forage maintains its feed value through most of winter providing ample time to fully utilize fall growth. Fall nitrogen fertilization is a gamble that significant rainfall will occur in late August and September. If fall rains come too late there will be no yield response. Unfortunately unused fall nitrogen fertilizer from conventional fertilizer materials is often lost during wet periods in late fall and winter. Poultry litter is an excellent fall pasture fertilizer. One benefit of poultry litter is that it is less likely to be lost over winter in years when early fall rains fail. So fall nitrogen from poultry litter will promote spring growth in years when dry conditions limit fall growth. When calculating poultry litter rates remember that only 60% of nitrogen in poultry litter is available as a fertilizer in the year of application. Two tons of poultry litter typically will provide 60 to 90 pounds of available nitrogen in the year of application, an ideal rate for fall fescue. Poultry litter is also an excellent source of phosphorus, potassium, sulfur and micronutrients. John Lory, Ag Ext.-Plant Sciences 573-884-7815 Weather data for the Week Ending August 23, 2005 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days* -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Depart Avg.Avg. reme reme from |Aug 1 from |Since from Station County Max.Min. High Low Mean avg. |Aug 23 avg. |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 87 67 96 62 76 +1 | 5.78 +2.92|2964 +452 St. Joseph Buchanan 84 66 92 64 75 0 | 6.22 +3.85|2833 +262 Brunswick Chariton 87 67 96 64 76 +1 | 5.28 +2.31|2899 +280 Albany Gentry 86 66 96 61 75 0 | 1.73 -1.08|2742 +150 Auxvasse Audrain 87 68 97 63 77 +2 | 3.91 +1.53|2937 +311 Columbia Boone 86 68 95 64 77 +1 | 6.50 +3.80|2972 +250 Sanborn Field Boone 86 70 96 65 78 +1 | 4.77 +2.06|3126 +348 Novelty Knox 86 66 93 60 75 0 | 2.63 +0.07|2752 +173 Linneus Linn 85 66 93 63 75 +1 | 2.78 +0.08|2770 +256 Monroe City Monroe 86 66 93 62 76 +1 | 4.10 +1.28|2854 +217 Versailles Morgan 88 69 970 67 78 +2 | 4.99 +2.21|3151 +392 Green Ridge Pettis 86 69 95 67 76 +1 | 4.14 +1.29|3017 +430 Lamar Barton 90 70 98 67 80 +2 | 2.50 -0.05|3068 +179 Cook Station Crawford 89 69 95 66 77 0 | 2.99 -0.01|2748 -74 Delta Cape | | Girardeau 90 71 95 69 80 +2 | 2.07 -0.10|3007 -95 Cardwell Dunklin 95 74 99 71 82 +3 | 0.85 -1.00|3345 +12 Clarkton Dunklin 94 73 10 70 82 +3 | 1.44 -0.36|3288 -6 Glennonville Dunklin 92 73 98 70 81 +2 | 1.53 -0.13|3256 -26 Charleston Mississippi 92 73 97 69 81 +4 | 1.78 -0.28|3185 +135 Portageville- | | Delta Center Pemiscot 92 74 97 69 82 +4 | 2.11 +0.33|3384 +124 Portageville- | | Lee Farm Pemiscot 92 75 97 69 82 +4 | 2.33 +0.50|3383 +144 Steele Pemiscot ** ** ** ** ** ** | ** ** | ** ** -------------------------------------------------------------------------------- **Complete data not available for report *Growing degree days are calculated by subtracting a 50 degree (Fahrenheit) base temperature from the average daily temperature. Thus, if the average temperature for the day is 75 degrees, then 25 growing degree days will have been accumulated. -------------------------------------------------------------------------------- Pat Guinan, Commercial Agriculture Program (573) 882-5908