In this issue
Soybean rust update
Watch for wheat scab
Pre-harvest interval drops for Warrior/Zeon in soybean
Soybean rust website expands to include soybean aphids
Update on soybean aphid on buckthorn
Pictures of springtails feeding on soybean cotyledons
Pale yellow and purple corn
Postemergence crabgrass control in corn
Herbicide selection for postemergence weed control in corn
2006 MSU Weed Tour
Glyphosate drift on wheat
Regional reports
A taste of summer weather

Last year it was too cold, and this year it’s been too dry. Until recently, weather in the Southern states has been hot and dry, so soybean rust is off to a slow start again. No new soybean rust has been found in Georgia despite recent rainfall and favorable temperatures. Similarly, there has been no rust found in Louisiana. Soybean rust has been found in northern Florida on kudzu and on kudzu in the southeastern corner of Alabama. Despite reports of rust in Mexico on soybeans grown for seed production and recently harvested, so far, no new soybean rust had been reported in Texas.

Sentinel plots will be monitored again this year in Michigan. Michigan’s sentinel plot locations for 2006 have been determined with input from the Michigan Soybean Promotion Council. Plots will be located in Allegan, Clinton, Gratiot, Saginaw, Tuscola, Sanilac, St. Clair, Shiawassee, Eaton, Ingham, Van Buren, Kalamazoo, Calhoun, Berrien, Cass, St. Joseph, Branch, Hillsdale, Lenawee and Monroe counties.

On the soy bean rust information front, the http://www.sbrusa.net/ has been renamed – Pest Information Platform for Extension and Education (PIPE) to reflect expanded coverage beyond rust. A number of new features have been added, including soybean aphid reporting, discussed in this issue by Chris DiFonzo. One of the features is a pest management toolbox, containing tactics, guidelines, a GFP (Good Farming Practices) tool, insurance documents and a chronological commentary of soybean rust reports for each state. Currently, under Tactics - USA you’ll find national soybean rust fungicide guidelines updated for 2006. Clicking on Guidelines -USA brings up information related to good farming practices. States have the option to add individual tactics or guidelines.

The GFP tool is a printable, interactive form that can be filled in to generate a report to document good farming practices taken by a grower to control soybean rust and/or aphids, information that is needed for crop insurance claims. Under Insurance Docs, you’ll find a list of documents needed to substantiate best management practices or to file an insurance claim. The chronological commentary allows you to view or print state commentaries and guidelines for a particular date or range of dates

Up to this point, risk of head scab throughout the state has been generally low, but growers should watch the weather. Wheat is entering the critical growth stages that are important for head scab infection. In the southwest and southeast parts of the state; wheat is heading and some is beginning to flower. In other parts of the state, wheat is in the boot stage or beginning to head out. Up to this point, wheat development has in Michigan been slow. Greg Shaner, field crops pathologist at Purdue University, noted in Indiana that wheat was taking six days after full heading to begin flowering this year. But the higher temperatures expected mean that wheat will now be developing more quickly, and the period between heading and flowering may be compressed.

As we approach this critical period for Fusarium head blight (head scab) infection, the latest weather forecasts are for warmer temperatures and some rain. Temperatures will be in the 70s to low 80s through the weekend with rain forecast for much of the state tonight and Friday morning. We could have more rain again Tuesday and Wednesday, and temperatures are expected to get into the 80s during the day and 60s at night; the dew point is also going to go up.

What does this mean in terms of scab? Temperatures are definitely in the favorable range for scab. With a higher dew point, the humidity will be higher, and wheat heads could be covered with dew for longer periods of time, so there will be increased periods of time when relative humidity will also be in the favorable range for the development of head scab. Relative to the weather forecast, risk is likely to increase during the next week. Weather conditions forecast throughout parts of the state will be favorable for scab infection during the next week or so. Growers considering an application of Folicur should evaluate their risk relative to potential scab infection in their area.

Syngenta just announced a reduction in the pre-harvest interval (PHI) for Warrior w/ Zeon Technology on soybeans only. The new PHI is 30 days, compared to 45 days. This change is particularly important for soybean aphid control. The recommended rates remain the same:

Soybean aphid, bean leaf beetle, cutworm, caterpillar species: 1.92 to 3.2 oz/ acre

Armyworm, stink bugs, grasshopper, etc: 3.2 to 3.84 oz/ acre

Spider mite = 3.84 oz/ acre

Many of you are aware of the soybean rust web site (http://www.sbrusa.net/) sponsored by USDA last year. That site provides a map that shows soybean rust detections in sentinel plots and on kudzu, an alternate rust host. There is also commentary provided by state specialists. Knowing the progression of the disease north will help producers target scouting and apply preventative fungicide applications.

For 2006, there is a new feature on the web site – maps for soybean aphid. When you enter the site, simply go to the drop down menu in the top right corner, under the date and select soybean aphid. Two maps appear on the right side of the screen. The top map shows “SB Aphid Observations.” As of this writing (May 25) this map is blank (it isn’t active yet), but once reports of soybean aphid come in, dots will appear. While USDA is funding the sampling some sentinel plots for aphids, additional research plots and production fields may be sampled in certain states by Extension educators, state government, university entomologists and others. Unlike the rust map, which only has two colors (green for no detection, red for detection), the color of the dots on the aphid map will reflect the number of SBA per plant with purple dots indicating fields or plots over the 250 per plant threshold. The second map has the “SB Aphid State Update,” commentary by state specialists. Note that the color of the state reflects when the commentary was last updated.

By clicking on Michigan, you can read commentary by me on aphids. I will also include my detailed management recommendations, if aphid populations increase. Some of this information may be redundant of the Field Crop CAT Alert, but I since can update the rust web site daily if needed, the information will be more up-to-date.

A note of caution about the soybean aphid web site – entomologists in the region agree it should not be used to make spray decisions in your individual fields. This is different from how the rust maps are used. Detections of rust near your location will help to time preventative fungicide applications across a region. However, detecting soybean aphid in your area and even having fields go over threshold do not necessarily indicate your individual fields should be treated. We definitely know from 2005 that soybean aphid populations during an outbreak differ dramatically from field to field and that some fields need to be treated while other do not. We also know from 2005 that optimal timing of insecticide applications protects yield, which argues for scouting as needed and making field-by-field decisions. Use the soybean aphid maps to get information about aphid populations in general, but do not use the maps to make a decision about whether or not to treat your own fields.

A few weeks ago I reported that entomologists from Purdue and Illinois found only two aphid colonies in their annual buckthorn survey. Both colonies were found near Bronson, Michigan. (see photos) This week I hit the jackpot and found 22 colonies on a single buckthorn shrub on the MSU campus. Although there are dozens of other buckthorn shrubs in the area, none of the others had aphid colonies. Some individuals in the colonies were winged, indicating they are about to disperse to soybean. On a positive note, there were at least 21 Asian ladybeetles on this same shrub, wiping out the colonies. Despite finding this single infested buckthorn, I still believe that aphid populations will be low this season.

The pictures accompanying this article show the feeding caused by tiny globular springtails on soybean cotyledons. (see photos) Springtails are common beneficial insects that eat decaying plant material, fungi or bacteria, breaking down residue and improving soil structure. Springtails are very common in fields with high residue and moist conditions. They sometimes move onto living plant material and feed, leaving a scraped or scarred appearance on cotyledons. Generally, springtail feeding does not cause economic damage. However, they are becoming an increasing problem in sugar beet production, reducing stand early in the season. This is probably partially due to the increased use of reduced tillage, which leaves more residue on the soil. In the case of soybeans, given a couple days of sunny warm weather, the plants will rapidly grow past the springtail feeding.

A number of calls have come in regarding discolored corn plants with one grower remarking “I’ve never seen corn turn so many colors before.” These symptoms are not unusual for Michigan but have been particularly prevalent this year. The pale yellow color is symptomatic of low photosynthetic activity and general nutrient stress experienced by the plant. Similarly, poor root growth can result in purple-colored corn. The main culprit is the recent cool, wet weather experienced across Michigan this spring.

Many factors contribute to the symptom of yellow corn seedlings. Sunlight drives the photosynthetic process and a lack of heat units results in slow seedling growth. Cool spring temperatures combined with saturated soil also limit corn seedling root growth and penetration into the soil. This confounds the slow growth of the corn plant by limiting nutrient uptake. Furthermore, the mineralization and plant availability of nutrients including nitrogen and sulfur is slowed down due to slower microbial activity in cool, wet soils. These same conditions can also result in purple-colored corn. The restricted root growth resulting from the saturated soils can cause a build up of sugars in the corn leaf. These sugars would normally be used for root growth but when accumulated in the leaf, result in the production of anthocyanins, which give the leaf a purple color. In addition, some corn varieties have inherently higher levels of anthocyanins. If the purple color persists after field moisture conditions normalize, the discoloring may be indicative of other root related problems such as a compaction problem or a phosphorus deficiency in the soil.

Cool, wet soils and “weakened plants” also set the stage for fungal and bacterial root disease in corn. In addition, weather-stressed corn is more susceptible to herbicide injury, which can also result in yellowing. Finally, weakened plants are more susceptible to damage from insects. Scouting for disease and insect pests is especially important in weather-stressed fields of corn.

There have been several questions about the possibility of failed preemergence herbicide applications and the likelihood of annual grass weed escapes, particularly more difficult to control weeds such as large crabgrass. Emerged large crabgrass is difficult to control in conventional systems with smooth crabgrass being even harder to control. An article in last year’s Field Crop CAT Alert noted the difference between the two crabgrass species (vol. 20. No. 8 – June 2, 2005).

Postemergence herbicides that suppress large crabgrass include: Accent Gold, Accent Gold WDG, Basis, Callisto and Steadfast. These herbicides give only fair control of this weed. Additionally, weeds must be very small to provide even fair control of this weed.

Fair control of large crabgrass and smooth crabgrass is also possible with Liberty (Liberty Resistant Corn only) or Lightning (Clearfield Corn only). The weeds should be no more than two inches tall. Glyphosate is the only postemergence herbicide that provides excellent control of large crabgrass and smooth crabgrass (Roundup Ready corn only).

For specific rates of these herbicides please refer to the 2006 Weed Control Guide for Field Crops(E-434).

There are several herbicide options for postemergence weed control in corn. The best choice for any given field depends on the specific situation. Three of the critical factors to consider when selecting a postemergence herbicide in corn are:

1) Rotation plans

2) Corn growth stage

3) Weed species/size in the field.

Table 1 describes crop rotation restrictions, corn growth stage limitations and effectiveness on common weed species for several postemergence herbicides. Herbicides in Table 1a can be used with any corn hybrid. (view table)

Table 1b includes herbicides that can only be applied to hybrids specifically resistant to the herbicide. (view table) For example, glyphosate only with glyphosate resistant (Roundup Ready) hybrids, Liberty only with Liberty resistant (Liberty Link) hybrids, or Lightning only with imidazolinone resistant (Clearfield) corn hybrids. Detailed information on crop rotation restrictions and effectiveness ratings is available in the 2006 Weed Control Guide for Field Crops(E-434).

We invite you to make plans to attend the annual Michigan State University Weed Tour, beginning at the MSU Botany Field Lab on Wednesday, June 28. The MSU Botany Field Lab is located on College Road just north of Jolly Road, south of MSU’s campus. Registration begins at 9:00 AM with the field tour kicking off at 9:30 AM. The tour will provide ample opportunity to look at research plots and participate in some short field presentations (Be sure to bring a hat and sun screen!). Participants can compare their favorite corn and soybean herbicide programs to other commercial programs and evaluate how new transgenic crops (CRW-corn) interact with weed management strategies. The morning tour ends with lunch.

The afternoon tour will begin at 1:00 PM at the MSU Horticulture Farm (College Road, south of Jolly Road) and will include weed control research in horticultural crops.

Pre-registration for the tour is $25 per person, which includes a tour booklet and a lunch ticket. If you have any questions, or would like additional information, please call Deb Misiak at 517-355-0271 ext. 1112.

Wheat submitted to the lab this week in the boot stage of growth showed a pattern of drift and specific symptoms characteristic of glyphosate injury. The wheat was stunted with discolored and often collapsed flag leaves. Specific leaf symptoms included interveinal yellowing, bleaching and/or reddening near the base of the flag leaf. (see photos)

Regional reports
1 -- Southeast
Ned Birkey

Weather
It has generally been nice with improving soil-drying conditions as the week progressed. We did have some very light frost earlier this week and late this week is forecast to have lows even in the 60s. Yesterday, farmers (May 24) were beginning to resume field activities after almost two weeks of delay. We had some rain overnight with more forecast for today and tomorrow.

Commodity reports
Alfalfa is ready to cut as the soil dries out. A few smart people got the first cutting up yesterday before last night’s rain. In mixed hay fields, the cool season grasses have been mature for a couple of weeks now. I have not seen any potato leafhoppers yet, though the wind pattern that is to bring us upper 80 temperatures this weekend from the Gulf will probably blow up these insects. Leafhoppers will be just in time for the new second cutting.

Corn is slowly turning from yellow to green. It has been almost exactly two weeks since any fieldwork has been done with some planting and spraying resuming yesterday as soils are continuing to dry out. Advanced fields are at V3. With the recent cool and cloudy weather, the corn plants seem to have been just “sitting still.” Fortunately most corn was emerged and many fields were not submerged. With the temperatures forecast to warm into the 80s, the corn should respond very quickly. Some fields will need to be replanted and there has been some scrambling this week to purchase seed corn.

Soybean planting resumed yesterday and may continue over the holiday weekend if the showers forecast for Thursday and Friday do not amount to too much. Farmers rotary hoeing or spraying cannot always cover entire fields because of variable soils with some parts of fields too wet. I have only seen a few fields emerged with advanced fields at the V2 leaf stage. I guess we are only half planted so there will be some planting and replanting going on at the same time.

Wheat is heading and flowering and has very good yield potential. There is powdery mildew of susceptible varieties. Some fungicide spraying has been done this week. The forecast for warm evening temperatures, sustained higher humidity and showers over about a 60-hour window will likely cause diseases such as Septoria and Fusarium head scab to develop.

2 -- Southwest
Bruce MacKellar

Weather
Fair conditions were a welcome change for growers. The drier conditions allowed producers to return to fieldwork, planting and spraying. St. Joseph County growers probably benefited the most from the return to sunshine that allowed seed corn planting to resume. Frost occurred on Monday and Tuesday mornings (May 22-23), causing some concern on lower ground fields. Rainfall returned on May 24 with areas in the southern tier of counties receiving 0.25 to 0.5 of an inch in limited areas.

Commodity reports
Commercial corn remains yellow from the cold temperatures and wet conditions. Corn that emerged in April and early May has pretty uniform stands. Fields that emerged after the rain event have some stand issues, but not enough to cause replanting in most areas of the fields. The earliest planted corn is still in the 4- to 6-inch height range. Grass weed escapes are still somewhat of a concern on some fields, particularly where mats of winter annual weeds caused uneven herbicide coverage. See the article of weed control in this issue of the Field Crop CAT Alert for more information on control of grasses post emergence.

There was some discussion about nitrogen leaching out of the root zone at the IPM Breakfast Meeting yesterday. Sandy soils with the ability to hold 1 to 2 inches of moisture per foot of soil at field capacity may have leached N below the current rooting zone if 3 or more inches of precipitation fell during the wet period. Heavier soils should have had less leaching potential and nitrate losses.

Seed corn producers are playing catch-up very quickly in our area. There are some inbred delay issues, but for the most part growers were able to get in their partner inbred lines without having to re-plant. Seed corn fields are yellow like the rest of the corn, but we expect the warmer temperatures next week to improve color dramatically. Cutworm and insect pest damage remains light at this point.

With warm temperature expected and plenty of soil moisture, both the corn crop and the weeds will probably see an explosion in growth. As was mentioned last week, there are misses in pre-emergence herbicide programs. Some of these weeds are extremely small at this point, but may get ahead of you quickly. Evaluate your pre emergence weed control performance to avoid problems.

Early planted soybeans are pushing their first tri-foliate leaves. Later planted beans are just emerging, and some beans are still being planted. There are very few signs of insect damage at this point, although bean leaf beetle feeding can be seen on some fields. I suspect that we may have had an infection period for SDS because of the saturated soils soon after soybeans were planted or had emerged on fields where soybean cyst nematodes have been a problem. SDS becomes a leaf disease later in the season, but often infection occurs at or soon after germination and emergence in the roots.

Alfalfa growth is at 20 inches, and we have reached 750 GDD41 recommendations for harvesting the first cutting in the southern portion of the region. We have begun the harvest in earnest this past week. Alfalfa weevils had been widespread. Fields treated for this pest have been yielding well and recovered well from early feeding damage. Watch the re-growth carefully for the presence of alfalfa weevil larvae.

In wheat, drier conditions have led to a reduction in threats from fusarium and powdery mildew. Fields are currently at flowering or early grain fill. We are at the window for head scab infection or are just beyond it in St. Joseph County, but other areas are likely to be further behind developmentally. If heavy rains or warm, cloudy conditions persist that leave the plants soaked for extended periods should appear, there may be more of a chance for fusarium and other diseases to rebound. There was a report of wheat rust somewhere in the region. Please refer to the information in this Field Crop CAT Alert for more information on wheat diseases.

3 -- West Central
Fred Springborn

Weather
The sun was shining at least part of the time this week. Scattered rain showers observed Thursday and Friday of last week and a 0.5 inch up to 0.7 of rain observed last night (May 24). Light frost on Monday and Tuesday. High air temperatures have been in the 60s and 70s with lows in the 30s. Low soil temperatures have been in the 40s. We have quite adequate moisture with little direct damage from excessive water. Cool temperatures have slowed plant growth.

Commodity reports
Corn planting is near 80% complete. Some planting was accomplished this week. Many fields have emerged. Growth stages range from seed still in the bag to V2. While color is improving, emerged corn appears yellow in many fields due to the recent cool, cloudy weather. Stands should be checked in fields planted two weeks ago.

Soybean planting was back underway yesterday. Growth remains slow on emerged fields. No dry bean planting has taken place yet.

Much of the wheat crop is in boot, and a few fields are heading. Powdery mildew is present at low levels low in the canopy. Oat stands and growth are generally good.

4 -- Central
Paul Gross

Weather
Areas of the region have been drying out over the past week. The north part of the region received light rains on Wednesday evening. There were three mornings of frost early in the week. For the most part, there was very little crop damage. Farmers were able to get back into the fields on a limited basis early in the week. Some were able to plant on Tuesday and Wednesday (May 23-24) on lighter, well-drained soils. Field activities over the past week include tillage and herbicide applications.

Commodity reports
The corn crop is emerging. Areas of the region received frost Sunday, Monday and Tuesday mornings. Temperatures were not low enough, and the crop is small enough that there was very little frost damage. However the crop is very yellow almost transparent due to the cold wet temperatures. The warm weather Wednesday and Thursday is helping bring the crop along. Very little planting progress was made this past week.

Soybeans are emerging slowly. There is some concern about how the stands will be on some of the early planted fields. Stands should be assessed as soon as possible after fields dry out and things warm up. We have seen some areas of fields where plants have rotted. With all the rains, most fields are in need of weed control. Herbicide applications will be applied as field conditions allow.

Wheat is in the boot stage and beginning to head. At this point powdery mildew is present in many fields, but low in the plant. Monitor the crop and determine if your variety has resistance to powdery mildew. The weather over the next 7 to 10 days will determine the potential for head scab. It appears weed problems may be an issue due to the rainy weather. We have observed small weeds in several fields.

Alfalfa harvest has begun in some areas. The crop is ready to harvest from a quality stand point. We have not seen any alfalfa weevil problems. Weather patterns over the next few days are ideal for the movement of leafhoppers up into Michigan. Start scouting after first cutting.

Dry bean planting has begun where field conditions allow. Most were able to fit ground but the rain halted planting.

Oats are doing very well with the cool, wet temperatures.

5 -- Thumb
Mark Seamon

Weather
Temperatures have increased in the past couple of days which have helped to dry many fields that have been wet for more than 10 days. Field work has been limited to well-drained fields. A light rain of 0.1 inches fell in Saginaw on Wednesday night (May 24).

Commodity reports
Alfalfa has made use of the rainfall and cool temperatures with active growth. The first cutting will begin as soon as weather conditions allow for those producers who are interested in high feed quality.

Sugar beet stands are gaining growth where stands are healthy. Seedling diseases are becoming easier to find now that fields can be walked. Micro-rate herbicide applications have resumed in many areas this week, but some fields have not dried enough to allow this yet. Weed size in these fields has become a consideration with herbicide rates and control options. Fungicide applications for Rhizoctonia control have been made where possible.

The wheat crop continues to grow and develop quickly. Most fields are at or near the boot stage with the northern and eastern Thumb being delayed due to cooler temperatures. Septoria and powdery mildew are prevalent on the lower plant in many fields. Most growers of white wheat are watching weather conditions and flowering timing closely to determine if a fungicide application is warranted. The value of wheat this year is a strong consideration in whether to protect against Fusarium head blight (head scab).

Most corn fields have consistent stands but yellow is the predominant plant color. Sunshine and warmer temperatures will get this crop back on track with fast growth and better plant health. Weed control is becoming a concern with fields that have a planned post emerge application. Interest in presidedress nitrate sampling is strong with concerns about nitrogen cost and the loss of nitrogen form excessive rainfall.

Soybean planting has not resumed in most areas in the past week due to wet field conditions. Many fields are just emerging after two to three weeks in the soil. Some growers are becoming concerned about seed being in cool and wet conditions for this long without emergence. Soil crusting is also causing concern where emergence is limited. The predicted rainfall at the end of this week combined with warmer temperatures should help growers determine if stands will be adequate.

A few dry bean fields have been planted in the Thumb, but it is limited. Most growers will begin planting next week or the fist full week of June.

Following a series of frosty mornings earlier in the week, a significant warming trend has taken place across the Great Lakes region as a weak upper air troughing feature approaches from the west. This system will bring a continued chance for rainfall in the form of showers and thundershowers Thursday (May 25) through much of the day Friday. Best chances for rainfall will be across southern sections of the state Thursday and Thursday evening, where 0.50- to 1.00-inch totals are possible. Rainfall totals elsewhere will generally remain in the 0.25- to 0.50-inch category. A few storms could become severe across southern sections of the Lower Peninsula late Thursday afternoon and evening with primary threats of high winds and hail. Temperatures will reach highs from the 70s north to low 80s south Thursday before cooling back the upper 60s to 70s statewide on Friday. Lows will generally fall to the 50s to low 60s through Saturday.

For the upcoming holiday weekend, mostly fair and warmer than normal weather is expected in response to the gradual formation a large upper air ridging pattern over the eastern half of the United States. Highs in many areas of the state will reach or exceed 80°F with some southern locations nearing 90°F Sunday and Monday. Dew point temperatures will also be on the increase, leading to muggy conditions during daytime hours. Some scattered showers and thunderstorms will be a possibility once again by Memorial Day (May 29) and Tuesday, May 30, but areal coverage is expected to be limited, with most locations remaining dry. Mean temperatures for the next week will likely average 3 to 6 degrees above normal, so a flush of new crop and insect growth and development is likely.

Medium‑range forecast guidance for at least the next one to two weeks is suggesting that the upper air ridging pattern across the eastern United States will continue to be a dominant weather feature, with some weakening possible during the 8-14 day time frame.

NOAA 6-10 day and 8-14 day outlooks (covering May 30 through June 3 and June 1-7) both call for the likelihood of above normal below normal temperatures state- and region-wide. Precipitation totals during the 6-10 day time frame are forecast to range from below normal in eastern sections of the state to above normal in the west, while below normal totals are predicted statewide during the 8-14 day period.

Nationally, warmer than normal temperatures are expected across much of the southern and western United States during these periods, and possibly for above normal precipitation totals across the extreme southeastern United States associated with what is expected to be a busier than normal tropical storm season in the western Atlantic Basin. Further ahead, the outlooks suggest warmer than normal temperatures for at least parts of the Great Lakes region for the late summer and fall