Ramsey County

TIME TO SCOUT FOR SOYBEAN APHIDS

      Soybean aphid populations have been low and below economic threshold levels so far (see NDSU Extension IPM Survey maps). However, aphid populations will continue to increase and soybean fields should be scouted. The current recommended threshold for late vegetative through R5 stages is 250 aphids per plant (field average) on 80% of the plants and increasing aphid populations. Scout 20-30 plants per field and cover at least 80% of the field. To determine if populations are actively increasing, check field over several visits. This threshold provides a 7-day lead time between scouting and insecticide treatment. Research from numerous trials in the upper Midwest, including North Dakota, indicates there is no yield loss at 250 aphids per plant. With higher commodity values, the threshold remains the same. However, response interval time will decrease to only 5 days. It is important to remember that there still is no yield loss at this threshold. Spraying early (below 250 aphids per plants or tank-mixing insecticide with glyphosate applications) is not recommended in North Dakota. Early insecticide or below threshold treatments simply remove any natural enemies in the field, resulting in a field that is open to re-infestation by immigrating aphids. This could lead to the necessity of re-spraying later in the season (source: Ian MacRae, UMN)

 SEQ CHAPTER \h \r 1                Two sources of weekly soybean aphid reports from multiple locations in North Dakota are available:

- the NDSU IPM website

http://www.ag.ndsu.nodak.edu/aginfo/ndipm/index.htm

- the Pest Information Platform for Extension and Education (PIPE).

http://www.sbrusa.net/

In PIPE, sentinel plots are monitored throughout the U.S. for soybean rust and soybean aphid. State commentaries are also provided.

 DEALING WITH LATE WEED ESCAPES IN CORN

        While herbicide advertising often talks about full-season weed control, for most weeds we only need herbicides to control weeds until the canopy has developed sufficiently to suppress any late-emerging flushes. Weed survival rates can be greater at earlier emergence dates but biomass and seed production of weeds emerging at mid-season can be suppressed more than 90% compared to weeds emerging with the crop.

        Many fields are likely to have greater problems with late-emerging weeds than normal. There are two primary causes for these infestations: 1) dry and cold conditions in May will suppress activation of soil-applied and excess rain in June will reduce the length of control provided by residual herbicides, and 2) poor canopy development due to cool temperatures, saturated soils and reduced stands will provide a favorable environment for weed growth.

        Fields should be carefully evaluated prior to spraying weeds in large crops. Weeds that emerge significantly later than the crop are at a competitive disadvantage with the crop due to the crop’s head start. While these weeds may survive and produce seed, their impact on the yield should be minimal unless they are thick enough to create a sod. For example, if you have 3 to 4 inch weeds in 30 inch corn it probably doesn’t warrant an additional weed control trip. Spraying late season crop may cause more damage to the crop than would be gained by eliminating late-emerging weeds. Most importantly, the majority of herbicide labels prohibit application to larger crop due to problems with crop tolerance or efficacy. Glyphosate has restrictions in RR crops also.

        Everyone expects weed-free field at harvest, sometimes it is best simply to live with the hand that’s been dealt. While late-emerging weeds in most fields are unlikely to impact yield, the seed produced by these plants will increase weed densities the following year. This increase in weed populations should be taken into account when developing weed management plans for 2009.

FINAL STAGES FOR FUNGICIDE APPLICATION TO WHEAT AND BARLEY

        The wheat and barley crops advanced considerably over the warm 4^th of July weekend, and many wheat crops flowered over that weekend.  For some producers, fungicide decisions have already been made, and attention will be turned to the later planted fields.

        For those later planted fields, applications of fungicides to control head scab at flowering stage also provide excellent control of leaf rust.  And the products available for head scab control also give excellent control of leaf rust and leaf spot diseases. 

        Example of leaf rust control:   In 2003 at the Carrington Research Extension Center, Blaine Schatz, superintendent of the Center, applied Folicur fungicide (4 fl oz/acre) to four varieties of spring wheat, at two growth stages:  Feekes 10 (boot stage), and early flowering (Feekes 10.51).

                On varieties 2375 (S), Reeder (MS), and Alsen (MR), the application at flowering gave much better control of leaf rust than applications at boot (from 10 to 45% better control).  On the most rust resistant cultivar of the four tested (Briggs), the flag leaf and flowering application gave equal control of leaf rust.  In ND on spring wheats, the development of leaf rust and Septoria fungal leaf spot generally gets going later in the season than in states to our south.  Application at fungicides at flowering often provides the 21 days of protection needed to get the crop through grain fill.

 USING GLYPHOSATE AND OTHER HERBICIDES PRE-HARVEST IN SMALL-GRAINS

        With winter wheat in the middle of grain-filling and other small grains not that far behind, it is now time to think about harvesting.  If green weeds in the crop will hinder the harvesting process there are several herbicides labeled for pre-harvest weed control (refer to the 2008 Weed Control Guide and the labels of approved products for additional details).  Weed control with pre-harvest herbicides, however, is generally disappointing as weeds at this time are tall, nearing maturity and slow growing.  Furthermore, green weeds can take a week or more to dry down even with an effective treatment. 

        Glyphosate, in addition to controlling weeds, is labeled for use in aiding the dry down of the crop itself (as opposed to controlling and drying down weeds in the crop).  Glyphosate is a systemic herbicide and takes from 7 to 10 days to effectively kill the growing parts of the crop, consequently an increased rate in dry down is not immediately visible.  Traditionally, fields that had excessive green material were swathed.  Swathing enables faster dry down than pre-harvest glyphosate if significant levels of green material are present in the crop.  A standing crop that has been treated with glyphosate, however, will dry faster than a swathed field after a rain. 

When using glyphosate pre-harvest observe the following guidelines:

1.  Apply glyphosate only after the crop has reached physiological maturity. For most varieties this occurs at a grain moisture content of about 30%.  At this moisture content the grain is in the hard dough stage; if you run your thumb nail across the kernel, the indentation will remain.  Applying glyphosate before physiological maturity can reduce yield, test weight and seed germination. 

2.  Because germination can be affected when applied too early, glyphosate should not be used in fields that will be used for seed or on barley intended for malt. 

3.  Pre-harvest applications of glyphosate must be made at least 7 days before harvest. 

As with all agricultural chemicals, read and follow the label when using herbicides pre-harvest in small grains.

BARLEY THRIPS HIGH IN CENTRAL NORTH DAKOTA

        High numbers of barley thrips (>10 thrips per stem) have been reported in the central regions of North Dakota near Harvey and McClusky. Sampling for thrips should begin when the flag leaf is first visible and continue until the head is completely emerged from the boot. Most thrips can be found under the top two leaf sheaths. The dark brown to black thrips can be found by unrolling the leaf sheaths away from the stem. Direct feeding on reproductive tissues also may result in reduced seed weight. With the high market value of barley, the economic threshold is lower in 2008 than in previous years. Using a cost of control of $8.00 per acre and value per bushel of $8.00, the current threshold is only 2.5 thrips per stem. Insecticide treatments are recommended before heading is complete. Methyl parathion (8 - 12 fl oz per acre) is the only insecticide registered for control of barley thrips in North Dakota. The pre-harvest interval is 15 days. Do not enter treated field within 48 hours after methyl parathion application.

NDSU Extension Service, North Dakota State University of Agriculture and  Applied Science, and U.S. Department of Agriculture cooperating.  Duane Hauck, Director, Fargo, North Dakota.  Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914.  We offer our programs and facilities to all persons regardless of race, color, national origin, religion, sex, handicap, age.  Vietnam era veterans status, or sexual orientation; and are an equal opportunity employer.

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524 4th Ave NE #5, 2nd Floor Ramsey County Courthouse
Devils Lake  ND  58301
701-662-7027
email - ramsey@ndsuext.nodak.edu

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