August 12, 2004
In this issue
§ Management of annual weeds following wheat harvest
§ Do you suspect herbicide resistance?
§ White mold in soybeans and dry beans
§ Ergot of rye and other small grains in 2004
§ Late blight in potatoes
§ Late Blight Open House Day at Muck Farm
§ Regional reports
§ Weather news
Annual weed densities are very high in wheat stubble this year. These weeds must be managed soon in order to prevent seed production. Several effective options are available for management of annual weeds in wheat stubble. However, these practices must be implemented before seed production to avoid significant additions of seeds to the weed seed bank.
After wheat harvest, weeds take advantage of available resources, especially newfound sunlight, and will grow rapidly, especially in years with adequate soil moisture in July and August. These weeds are capable of producing large amounts of seed prior to a killing frost.
Common ragweed, velvetleaf, common lambsquarters, redroot pigweed, and foxtail species are examples of common summer annual weeds in wheat stubble. At this time of the year these weeds are completing their life cycles by flowering and producing seed. The main goal following wheat harvest is to prevent or reduce weed seed production. Post-harvest weed control options include tillage, mowing, and herbicides. In general, management of annual weeds in wheat stubble is not difficult, however timeliness is critical.
Tillage is a viable option for control of both broadleaf and grass weeds. Mowing will reduce seed production of most grass and broadleaf weeds. However, mowing is often less effective on grasses since seeds can be produced on tillers low on the plant. Glyphosate and 2,4-D are common herbicides used for post-harvest weed management in wheat stubble. Refer to the herbicide labels for appropriate rates, adjuvants, and tank mixes.
Several weed species have developed resistance to popular herbicides used in Michigan. There are at least 12 weed biotypes resistant to one or more herbicides in the state. These herbicide-resistant weed species have been documented in field, vegetable, and fruit crops, as well as tree plantations and nurseries throughout Michigan.
Once growers identify and confirm an herbicide-resistant weed, they can then implement appropriate management strategies to prevent or limit weed seed spread. If you suspect resistance in any weed species and would like to confirm this, seedheads can be collected upon maturity and submitted to MSU Diagnostic Services for an herbicide resistance screen.
The next several weeks prior to harvest are perfect for collecting mature, viable weed seed. Select plants that were definitely sprayed (not along field edges or sprayer skips). Harvest seedheads by cutting the stem just below the seedhead. Place seedheads into a brown paper bag or collect seed in a small envelope or container. Never seal plants or seed in plastic!
Fees associated with herbicide-resistant weed testing are generally $30 per sample (a sample could include multiple plants of the same species from one field). Two exceptions to this fee are marestail (Conyza canadensis) and common lambsquarters (Chenopodium album) from Michigan soybean fields. These two weeds will be screened for resistance and costs will be covered by checkoff dollars through the Michigan Soybean Promotion Committee.
Please contact Steven Gower (517-432-9693, sgower@msu.edu) with any questions regarding sample collection. Send samples to: Diagnostic Services, 101 Center for Integrated Plant Systems, East Lansing, MI 48824-1311, Attn: Steven Gower.
White mold, caused by the fungus Sclerotinia sclerotiorium, occurs in years of excessive moisture. As a general rule, an average of three inches of rain over any two-week period provides sufficient moisture for sclerotia to germinate and produce ascospores. This translates into continuously wet soils for ten days. Early row closure to maintain a wet soil surface is important. The last week of June is the time to start adding up the rainfall totals, and continue through July 15-20. It would appear that some areas of the state may have received sufficient rain since the last week of June to keep the soils wet enough. Continued wet weather should favor germination of the sclerotia. Sclerotia are the black, hardened structures that allow the fungus to survive for many years in the soil, and the ascospores are responsible for infecting the plants during times of susceptibility. Ascospores only infect flowers, so the production and release of ascospores is important only during flowering.
In both soybeans and dry beans, the earlier stages of flowering are more important than later stages. Therefore, chemical controls are only economically effective when applied at the earlier stages of flowering. In dry beans, the best results have been obtained when Topsin M is applied prior to 100% bloom (100% of the plants have at least one open flower) at the rate of 1.5 lbs per acre. Significant losses in yield occur only when a substantial number of plants are infected, generally between 25% and 35% infection will be required before losses are observed. This is true for both soybeans and dry beans. This will depend somewhat on the pattern of plant infection, but healthy soybeans and dry bean plants will compensate for yield losses in infected plants. Fields with a history of white mold are the most likely candidates for an economic return from chemical control applications.
Fungicides have been less effective at controlling white mold in soybeans and are not recommended. Some control has been achieved when the herbicide Cobra was applied at the R1 growth stage. However, timing is critical and if white mold does not develop a yield reduction due to the Cobra will occur. Cobra has not been effective every year or in every trial. Under low disease pressure, yield protection may not occur. Cobra was most effective when used in conjunction with soybean varieties highly susceptible to white mold. MSU field trials used 6 oz of Cobra and 1 pint of crop oil/acre. The University of Wisconsin has shown similar results using 2-4 oz of Cobra/acre.
Ergot, caused by the fungus Claviceps purpurea, is a disease of cereal crops and grasses. The disease causes reduced yield and quality of grains and hay and also causes a livestock disease called ergotism, if infected grains or hay are fed. The disease cycle of the ergot fungus was first described in the 1800s, but the connection with ergot and epidemics among people and animals was known several hundred years earlier. Ergot's medicinal applications and animal poisoning properties first called attention to this plant disease. Human poisoning was common in Europe in the Middle Ages when ergoty rye bread was often consumed.
Ergot occurs to some extent every year on cereals and grasses in Michigan. The disease is generally more prevalent in rye and triticale than in other cereals. Although the crop loss caused by this disease is important, the effects of the ergot's alkaloid toxins on man and animals is of much greater significance. There has been an unconfirmed report of ergot in rye in Michigan in 2004.
Ergot may affect the market grade of grain. In the commercial grain trade, wheat is graded as "ergoty" when it contains more than 0.05 percent by weight of the ergot sclerotia; rye is graded as "ergoty" when it contains more than 0.3 percent by weight of ergot sclerotia, and triticale, oat, or barley are "ergoty" when they contain more than 0.1 percent.
Additional information of ergot of rye can be found at the
following web sites:
http://www.botany.hawaii.edu/faculty/wong/BOT135/LECT12.HTM
http://www.ext.nodak.edu/extpubs/plantsci/crops/pp551w.htm
Late blight has been confirmed in many fields in several counties in the Lower Peninsula. Recommendations for control measures can be found at: http://www.lateblight.org or in the May 19, 2004 Vegetable CAT Alert.
It is vital that loci (areas with plants with greater than 20 percent foliar or stem lesions) are chemically destroyed with gramoxone (rate = 1.5 pt/A) 30 rows either side of the last visible lesion and 100 feet along the rows. Lesions do not become visible until seven days after infection. Given the near perfect conditions for late blight development this season, which include recurring and continuous rain days, as well as steady and sometimes-strong winds, the spores of this disease are plentiful and are carried both within crops and between crops.
Fungicide programs must include a translaminar late blight product at this stage and continue until the epidemic abates; these include Previcur Flex, Tanos, Curzate, Acrobat, and Gavel. These fungicides are best mixed with a residual laminar protectant such as a chlorothalonil-based or EBDC-based product or Omega at full label rate. Antisporulant products such as Supertin, Agritin, or the copper products Champ and Kocide should also be considered in the mixture, especially where late blight is present in the field.
Given the dramatic re-appearance of late blight in Michigan, it has been requested by many in the potato industry that the late blight open day at the Muck Farm should be held this year. Arrangements still need to be finalized, but the tentative date is August 26 (Thursday) from 10:00 AM to 12:00 PM followed by a lunch sponsored by the Michigan Potato Industry Commission.
Corn is well past pollination across the southeast region. Early kernel counts are encouraging in fields that developed well through wet weather. Nitrogen and potassium deficiency symptoms are common, despite fertilizer application rates based on soil test results. Even fields where PSNTs were used to assess need of nitrogen application show yellowing along leaf mid-ribs.
Damaging insects in soybeans have been held in check by consistent, sometimes heavy rainfall. We do have fields where white mold has developed. This was expected, given wet weather patterns that have passed through our region. Some farmers report applying fungicides to control other diseases in soybeans, however, most farmers are on cruise control between now and harvest. After this week even intervention to control rising insect populations would be questionable.
Wheat harvest ended a couple of weeks back. Yields in our region were down 20 to 30% from normal. Test weights were adversely affected by weather, with test weights of 49 to 56 commonly reported.
High temperatures were
above 80 degrees 5 out of the last 21 days and below 70, 3 out of the last 21.
Low temperatures have been in the upper 40s to lower 60s. Rainfall totals
have been variable. Some areas of the region have received enough rainfall to
maintain adiquate soil moisture while others have received only a few hundreths
of an inch at a time and have very dry surface soils.
The third cutting harvest of alfalfa is progressing and complete on many farms. Fields need to be monitored for potato leafhopper, though numbers are declining in many areas. Harvesting dry hay continues to be very difficult everywhere.
Wheat harvest is generally complete. Yields were 10 to
20% below average. Vomitoxin levels were variable and generally above 3ppm. Oats
and barley are being harvested and yields are generally good.
The corn condition overall is
fair to good but growth is behind normal. We will need some good summer time
weather to make this crop.
Soybeans, like corn, are variable in condition and growth stage. Soybean aphid numbers remain low. Dry beans are growing well overall but are behind normal in development.
The word variable describes the weather here. Spotty rainfall has occurred in some places but most growers in the area are becoming concerned with soil moisture due to the high use of water by the crop and limited rainfall. Cool temperatures (highs in the 60s) are concerning growers with late planted crops.
The potato leafhoppers continue to feed on many alfalfa fields. Much of this crop continues to grow well.
The sugar beet crop is looking better than most crops in this area. Cercospera leafspot has been found in most fields but has been slow in development this year. Refer to the website for detailed local data at: www.MichiganBeets.com.
This site will help you in decision making with fungicide application timing. Light colored leaves are showing up in some areas. This seems most prevalent where the soil was saturated for an extended period and may have caused denitrification.
Most early planted corn is looking and has had good weather conditions during pollination. Late planted corn is pollinating at this time, also with good conditions. The taller corn now has blocked the view of problem areas in many fields so we dont have to look at it.
Wheat harvest has wrapped up in this area with less than record-breaking yields but not a bad crop. Vomitoxin levels were variable with the highest levels in southern Saginaw County and lower levels in the eastern and northern Thumb. This appears to be related to the date of flowering of the wheat. MSU wheat variety trial results can be found on-line at: web1.msue.msu.edu/msuwheat/Variety_Results.html for those making planting decisions for this fall.
Growth has been slow but soybeans are looking better with each week. Soybean cyst nematode symptoms are appearing in some areas. Pod development on early planted soybeans looks good.
Many dry bean fields are looking good now. Some root diseases may cause some loss of yield but many fields have outgrown above ground plant symptoms.
Cool weather the past week has slowed growth way down again. Lows in the upper 40s and highs in the 60s. Rain showers have occurred almost daily the past three days. Rain totals of 1 to 2 inches are common. Warmer weather this weekend should get things back on track.
Corn is all tasseled now and looking pretty good. A late fall will be necessary to finish most fields.
Wheat harvest started last week with yields running from 40-70 bu/acre. Test weights are running very good ranging from 57-61. Scab is spotty and not too bad.
Soybeans are starting to pod up nicely, but are fairly short yet. Again, a late fall will be necessary. Aphids have been found but in extremely low densities.
Dry beans are filling in the rows nicely with pod set and filling occurring now.
Second cutting of alfalfa is completed now with yields hitting on the high side of average. Quality has been good with great weather and rainfall this year.
Oats and rye are almost ready for harvest. Potatoes are bulking nicely with no major diseases noted to date.
A fall-like upper air troughing pattern will persist over the Great Lakes region and much of the northeastern US for the next several days, which will lead to the continuation of an unseasonably cool weather pattern across the state into the upcoming weekend. Given unusually cold air in the trough above the surface, scattered showers and isolated thundershowers are possible Thursday and Friday, with less likelihood in the Upper Peninsula. Drier weather is expected by late Friday and should continue into the weekend. Temperatures during the next few days will remain well below normal with highs ranging from the low 60's north to the low or mid 70's south and lows remaining in the upper 40's and low 50's. A warming trend is expected to bring temperatures back to normal levels for Monday through Wednesday. The next chance for significant rainfall will be early next week, most likely in the Monday or Tuesday time frame.
The upper air troughing pattern mentioned above has persisted off and on for much of the current growing season since late May. It is meteorologically very unusual to see a pattern continue this long, even in a stable season (summer, winter). That being said, latest forecast guidance in the medium range time frame suggests an overall continuation of the upper air troughing pattern with northwesterly flow expected across the Great Lakes region during the next one to two weeks. Not surprisingly, the NOAA 6-10 day outlook, covering August 17-21 calls for below normal temperatures and above normal precipitation across Michigan. The 8-14 day outlook for August 19-25 calls for normal temperatures across the state, with above normal precipitation expected in the southern half of the Lower Peninsula and normal precipitation expected in the rest of the state.