Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 16, No. 8 Article 1 of 5 May 13, 2006 Fusarium Head Blight or Scab of Wheat By Laura Sweets Fusarium head blight or scab of wheat develops on plants in the flowering to early grain fill stages of growth. Although winter wheat in south Missouri began flowering more than a week ago, the winter wheat in much of the rest of the state is just beginning to flower. So the time for possible infection by the Fusarium head blight fungus is at hand. Infection is very dependent on environmental conditions while wheat is in susceptible stages of growth. Moderate temperatures in the range of 77-86 degrees Fahrenheit, frequent rain, overcast days, high humidity and prolonged dews favor infection and development of scab. Weather conditions over the next week or so will determine the extent and severity of scab in this year’s wheat crop. Fusarium head blight or scab problems will be more severe if rains coincide with flowering of wheat fields. Many parts of the state have been unusually dry but the cool, rainy and cloudy weather over the April 29-30 weekend and the scattered rains the first week in May could be conducive to scab problems in areas of the state in which the wheat crop is flowering. The characteristic symptom of scab on wheat is a premature bleaching of a portion of the head or the entire head. Superficial mold growth, usually pink or orange in color, may be evident at the base of the diseased spikelets. Bleached spikelets are usually sterile or contain shriveled and or discolored seed. Scab is caused by the fungus Fusarium graminearum. This fungus overwinters on host residues such as wheat stubble, corn stalks and grass residues. Spores are carried by wind currents from the residues on which they have survived to wheat heads. If environmental conditions are favorable, i.e. warm and moist, the spores germinate and invade flower parts, glumes and other portions of the spike. Scab infection occurs when favorable environmental conditions occur as the wheat crop is in the flowering to early grain fill stages. Unfortunately, the detrimental effects of scab are not limited to its adverse effects on yield. The fungi which cause scab may also produce mycotoxins. Vomitoxin (deoxynivalenol or DON) and zearalenone may occur in wheat grain infected by scab fungi. This is a primary concern where grain is fed to non-ruminant animals. Ruminants are fairly tolerant of these two mycotoxins. Also, the fungi which cause scab may survive on the seed and can cause seedling blight and root rot problems when scabby grain is used for seed. At this point in the season there are no management options available for controlling scab on wheat. Growers should be scouting fields to get a feel for incidence and severity of scab in this year’s wheat crop. Because of possible mycotoxin concerns and seed quality concerns, grain from fields with scab may require special handling. Wheat planted on corn, sorghum or wheat residue (even wheat double cropped with soybeans) has a greater risk for scab. Laura Sweets, 884-7307 ********************************************************************* Article 2 of 5 May 13, 2006 Spray-Smother-Spray By Craig Roberts and Kevin Bradley Nearly all of Missouri’s tall fescue is infected with a fungus known as the "endophyte." The tall fescue endophyte causes fescue toxicosis, a serious disorder in cattle, horses, and sheep. Fescue toxicosis is characterized by poor health and production, including low rate of gain, poor milk production, and poor reproduction. While many producers manage tall fescue to minimize the effects of toxicosis, other producers plan to replace their toxic tall fescue with another forage. For these producers, it is time to begin thinking of killing of the old tall fescue. Normally, a stand of grass can be killed with a high rate of glyphosate, which is sold under a variety of different trade names but is perhaps most commonly known as Roundup. With toxic tall fescue, however, killing the stand requires more. That is because a single spray does not kill all the individual plants. Many plants are covered by dung piles; these plants avoid herbicide contact and often emerge later in the year. Also, a single spray does not kill the tall fescue seed present in the soil. This seed, still infected with the endophyte, can germinate and provide toxic seedlings long after the field is sprayed. For these reasons, Missouri Extension recommends replacing toxic tall fescue with a recipe known as "spraysmother- spray." There are other recipes being explored in other states, but the spray-smother-spray recipe is a proven method in Missouri. The entire procedure can be done in four months and will provide excellent summer pasture in the process. It calls for spraying glyphosate in the spring, no-tilling a smother crop in the summer, and establishing the new grass in the fall. (See Figure 1.) The initial spray is in late May--between May 15 and May 21--which is about 1 week before a summer annual crop would be planted. Glyphosate should be applied at a rate of at least 2 lbs per acre, or 2 quarts per acre of a 4 lb/gallon glyphosate formulation. The smother crop is planted on or near June 1, and it is usually pearl millet or a hybrid of sorghum x sudangrass. The smother crop is grazed all summer and sprayed with a second application of Roundup in late August--between August 15 and August 21--about 1 week before the new coolseason grass is planted. The new grass is often MaxQ tall fescue, which contains no detectable levels of toxins but offers excellent pasture and livestock performance. In northern Missouri, the new grass is sometimes a blend of orchardgrass and endophytefree tall fescue. If replacing toxic tall fescue is your goal, plan ahead. And begin planning for the first step--spraying tall fescue in late May. For more information, contact your local University Extension office. Figure 1. Recipe for Spray-Smother-Spray, a method to replace toxic tall fescue pasture with a cool-season grass. *This article is reprinted from an article published in the Spring 2006 issue of Missouri Grasslands. Craig Roberts Kevin Bradley University of Missouri ********************************************************************* Article 3 of 5 May 13, 2006 Winter Wheat Update- May 9, 2006 By Laura Sweets Thus far this year the primary disease problems on winter wheat throughout the state have been virus diseases. Barely yellow dwarf is quite wide spread this year. Symptoms range from scattered plants showing discoloration of the flag leaf and leaf below the flag leaf to small, somewhat circular patches of plants that are stunted, more upright in growth, poorly tillered and discolored to large areas of fields that are showing symptoms. The barley yellow dwarf virus is spread or vectored by several species of aphids. At this point in the season it is difficult to determine if infection of wheat plants with the barley yellow dwarf virus occurred last fall, over the winter months, early this spring or later in the growing season. Although, the earlier that plants were infected with the virus, the more severe symptoms are likely to be and the greater the potential for yield loss. In parts of the state in which moisture stress has been severe some of the plants infected with barley yellow dwarf may now be showing a firing of the leaf tips and a more brown than purple discoloration of the leaf tips from a combination of moisture stress and barley yellow dwarf. In addition to barley yellow dwarf, winter wheat samples submitted to the Plant Diagnostic Lab have also tested positive for wheat spindle streak mosaic virus, wheat soilborne mosaic virus and most recently wheat streak virus. Symptoms of wheat spindle streak mosaic and wheat soilborne mosaic usually occur early in the season when temperatures are cooler and then decline or fade away as temperatures increase. Wheat streak mosaic is favored by hot, dry conditions. The unusually hot, dry conditions throughout much of the state the first three weeks in April could explain the earlier than normal appearance of wheat streak mosaic. Management options for winter wheat virus diseases are primarily preventative treatments. At this point in the season there are no effective management options. Foliage diseases have not been very evident this season. It is possible to find a few lesions of Septoria leaf blotch in some fields. Powdery mildew has been found in some fields that had high levels of greenbug or other aphids earlier in the season. Leaf rust and stripe rust have not been very prevalent or severe. Most of these foliage diseases are favored by wet, overcast, humid and cloudy weather. The unusually hot and dry conditions for much of April have limited the development of foliage diseases on winter wheat. The recent change to cooler temperatures and rain over the past weekend might lead to the development of leaf rust, stripe rust or Septoria leaf blotch. The later in the season that these diseases develop the less likely they are to cause significant yield loss. Over the last few days I have had several phone calls related to loose smut of wheat. Loose smut is quite easy to see in the field at this point in the season. The kernels on infected heads are replaced with masses of powdery black spores. So the heads have a very obvious, black, powdery appearance. These spores are eventually dislodged by wind and rain, so later in the season the smutted stems are less evident and only the bare rachis will be left. Spores produced on smutted heads now are being wind carried to adjacent plants in the field and infecting through the flowers. The fungus that causes loose smut survives within the embryo of wheat seeds. If infected seed is planted, the plants growing from those seeds will be infected and develop smutted heads the next season. If seed from a field that has a "small" amount of smut in one season is used for seed, the field planted with that seed may have a substantially higher level of smut. Loose smut is best controlled by planting either disease-free seed or using a systemic fungicide seed treatment. Now is also the time that we expect scab or Fusarium head blight to infect flowering wheat plants. See separate article in this issue for more information on Fusarium head blight. Laura Sweets, 884-7307 ********************************************************************* Article 4 of 5 May 13, 2006 Scattered Problems with Black Cutworm Larvae By Wayne Bailey Although high numbers of black cutworm moths were captured in central Missouri, larval infestations and damage reports have been light statewide. Although few reports of damage are good for producers, it does question the precision or accuracy of the predictive model which uses intensive moth capture numbers and degree day calculations to predict first cutting by 4th instar BCW. Many factors can affect the growth or decline of a particular insect population. Traditionally, we know that BCW larvae have the potential to damage corn for about two weeks following seedling emergence. Late planted corn is at greater risk from this pest due to a better "fit" of larval development with the presence of seedling corn plants. Additionally, the presence of winter annual weeds and the timing of their control in the spring season also may influence numbers of this pest. In contrast, some factors which may hinder BCW populations may include: * Low BCW moth numbers migrating into the state * Trap captures not reflective of actual BCW moth population present in trap area * Windy conditions during the egg laying period * Spring tillage * Insecticide seed treatments or planting time applications of insecticides * Early planted corn that is too large to sustain larval damage * Heavy rains occurring during larval emergence from eggs or when larvae are in the 1st instar stage of development * High numbers of beneficial agents present in fields (corn field ants, insect predators, parasites, fungal and bacterial pathogens) In past years the BCW model generally has performed with moderate to high precision. It is essential that we better understand the insect behavior and host interactions that occur in years of low precession if we are to continue to improve the model. Wayne Bailey 573-864-9905 ********************************************************************* Article 5 of 5 May 13, 2006 Weather data for the Week Ending May 8, 2006 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days^ -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Deprt Avg. Avg. reme reme from |May 1- from |since from Station County Max. Min. High Low Mean avg. |May 8 avg. |Apr 1 avg ---------------------------------------------------------|------------|------------ Corning Atchison 68 47 80 41 58 -1 | 0.37 -0.73 | 362 +207 St. Joseph Buchanan 65 49 77 42 57 -3 | 0.42 -0.59 | 344 +156 Brunswick Chariton 68 48 76 41 58 -2 | 0.85 -0.41 | 389 +190 Albany Gentry 66 44 77 37 57 -3 | 0.20 -1.12 | 303 +134 Auxvasse Audrain 69 49 76 41 59 -1 | 0.95 -0.59 | 394 +196 Columbia Boone 68 49 76 43 59 -1 | 0.53 -0.89 | 403 +170 Sanborn Field Boone 69 51 77 44 60 -1 | 0.63 -0.83 | 451 +208 Novelty Knox 68 45 75 37 57 -2 | 1.27 -0.14 | 322 +136 Linneus Linn 68 45 77 36 57 -2 | 1.26 -0.13 | 326 +152 Monroe City Monroe 68 47 76 38 58 -2 | 0.48 -1.00 | 350 +140 Versailles Morgan 70 51 79 46 59 -2 | 0.81 -0.70 | 445 +166 Green Ridge Pettis 68 50 78 45 59 0 | 0.17 -1.36 | 404 +221 Lamar Barton 69 52 83 47 60 -1 | 2.20 +0.72 | 473 +195 Cook Station Crawford 70 47 81 42 58 -4 | 0.32 -1.10 | 425 +130 Alley Spring Shannon 71 51 81 46 59 -1 | 3.19 +1.70 | 434 +177 Round Spring Shannon 70 51 81 46 59 -1 | 2.08 +0.59 | 433 +176 Delta Cape 72 53 81 47 62 -1 | 1.00 -0.33 | 469 +124 Girardeau | | Cardwell Dunklin 73 56 86 49 64 -1 | 1.14 -0.36 | 607 +189 Clarkton Dunklin 72 55 83 48 63 -2 | 1.41 +0.41 | 560 +155 Glennonville Dunklin 72 55 84 49 63 -2 | 1.72 +0.73 | 566 +157 Charleston Mississippi 72 54 83 47 63 0 | 1.38 +0.06 | 522 +190 Portageville- | | Delta Center Pemiscot 73 56 85 51 64 -1 | 0.94 -0.36 | 593 +189 Portageville- | | Lee Farm Pemiscot 73 57 85 50 64 0 | 0.81 -0.52 | 600 +205 Steele Pemiscot 74 58 86 53 65 0 | 0.85 -0.61 | 637 +235 -------------------------------------------------------------------------------- * 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 ********************************************************************* Vol. 16, No. 8 Article Special May 13, 2006 A lot of Questions About Some Tough Weeds By Kevin Bradley It seems that lately I've gotten a lot of calls about the same weeds — all of which are hard-to-control and none of which are easily eliminated. Most of these are not widespread problems throughout the state, but in the areas where they occur, I would definitely watch out for them and try to keep them from developing into more of a problem. Unfortunately, there hasn't been a lot of research conducted on these weeds and there isn't much information available in the weed science literature, but I have attempted to provide a summary of what we do know about these weeds in this article. Field Horsetail (Equisetum arvense) Field horsetail is a perennial with a [Figure 1] spreading rhizome system from which new plants arise. Field horsetail is known by a variety of different common names, usually dependent on where you are in the state. Some call it scouring rush, some call it ribbon grass, and it is even called "poor-man's-tinker toys" in some areas. As with johnsongrass or any other perennial plant that has rhizomes, the underground root structures are what make these plants difficult to control. Field horsetail is also unique in that two types of stems, and two different types of growth habits, occur within the same plant. The first type of stems to appear in the early spring are the unbranched, reproductive stems (Figure 1). These stems have "cones" at their ends, are often whitish to pink in color, round in cross-section, without leaves, and often grow to one or two feet in height. The second type of stems or growth habit that appears later in the season are the vegetative stems. These are highly branched and resemble a horse's tail, thus the name (Figure 2). In Missouri, field horsetail is probably most common in wet areas such as ditchbanks around corn and soybean fields. It has a tendency to encroach into the low-lying or wet areas of these fields from the ditchbanks and it will thrive in these areas once it is established. Since it has rhizomes, any kind of shallow tillage such as chisel plowing or disking only serves to spread the rhizomes and magnify the problem. Few herbicides provide effective control of field horsetail in either corn or soybean. Many studies have shown that standard and even high application rates of glyphosate are virtually ineffective on this species. Some research conducted by weed scientists in Canada has shown that in corn, sulfonylurea herbicides like Beacon and Permit in combination with dicamba (Banvel, Clarity, Distinct) should provide about 80% field horsetail control during the season of treatment as long as the applications are made to the vegetative stems. Given the nature of its extensive root system, I'm not sure how much long-term field horsetail control is actually provided by these treatments, but at least the competitive effects of this weed are being reduced during the season of treatment. This research has also revealed that Python and Hornet are some of the only preemergence herbicides that will provide some degree of residual control of field horsetail, so inclusion of this product in with a burndown herbicide is another option to consider. In soybeans, glyphosate in combination with Python as a preemergence burndown treatment is one of the only options available for field horsetail. As mentioned previously, Python is one of the only products that offers any residual activity of field horsetail. And, unfortunately, no effective postemergence treatments have been identified in soybean. Follow-up applications of glyphosate will only provide minor suppression at best. In noncrop areas (which on some labels includes non-irrigation ditchbanks), Telar, Oust, and Surmount are a few of the herbicides that are labeled for application on field horsetail. Each of these herbicides is very persistent and can cause severe injury to crops so extreme care should be taken when applying these herbicides near or in areas that will be planted to corn and soybean. Asiatic Dayflower (Commelina communis) Asiatic dayflower is an annual weed in the monocot family that is becoming more of a problem particularly in no-till soybean fields throughout the Midwest. Asiatic dayflower has blue flowers and roots at the ground where it comes in contact with the soil. It forms dense colonies that can cause severe yield losses in both corn and soybean (Figures 3-5). Few herbicides provide acceptable control of Asiatic dayflower in soybeans. Recently, weed scientists at Iowa State have conducted a number of trials to identify treatments for the management of this species. This research has revealed that in soybeans, Spartan, Firstrate, and Sencor are some of the only active ingredients that will provide acceptable Asiatic dayflower control when applied preemergence. Similarly, Firstrate is one of the only conventional herbicides that will provide acceptable control of this species when applied as a postemergence treatment in soybeans, but applications must be made before this species reaches six inches in height. Many other preemergence and postemergence herbicide treatments that have been evaluated, including Command, Dual, Define, Valor, Resource, Cobra, and Aim, provide little to no control of Asiatic dayflower. Glyphosate at standard rates in Roundup Ready soybeans will usually only provide some degree of suppression, and the calls I've received lately regarding this weed suggests to me that our common glyphosate burndown programs are providing little to no control of this species. Other research has shown that increasing the rates and making at least two applications of glyphosate can provide higher levels of Asiatic dayflower suppression and also that three applications of glyphosate at 0.75 lb a.e. per acre can provide about 80% control. Based on all of the available research, it seems clear that preemergence programs that include Sencor or Firstrate are the most effective and economic way to manage this species in soybean. Field Pansy (Viola rafinesquii) Field pansy is a winter annual that can germinate in either the fall or spring, and is sometimes also called "Johnny-jump-up". Field pansy has attractive pale yellow to purple flowers and will only reach 5 or 6 inches in height when fully mature (Firgures 6 and 7). Field pansy is another weed that is not controlled easily by glyphosate in the spring, or even by standard glyphosate plus 2,4-D burndown treatments. Recently, weed scientists at Kansas State have conducted research on this species, where it is also becoming more and more troublesome. This, and other research has revealed that fall applications, especially fall applications of herbicides with residual activity, will provide good control of this species. Research has also shown that even a single glyphosate application in the fall will provide good control of this species, while this same treatment in the spring is virtually ineffective on field pansy. If fall applications are not made and this weed is present in the spring, the addition of dicamba (Banvel, Clarity, Distinct) to a glyphosate burndown will provide good control of field pansy. Some researchers have found that even as little as 2 fluid ounces of Clarity per acre plus glyphosate plus 2,4-D will provide essentially complete control of field pansy. Another option is to increase the rate of dicamba and drop the 2,4-D from the mix altogether. If you have significant infestations of these weeds or have found any other successful strategies for their control, I'd be interesting in hearing about them: bradleyke@missouri.edu. Kevin Bradley bradleyke@missouri.edu