Integrated Pest and Crop Management Newsletter Vol. 17, No. 4 March 30, 2007 ********************************************************************** Check Winter Wheat Fields for Virus Diseases By Laura Sweets This is the time of the year when symptoms of wheat spindle streak mosaic, wheat soilborne mosaic and barley yellow dwarf may be quite evident in winter wheat fields. So far only a few questions on wheat have come in. One sample did test positive for wheat soilborne mosaic virus and the others were abiotic problems related to winter survival. Both wheat spindle streak mosaic and wheat soilborne mosaic tend to be more severe when wet conditions occur after planting in the fall or in the late winter/ early spring months. Most of the state was dry last fall and has been dry this spring until just recently, so wheat spindle streak and wheat soilborne might not be expected to be widespread or severe this season. Although there are no rescue treatments for wheat virus diseases, it is still a good idea to scout fields for plants showing virus symptoms and to send in samples to identify the virus or combination of viruses that are present so that proper preventative management measures can be used the next time wheat is planted in that field. Descriptions of the wheat virus diseases most likely to occur on winter wheat in Missouri are given in the following paragraphs. Symptoms of wheat spindle streak mosaic appear in early spring as yellowgreen streaks or dashes on the dark green background of the leaves. These lesions usually run parallel to the leaf veins and tend to be tapered at the ends giving the lesions a spindle shaped appearance. Foliage symptoms are most obvious when air temperatures are about 50 degrees F. As temperatures warm-up, foliage symptoms of wheat spindle streak mosaic tend to fade. Plants may be slightly stunted and have fewer tillers than normal. Wheat spindle streak mosaic tends to be more prevalent in lower, wetter areas of field. The virus which causes this disease is soilborne and is spread by the soil fungus Polymyxa graminis. Wet falls tend to favor outbreaks of wheat spindle streak mosaic the following spring. Wheat soilborne mosaic causes light green to yellow green to bright yellow mosaic patterns in leaf tissues. Symptoms are most evident on early spring growth, and warmer temperatures later in the season slow disease development. Symptoms of wheat soilborne mosaic are not always particularly distinctive and might occur as a more general yellowing similar to that caused by nitrogen deficiency. Infected plants may be stunted. This disease may be more severe in low lying, wet areas of a field. The soilborne wheat mosaic virus survives in the soil and is spread by the soil fungus Polymyxa graminis. Again, wet falls tend to favor outbreaks of wheat soilborne mosaic the following spring. Barley yellow dwarf is an extremely widespread virus disease of cereals. Symptoms include leaf discoloration ranging from a light green or yellowing of leaf tissue to a red or purple discoloration of leaf tissue. Discoloration tends to be from the leaf tip down and the leaf margin in towards the center of the leaf. Plants may be stunted or may have a rigid, upright growth form. Symptoms are most pronounced when temperatures are in the range of 50- 65 degrees. The barley yellow dwarf virus persists in small grains, corn and perennial and annual weed grasses. More than twenty species of aphids can transmit the barley yellow dwarf virus. Symptoms may be more severe and yield losses higher if plants are infected in the fall or early in the spring. Infections developing in late spring or summer, may cause discoloration of upper leaves but little stunting of plants or yield loss. The other virus disease likely to occur on winter wheat in Missouri is wheat streak mosaic, but symptoms of this disease are not usually evident until later in the season when air temperatures increase. Wheat streak mosaic causes a light green to yellow green mottling and streaking of leaves. Symptoms may vary with variety, virus strain, stage of wheat growth when plants are infected and environmental conditions. Plants may be stunted. As temperatures increase later in the spring, yellowing of leaf tissue and stunting of plants may become more obvious. The wheat streak mosaic virus is spread by the wheat curl mite. Symptoms are frequently found along the edges of fields where the mite vector first entered the field. Both the wheat streak mosaic virus and the wheat curl mite survive in susceptible crop and weed hosts. Thus, the destruction of volunteer wheat and weed control are important management options for wheat streak mosaic. A management program for virus diseases of wheat should include the following steps: * Plant good quality seed of resistant varieties. * Avoid planting too early in the fall to minimize opportunity for insect vectors to transmit viruses to young plants. * Destroy volunteer wheat and control weed grasses. * Maintain good plant vigor with adequate fertility. Laura Sweets sweetsl@missouri.edu ********************************************************************** Potential for Alfalfa Weevil Problems High By Wayne Bailey Problems with alfalfa weevil larvae began this past week with a few alfalfa fields requiring insecticide applications in southern and central Missouri. Alfalfa weevil larvae grow through 4 instars or larval stages (worm stages) on their journey from egg to adult weevil. Eggs are laid inside alfalfa plant stems beginning in late fall, on winter days when temperatures go above 50 degrees F, and in early spring. At present, numerous larvae (1st and 2nd instars) have hatched and can be found in the upper terminal buds of alfalfa plants in fields throughout southern and central regions of the state. These larvae are likely the result of fall or early winter laid eggs and are often seen initially as problems on the south facing slopes of fields. Small larvae in the 1st and 2nd instar stages of growth typically feed inside plant terminals where they are difficult to find and are protected from harsh spring weather conditions. Damage from these early instars is often minor and seen as "pin hole" damage on expanding alfalfa leaflets. As temperatures warm, additional eggs will hatch, plus existing small larvae will rapidly grow into 3rd and 4th instars. These larger instars readily move about the plant and feed on alfalfa foliage. They may consume significant amounts of leaf tissue which typically results in substantial economic loss of alfalfa yield and forage quality. In addition, heavy defoliation also reduces alfalfa competition with weeds and may result in increased weed populations. Alfalfa producers should scout alfalfa fields throughout the state as problems can quickly develop and result in substantial loss of forage yield and quality. One unknown, but important factor is whether the recent sustained rainfall over most of Missouri will result in the development of a fungal pathogen (Zoophthora phytonomi) in the alfalfa weevil larval population. This fungal pathogen is present in most years, but infection rates of the pathogen are most successful in wet years. Infected alfalfa weevil larvae slow their feeding activities, turn from light green to pale yellow in color and die within a few days of becoming infected. If this pathogen develops early in the season, it can decimate larval alfalfa weevil populations. Whether is does so this year in Missouri is yet to be determined. Scouting for alfalfa weevil is best accomplished using a 3-5 gallon bucket and a sharp knife. Producers are encouraged to sample 10 alfalfa stems at each of five random locations in a field for a total of 50 stems per field. At each of the five locations, the scout should carefully cup the terminal of each alfalfa stem and then cut the stem off near the soil surface. The stem is then carefully placed inside the bucket and vigorously tapped to dislodge any larvae present. It is necessary to cup the terminal with your hand during removal of the stem from of the plant to prevent the larvae from being flipped from the terminal during stem removal. If the alfalfa weevil population has reached the economic level of one or more larvae present per stem of alfalfa (50 or more larvae per 50 stems) and 30 percent or more of the alfalfa stems show feeding damage, then control is justified. Recommended methods for control of the alfalfa weevil larvae include: insecticide application, early cutting, grazing and biological control. Insecticides If an insecticide application is required in order to control alfalfa weevil larvae, select from the list of insecticides labeled and recommended for alfalfa weevil control on alfalfa. Rates are given as amount of product applied per acre (See table at the end of article). Early Cutting Early cutting of alfalfa is an alternative to insecticide applications if the alfalfa is within 7-10 days of the normal harvest stage of 1/10 bloom. Early cutting will cause the death of most alfalfa weevil larvae through mechanical crushing by hay conditioners or dehydration from the sun following the removal of the alfalfa canopy. After forage removal, the field should be monitored to detect a possible resurgence in larval numbers. Grazing Grazing is being used by some Missouri producers to reduce the numbers of alfalfa weevil eggs and larvae. Grazing is initiated when weevil numbers reach or are approaching the economic threshold and the alfalfa plants are more than 6-8 inches in height. Grazing is generally accomplished using a management intensive grazing method in which a large number of cattle are placed on a small amount of acres and quickly remove the alfalfa growth. As the alfalfa is grazed to normal harvest level, eggs and larvae that are present are destroyed. Data from Missouri indicate that alfalfa weevil larval numbers are reduced by about 98 percent with mechanical harvest and about 90 percent by cattle grazing in a management intensive grazing system. These reductions in larval numbers can effectively eliminate the risk from alfalfa weevil as long as most spring laid eggs have hatched. This method of alfalfa weevil control is not without risks. Fields should not be grazed when wet and susceptible to damage from cattle hooves. Bloat also must be a concern as producers must take precautions to prevent bloat from occurring to cattle. Your local extension office can provide additional information concerning grazing precautions. Producers should continue to scout alfalfa after grazing to determine whether larval or adult alfalfa weevil numbers again reach economic levels and require further control. Biological Control Biological control is a long-term control strategy that can help keep alfalfa weevil numbers below damaging levels. Five species of biotic agents are now commonly found associated with the alfalfa weevil in this state: four parasites and a fungal disease. The parasites are all introduced species from Europe as is their host the alfalfa weevil. Bathyplectes curculionis, a larval parasite, moved into the state with the alfalfa weevil in the 1960s. Similarly, the fungal disease, Zoophthora phytonomi, was first detected in Missouri in the early 1970s. Both of these biotic agents occur throughout the state and cause some mortality of alfalfa weevil larvae. The three other parasites have a limited range in the state, but are increasing in distribution. The two larval parasite, Bathyplectes anurus and Oomyzus incertus, and an adult parasite, Microctonus aethiopoides, have been established in Missouri as a result of parasite release programs conducted during the 1970s and 1980s. These parasites have a limited distribution, but should increase in importance as they move to other Missouri counties. Producers can help conserve and increase the number of parasites on their farms by using pesticides only when needed and leaving a small area of alfalfa standing when the first cutting is removed. The alfalfa that has not been treated with an insecticide and is not harvested during first cutting will serve as a reservoir for many parasites and predators that attack alfalfa weevil. This alfalfa can be harvested at second and later cuttings because most of these parasites will mature shortly after removal of first alfalfa harvest. ####################################################################### # Recommended Insecticides for Larval Alfalfa Weevil Management - 2007# #---------------------------------------------------------------------# # Insect Pest: Alfalfa weevil Larvae: # #---------------------------------------------------------------------# # Chemical Name # # Common Name # # Rate of Formulated Material # # Rate of Active Ingredient (a.i.) # #---------------------------------------------------------------------# # Beta-cyfluthrin # # *Baythroid XL # # 1.6 to 2.8 fl oz/acre # # 0.0125 to 0.022 lb a.i./acre # #---------------------------------------------------------------------# # Carbofuran # # *Furadan 4F # # 1/2 to 2 pts/acre # # 0.25 to 1 lb/acre # #---------------------------------------------------------------------# # Chlorpyrifos 4E # # *Lorsban 4E # # 1 to 2 pts/acre # # 0.5 to 1 lb/acre # #---------------------------------------------------------------------# # Chlorpyrifos 4E # # *numerous products # # see specific labels # # see specific labels # #---------------------------------------------------------------------# # Methyl Parathion # # *Chemnova Methyl 4EC # # 1 pt/acre # # 0.5 lb a.i./acre # #---------------------------------------------------------------------# # Gamma-cyhalothrin # # *Proaxis # # 2.56 to 3.84 fl oz/acre # # 0.02 to 0.03 lb a.i./acre # #---------------------------------------------------------------------# # Phosmet # # Imidan # # see specific label # # see specific label # #---------------------------------------------------------------------# # Zeta-cypermethrin # # *Mustang Max # # 2.24 to 4.0 fl oz/acre # # 0.014 to 0.025 lb a.i./acre # #---------------------------------------------------------------------# # Carbaryl # # Sevin 4F # # 1.5 qts/acre # # 1.5 lb a.i./acre # #---------------------------------------------------------------------# # Carbaryl # # Sevin XLR Plus # # 1.5 qts/acre # # 1.5 lb a.i./acre # #---------------------------------------------------------------------# # Lambda-cyhalothrin # # *Warrior # # 2.56 to 3.84 fl oz/acre # # 0.02 to 0.03 lb a.i./acre # #---------------------------------------------------------------------# # Lambda-cyhalothrin # # *Numerous products # # see specific labels # # see specific labels # #---------------------------------------------------------------------# # Read and follow all label direction, precautions, and restrictions. # # * Designated a restricted use product. # ####################################################################### Wayne Bailey, 573-864-9905 ********************************************************************** Days Suitable for Fieldwork in Missouri By Ray Massey The number of days available to complete land based activities influences input (e.g., variety/hybrid planted, pesticide used) and machinery decisions. Limited fieldwork days during critical times, such as tillage, planting and harvest, require careful management. A large machinery complement will complete field work quickly but can increase ownership costs. A small machinery complement may have fewer ownership costs but cause delays of some key activities that affect productivity. The size of machinery that can efficiently complete the necessary activities depends on how many days it can actually be used in the field. The Missouri Agricultural Statistics Service (MASS) reports the number of days each week suitable for field work starting around the first week of April. Historically, this has been early enough to cover the usual corn planting dates of mid-April to mid-May. However, corn planting has been occurring much earlier in recent years. The USDA reported 46 percent and 50 percent of corn was planted by mid-April in 2005 and 2006, respectively. Unfortunately, no suitable fieldwork days data prior to April exist for Missouri. MASS provides estimates of fieldwork days in each of the nine reporting districts. A summary of the average number of weekly fieldwork days from 1977 to 2006 for three key seasons is shown in table 1. Estimates are for seven day work weeks. If fieldwork will not normally be done on Sundays or holidays, subtract 0.7 days per week. The complete data by individual week can be accessed at http://agebb.missouri.edu/mgt/fieldwork.htm. If your particular interest lies in determining the probability of completing a particular field activity within an acceptable time period, FAPRI has developed an excellent spreadsheet tool. It allows the user to enter information about 1) preferred start and ending date, 2) acres worked and 3) equipment descriptions. Using the historical frequencies of days suitable for fieldwork, it returns an estimate of the percent of time that you will be able to complete the work within the required time frame. This spreadsheet can be downloaded at http://www.fapri.missouri.edu/. ###################################################################### # Table 1. # # Estimated Number of Days Suitable for Fieldwork in Missouri. # #--------------------------------------------------------------------# # MO # # From To NW NC NE WC C EC SW SC SE state # #--------------------------------------------------------------------# # 27-Mar 5-Jun 3.3 3.0 3.1 3.3 3.5 3.4 4.2 4.2 3.6 3.5 # # 5-Jun 28-Aug 4.7 4.7 4.9 4.9 5.1 5.1 5.4 5.5 5.2 5.0 # # 28-Aug 20-Nov 4.6 4.4 4.7 4.7 4.8 4.8 5.2 5.3 4.9 4.8 # ###################################################################### Ray Massey masseyr@missouri.edu ********************************************************************** Wireworm Baits and Preplant Decisions for Corn By Wayne Bailey Wireworm is a group of insects which are often difficult to scout and manage. One method used to determine wireworm numbers prior to planting is the use of a solar baiting system. It can effectively estimate wireworm larval populations present at a site. The scouting technique consists of placing bait stations or traps at several locations within a crop field. A minimum of two bait stations per acre is recommended, but in reality establishing 5 to 10 bait station per 30 to 40 acres of crop field should be sufficient if traps are properly located. In order to gain accurate estimates of the wireworm population, traps should be located in high risk areas such as in any grassy areas of the field or in areas where wireworms caused injury in previous seasons. Although trap placement in fields may occur 2-3 weeks prior to planting of the corn crop, traps placed 7-10 days prior to planting provide more accurate estimates of wireworm numbers as wireworms often remain deep in the soil until soil temperatures warm in the spring. This trapping technique consists of digging a 4-inch deep by 6-9 inch wide hole at the soil surface. Place into the hole a two to one cup equal mixture of untreated corn and wheat seed which has been pre-soaked for 24 hours prior to use in order to speed up seed germination.. Fill and slightly mound each station with soil. Cover each mound with an 18-inch square of black polyethylene plastic (appropriate sized trash bag) followed by a oneyard square sheet of clear polyethylene or similar clear plastic bag. Cover the edges of the plastic layers with soil to prevent wind damage. The black plastic layer absorbs heat and the clear plastic helps retain heat in the soil producing a "greenhouse effect" which allows for more rapid germination of the bait seed. Carbon dioxide is produced during the germination process and attracts wireworms to the bait. Just prior to planting, remove the plastic layers and soil from the bait and count the number of wireworm larvae in and around the bait. If the average number of wireworm larvae collected in all baits located in the field average one or more per bait station, the economic threshold has been exceeded and treatment is justified. If an economic infestation is found, control options implemented before or at the time of planting are recommended. Management options include such strategies as use of liquid or granular insecticides at planting or planting insecticide treated seed. Rescue treatments for this soil inhabiting insect pest are not available. Wayne Bailey 573-864-9905 ********************************************************************** Testing for wheat viruses at the MU Plant Diagnostic Clinic By Simeon Wright The University of Missouri Plant Diagnostic Clinic has begun ELISA testing wheat samples for viruses again this year. In our first testing this year, we have detected wheat soilborne mosaic. Having symptomatic plants tested can help you determine what is wrong with the plants and make management decisions for your current crop as well as future crops. We generally test for four common viruses including wheat spindle streak, wheat soilborne mosaic, wheat streak mosaic, and three common strains of barley yellow dwarf. Sample Collection and Submission The best samples are dug to include part of the root system and wrapped in dry paper towels placed inside a plastic bag and quickly shipped to the clinic early in the week to avoid delay that leads to decay during shipment. The general fee for sample submission is $15 plus $10 for virus testing by ELISA. More information on sample submission, fees, and submission forms can be found at our Website http://soilplantlab.missouri.edu/plant/ or at your local extension office. Simeon Wright 573-882-3019 wrightsi@missouri.edu ********************************************************************** Measure Planter Maintenance and Performance in BTUs By Bill Casady As ethanol and biodiesel plants spring up on the landscape across the state and country, it's more evident now than ever that planting is all about preparing to capture solar energy. It's a long tradition that during the spring of the year we prepare to install living solar collectors, but now an increasing amount of that energy stored in our crops is converted to serve our energy needs. Improvements in agricultural technology continue to increase efficiency that can often be measured from one year to the next. Ultimately, however, it is good management of the technology and thorough maintenance procedures that determine performance and net value of a crop for a given farm. The primary goal of good planting performance is to achieve a uniform and evenly-emerged stand so all plants have an equal chance to capture and store energy. Just like the cells of a solar collector, the plant canopy should be designed so there is a plant for every space and a space for every plant. Skips and doubles decrease plant performance. Maintenance of seed metering components and a cautious attitude toward ground speed can improve in-row spacing. If the planter seems to be able to place seed at the correct depth at relatively high speed, then we've only accounted for half of the needed precision. Any variation in the time it takes the seed to make its way to the soil is amplified at higher ground speeds. The result is two seeds arriving closely together and a hole in the canopy where that late seed should have landed. For that small section of row with substandard seed placement, grain and energy production might be as little as 50 percent of target. The best method for covering a lot of acres in the day is to keep the planter rolling. That means having the proper amount of help or the right kind of equipment to tend the planter, a fresh operator if needed, someone to monitor planter performance for the operator and preseason maintenance that detects and prevents potential breakdowns before they occur. Timeliness is way more important than the cost of a few partially worn parts that might still have some life left in them. Replace those parts before they break. Poor control of planting depth also results in erratic seedling emergence. The later emerging or less vigorous seedlings due to poor emergence are shaded. These plants use valuable resources but may fail to perform well enough to produce seed. Use row cleaners when necessary to create more uniform conditions for seed placement. Row units continuously encounter subtle changes in the soil due to differences in residue and changing soil structure from harder soil aggregates to loose soil. Row cleaners can't compensate for every condition. Again, cautious ground speed is the key that allows the dynamic components of the planter mechanisms to react to changing conditions and properly place the seed. The faster we travel, the more dynamic the situation becomes and the less likely the row unit can respond quickly enough to compensate. Most planters are capable of uniform depth and placement. The keys to efficient planting to install a uniform living solar collector are preseason planter maintenance, cautious speed and good support to keep the planter rolling. The result is better net energy . . . and better net return on your investment. Bill Casady 573 882-4370 ********************************************************************** Weather Data for the Week Ending March 25, 2007 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days^ -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Depart Avg.Avg. reme reme from |Mar 1 from |since from Station County Max.Min. High Low Mean avg. |Mar 25 avg |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 70 49 84 36 59 +16 | 0.85 -0.89 | * * St. Joseph Buchanan 68 51 80 38 59 +15 | 1.31 -0.29 | * * Brunswick Chariton 69 50 78 40 60 +15 | 1.74 -0.18 | * * Albany Gentry 68 49 82 33 58 +15 | 1.38 -0.62 | * * Auxvasse Audrain 70 51 80 40 60 +16 | 1.44 -0.79 | * * Columbia Boone 70 53 78 42 61 +15 | 1.69 -0.52 | * * Sanborn Field Boone 70 54 79 43 62 +16 | 1.66 -0.57 | * * Williamsburg Callaway 70 52 78 41 61 +17 | 2.13 -0.10 | * * Novelty Knox 68 48 76 30 58 +14 | 2.82 +0.93 | * * Linneus Linn 68 49 77 33 59 +16 | 2.06 +0.35 | * * Monroe City Monroe 69 48 77 31 59 +14 | 2.06 -0.03 | * * Versailles Morgon 72 56 78 46 63 +15 | 2.07 -0.29 | * * Green Ridge Pettis 70 55 76 45 62 +17 | 1.32 -0.96 | * * Lamar Barton 71 57 76 52 64 +16 | 3.41 +0.65 | * * Cook Station Crawford 74 52 81 46 64 +16 | 0.88 -1.90 | * * Alley Spring Shannon 76 49 82 38 63 +16 | 1.13 -1.79 | * * Round Spring Shannon 76 50 83 38 62 +15 | 1.24 -1.68 | * * Delta Cape | | Girardeau 75 51 82 43 63 +14 | 1.11 -1.77 | * * Cardwell Dunklin 79 54 85 44 66 +14 | 0.35 -3.07 | * * Clarkton Dunklin 77 54 84 44 66 +15 | 0.67 -2.22 | * * Glennonville Dunklin 77 56 83 46 67 +16 | 0.63 -2.24 | * * Charleston Mississippi 75 55 82 47 65 +16 | 1.33 -1.60 | * * Portageville- | | Delta Center Pemiscot 79 57 85 48 67 +16 | 0.43 -2.78 | * * Portageville- | | Lee Farm Pemiscot 79 56 85 48 68 +17 | 0.48 -2.74 | * * Steele Pemiscot 80 55 87 46 67 +16 | 0.45 -2.96 | * * -------------------------------------------------------------------------------- * 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 GuinanP@missouri.edu