Vol. 20, No. 8, June 2, 2005

Soybean aphids are early in Michigan and surrounding states

Purple corn likely from cool weather this spring

Regional reports

Christina DiFonzo, Entomology

Here is an aphid update from several states, including Michigan.

Pat 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. 

During the 2005 season we are compiling all of our CAT Alert articles on soybean aphids and soybean rust at one web site. Each week any new articles are added to the collection. To view the aphid, articles visit: http://www.ipm.msu.edu/soybean/aphid.htm

To view the rust articles, go to: http://www.ipm.msu.edu/soybean/rust.htm

Identification and postemergence control of crabgrass in corn

Steve Gower
MSU Diagnostic Services
Kathrin Schirmacher and
Jim Kells ,
Crop & Soil Sciences

Large crabgrass can have a prostrate, spreading, to upright habit that is capable of rooting at the nodes.  The leaf sheath and both surfaces of the leaf blade are densely hairy.  Large crabgrass has a jagged, membranous ligule and no auricles.  Leaf blades are generally shorter, wider, and tapered compared with blades of most other grasses.

Smooth crabgrass is very similar in habit and appearance to large crabgrass.   The main difference is the amount of hair on the plant.  The leaf sheath and leaf blade of smooth crabgrass is hairless or only sparsely hairy.  Also, the lower leaves of smooth crabgrass usually contain a tuft of long hairs on either side of the leaf base. 

Fall panicum may be differentiated from crabgrass most easily by its hairy ligule.  The first few leaf blades of fall panicum may have hair only on the lower surface with a hairy leaf surface.  Seedlings become less hairy with age and completely lack hairs at maturity.  Other distinguishing characteristics of fall panicum include a prominent white midrib and no hairs on the sheath margins.  

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 2 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 2005 Weed Control Guide for Field Crops (E-434).

Kurt Thelen
Crop & Soil Sciences

There have been a number of reports of purple colored corn seedlings this year.  These symptoms are not unusual for Michigan but have been particularly prevalent this year due primarily to the cooler than normal weather.  There are several factors that contribute to the purple color, but the main culprit is the cool weather, which has plagued the Northern corn-belt this spring.

Restricted root growth resulting from cold soils can cause a build up of sugars in the corn leaf.  These sugars would normally be used for root and shoot growth but when accumulated in the leaf, result in the production of anthocyanins, which give the leaf a purple color.  If the purple color persists after field conditions normalize, the discoloring may be indicative of other root related problems such as a compaction problem or phosphorus deficiency in the soil. In addition, some corn varieties are genetically predisposed to have inherently higher levels of anthocyanins.  These varietal differences are readily apparent when viewing variety trial plots this time of year, however, they do not appear to affect final grain yield.

Growers in the sugar beet producing areas of the state often report an increased incidence of purple colored corn following sugar beet.  This phenomenon was investigated by Don Christenson at MSU in the mid 1990’s.  The work did not find a correlation with sugar beet carry-over herbicides, soil P levels, and did not appear to be an artifact of soil compaction.  The results indicate there may be an association with the sugar beet residue and early season purpling of rotational corn. Nevertheless, the increased incidence and severity of purpling following sugar beet was not detrimental to corn yield.

The good news is that corn will generally overcome early season purpling with a dose of warmer weather.  Continue to monitor nutrient levels, particularly nitrogen.  Once the weather turns, the corn should outgrow these discoloration symptoms.

The 2005 Guidelines for soil nitrate test for corn have been posted at the CAT Alert web site: http://www.ipm.msu.edu/CAT05_fld/TestCorn.htm

Darryl Warncke
Crop & Soil Sciences

Plant tissue analysis can complement soil testing for long term nutrient management or can be used to troubleshoot growth problems.  Soil testing indicates the available nutrient status of the soil.  However, sometimes plants are not able to take up adequate amounts of essential nutrients due to certain unfavorable soil conditions, such as soil compaction.  Plant tissue analysis provides a nutrient profile of the plant that can reveal nutrient deficiencies or imbalances, whether severe or marginal.  Certain parts of the plant provide a better indication of the nutrient status than others.  In general, the youngest fully developed (YFD) leaf is a good diagnostic tissue for which there are interpretation guidelines.  For young plants collect the whole above ground portion of the plant. 

Table 1 provides guidelines for sampling selected field crops. Collect samples from 20 to 30 plants within the area of interest.  When using plant tissue analysis to troubleshoot a growth problem, collect samples from both the poor growth area and a good growth area.  This comparison is better than comparing the results to the standard interpretation guidelines. Dry the plant tissue before sending it to the analytical lab.  

Pat Hart
Plant Pathology

There have been several reports of powdery mildew beginning to show up on flag leaves.  The results of replicated trials at several locations in past years in Michigan strongly suggest that applying fungicides to control powdery mildew will rarely provide economic returns, even when disease pressure is high. Yield increases over the untreated controls are often not significant, and when they are, they are in the 5 bushel per acre range and only when yield potentials are very high, i.e. greater than 70 bushel per acre. Only on the most susceptible varieties have increases of 10 bushel per acre or more been observed.   A highly susceptible variety would be similar to the old Pioneer 2510.  The occurrence of powdery mildew on leaves low in the canopy is not a good indicator of the potential for powdery mildew to develop on the flag leaf.  Also, with the warmer and dryer weather, powdery mildew should not continue to increase.  Last year’s severe epidemic of Septoria leaf blotch is not a good indicator that this disease will be a problem this year, and preventative sprays with a fungicide are not warranted.

Stripe rust of wheat, a new emerging disease, has been reported in states west of Michigan, but not yet in Michigan.  Potentially more important than wheat leaf rust, this disease would have to show up in wheat prior to the heads being fully emerged for a fungicide action plan to be implemented.  The only fungicide approved at this time would be Tilt, and it cannot be applied after the heads are fully emerged and flowers (i.e. anthers) are visible.  Although it was observed in Michigan last year, it did not become a problem and was not widespread.

Pat Hart
Plant Pathology

The U. S. EPA has approved the use of Folicur for head scab (Fusarium Head Blight) of wheat.  The following label restrictions must be adhered to.

1)    One application of Folicur may be made using ground or aerial equipment at a rate of   4 fluid ounces of formulated product per acre per year.

2)    A maximum of 250,000 acres of wheat in Michigan may be treated.

3)    Application may not be made within 30 days of harvest. Straw cut after harvest may be fed or used for bedding.

4)    This specific exemption expires June 25, 2005.

The Pennsylvania State Scab Model is predicting a low probability of wheat scab developing on wheat heading on May 31, except for two very small areas in the Thumb and in southwest Michigan.  When wheat is planted into corn residue the potential increases significantly for many areas of the state, but that is assuming the wheat is flowering on this date. It would appear that at this time an application of Folicur is not warranted for scab control. 

Regional reports

1 – Southeast

Weather
Our weather has been unexpectedly mild and dry, with very little rain this past weekend (May 28-29), though the forecast was for rain every day. Although we are still behind last year in growing degree days, we will catch up a bit this week.

Commodity reports
Alfalfa is being cut as farmers feel they can harvest before the rain forecasted to arrive here Sunday, Monday and Tuesday.  There is more feeding by alfalfa weevil, but not at alarming levels.  Farmers will cut hay rather than spray for this insect at this time. Potato leafhoppers are also present, though at low levels.

Corn is growing nicely with some warmer temperatures. Advanced fields are at the V4 growth stage, still shorter than we would prefer.  Post herbicide spraying is being done and sidedressing of nitrogen is in full swing.

Soybeans are at the first or second trifoliate stage with soybean aphids present, though not at soybean “sucker” levels.  No major weed problems or spraying done on soybeans at this time as attention is focused on hay or corn.  Sentinel plots are at the same stage as other fields.

Wheat is mostly headed out at this time. The dry weekend has helped ease concerns of a major disease outbreak.  With rain again forecast for this coming Sunday, Monday and Tuesday farmers will expect this to facilitate some head scab. 

Bruce MacKellar

Weather
Dry weather continues for the region with irrigation systems beginning to be used to help add moisture to the upper soil profile in many areas.  In visiting with the conservation districts staff conducting irrigation scheduling, I learned there is a great deal of variability in soil moisture contents based on the type and timing of tillage operations this spring.

Commodity reports
For alfalfa, the current dry spell has allowed producers to get a good portion of the first cutting off without getting the crop wet.  We have seen just a few potato leafhoppers in the fields so far, but if their numbers increase, it is important to watch alfalfa re-growth for this pest.

Commercial corn is V3 – V1.  Weed control misses continue to be a challenge in some fields. Grass weed species seem more prevalent than broadleaf weeds where control is problematic. Some early-planted glyphosate tolerant fields are approaching the time for an application because the weeds are growing rapidly.  There continues to be very little insect pressure at this point.

Seed corn has a wide range in plant size depending on when the crop was planted. Very little is left to plant. Most fields are looking very good at this time.

Most soybean early planted fields are in the first trifoliate leaf stage.  There are some signs of bean leaf beetle feeding in many fields, but all are well below threshold.  I have seen more stand damage from groundhogs and geese than from cutworms so far this year.  It appears to be about the right time for post emergence weed control to be applied to early planted beans and fields are beginning to be treated with post emergence programs. Non-RR pre-emergence weed control programs look to have worked good so far. We have begun to see evidence of Septoria brown spot in some fields. This is our first soybean rust “look-alike” disease of the season. 

I have not seen soybean aphids in the southwest yet, and I have looked at several fields. Chris DiFonzo reported finding soybean aphids this morning on the MSU Campus, as have most of the states in the Midwest. We will be watching the development of this pest carefully throughout the season. MSU has several research sites being established in the region this summer to evaluate the effect of foliar fertilization on plant yield in aphid infested fields, and to look at biological control insect prevalence in fields and as well as soybean rust sentinel plots.

Potatoes continue to look excellent, taking advantage of the warmer and sunny conditions (with irrigation water) to grow rapidly.

Wheat is flowering in the southwest region. Dry conditions continue to reduce the chances that Fusariun head scab will be a problem for fields in the southern portion of the region.  Under these drying conditions, growers that are raising wheat where irrigation is available have been putting on water to meet the crops moisture needs. Powdery mildew is present in most fields to some degree but really has not presented much of a problem in St. Joseph County this year.

Fred Springborn

Weather
Scattered showers yielded only one or two tenths of rain in the region over the Memorial Day weekend and most of the region stayed dry. Summer weather has arrived as high temperatures have reached up into the 70’s to low 80’s F. Low air temperatures have been in the 40s F.  Low soil temperatures are remaining solidly in the 50’s F. Base 41 GGD totals as of May 31 are: Ionia 749, Entrican 638, Big Rapids 650, Fremont 705. For other totals go to: http://www.agweather.geo.msu.edu/agwx/current/report.asp?fileid=base41gdd

Commodity reports
Stems are elongating in oats. Most oat fields have had their herbicide application. Wheat is in boot, Feekes stage 10.1 in the Montcalm area. Powdery mildew is present in many fields.

Corn growth is improving with the warmer temperatures. Much of the crop is in the V1 to V2 growth stage.

Dry bean planting is progressing rapidly. Fifteen percent of the crop is planted with much more progress expected this week. Soybean planting is essentially complete. Much of the crop has now emerged. Soil crusting has been an issue on the heavier soils.

Alfalfa harvest is in full swing. Every piece of haying equipment in the area is being used to make hay while the sun shines. Ten  to 15 percent of the crop is already in a silo and much more progress will be made by the end of the weekend. Grasses are maturing fast so they likewise need to be harvested. Over-mature pastures need to be clipped or cut for hay to get rotations back under control.

Paul Gross

Weather
The region received widely scattered showers over the Memorial Day weekend. Some areas received about one tenth of an inch while other areas were dry. The warmer weather has been beneficial in getting corn and soybeans up and going. While we have adequate subsoil moisture, rain would be beneficial.

Commodity reports
The warmer weather over the past week has really brought the corn crop around. Most of the yellow color is disappearing and the stands look good. We are seeing some purple corn in some areas. There are several factors that can cause the purple corn, including phosphorus deficiency, variety, and sugar buildup due to cool temperatures. We expect the purple to disappear as the weather warms and the crop progresses. Nitrate tests should be taken now to determine sidedress nitrogen needs.

The soybean crop is planted and emerging. There are reports of emergence problems in some areas. Some replanting has taken place due to slug damage and poor stands. Some growers have been rotary hoeing. Herbicide applications are being made at this time.

The wheat crop is in the boot stage. We are seeing powdery mildew in most fields. In some fields it has reached the leaf below the flag leaf. No other foliar diseases have been seen at this time. Continue scouting field for foliar diseases.

Alfalfa harvest has begun this week. Farmers are reporting good yields and quality should be good. No reports of alfalfa weevil. Scout fields that have been harvested for weevil.

Dry bean planting began this week. We expect to wrap up planting this week if the weather holds.

Sugar beets stands are variable. There are good excellent stands and some poor stands.

Oats and barley look very good at this time.

Mark Seamon

Commodity reports
First cutting of alfalfa has begun and is looking like pretty good yields. Other fields are growing nicely. 

The sugar beet crop has seen some great growth in the past week.  Micro rate herbicide applications are staying on time with good weather conditions for spraying. 

The wheat crop has progressed to the Feekes 9-10 with a good many fields on the boot stage.  Powdery mildew is easy to find on lower leaves but not much moving up the plant.  

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 emergence is looking good with most soybeans just emerging through unifoliate stage.