Vol. 20, No. 9, June 9, 2005

When to take action for soybean rust

Alfalfa fertilization after first cutting

Regional reports

Patrick Hart
Plant Pathology

Soybean rust still has only been found on volunteer soybeans in a single county in Georgia and on kudzu in four counties in Florida. Scouting for soybean rust continues in states south of Michigan, and if found would trigger intense scouting of soybean sentinel plots planted throughout Michigan.

There has been some suggestion by members of the chemical industry sales community that spraying fungicides for soybean rust should begin in Michigan when the disease is found in soybeans as far south as Louisiana. This is not true and would be a waste of money and time. Due to the intense monitoring for soybean rust throughout the United States, Michigan soybean growers will have sufficient warning to apply fungicides in a timely manner and not before the disease has appeared in northern Ohio and Indiana.

The Extension Plant Science, Econ and Ag Engineering specialists at South Dakota State University recently collaborated to produce an eight-page publication on Asian soybean rust. It also includes a section on soybean aphid.

To download a copy of the publication in pdf, visit:
http://agbiopubs.sdstate.edu/pub_description.cfm?Item=ABS205

Patrick Hart
Plant Pathology

The Pennsylvania State Wheat Scab prediction model for wheat not planted into corn residue is predicting low to moderate probability of scab in areas where flowering is just now beginning. Wheat planted into corn residue has a high probability of scab in many areas of the state. Wheat is in the earliest stages of flowering in many areas. Wet weather is predicted over the next five to six days, and could influence the development of scab in areas that are just beginning to flower. It is important to consult the model when flowering first occurs, and for the first few days into flowering, to obtain an accurate estimate of the probability of wheat scab occurring in your area. High-risk predictions before flowering may not be accurate.

The older Penn State Model is also predicting a moderate-low to moderate scab, regardless of corn residue. However, in the Pigeon, Michigan area the probability as of June 9 was 67 percent, and 37 percent in Saginaw and 20 percent in Sandusky. Clarksville was at 54 percent.

The Folicur label states that Folicur can be applied through the beginning of flowering, and that wheat which has been treated with Folicur cannot be harvested within 30 days. Therefore, Folicur should be applied between when flowering is first observed in a field and seven days later. This should keep applications within the label restrictions. Also, Folicur is more effective when applied early versus being applied later into flowering.

Christy Sprague
Crop & Soil Sciences

Postemergence herbicide applications for weed control in soybean are quickly approaching. The hot weather has both weeds and soybean actively growing. With these approaching applications there are several things that should be considered to maximize weed control with glyphosate in Roundup Ready soybean. Following these guidelines can help reduce the risk of glyphosate failures, as well as reduce the chances of lower soybean yields due to weed competition.

Glyphosate formulations
There are over 30 different glyphosate products that growers in Michigan can choose from for weed control in Roundup Ready soybean. With all of these choices, it is important to keep in mind that not all glyphosate formulations are created equal. Knowing your glyphosate product is essential to achieving optimum weed control. There are two main differences in the many available glyphosate products. Glyphosate products can differ in the concentration of glyphosate acid in the formulation (glyphosate acid is what kills the weed). This concentration is expressed as pounds acid equivalent per gallon (lb a.e./gal). Different glyphosate concentrations will change the amount of product used for the various formulations. Table 1 is a compiled list of several glyphosate products and the product use rates for equivalent amounts of glyphosate acid per acre.

Another difference in glyphosate products is whether a surfactant needs to be added to the spray solution or if the formulated glyphosate product has a built-in adjuvant package. Products like Roundup WeatherMax, Touchdown Total and several others have built-in adjuvant systems. Even though all of these products have a built-in adjuvant system there can be, and many times are, differences in the type of surfactant formulated in the product. These differences may equate to differences in weed control under extreme conditions. However, under most conditions there are no differences between these products, especially when they are used at the correct rates at the appropriate application timings. For products where the addition of a surfactant is recommended, add a high quality non-ionic surfactant at 0.25 to 1.0% v/v. Table 1 also includes information on whether the addition of a surfactant is recommended for a particular glyphosate product.

Addition of ammonium sulfate (AMS)
Ammonium sulfate (AMS) should always be added to all glyphosate products. We recommend adding dry spray grade AMS at 17 lbs/100 gal or the equivalent of 17 lbs/100 gal of liquid AMS products. The addition of AMS minimizes the negative effect of hard water on glyphosate activity and is important for velvetleaf control, regardless of water quality.

Application rate
Applying the appropriate glyphosate rate in Roundup Ready soybean is important for consistent weed control. Proper glyphosate rates should be based on weed type, weed size and spray volume. In most cases the appropriate rate to use for weed control in Roundup Ready soybean is 0.75 lbs a.e./A of glyphosate. This rate will effectively control several annual weed species between two and eight inches tall. However, if weeds become larger, the glyphosate rate should be increased to adequately control these weed species. In addition, by matching the appropriate glyphosate rate to the correct weed size you reduce your chances of weed control failures under extreme conditions.

Application timing
Glyphosate application timing is everything! It is important to make timely glyphosate applications to minimize the chances of soybean yield loss due to early-season weed competition and to maximize weed control. Through MSU research the optimum time for glyphosate applications is when weeds are four inches tall in narrow-row (7.5 and 15 inches) soybean and six inches tall in wide-row (30 inches) soybean. Controlling weeds at these times reduces the chances for soybean yield loss, as well as reduces the risk of weed control failures of larger weed that may be under stressful conditions (drought, stem-boring insects, coverage issue, etc.).

Application technologies
Drift reducing nozzles or drift reducing agents are frequently used when applying glyphosate to reduce or prevent off-site particle drift. When using these technologies it is important to know their limitations. Using these technologies without the proper spray pressure and spray volumes can lead to reduced weed control with glyphosate. To maintain effectiveness with these technologies make sure to follow manufacturer’s recommendations on pressure and volume, apply the appropriate glyphosate rate for the target species, and always check for a uniform spray pattern. Combinations of some of these technologies can reduce spray coverage that may result in reduced weed control. Following these guidelines, particularly checking the spray pattern, can help determine if the weeds are receiving an adequate dose of the herbicide for weed control.

Tank-mixtures with other pesticides and fertilizers
There have been several questions on whether insecticides or fungicides can be tank-mixed with glyphosate for control of insects and diseases. While there does not appear to be any antagonism between these products due to physical incompatibility. There are two important things to consider before tank-mixing insecticides or fungicides with glyphosate, application timings and application methods. Generally, glyphosate applications for weed control should be made relatively early in a soybean crop (four- to six-inch weeds, depending on row-width). Many times when these applications are made insects, such as soybean aphids, or diseases will not have reached threshold levels in soybeans to make these applications useful or economical.

Additionally, if glyphosate applications are postponed until insects or diseases are at threshold levels chances are you have already reduced your soybean yield due to weed competition. Application methods also differ between glyphosate and insecticides or fungicides. Generally, glyphosate applications are made at lower pressures and spray volumes to reduce herbicide drift. However, for optimal control of insects or diseases, insecticides and fungicides are usually applied at higher volumes and pressures to increase coverage of the target species. With these considerations in mind, there probably will be very few times when it would be appropriate to tank-mix glyphosate with an insecticide or fungicide.

Glyphosate activity can be compromised when it is tank-mixed with foliar fertilizers. Glyphosate tank-mixtures with foliar manganese (Mn) fertilizers have resulted in reduced control of several weed species. There are several ways to reduce the risk of this antagonism. The best method is to make separate applications of the manganese fertilizer and glyphosate, making the manganese application first. However, separating these applications may not be an option for some growers. Another way to reduce this antagonism is to make sure to use a fully chelated manganese (Mn-EDTA) fertilizer in the tank-mixture. This form of manganese fertilizer has been reported to be the least likely to reduce glyphosate activity. Again it is important to use the appropriate glyphosate rate for the target species and always add AMS.

Following these guidelines will help maximize glyphosate performance and reduce the risk of soybean yield loss due to weeds in the 2005 season.

Darryl Warncke
Crop & Soil Sciences

Alfalfa utilizes large amounts of potassium, 45 to 50 pounds K₂O per ton of hay. Timing of potassium application is important because alfalfa will accumulate more potassium than required if it is readily available to the roots. Therefore, it is best to split-apply potassium. After first cutting is a good time to replace potassium removed in the harvest hay and provide adequate potassium for the second and third cuttings. Broadcasting 175 to 250 pounds of 0-0-60 fertilizer per acre will replace the potassium removed in 2 to 3 tons of alfalfa, respectively.

Boron deficiency is most likely to occur in second and third cutting alfalfa, especially on sandy soils. This is because soil moisture conditions are more likely to be limited during this growing period. Boron moves toward the root in the water the plant takes up from the soil. When there is adequate soil moisture, boron supply to the roots is good. But, when soil moisture conditions are limited, the supply of boron to the roots is reduced. Increasing the boron concentration in the soil water improves the supply of boron to the roots. To prevent or minimize the likelihood of boron deficiency, apply two pounds of boron per acre in the broadcast fertilizer. Another option is to include 0.3 lb boron per acre in foliar pesticide sprays.

Regional reports

1 – Southeast

Weather
We have had virtually continuous forecasts for rain since the Memorial Day weekend, including a storm this past Sunday (June 5) with damaging wind but no rain. I have three words for the weather forecasters and their predictions; “Eat our dust!” We are seriously dry with all crops affected. Even some hay fields have been cut to entice the precipitation.

Commodity reports
Alfalfa cutting is in full swing with the dry weather being a real bonus to get the first cutting off. Despite the dry conditions, early second growth is doing well. Potato leafhopper populations will quickly explode with the warm temperatures.

Cornfields are not generally uniform as sandy areas are stunted and plants are rolling leaves. Some plants will die shortly without rain, partly because these plants simply don’t have a well-developed root system yet. Sidedressing and post herbicide sprays are quickly winding down. We have had spot and localized shortages of nitrogen. Advanced fields are at the V6 stage, but most fields are in serious need of moisture. The dry conditions will force roots to go down after moisture, which will help stabilize plants versus having abundant early season rain and a shallower root system.

Soybeans are not growing quickly due to dry soil conditions with advanced fields at the V3 stage. Soybean aphids are present with one farmer tank mixing an insecticide with his post herbicide spray and spraying for weeds and aphids. There are a very few Asian lady beetles out as well. This will be a long summer for soybean farmers with relatively low prices, aphids, soybean cyst nematodes, spider mites and the fear of rust. Post spraying for weeds is in full swing.

Wheat is in various colors of green with some fields turning yellow very quickly this week. The lack of rain will hurt yields, though the dry conditions will ease fears of diseases. Some farmers have been spraying for aphids this past week.

Tips for avoiding drift
The drift of field spraying is always a challenge with winds and non-farm neighbors. Many farmers have their booms too high causing more drift. The 110-degree nozzles are engineered for about 17 to 19 inches above the target, which provides 100 percent overlap coverage.

Bruce MacKellar

Weather
Severe thunderstorms on Sunday, June 5 produced wind damage to barns, trees and to some center pivot irrigation systems in the Sturgis, Burr Oak and Colon area. Thunderstorms that arrived overnight on June 8 dumped as much as four inches of precipitation from extreme northern St. Joseph up through Kalamazoo County. High temperatures are causing concern for the plants that were submerged. Previously dry conditions allowed most of this excessive precipitation to infiltrate quickly.

Commodity reports
The commercial corn crop is really responding to the warmer temperatures. The most advanced early-planted commercial corn is V5 to V6 (12-15 inches in height). This stage of growth is where the plant begins to determine the yield potential by establishing the number of rows of kernels that will be on the ear. Insect and disease incidence remains light. We have the first reported catch of European corn borer (ECB) moths in the area around June 2. High temperatures forecasted moving the development of this pest along quickly. ECB moth catches have reportedly remained low at this point. At the Constantine weather station, we have received 186 GDD50 since June 1. From this information if the warm weather continues, we may expect the following for European corn borer larvae in the Kalamazoo, St. Joseph County area: first egg hatch should occur on or about June 10, peak egg hatch from about June 12-17, second instar larvae to appear around June 18-20, and fourth instar (when the larvae bore into the stalk) about 10 days later.

Seed corn continues to look excellent in most areas. The crop is progressing well. Sidedress operations are beginning to get underway in early planted seed fields.

Corn in areas affected by flooding from the heavy rainfall on June 8. Areas affected by the heavy rainfall may begin to show problems from the storm. In one respect, if the heavy rainfall had to happen, it occurred at a good time. The soil was very dry prior to the storm. Even a couple hours after the conclusion of the storm, the majority of the water in the ponded areas has infiltrated into the soil profile. I think that the key issue affecting the overall damage that will be caused by the storm is subsequent rainfall events. If we get more significant precipitation in these areas in the next couple of days, the soils most likely will not be able to drain quickly. Plant death can occur in flooded conditions in less than 24 hours if the temperatures are above 77°F.

We can expect to see some longer-term affects from the saturated soils even if the flooded plants do not die. The growing point for V3 - V5 corn is near the soil surface. It needs oxygen to continue respiration. Saturated soils will set the plants back two to three days. To determine if flooded plants are likely to die, split the plants and look at the tissue near the growing point of the plant. It normally should be whitish in color. If it begins to turn dark or watery, it is not a good sign.

The other major issue in both seed and commercial corn in these areas may be nitrogen loss. Probably the most accurate way to determine nitrogen losses is by taking a pre-sidress nitrate sample. Nitrogen fertilizer applications made to fields at this point could have been lost through leaching and through denitrification. Warmer soil temperatures increase the potential for denitrification losses of applied nitrogen.

Early planted soybeans are finally growing well. Fields vary between early V2 and V1. There have been some signs of bean leaf beetle feeding in fields. So far, I have not seen any soybean aphis in fields in southwest Michigan. We tend to have less common buckthorn, the soybean aphid overwintering host, in this area, so we have traditionally found this pest later in our area than in mid-Michigan. We will continue to monitor for this pest.

Snap beans are growing rapidly due to the high temperatures. There has been some bean leaf beetle feeding on these plants as well, but well below the level that should cause concern.

The early-planted potatoes are flowering. Most fields continue to look very good. We have seen some incidence of leaf necrosis in some fields.

Much of the alfalfa has been harvested. Watch re-growth carefully for potato leafhoppers. Their populations are low right now, but this push of warm air from the southwest is often the event that deposits the first substantial populations of this pest.

Wheat is in early grain fill in many areas of southwest Michigan. We expect the incidence of fusarium to be light because of the dry conditions during and prior to flowering.

Fred Springborn

Weather
Scattered showers yielded almost nothing to a 0.1 of rain for some and an inch or more of rain for others in the region over the past week. Many parts of the region are in need of rain. Summer weather has prevailed as high temperatures have reached up into the upper 80s F. Low air temperatures have been in the 60s F. Low soil temperatures are in the 60s F.

Commodity reports
Oats are progressing rapidly. Many fields have flag leaves appearing. Wheat is flowering or near flowering in the Montcalm area.

Corn growth has improved and is rapid with the warmer temperatures. Much of the crop is in the V3 to V5 growth stage. European corn borer moth flight has begun. Weed control is a concern in many fields where not enough rain was received to activate preemergence herbicides.

Dry bean planting is progressing rapidly. Seventy percent of the crop is planted with more progress expected this week. Emergence of dry bean has been very good thus far.

Soybeans are growing rapidly and are in the V1 to V3 growth stages.

Alfalfa harvest progressed quickly and is now on hold on many farms due to the weather forecast for scattered rain showers. Sixty to 70 percent of the crop is in a silo. Alfalfa weeveil is over threshold in many fields that have not yet been cut. GDD41 totals have passed 750 in Ionia, Entrican, Big Rapids and Fremont.

Paul Gross

Weather
The region received widely scattered showers over the past week. Amounts varied from a few tenths to over an inch. For the most part, soil moisture is on the short side but not severe. Many farmers are saying the dry conditions are forcing crops to develop deep root systems that will be beneficial as the growing season progresses. The heat over the past week has allowed near maximum growing degree day accumulations.

Commodity reports
The corn crop ranges from two to ten inches tall. The warm weather has been near ideal for rapid growth. There are many fields that will need herbicide applications very soon as the weeds are beginning to compete with the crop for water and nutrients. Stands are good, and there are no problems reported at this time. The number of growers nitrate testing is increasing due to the higher nitrogen prices.

Soybeans have progressed nicely over the past week with the warm weather. Some of the light showers this past week softened the crust and many beans have emerged that many thought would not make it. In some cases there has been replanting and with the emergence of the first plantings populations will be high. There are no reported problems at this time.

The wheat crop ranges from heading to flowering. There is powdery mildew in many fields but low in the plant. We are in the window for folicur applications for head scab but conditions have not been favorable the development of this disease. Continue to monitor the weather and scout fields for foliar diseases.

Alfalfa harvest is about 65 percent complete. Some farmers are done – others are just getting underway depending on yield and quality needs. There are no reports of leafhoppers or alfalfa weevil at this time. Scout fields after they have been cut for these pests.

Dry bean planting is about 75 percent complete. Some of the early-planted fields are beginning to emerge. Scout fields for potato leafhoppers.

Oat and barley are doing very well at this time. No problems reported.

Sugar beets are growing rapidly. There are some weed issues in some fields. First cultivations are being made at this time.

Mark Seamon

Weather
Temperatures in the 80s have really helped plant growth -- both crops and weeds. Rainfall has been variable due to thunderstorms that have dumped inches in some areas and missed other areas.

Commodity reports
First cutting of alfalfa has been stalled by rainfall but is well underway. Some growers have finished harvest but others need a few more dry days.

Sugar beets have seen some great growth in the past week. A few great fields continue to grow well while others have plants that are 12 inches wide next to plants that are 4 inches wide. Plant health is good.

The wheat crop has progressed to the Feekes 10-10.5 with most fields flowering for a couple of days. Powdery mildew is easy to find on lower leaves but not much moving up the plant. Fusarium head blight is being discussed

The corn crop is looking good in most areas. Recent warm temperatures are helping with growth and development. Some fields are showing purpling of leaves, especially in fields that were sugar beets in 2004.

Soybean growth is looking good with many soybeans in the unifoliate to first trifoliate stage. Some fields are starting look pretty weedy. Rain has kept some growers from spraying when they intended

Planting is near 50 percent complete in dry beans. Most fields that have been planted have received significant rainfall before emergence. The effect of this is yet to be seen but past experience has shown significant yield loss from this situation.

Dave Glenn

Weather
Spotty rains and thunderstorms have helped, but have varied with 0.10 to 1.6 inches this past week. Warmer temperatures have really helped corn and soybeans pop out of the ground and move along quickly.

Commodity reports
All corn is now up and between just germinated and 3 leave stage. A lot of yellow corn is around yet, but the rain and warmer temperatures is changing that.

Wheat is heading or in the boot in some cases. The dry weather has caused wheat to be very short this year. Some powdery mildew is evident in fields but not on the upper leaves yet.

Soybeans are all in and germinated. Most fields have just the first trifoliate emerging. Stands seem to be excellent to vary. The rain is now germinating the rest of the seed in no-till fields so we could have varied growth patterns.

Dry beans are going in as of last week. Only about 30 percent are in to date.

Alfalfa is being cut with some damage to leaves from insects. The biggest problem is the lack of moisture and short growth. Many producers are waiting for rain and more tonnage, and the quality is getting away from them. Grasser fields have been headed out for a while now.

Jeff Andresen
Agricultural Meteorology
Geography

Welcome to summer
Last weekend, the jet stream pattern across North America flip-flopped from the recent western ridging/eastern troughing pattern to western troughing/eastern ridging. This change allowed warm and humid air from the Gulf of Mexico back into the Great Lakes region after an extended absence, culminating in a round of turbulent weather across the state Sunday (June 5), when severe thunderstorms spawned several tornadoes, high winds and widespread power outages. A stationary frontal boundary marking the edge of warm, tropical air to the south and cooler, drier air to the north has stretched across the Lower Peninsula since Monday and will continue to very slowly wander north- and southward across the state during the next several days. This will set the stage for an almost daily chance for showers and thunderstorms into early next week. Overall, while rainfall probabilities will likely be limited to 30 or 40 percent probability on any given day, the extended number of days with possible rainfall should result in some precipitation in most areas of the state by the beginning of next week.

The general lack of widespread rainfall during the past several weeks is a growing concern, especially when combined with the recent hot temperatures (daily reference evapotranspiration rates this week have been near 0.25 inches/day). Seasonal rainfall deficits (since April 1) now generally range from about two to three inches in the Upper and northern Lower Peninsulas to as much as five to six inches in southwestern and south central sections of Lower Michigan. Note that normal rainfall for the same period in these areas is on the order of 7.0-7.5 inches. Temperatures will vary from north to south across the state during the next several days with daytime highs ranging from the upper 60s in northern lakeshore areas to the upper 80s or low 90s in some southern locations. Low temperatures will range from the 50s far north to the 60s in the south.

In the medium range time frame, forecast guidance is having trouble identifying a dominant jet stream pattern, resulting in a discontinuous and variable outlook of somewhat lower than normal confidence. The 6-10 day outlook (for June 14-18) calls for above-normal temperatures and for precipitation to range from below normal over eastern sections of the state to above normal in the western Upper Peninsula. During the 8-14 day time frame (covering June 16-22), the outlook calls for below normal temperatures and for near normal precipitation totals statewide.

New NOAA long lead outlooks
In the equatorial Pacific region, sea surface temperatures edged back to near normal levels following several months of warmer than normal readings and weak El Nino conditions. The neutral/near normal temperatures are expected to continue through at least the upcoming fall season, possibly followed by warmer than normal and El Nino conditions once again by next winter. Without a clear positive or negative ENSO signal, long lead outlooks for the upcoming months are generally vague. The outlooks do call for the increased likelihood of cooler and wetter than normal conditions for the bulk of the summer months in areas to our west from the central and northern Great Plains westward into the Rockies. For nearly all of Michigan, however, the official outlook for the June-August period calls for the “climatology” scenario of near equal odds of below, near, and above normal temperatures and precipitation. The only exception is the western Upper Peninsula, where odds during this period favor below normal temperatures. With or without expectations of any clear longer term major patterns, the best strategy for weather watchers is likely remains a concentration on medium range forecast products (one to two weeks into the future) with particular attention to any forecast major jet stream pattern shifts (e.g. the pattern change late last week), and a continuing consideration of climatological normals as a reference (daily temperature and growing degree day normals for a number of sites around the state can be found online at http://www.agweather.geo.msu.edu/agwx/current/ ).