Integrated Pest and Crop Management Newsletter Vol. 17, No. 9 May 14, 2007 ********************************************************************** Field Crop Disease Observations- May 14, 2007 By Laura Sweets Wheat This has been a difficult season for the wheat crop. Effects of the low temperatures are still showing up in fields across the state. As the crop begins to head, head distortion and sterile glumes may be evident. There have been a few reports of loose smut showing up on plants in the boot stage or beginning stages of head elongation. 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. Weather conditions have been conducive for the development of Fusarium head blight or scab in many areas of the state—see accompanying article in this issue of the newsletter. Foliage diseases with the exception of powdery mildew have not been particularly widespread or severe. Most of the foliage diseases of wheat are favored by periods of free moisture on the leaf surfaces so the weather conditions over the next 7-14 days will determine if diseases such as Septoria leaf blotch, leaf rust and/or stripe rust buildup in the crop. Descriptions of the wheat foliage diseases and a table of fungicides labeled for use on wheat appeared in the April 27, 2007 issue of the Integrated Pest and Crop Management Newsletter. Most of these fungicides cannot be applied after Feekes growth stage 10.5 (full head emergence), so if a field has begun to flower, it is too late to apply a foliar fungicide. There have been some reports of light green to yellow-green flecking and/or striping on wheat leaves, especially the flag leaf. Some wheat varieties, including Bess and Truman, have a tendency towards a genetic flecking which produces light green to yellow-green flecks or specks in the leaf tissue. These are usually evident as distinct small, oval to oblong lesions in the leaf tissue. In some samples, particularly from central Missouri, the discoloration is occurring as light green to yellow-green longer streaks or stripes in the leaf tissue. These streaks run parallel to the mid-rib. The leaves may also have a slightly desiccated or dry appearance. Several samples showing the streaking symptoms were tested for virus diseases and were positive for wheat streak mosaic. This is the virus disease spread or vectored by the wheat curl mite. Damage from wheat streak mosaic is usually most severe during periods of hot, dry weather. No controls are feasible at this time. Corn So far there have been very few reports of any disease problems on corn. Delays in planting because of wet conditions and delayed emergence because of cool, wet conditions are the most evident problems. As corn begins to emerge seedling blights may be evident. Descriptions of corn seedling blights were covered in the May 4, 2007 issue of the Integrated pest and Crop Management Newsletter. Soybeans Relatively few acres of soybean have been planted thus far. My early planted soybean seed treatment trial in central Missouri (planted April 10) is showing a range of seed decay and seedling blight symptoms including Pythium seed decay, Phytophthora seed decay and seedling blight and Rhizoctonia seedling blight. If the current weather pattern continues soybean seed and seedling blights could be a more significant problem than they have been for the last few years. This might be a good year to consider the use of a soybean seed treatment fungicide. See the January 26, 2007 issue of the Integrated Pest and Crop Management Newsletter for information on soybean seed treatment fungicides. The soybean rust situation has taken an interesting twist since May 8. Most of the southern states have been dry, so environmental conditions have not been favorable for rust development on kudzu, soybeans in sentinel plots nor soybeans in commercial fields. However, on May 8 a sample suspected of having Asian soybean rust was collected in New Iberia, Louisiana. The sample was examined microscopically and then tested using both ELISA (immunoassay test strips) and PCR. The sample was positive for Asian soybean rust. So far soybean rust has only been found at the one site in Louisiana and both incidence and severity at that site are low. But the presence of soybean rust so early in the season is of concern. At this point in the season, soybean rust is active on kudzu in six counties in Florida and the one site in Louisiana. No currently active sites of soybean rust are reported in Alabama, Georgia, Mississippi or Texas. Updates from southern states are available on the IPM PIPE Website (http://www.sbrusa.net). Laura Sweets SweetsL@missouri.edu ********************************************************************** 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 ranges from heads emerging to 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 wet and the initial forecast for the week of May 7-11 with moderate chances for rain almost every day would have been quite conducive to scab problems in areas of the state in which the wheat crop is flowering. The forecast was changed to slightly lower changes for rain for much of the week of May 7-11 but light rain, heavy dew and high relative humidity would still be favorable for scab infection and disease development. 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 SweetsL@missouri.edu ********************************************************************** Wet weather and nitrogen loss By Peter Scharf Heavy rainfall and flooding in the western part of the state has resulted in lots of questions about nitrogen loss. This is a crucial question that may have serious implications for corn yield and profitability. Back in 2005, we estimated nearly 2 million bushels of lost yield potential in the Holt County Missouri River bottom alone due to N deficiency. This estimate was based on an aerial photo survey and research-based relationships between corn yield and color. This N deficiency was caused by heavy rains over Memorial Day weekend, but no actual flooding of fields. On fields that have gone under water, losses are likely to be even more severe. For fields that have gone under water but the corn survived well enough to keep the stand, yield response to applying more N now is highly likely. I would say that it is essential to get additional N on these fields. A general target rate for additional N might be 40-60 lb N/acre in fields that have been submerged. Chances are good that many of them will need more. Which ones? Factors that would lead to greater losses include: sandy texture, well drained, longer submergence, N source was not ammonia, or was ammonia applied in the fall. Consider applying higher rates on fields with more than one of these risk factors. For fields that were not submerged, but received excessive rainfall, it’s likely that additional N would give a yield response, but not as much as fields that have been submerged. The same risk factors apply, except that poor drainage also increases risk of N loss in these fields. Peter Scharf University of Missouri ScharfP@missouri.edu ********************************************************************** Flood effects on grain crops By Bill Wiebold The flood of 2007 was really three interrelated events. Heavy rains produced increased runoff that caused flash flooding. These floods are often short-lived and the flooding water is moving quickly. Low areas in fields, even those separated from rivers or streams, with slow or poor drainage also experienced flooding. In this type of flood, water will collect or pond in a portion of, or perhaps, the entire field. This type of flood may last longer than flash floods and the water is moving very slowly or not at all. The final event happened as water drained into tributaries of the Missouri River. The major river floods occurred as river water levels rose above flood stage, the levees were breached, or tributaries flooded as water backed up into them. Although these floods differ in some important aspects all of them can cause death or harm to crop plants. The primary damage to plants (other than lodging) from flooding or ponding is oxygen deprivation. The oxygen content of water is much lower than air—even air within the soil. Water in soil (water-logging) or above the soil surface (flooding) means there is much less oxygen available to plants. Living plant tissues including roots, require oxygen for respiration from which high energy compounds are made. These compounds are required for nearly all other life reactions. Low oxygen availability means that the entire process of respiration slows. If oxygen levels decrease too much, plant respiration changes to a pathway similar to fermentation. While some live-sustaining energy is produced during fermentation, energy production is reduced by up to 95 percent. So, one effect of low oxygen is drastically reduced metabolism which can sharply reduce yield and, if long enough in duration, cause death to a portion or the entire plant. Fermentation produces several chemicals including lactic acid, acetaldehyde, and ethanol that are harmful to plants. The most problematic chemical is lactic acid, not from direct toxicity, but because of its effect on cell pH. Accumulation of lactic acid lowers pH. If pH drops too much, cell enzymes denature or precipitate out of solution. Most plant and tissue death is probably related to this acidosis. The extent of the damage of flooding on plants is related to at least three factors: the temperature of the water, the amount of water motion, and the duration of the flood. Temperature is related to the speed of respiration. The faster the respiration the quicker oxygen is depleted and the sooner fermentation begins. Warm water speeds respiration, oxygen use, and cell death. The faster water moves the greater the degree of turbulence. This water turbulence oxygenates the water, slightly. Increasing oxygen content of the water slightly decreases the impact of flooding on plants. Duration of the flood is important because many of the effects of low oxygen on plants are reversible if the duration is not too long. Long durations allow for increased oxygen depletion and the build up of harmful chemicals. Although local conditions influence the effects, 36 to 48 hours is the often the tolerable limit. Soil drainage properties can aggravate the flooding effect. Soils high in clay content or with other drainage restrictions prolong the flooding and remain water-logged after flood waters recede. Location of the plant’s growing point may affect response to flooding. Growing points are areas of intense cell growth and rapid respiration. In general, corn can tolerate flooding better than soybean. But, if flooding occurs in the spring, the corn growing point is near the soil surface (below or above) making it likely to be submersed longer. The soybean growing point is located at tip of stem and may remain above water. Effects from flooding may last long after flood waters recede. Soybean plants may turn yellow because oxygen for nodule function had been reduced. This nitrogen deficiency should be temporary. Corn may suffer from N loss through de-nitrification. Unless more N is supplied, permanent yield reduction is possible. Sometimes flood waters deposit silt and residue on leaves. Photosynthesis will be reduced until the soil and residue are washed from the leaves by subsequent rain. Finally roots are often damaged, and thus, more susceptible to disease organisms. Disease symptoms may not appear until several weeks or even months after the flood event. Bill Wiebold WieboldW@missouri.edu ********************************************************************** Black Cutworm Problems Continue in Missouri By Wayne Bailey Black cutworm larvae problems have occurred in numerous Missouri corn fields. Many fields have required insecticide applications during the past two weeks as larvae reached the 4th instar stage of development and began cutting corn seedlings. Additional problems with this pest are possible for the next two weeks in those fields where corn seedlings are smaller than about the 5th leaf stage of development. Scouting should continue in all fields, but especially in late planted fields where corn seedlings are just emerging or small in size. For more information on the black cutworm predictive model and the counties currently monitoring for black cutworm, please visit our Website at: http://ipm.missouri.edu/pestmonitoring/blackcutworm/index.htm. Wayne Bailey BaileyW@missouri.edu ********************************************************************** True Armyworm Larvae Problems Severe in Some Areas of the State By Wayne Bailey Elevated numbers of true armyworm moths present in Missouri during the past four weeks have resulted in economic infestations of larvae in fescue seed field and grass pastures, wheat fields, and in seedling field corn. Low levels of larvae can be found in most fields in central and southern regions of the state, although a majority of heavy infestations are present in south central and southwestern Missouri counties. Infestations have followed the typical pattern of first attacking fescue seed fields and grass pastures, followed by infestation in wheat and seedling corn. Many acres of these crops have been treated over the past 2½ weeks with much effort going to protect seedling corn at this time. Remember that small true armyworm larvae are nocturnal feeders (feed at night) and feed from the soil surface upward on the host plants. As larvae grow in size, they will feed during daylight hours and spend time higher in the plant canopy. Young larvae are pale green to light tan in color, but change to dull tan-yellow to brown as they grow. Larvae have smooth bodies with three dark lines running the length of the worm (one on top and one down each side). Some larvae will have a lighter tan-orange line present on each side of the body running from front to back of the larvae. The main identifying characteristic for true armyworm larvae is the presence of a dark triangle or spot located on the outside of each leg of the four pair of prolegs (legs found near the center of the caterpillar’s body). Larval head capsules may be yellow, tan or green in color and mottled with darker brown coloration. True armyworm moths have grayish-brown to tan forewings, each with a white spot in the center and grayish-white hind wings. Three or more populations of true armyworm occur in Missouri each year, although the first generation tends to attack field crops before moving to turf and other host in later generations. In addition to feeding on plant foliage, some populations of true armyworm larvae will also cut fescue seed and wheat heads from plants as the larvae approach maturity. Larvae grow to about 1½ inches in length and often move from field to field as each food source is exhausted. Thus their name of Armyworm which suggests they move or march in large numbers to new food sources once a food source has been exhausted. Treatment is warranted when an average of 4 or more non-parasitized, half-grown or larger worms per square foot are present. The economic threshold for head cutting in fescue seed fields and wheat is to treat when 2-3 percent or more of the heads are cut from fescue or wheat seed stems. The threshold for field corn is to treat when 25 percent or more of seedling corn plants exhibit foliar damage and larvae are present. Because corn seedlings are often attacked by later instars of this pest, damage from feeding larvae can be very severe. It is common for all foliage of corn seedling to be consumed by true armyworm larvae. This pest has been known to attack much larger corn where they often strip all leaf tissue from these larger plants. Insecticides Recommended for Control of True Armyworm in Wheat -------------------------------------------------------------------------------------- | Chemical | Trade name | Rate of Formulated | Placement/ | | name | | Material/Acre | Comments | |-------------------|-------------------|--------------------------|------------------| |beta-cyfluthrin | *Baythroid XL | 1.0 to 1.8 fl oz/acre | foliar broadcast | |zeta-cypermethrin | *Mustang Max | 1.76 to 4.0 fl oz/acre | foliar broadcast | |gamma-cyhalothrin | *Proaxis | 1.92 to 3.20 fl oz/acre | foliar broadcast | |spinosad | Success | 3 to 6 fl oz./acre | foliar broadcast | |spinosad | Tracer 4SC | 1.0 to 3.0 fl oz/acre | foliar broadcast | |lambda-cyhalothrin | *Warrior | 1.92 to 3.20 fl oz/acre | foliar broadcast | |lambda-cyhalothrin | *several products | see specific label | foliar broadcast | -------------------------------------------------------------------------------------- Insecticides Recommended for Control of True Armyworm in Tall Fescue ------------------------------------------------------------------------------------ | Chemical | Trade name | Rate of Formulated | Placement/ | | name | | Material/Acre | Comments | |------------------|------------------|-------------------------|------------------| |malathion | Malathion | see specific labels | foliar broadcast | | | several Products | | | |------------------|------------------|-------------------------|------------------| |zeta-cypermethrin | *Mustang Max | **2.8 to 4.0 fl oz/acre | foliar broadcast | |------------------|------------------|-------------------------|------------------| |carbaryl | Sevin XLR Plus | 1 to 1 1/2 quarts/acre | foliar broadcast | |------------------|------------------|-------------------------|------------------| |spinosad | Success | 3 to 6 fl oz./acre | foliar broadcast | |------------------|------------------|-------------------------|------------------| |spinosad | Tracer 4SC | 1.0 to 3.0 fl oz/acre | foliar broadcast | |----------------------------------------------------------------------------------| |**Note, FMC recommends a minimum rate of 3 oz/acre for true armyworm control | ------------------------------------------------------------------------------------ Insecticices Recommneded for Control of True Armyworm in Field Corn ---------------------------------------------------------------------------------------- | Chemical | Trade name | Rate of Formulated | Placement/ | | name | | Material/Acre | Comments | |--------------------|-------------------|--------------------------|------------------| |permethrin | *Ambush | 6.4 to 12.8 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |esfenvalerate | *Asana XL | 5.8 to 12.8 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |cyfluthrin | *Baythroid XL | 1.6 to 2.8 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |bifenthrin | *Capture 2EC | 2.1 to 6.4 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |bifenthrin | *Capture 2EC | 3.4 to 6.8 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |bifenthrin | *Fanfare 2EC | 2.1 to 6.4 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |methoxyfenozide | Intrepid | 4 to 8 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |methomyl | *Lannate LV | 0.75 to 1.5 pt/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |chlorpyrifos | *Lorsban 4E | 1 to 2 pts/acre | foliar broadcast | | |*numerous products | see specific labels | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |zeta-cypermethrin | *Mustang Max | 3.2 to 4 fl oz | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |micro encapsulated | *Penncap-M | 2 to 3 pts/acre | foliar broadcast | | methyl parathion | | | | |--------------------|-------------------|--------------------------|------------------| |permethrin | *Pounce | 3.2 EC 4 to 8 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |lambda-cyhalothrin | *Proaxis | 2.56 to 3.84 fl oz/acre | foliar broadcast | | |*numerous products | see specific labels | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |carbaryl | Sevin XLR Plus | 2 to 4 pts/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |spinosad | Success | 3 to 6 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |spinosad | Tracer 4SC | 2 to 3 fl oz/acre | foliar broadcast | |--------------------|-------------------|--------------------------|------------------| |lambda-cyhalothrin | *Warrior | 2.56 to 3.84 fl oz/acre | foliar broadcast | |--------------------------------------------------------------------------------------| |Read and follow all label direction, precautions, and restrictions. | |* Designated a restricted use product. | ---------------------------------------------------------------------------------------- Wayne Bailey 573-864-9905 (cell) BaileyW@missouri.edu ********************************************************************** Several Insects Present in Wheat Fields By Wayne Bailey A survey of wheat fields conducted the past two weeks found several different insects and other pest present in wheat fields. A few of the pest found included slugs, grass sawflies larvae, true armyworm larvae, brown stinkbugs, cereal leaf beetles and a few aphids. The slugs were tentatively identified as brown garden slugs which often occur in fields with high levels of plant residues. They can cause economic damage in field corn and soybean, but are generally not considered a spring pest of wheat in Missouri. Both grass sawfly larvae and true armyworm larvae were present in some fields. The grass sawfly can cause defoliation of wheat, but rarely reaches the high numbers of larvae necessary to do so. In contrast, the true armyworm larvae can cause considerable damage if populations reach or exceed economic threshold levels. True armyworm larvae have four pairs of prolegs (pairs of legs in the center of the body) with each leg displaying a dark brown to black triangular blotch on the outside of each leg. Additionally, the larvae have three distinct dark lines running the length of worm. Grass sawflies have greenish yellow bodies, an amber to yellow head capsule with two distinct black eyespots. The grass sawfly larvae have seven to eight pairs of abdominal prolegs which occur on most of the abdominal segments of these larvae. Brown stinkbugs were numerous in some fields although below the threshold of one stinkbug adult or nymph present per 10 wheat heads when in the milk stage of growth. In Missouri brown stinkbug are not considered an important pest of wheat. Low numbers of cereal leaf beetle larvae are present in some wheat fields, although well below the economic threshold of one or more larvae present per flag leaf. This pest is seen as small brown larvae which slowly moved up and down the flag leaf as it feeds and removes the green layer of tissue from the surface of wheat flag leaves. If you rub the larvae, the outer dark covering will be removed to reveal a small yellowish larva. This dark, moist covering is produced and used by larvae to protect them from parasitic and predaceous insect. Populations of several species of aphids were present in fields, but at relatively low numbers. The greenbug and bird cherry-oat aphids are the most important aphids in small grains with some fields treated during the past two weeks in southwest Missouri. Populations of English grain aphids have been found infesting wheat heads in these areas. Although lady bird beetles were actively feeding on these populations in most fields, some English grain aphid populations exceeded the economic threshold of 50 to 100 aphids per head and were controlled with insecticide applications. Wayne Bailey BaileyW@missouri.edu ********************************************************************** Miscellaneous Insect Problems Observed During Past Week By Wayne Bailey Other insect populations of minor concern at this time are reports of variegated cutworm problems in alfalfa, bean leaf beetle in first planted soybean, and relatively high numbers of European corn borer moths in light traps. Variegated cutworm is an occasional pest of alfalfa following removal of first cutting. High numbers of moths earlier this season have resulted in a limited number of fields where this pest has reached economic levels. The identifying characteristic for variegated cutworm larvae is a row of small yellow spots or diamonds running down the length of the back. Problems typically occur when larvae grow to a large size and feed on developing tillers as they emerge from the crown of the alfalfa plants following first harvest. Feeding by this pest can delay regrowth of alfalfa plants by two to three weeks. In addition, lack of the alfalfa canopy often results in excessive weed (non host plants for cutworms) growth. Variegated cutworm are present in most years, but are often killed by insecticide applications for alfalfa weevil or potato leafhopper. Bean leaf beetles have required control in some early planted fields where beetles have congregated as they move to soybean fields from overwintering sites in wooded field borders. Bean leaf beetles are good flyers and readily seek out early planted soybean fields. European corn borer moths are being captured in relative high numbers in blacklight traps. Numbers are not as high as 10 years ago and prior to Bt ECB corn varieties, but they are much higher than captures during the past three years. These elevated populations may not develop into economic infestations of this pest, but growers should scout for first generation eggs and larvae if they are not using a Bt ECB corn variety. Additional information on scouting and thresholds for ECB will be provided in the next newsletter. Wayne Bailey 573-864-9905 (cell) BaileyW@missouri.edu ********************************************************************** Preemergence Herbicides in Roundup Ready Soybean? By Kevin Bradley Even as recent as a year or two ago even the mention of a preemergence herbicide application in Roundup Ready soybeans at a grower meeting or field day would have brought a few laughs from the audience. This past season, however, I noticed a little more acceptance of this practice and from what I can tell, applying residual herbicides in soybean, even Roundup Ready soybeans, appears to be gaining a little ground in Missouri. Don't misunderstand me, the efficacy and economics of a properly timed two-pass glyphosate program in Roundup Ready soybeans is hard to beat. However, there are still some reasons you may want to consider the use of a residual herbicide in your soybean weed management program. First, residual herbicides may be a good option for you simply from an "insurance" or yield protection standpoint. Often, a properly timed early postemergence glyphosate application to weeds that are 4- to 6-inches tall somehow mysteriously turns into an application where the weeds have reached 10- or 12-inches tall and the soybeans are barely noticeable. Without fail, I see this in some Missouri fields each year. Last year it seemed to be particularly bad. The reasons are many; it may have been too wet and you couldn't get in the field to spray, there is just too much to do and too many acres to cover, etc., etc. Regardless of the reason, when this type of situation occurs some yield has already been lost. To see the effects of increasing weed sizes and weed competition on soybean yield loss for yourself, go to http://weedsoft.unl.edu/weedsoftApps.htm and use the WeedSOFT yield loss calculator. This is a tool developed by a number of university weed scientists that enables you to estimate the season-long yield loss, as well as the yield loss that has already occurred, for soybeans that are at a particular stage of growth and infested with specific weed species. It will also estimate the additional yield loss that may occur if you delay treatment. Another reason you might want to consider the use of a residual herbicide in Roundup Ready soybeans is due to the increasing number of glyphosate-resistant weeds that are being identified in Missouri and throughout the U.S. Almost exclusively, these weeds have been discovered in continuous Roundup Ready cropping systems where glyphosate has been used as the sole active ingredient for weed control. In Missouri, perhaps the most concerning development is the confirmation of glyphosate-resistant common waterhemp that occurred in northwest Missouri in 2006. Since this initial confirmation, we have conducted greenhouse research on waterhemp populations sent in last year from other locations around the state and have found glyphosate-resistant waterhemp in at least 5 other counties. One of the best ways to prevent these kinds of situations from developing is to rotate to herbicides other than glyphosate that act at an alternate site of action, such as with preemergence residual herbicides. In our research, some of the more effective residual herbicides used in soybean for common waterhemp include S-metolachlor (Dual II Magnum, Cinch, etc.) and premixes containing S-metolachlor (Boundary, Prefix CP), sulfentrazone (Spartan) or premixes containing sulfentrazone (Sonic, Authority First), flumioxazin (Valor) or flumioxazin premixes (Gangster, Valor XLT), and alachlor (Intrro). Kevin Bradley 882-4039 ********************************************************************** Weather Data for the Week Ending May 14, 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 |May 1 from |since from Station County Max.Min. High Low Mean avg. |May 14 avg |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 85 60 90 55 72 +10 | 4.89 +2.95 | 486 +257 St. Joseph Buchanan 82 61 86 56 72 +10 | 5.96 +3.85 | 466 +197 Brunswick Chariton * * * * * * | * * | * * Albany Gentry 83 57 88 50 71 +9 | 7.63 +5.48 | 427 +186 Auxvasse Audrain 82 61 87 56 71 +9 | 1.76 -0.64 | 483 +204 Columbia Boone 82 61 86 58 71 +8 | 2.48 +0.11 | 489 +172 Sanborn Field Boone 83 63 88 59 73 +10 | 2.21 -0.20 | 529 +197 Williamsburg Callaway 84 60 89 55 71 +9 | 1.32 -1.10 | 497 +222 Novelty Knox 82 59 87 54 70 +8 | 2.68 +0.34 | 404 +143 Linneus Linn 83 59 87 52 71 +9 | 2.97 +0.43 | 439 +191 Monroe City Monroe 83 59 87 54 71 +8 | 1.04 -1.31 | 435 +147 Versailles Morgan 84 61 87 59 72 +8 | 4.46 +2.06 | 531 +167 Green Ridge Pettis 82 60 86 58 71 +9 | 2.07 -0.36 | 482 +222 Lamar Barton 82 62 87 58 71 +7 | 2.62 -0.02 | 492 +123 Cook Station Crawford 85 56 87 51 70 +6 | 1.28 -1.26 | 493 +111 Alley Spring Shannon 86 56 89 52 70 +7 | 2.74 +0.15 | 473 +130 Round Spring Shannon 87 57 90 51 70 +7 | 2.70 +0.15 | 481 +137 Delta Cape 84 63 87 56 72 +6 | 2.86 +0.49 | 544 +96 Girardeau | | Cardwell Dunklin * * * * * * | * * | * * Clarkton Dunklin 87 63 90 55 75 +7 | 1.55 -0.30 | 585 +68 Glennonville Dunklin 85 65 87 57 74 +7 | 3.12 +1.35 | 591 +73 Charleston Mississippi 85 64 86 57 74 +8 | 1.99 -0.27 | 582 +146 Portageville- | | Delta Center Pemiscot 87 65 90 59 75 +8 | 1.00 -1.23 | 631 +114 Portageville- | | Lee Farm Pemiscot 87 65 91 58 75 +8 | 1.69 -0.58 | 633 +124 Steele Pemiscot 89 66 92 59 77 +9 | 0.33 -2.27 | 656 +138 * 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