Soybean aphid, Part III: Insecticides |
If soybean aphids (SBA) are a problem in 2004, what can you do? Scouting for aphids is the first step. Optimal aphid control and yield return depends not only on insecticide application, but also on the timing and method of application. Insecticide efficacy § Lorsban 4E, an organophosphate, exhibits a "fuming" action, especially under high temperatures. This greatly improves coverage under a tall canopy or in drilled beans. § Furadan, a carbamate, is systemic. Aphids are exposed to the insecticide not only through contact, but as they feed on plant sap. § Warrior has provided the most consistent control of all of the pyrethroid insecticides across many university efficacy trials. Efficacy versus yield Other insecticide issues § As far as human safety, organophosphates (Dimate, Lorsban, Penncap) and carbamates (Furadan) are generally more hazardous than pyrethroids (Asana, Baythroid, Mustang, Warrior). However, any insecticide can cause health problems if misused, and applicators can reduce exposure by following Personal Protective Equipment (PPE) guidelines on the pesticide label. § If spraying in August, check labels for pre-harvest intervals. PHIs for commonly used products range from 21 (Mustang) to 28 (Lorsban) to 45 (Warrior) days. However, if sprays are properly times (see following section), the chance of running into the PHI is less. § All of the insecticides mentioned in this article are restricted use with the exception of dimethoate, and require the applicator to be certified. § All of the conventional insecticides kill beneficial insects present in the field. Therefore, insecticide should be chosen based on a combination of factors - not only efficacy but also safety, price, availability and pre-harvest interval. Once a choice is made, spray timing and coverage are the most critical factors in SBA control and yield response. Making insecticides work harder
for you Spray methods. When spraying for aphids, keep three goals in mind - coverage, coverage, coverage! Applications optimized for coverage use increased pressure, more gallons per acre and smaller droplets. There are also specific nozzle types designed for insecticide applications that improve spray coverage. Poor coverage may explain some of the problems with certain applications in 2003. Remember, unless a product is systemic, conventional insecticides kill aphids by contact. Remember, too, that soybean aphids are found on the undersides of leaves, and they are all females producing quickly without mating. If coverage is poor, aphids left behind after the application can rapidly reproduce and recolonize the plant. Tank mixing. There is a lot of interest in tank mixing glyphosate with insecticide to save trips across the field. While there are no crop injury or compatibility problems I foresee from such a practice, the optimal timing and method of application probably differs between the herbicide and the insecticide. § The optimal timing for aphid control usually occurs between mid-July and early August, after the optimal timing for glyphosate in soybean at a 4-inch weed height. § Insecticide applications should maximize coverage (see above), while glyphosate applications should maximize drift control (lower pressure, larger droplet size, drift control agents, and different nozzles). Still want to learn more about soybean aphid scouting, thresholds and control? Visit the North Central Soybean Research Program's web site to view a copy of the latest information from researchers across the Midwest: http://www.planthealth.info/aphidinsert/aphidinsert.htm |
Prepare for a cicada invasion |
Some parts of Michigan and surrounding states will have a major hatch of 17-year cicadas in May and June. This year's brood (Brood X) is the largest of the 17-year cicada broods, and encompasses parts of 15 states (including southern counties of Michigan). Entomologists like myself get pretty excited by such occurrences - it's kind of like the Olympics for us, except it's every 17 years. However, given past experience with cicada hatches, the Region 5 EPA Office in Chicago suggests "preparing for the emergency" in case homeowners, businesses and schools "panic." So to prepare you against the panic, here are some web sites for additional information. The University of Michigan site is very good and includes a map for Brood X. University of Michigan: http://www.ummz.lsa.umich.edu/magicicada/Periodical/Index.html Cicada Mania: http://www.dancentury.com/cicada/cicadalinks.html News articles: http://www.freep.com/news/statewire/sw94367_20040311.htm http://www.centredaily.com/mld/centredaily/news/local/8163648.htm |
Herbicide selection in winter wheat past Feeke's Stage 6 |
Once wheat has passed Feeke's Stage 6, the risk of herbicide injury from 2,4-D, MCPA, Banvel/Clarity, or Curtail increases and application of these herbicides is not recommended. In this situation, the remaining herbicide options are Harmony Extra, Harmony GT, Express, Buctril, and Stinger. Harmony Extra, Harmony GT and Express can be applied to wheat until the flag leaf is visible (before Feeke's Stage 8). Buctril and Stinger can be applied to wheat up to boot stage (before Feeke's Stage 9). Each spring there are questions about the risks associated with 2,4-D or MCPA application to wheat past Feeke's Stage 6. Wheat tolerance of 2,4-D is highest between Feeke's stages 3 and 6 and is lowest in Feeke's Stages 9 and 10. Between stages 6 and 9, sensitivity to 2,4-D gradually increases as wheat growth stage advances. Thus, the risk of injury increases as wheat growth stage advances between stages 6 and 9. Severe injury is highly probable when 2,4-D is applied at Feeke's stages 9 and 10. MSU recommends that application of 2,4-D to wheat be made after wheat has reached Feeke's stage 3 but prior to Feeke's stage 6. If growers choose to apply 2,4-D at later stages, they need to understand the associated risk. This risk can be minimized by applying the amine form of 2,4-D or reducing the rate of a 2,4-D ester. A much better alternative on wheat past Feeke's stage 6 is to use another herbicide with a wider application window that is effective on the weeds present in the field. |
Delayed herbicide application in corn |
Dry
weather in April has allowed farmers to plant corn earlier than
usual with a large amount of corn planted before May 1. High winds
across the state during the last week of April created challenges
for herbicide application following planting. Therefore, it is likely
there will be many situations where corn has emerged before preemergence
herbicides have been applied. In
fields with emerged corn and no herbicide applied, growers have
two primary options: 1) Use an herbicide program typically
applied before emergence or 2) Switch to a total postemergence strategy.
There are several possible herbicide programs with each strategy. The
accompanying table lists herbicides typically applied preemergence.
Many of these herbicides are also labeled for application after
corn emergence. Four of the preemergence herbicides listed, Axiom,
Axiom AT, Lasso and Princep, should only be applied before corn
emergence. To avoid confusion, tank mix combinations are not included
in the table. Details on the specific restrictions for tank mixtures
can be found on the herbicide labels. Although some herbicide labels
allow application to emerged corn using 28 percent liquid nitrogen
fertilizer as the herbicide carrier, we advise that all herbicide
treatments to emerged corn be applied with water as the carrier.
Applying herbicides to emerged corn with 28 percent liquid nitrogen
as the carrier poses a risk of severe crop injury. This risk is
increased under cool, cloudy conditions prior to application, a
common occurrence in Michigan. Preemergence
herbicides should be applied as soon after planting as possible.
Delayed application increases the risk of poor herbicide performance,
especially for grass control. When herbicide application is delayed
until after crop emergence, rotary hoeing is recommended. The rotary
hoeing may be done before or after the herbicide application but
must be done when the weeds are very small. If the delayed application
includes Banvel/Clarity, Distinct, Marksman (or other herbicides
containing dicamba), or Prowl/Prowl H2O/Pendimax, corn
safety will be greater if the rotary hoeing is done before herbicide
application. Herbicide
options for total postemergence weed control are dependent on the
seed planted in the field. Many postemergence herbicides can be
used on any corn hybrid, while others such as Liberty, Lightning,
and glyphosate require herbicide resistant hybrids. For details
on postemergence herbicides for corn, see Extension Bulletin E-434
at:
|
Considerations for weed control in non-GMO soybean |
Even with the substantial number of Roundup Ready soybean acres in the state this year there are several producers that will be growing non-GMO soybeans. Since some of these producers haven't planted non-Roundup Ready soybeans for several years, there are few pointers that should be remembered for effective weed control in conventional (non-GMO) soybeans. It is important to start clean! As with all weed control strategies, starting with a weed-free seedbed is essential. This can either be done with tillage or an effective preplant burndown herbicide treatment. In no-till soybeans using an effective burndown treatment is particularly important since typical postemergence soybean herbicides will not adequately control typical no-till weeds. For adequate control of several of these no-till weeds, 2,4-D, glyphosate, or a combination of the two should be used in the burndown treatment. When including 2,4-D ester in the burndown treatment, this application should be made at least one week prior to soybean planting. Producers of non-GMO soybeans should also consider using a preplant or preemergence herbicide with residual activity as a foundation program for hard to control weeds such as common lambsquarters, common ragweed, giant ragweed and eastern black nightshade. Relying on a total POST program for control of these weeds can be difficult. Control of these weeds has also been difficult in Roundup Ready soybeans programs so it is important to control these species with a two-pass herbicide program. By waiting to control these weed with a total POST program many times these weeds can become two large, may be affected by the environment (hardened off by hot-day weather) or may just not be effectively controlled. Getting a start on controlling these weeds early in the season will insure greater overall success for your weed control program. Also using a two-pass program with a preplant or preemergence herbicide application limits the use of "rescue" herbicide treatments late in the season that can further stress soybean growth on previously injured soybeans. Make timely POST applications. Many producers have been accustomed to controlling large weeds by increasing the rate of glyphosate in Roundup Ready soybean. Unlike glyphosate many of the POST herbicides used in non-GMO herbicides are not very effective on large weeds. It wasn't too long ago when the application window for POST applications in soybean was between two- and four-inch tall weeds. So, remember, when using a non-glyphosate based program, herbicides need to be applied before weeds exceed four inches tall for adequate control. Applying a preplant or preemergence herbicide will also help extend this window by providing some early season control of these weeds. Are herbicide resistant weeds a problem on your farm? There are several populations of ALS-resistant and triazine-resistant weeds around Michigan. If herbicide resistance has been a problem on your farm in the past, take this into account when planning your weed control strategy in conventional soybeans. For example, if you have ALS-resistant common lambsquarters relying on a POST program of Harmony GT or Raptor would not control this weed. However, there are several soil-applied herbicides that can effectively control common lambsquarters season-long. To determine the effectiveness of herbicides on common lambsquarters and several other weeds consult the MSU Weed Control Guide for Field Crops (E-434) http://web1.msue.msu.edu/iac/434/. For weed control in non-GMO soybean, I strongly recommend a two-pass program that consists of a preplant or preemergence residual herbicide followed by a postemergence program. Using a two-pass program with a residual herbicide may add to the overall cost of your weed management program, but this program will result in overall more consistent control of several weed species. |
Stewart's wilt risk in sweet corn and seed corn in Michigan -temperature profiles for winter 2003-04 |
Stewart's wilt is a disease of corn caused by the bacterium Pantoea stewartii. It is transmitted to corn seedlings during feeding by the corn flea beetle, Chaetocnema pulicaria. Bacteria invade the vascular tissue of the plant; disrupt nutrient and water flow and cause leaf lesions, leaf wilting, barren stalks or plant death. Disease severity depends on the variety and on plant age at the time of infection. Early plantings of highly susceptible seed corn inbreds and sweet corn hybrids are likely to have the most severe symptoms. The bacterium is carried in the digestive tract of the corn flea beetle. Stewart's wilt severity is thought to be dependent on the overwintering survival of infected corn flea beetles, which in turn is dependent on winter temperatures. The overwintering habitat of the vector is not well understood, but is thought to be in the upper soil profile and in the root zone of grasses. The temperature profiles of the upper soil, as well as the duration of temperature below a critical threshold, may result in a more accurate prediction of corn flea beetle survival. High-risk indices were recorded in winters of 1997-98, and low risk indices in 1998-99 and moderate in 2000-03. The temperature of soil (surface, 6-, 12- and 18-inch depth) was monitored at various locations within fields in different Michigan counties in 2003-04 (Three Rivers, St. Joseph Co.; Samaria, Monroe Co.; Manchester, Washetenaw Co.; Entrican, Montcalm Co.). The soil temperature profiles for December 1, 2003 through February 29, 2004 are shown in Figure 1. The soil temperature at the surface indicated that at Samaria, Entrican and Manchester the likelihood of survival of corn flea beetle was unlikely. However, the temperatures at each of the different soil depths indicated that survival was possible. The range of temperature and percentage of time at different temperatures also indicated that in the soil the temperature was probably tolerable for overwinter survival at each location. In additional studies conducted in Monroe and Macomb counties in 2003, yellow sticky traps monitored overwintering survival of corn flea beetles in different sites. Traps placed in these sites during summer 2003 were collected and replaced weekly. Corn flea beetles captured on these traps were counted. In 2003, very few corn flea beetles were recovered indicating a low carryover from 2002 as predicted from the temperature survey of 2002-03. Many growers have determined that they will use an insecticidal seed treatment as an insurance against Stewart's wilt in 2004 for two reasons; the temperature predictor is unreliable and seed is usually treated during the winter months prior to the end of February (the end of the prediction period). Currently, the authors are predicting that the risk potential for corn flea beetle survival is moderate for 2004. |
| Regional reports |
Weather news |
Widespread rains fell over much of the state last weekend, complicating spring fieldwork operations but easing abnormally dry conditions across southern sections of the state. In the wake of the precipitation, relatively clear, calm nights, dry air, and strong radiational cooling resulted in widespread frost and freezing temperatures across much of the state on the mornings of May 3 and 4. The first week in May marks the average date(s) of last freezing temperatures of the spring season across many sections of the Lower Peninsula. In western Michigan along the lakeshore, it is earlier; in northern interior areas of the state, it is later. Looking ahead, a very active weather pattern is expected across the region into early next week. On Thursday (May 6), a cool front will approach Michigan from the west, the next of a series of several frontal passages likely to affect the state during the next several days. Look for the chance of showers and a few thundershowers statewide Thursday afternoon into Thursday evening. Some thunderstorms in southern sections of the state could be severe with hail and damaging winds. Friday will be mostly dry and cool with increasing clouds late, as the same front that passes through on Thursday will return from the south as a warm front. As a result, expect another round of showers and thunderstorms to begin again overnight Friday, mainly in southern sections of Lower Michigan. For the remainder of the weekend this frontal boundary is expected to waver just south of Michigan, serving as a focusing mechanism for periods of showers and thunderstorms. Best chances for rainfall, some of it heavy, will be in southern sections of the state. Temperatures will depend greatly on the exact position of the frontal boundary with daytime readings reaching the 70's and low 80's to the south of the front with 40's, 50's and 60's to the north. Low temperatures will range from 30's and 40's north to the 40's and 50's in the south. Medium-range forecast guidance is consistent with the emerging weather pattern mentioned earlier with an upper air trough over the western US (This should bring some relief to those battling wildfires in CA.) and a broad upper air ridge across the central and eastern US. An active storm track is expected on the northern edge of the ridge from the central Great Plains northeastward into the Great Lakes region. For Michigan, both the 6-10 day outlook (covering May 10-14) and 8-14 day outlooks (covering May 13-19) call for near normal temperatures. Precipitation is expected to be above normal state- and region-wide. |