May 27, 2008
In the past week I have gotten a couple of reports of tan spot
in winter wheat in the county. It may be worth taking a few minutes to scout
your fields. For more information on Tan Spot refer to
http://www.ag.ndsu.edu/pubs/plantsci/smgrains/pp766w.htm
REMEMBER TO PLANT THE
NON-BT CORN REFUGE REQUIREMENT FOR BT CORN
Janet Knodel
Extension Entomology
janet.knodel@ndsu.edu
As part of your farm’s Insect Resistance Management (IRM) Plan for growing Bt
corn, a non-Bt corn refuge is required by the U.S. Environmental Protection
Agency. Refuge corn acres are hybrids that do not contain the Bt insect trait.
The purpose for planting a corn refuge is to prevent or delay the development of
resistance to Bt traits.
In return, the sustainability of Bt corn should be improved, so Bt corn is
around as a pest management tool against corn insect pests for a long time.
Twenty percent of the corn acreage must be planted as a Bt corn refuge on each
farm where Bt corn is planted. Remember, it’s the law! There are different
configurations and distance requirements for planting the refuge depending on
the traits. (See following references.) A new University of Wisconsin Extension
publication, Insect Resistance Management and Refuge Requirements for Bt Corn -
A3857 (authors Cullen, Proost and Volenberg) answers frequent questions about
IRM and the refuge requirements and configurations. Examples of questions
answered by this bulletin include:
What is insect resistance management (IRM)?
Why is IRM important?
What happens if I don’t plant a refuge?
Who checks for IRM compliance?
What are the refuge requirements for single Bt trait hybrids with Lepidoptera
(“caterpillar”) protection?
What are the refuge requirements for single Bt trait hybrids with corn rootworm
protection?
What are the refuge requirements for stacked Bt trait hybrids with both
Lepidoptera and corn rootworm protection?
How do you select the best Bt insect trait package?
How long will Bt insect traits work?
Where are Bt traits expressed in the corn plant?
What if the Bt corn hybrid is not controlling the targeted insect?
Copies can be ordered from the UW Ext. Learning Store:
http://learningstore.uwex.edu/Insect-Resistance-
Management-and-Refuge-Requirements-for-Bt-Corn- P1269C252.aspx Another
educational website is the National Corn Growers Association website with their
online course on Insect Resistance Management Learning Center:
http://www.ncga.com/biotechnology/insectMgmtPlan/ index.asp DTN and the National Corn Growers Association also hosted a free web
seminar on Bt corn insect resistance and refuges. The session was designed for
corn producers, Extension specialist, county agricultural agents, crop
consultants and other educators. The link to see/hear the webinar is:
http://www.dtnag.com/promo/resistance
COLD TEMPERATURES DELAY
ALFALFA WEEVIL EMERGENCE
Janet Knodel
Extension Entomology
janet.knodel@ndsu.edu
Last year, the southern half of North Dakota had accumulated enough degree day
(DD) units, 300 weevil DDs (base 48 F), to start field scouting for alfalfa
weevil activity by May 22, 2007. In contrast, this year the DD accumulations are
much lower and range between 100- 142 weevil DDs in the southern half. Alfalfa
weevil infestations have been increasing in incidence and severity over the last
several years. However, it is difficult to predict if weevil populations will be
higher again this year. Alfalfa weevils overwinter as adults in plant debris,
woodlots, and ditches. As temperatures warms up adults migrate to alfalfa field
to lay eggs. By using degree days with a base of 48F, the life stages and
development of alfalfa weevil can be predicted (see degree day table).
Go to the insect section in the NDAWN website: http://ndawn.ndsu.nodak.edu/insectdd-form.html and select the degree day base of 48F to determine the accumulated degree days for your location.
As of this morning 5/27/08 degree days for Alfalfa weevil were at 165.
CONTROL OF DANDELION IN NO-TILLAGE BROADLEAF CROPS
Jeff Stachler
NDSU Extension Sugarbeet Weed Scientist
jeff.stachler@ndsu.edu
Several calls have been received about the control of dandelion in no-tillage broadleaf crops. The ideal time to control dandelion with herbicides is in the fall. Control of dandelions with herbicide applications in the spring is possible, but usually variable and with fewer options. In soybeans, the most effective preplant treatment for the control of dandelions is glyphosate plus 2,4-D ester plus a cloransulam-containing herbicide (Authority First, FirstRate, Gangster, or Sonic). The user must carefully weigh the value of the cloransum (FirstRate) component as it is a long residual herbicide and rotation to barley, canola, flax, sugarbeet, and sunflower is 30 months plus a bioassay. Mixtures of glyphosate plus 2,4-D ester can effectively control dandelion, however, control tends to be less consistent and is dependent upon the rate of each product. The minimum rate of glyphosate and 2,4-D ester in this mixture should be 0.75 pounds acid equivalent per acre (lb ae/A) and 0.5 pounds active ingredient per acre (lb ai/A), respectively. Higher rates of glyphosate and 2,4-D ester usually improves the consistency of control, especially rates of 2,4-D ester at 1.0 lb ai/A. Planting of soybeans must be delayed after preplant application of 2,4-D ester. Soybeans can be planted 7 days after application of 2,4-D ester at 0.5 lb ai/A (usually 1 pt/A, although some 2,4-D formulations are more concentrated) and usually 30 days after application of 2,4-D ester at 1.0 lb ai/A. The 2,4-D formulation, E-99, can be applied at 1.0 lb ai/A 15 days prior to planting of soybean. Glyphosate applied alone at 1.5 to 2.25 lb ae/A can control dandelion. This is especially important if soybeans have been planted but have not emerged or growers are not willing to delay planting of soybeans. Preplant application of Valor plus glyphosate plus 2,4-D ester can provide rapid activity on dandelion, but dandelions are more likely to regrow compared to previously mentioned treatments. Ammonium sulfate must always be included with glyphosate applications. Application of effective herbicides prior to or at the time of flowering of dandelions can provide somewhat effective control of seedling dandelions, because viable seeds have not been produced. However, if dandelion seed has been produced prior to preplant herbicide applications, the inclusion of Gangster should provide the most effective residual control of seedling dandelions. Valent claims Valor will control seedling dandelions, however limited research data is available to support their claim. Cloransulam applied alone provides only limited residual control of dandelions. After emergence of glyphosate-resistant soybeans, only two options exist for fair to excellent control of dandelions. Those options include glyphosate applied at 1.5 lb ae/A followed by glyphosate at 0.75 lb ae/A or glyphosate applied at 1.1 to 1.5 lb ae/A plus FirstRate at a minimum of 0.3 ounce per acre. Control of dandelions in other no-tillage broadleaf crops (sunflower, flax, etc.) hinges upon the success of preplant herbicide applications. Since 2,4-D ester is not available for use in preplant applications of these crops, the proper rate of glyphosate is key to successfully controlling dandelion. Apply glyphosate at 1.5 to 2.25 lb ae/A prior to planting of other broadleaf crops. Glyphosate may be applied after planting, but it must be applied prior to crop emergence and control of dandelion may be reduced due to plants being damaged during the planting process
EARLY CROP DEVELOPMENT IS SLOWED BY COOL WEATHER IN 2008
Joel Ransom
Extension Agronomist for Cereal Crops
joel.ransom@ndsu.edu
This spring, conditions have generally
been favorable for planting crops except where extremely dry conditions
currently prevail. Drought is becoming a concern in a growing area of the state
. Additionally, cool temperatures are slowing development of emerged crops
and/or delaying emergence. So how do temperatures this spring compare with
previous seasons? Assuming a planting date of April 15th, wheat growing degree
days accumulations (GDDs) this season are 210 to 340 GDDs behind 2007 and 25 to
160 GDDs behind the long-term average, depending on the location in the state
(see following table). Typically, we can expect to accumulate 20 to 25 wheat
GDDs during this time of the year, so in terms of calendar days the small grain
crops are running about seven to ten days behind last year and one to six days
behind the long term average. Though the cooler weather we are experiencing this
season slows development (probably at least one leaf stage behind the long-term
average), it is also means that we are losing less water to evapo-transpiration
which is good news given the dry conditions we are experiencing. Furthermore,
yield potential development in small grains is favored by cool temperatures
during vegetative growth, particularly if other factors are not limiting. Corn
GDD accumulations this season (assuming a 1 May planting date) also
significantly lag behind those for the same period in 2007 and for the long-term
average. Corn GDDs are calculated using a 50 degree base (compared to 32 degrees
for small grains), so they accumulate more slowly than wheat GDDs. Since corn
GDDs typically accumulate during mid-May at the rate of about 9 to 10 per day,
corn development is running about a week behind last year in terms of calendar
days but only two or three days behind the long-term average. It usually takes
about 125 corn GDDs before corn emerges, so we should start to see some of the
early planted corn beginning to emerge soon. Corn emergence is favored by
relatively warmer temperatures and the colder temperature we have experience is
not only delaying emergence, but it will likely decrease the uniformity in the
timing of corn emergence. Uniformity of emergence in corn is a basic component
of a high yielding crop.