CMEG Crop Management Extension Group

Field Crop News

Website Address: http://fcn.agronomy.psu.edu/

June 10, 2008    Vol. 08:14

IN THIS ISSUE:

Weather Outlook — Paul Knight, Pennsylvania State Climatologist

The hot spell will end on Tuesday night (with a bang in most of eastern Pennsylvania) and be followed by warm, but much less humid air on Wednesday. Humid air will begin to return to western parts of the state on Thursday and across the region on Friday. A few thunderstorms are likely in the western third of the Commonwealth later Friday. A cold front crossing the region on Saturday will produce some showers and thunderstorms. Most sections will receive between 0.25–0.50 inches with parts of central and southern Pennsylvania receiving nearly an inch of rain. The clouds and showers may persist in southeast counties during Sunday morning and a shower is likely in the northwest by sundown, but most sections will stay dry and turn less humid and a bit cooler.

Several surges of cooler, drier air are likely next week, each triggering scattered showers and a few thunderstorms. Rainfall in most areas will average below normal (which is about an inch a week) and temperatures will return to or slightly below seasonal levels during the latter half of next week. There are no clear indications of another heat wave during June and in fact, odds favor a cooler and drier than normal weather pattern for the second half of the month. This will aggravate the dry conditions in the northern tier, which is already only at 60-80% of normal rainfall for the spring. The southern counties will find some welcome respite from the frequent showers. It still seems likely that July will be slightly cooler and wetter than normal.

Check out the predicted Growing Degree Days (base 55) for Pennsylvania for the next two weeks at: http://climate.met.psu.edu/data/regional_gdd.php

Timely Post Control of Weeds Helps Produce High Yields in Soybean — Bill Curran, PSU Weed Specialist

With soybean grain prices hovering around $14/bushel, the need for timely weed control to maximize crop yield has never been higher. A rule to getting good weed control and saving crop yield is starting clean at planting. This can either mean preplant tillage or a burndown herbicide. Planting soybeans into fields with actively growing weeds or an uncontrolled cover crop is risky at best. Fortunately, there has been some research examining the impact of single pass programs in no—till Roundup Ready soybeans on soybean yield and profitability. In full-season soybeans, we generally recommend spraying glyphosate at the V3 to V4 soybean stage (about 4 to 6 weeks after planting) because common weeds that emerge and grow up to this time generally won’t reduce yield. But this assumes weeds were controlled with a burndown treatment or with preplant tillage. Weeds that have a week, or two, or more head start on soybeans will need to be controlled earlier.

In a study conducted at the University of Guelph in southern Ontario, researchers compared different timings of glyphosate in no—till Roundup Ready soybeans in five experiments (Swanton et al. 2000. An economic assessment of weed control strategies in no—till glyphosate—resistant soybean (Glycine max). Weed Technol. 14:755–763). They used a standard rate of a glyphosate product and looked at different application timings. Soybean yields with a single preplant burndown treatment were lower (22 bushel/acre yield) because of weeds that emerged after planting. Soybean yields were higher with a single application in season at either the unifoliate or 1 to 3 trifoliate stages (about 35 bushel/acre). However, competition from weeds emerging before soybean planting reduced the yields with the 1 to 3 trifoliate stage timing. Soybean yields were the greatest when either a preplant burndown treatment was followed with glyphosate at the 1 to 3 trifoliate stage or an early post timing (unifoliate) application was followed with a second treatment (42 bushel/acre). Gross returns (crop value minus costs of treatment) also showed that it was profitable to make the burndown treatment. In these experiments, the burndown treatment added an extra $26/acre return over the single application at the 1 to 3 trifoliate stage (and that was back when soybeans were under $7/bushel). Certainly the cost of the herbicide and application as well as grain prices will impact profitability.

Maybe more importantly, it appeared to be less risky if a burndown treatment was used in combination with glyphosate in season. The preplant burndown treatment followed by glyphosate in crop had the lowest variation. In other words, this treatment was quite consistent (or had low risk) in producing high yields and high gross returns. That’s a good combination to have. I believe that the bottom line is that without a two—pass program in no—till soybeans, a 10% yield reduction is not unusual and it could be much more than that. In today’s dollars, 10% of a 50 bu/acre soybean crop is worth about $70. Another factor in favor of timely weed control includes a greater potential to select for resistant or tolerant species with single or later applications to larger weeds. The presence of glyphosate resistant horseweed or tolerant lambsquarters or other weeds should be considered in the mix.

Johnsongrass and Pokeweed Management — Bill Curran, PSU Weed Specialist

It’s again the time of year that pokeweed starts to become very visible in soybean and corn fields around the state. Here are a few reminders about this prevalent problematic weed.

Pokeweed is a simple perennial emerging from the same taproot each spring and spreads within a field or between fields by seed production. It’s important to target the plants prior to successful reproduction since the seeds can persist up to 40 years in the soil and can be dispersed by birds (robins, starlings, others) potentially spreading new infestations wherever these birds fly and/or roost. Control of this weed is fairly difficult with single postemergence herbicide treatments and multiple tactics are often necessary. Regardless of the crop or herbicide treatment, make sure the spray boom height is up above the pokeweed and use spray tips and a carrier volume (i.e. >10 GPA) to maximize coverage.

In corn, effective treatments include dicamba (Banvel, Clarity, Sterling) generally mixed with a sulfonylurea (Northstar, Yukon, Celebrity Plus, etc.), or Callisto or Status. Apply when pokeweed plants are less than 12 inches tall if possible. In Roundup Ready corn, use glyphosate (0.75 lb ae/A) when plants are at least 8 inches tall and make a second application if necessary.

In soybean, glyphosate is fairly effective and control can be increased by tank mixing with FirstRate, Classic, or Synchrony STS. Again, other factors (application timing, boom height, etc.) may also play a role in successful control. In Roundup Ready soybeans use at least 0.75 lb ae/A applied when pokeweed plants are at least 8 inches tall. Make a second application if necessary. In soybeans that are not Roundup Ready, use Synchrony STS (0.5 oz/A) or Classic + Harmony GT tank mixes.

Johnsongrass is a perennial weed that emerges from seed and overwintering rhizomes. Because johnsongrass emerges over an extended period of time from both seeds and rhizomes, it can be difficult to successfully control with a single post application. Systemic herbicides are most effective on rhizome control when applied at the late boot to early heading stage of growth or in early fall. As with most perennials, translocation of the systemic herbicide improves as the plant turns reproductive or as it prepares to overwinter. However, application this late to both corn and soybean is difficult if not impossible due to the size of the crop, increased problems with spray coverage (in corn), and the risk for weed competition due to lateness of the application. Therefore, as a compromise, most applications to corn or soybean should occur when the johnsongrass is between 12 and 24 inches tall. In Roundup Ready corn and soybean, apply 0.75 to 1.5 lb ae/acre (1 to 2 qt of a 3 lb ae/gallon product) in 3 to 10 gallons of water. Increase the rate to 1.5 lb ae/acre when applying above 10 gallons per acre. Other effective herbicides for corn include the sulfonylurea (SU) herbicides (Accent, Beacon, Option, Steadfast, Stout, etc.). Some local applicators and consultants have suggested that tank-mixing the SU’s with glyphosate may provide improved control of johnsongrass. At a minimum, the SU’s that have some soil residual activity could help control seedling johnsongrass for a short period following application.

In addition to glyphosate in Roundup Ready soybean, the ACCase inhibitor herbicides (Assure, Targa, Select, Fusilade, Fusion, etc.) also have activity on johnsongrass and can be used in both RR and non—Roundup Ready soybeans. Application timing is similar to the previously mentioned products. Finally, a word of caution, johnsongrass biotypes resistant to glyphosate (Argentina and Arkansas), the ALS inhibitor herbicides (Texas and Indiana), and the ACCase inhibitor herbicides (Mississippi, Kentucky, Tennessee, Virginia, Louisiana) have been reported after “too frequent” repeated use of these herbicide modes of action.

Escaped Weeds in Corn — Bill Curran, PSU Weed Specialist

Because of the wet May we experienced in much of the state, some preemergence herbicide programs may be challenged to last long enough in corn. This is especially true for April planted corn that is now 6 or more weeks into the season and where annual grasses are a problem. A number of products are available for annual grass control in corn postemergence. The table below provides a quick summary. Keep in mind that the crabgrass species are particularly difficult to control with conventional POST corn herbicides. Read the fine print on the labels for specific species and adjuvant recommendations and follow all label directions.

Table 1.  Selected postemergence annual grass herbicides for corn.
Herbicide Crabgrass spp. Foxtail spp.*
  • *May be less effective for yellow foxtail and fall panicum.
  • **Includes Celebrity and Celebrity Plus
  • ***Less effective on smooth crabgrass and atrazine will improve performance.
  • ****Not smooth crabgrass.
  • *****Labeled up to 6 inch giant foxtail.
  • ******Suppression only; not smooth crabgrass.
Accent** - 2-4 inches
Callisto 2 inches or less -
Glyphosate (1X) 4-6 inches 4-6 inches
Impact*** 3 inches or less 3-4
Laudis*** 2 - 3 inches or less 3 inches or less
Liberty (34 fl. oz) 4 inches or less 4 inches or less
Lightning 1-3 inches 1-6 inches
Option 2 inches or less**** 3 inches or less*****
Resolve Q 0.5 inches or less**** 1-2 inches
Steadfast 1 inch or less****** 4 inches or less
Stout - 4 inches or less

Burcucumber Control in Corn — H. Grant Troop, No—Till Agronomist, Capital Region

It’s that time of year to get burcucumber control done. Left uncontrolled, field harvest can be difficult or impossible if the infestation is severe. No-till can aid in burcucumber control because you can keep any new seed that may be produced on the soil surface. With tillage the seed is mixed into the tillage layer. When seed is blended into tillage layer the “seed bank” becomes very difficult to manage. The large burcucumber seeds can germinate and emerge from deep in the soil. Deeper seeds often emerge later in the season, so several flushes of burcucumber often occur in tilled fields. In no-till fields with the seeds on surface, the seeds germinate and emerge close together instead of over several flushes. This will make herbicide applications more effective as almost all of the burcucumber that will emerge during the season will emerge close to the same time.

Some of the better herbicide treatments to control burcucumber are:

Atrazine may be added for corn 4–12” tall.

See herbicide labels for all restrictions and tank mixing instructions.

Bean Leaf Beetle in Fields of Young Soybeans — John Tooker, PSU Entomology Specialist

Reports indicate that some of the early-planted soybean fields around Pennsylvania have sizeable populations of bean leaf beetle (BLB). In “normal” years, BLB does not usually cause extensive damage to soybean seedlings and any damage that is caused can be tolerated by the young plants. In the current year, however, when there has been so much variation in soybean planting, growers need to be aware that populations of BLB may be gathering in a few “early emerging” fields, the risk of damage is higher, and treatments may be necessary.

Adult BLB coloration is variable, but can range from yellowish-brown to green to red and they usually have four black spots on their wing covers. They always have a black triangle just behind their thorax. They overwinter in leaf litter and become active in April when they tend to move into alfalfa or other legumes to feed and begin mating. When soybean emerges, adults move into these fields, feeding on young seedlings (V1– or V2–stage) and laying eggs. The larvae feed on soybean roots and develop into the second generation of adults, which tend to be economically important, causing damage by feeding on soybean pods as they are filling. This feeding can increase the vulnerability of seeds to moisture and pathogens. These adults can also clip off entire pods. BLB is also a concern because it transmits some viruses including bean pod mottle virus (BPMV), which can decrease seedling vigor and reduce grain quality and yield.

Adults feeding on young soybean leaves make circular holes between the major veins and these holes should appear quite different than the jagged holes caused by grasshoppers or caterpillars. Seed treatments can be used to combat such early season BLB damage, but if populations are large and stand establishment appears doubtful, a rescue treatment may be warranted. Rescue treatments may be even more justified if symptoms of BPMV were prevalent in nearby soybean fields last year. One of the most obvious symptoms of BPMV is stems that stay green until harvest. The best way to control the virus is to control the beetle that vectors it (BLB). One of the published thresholds for BLB says to treat young soybeans if 20% of plants are defoliated, beetles cause gaps in rows of one foot or more, or beetles defoliated at least one seedling per foot of row.

Wet May — Nitrogen Loss — PSNT — Douglas Beegle

I understand that at least in some parts of the state this May was the second wettest May on record! So as farmers get into sidedressing time they are wondering if the N they applied early is still there. All of that rainy weather certainly set us up for major losses by leaching and/or denitrification which could result in very significant losses of N from the soil. Unfortunately, because of the dynamic nature of N in the soil and the very site specific nature of N behavior, it is impossible to make a blanket statement about N status across the state.

Fortunately, we do have the Pre-sidedress Soil Nitrate Test (PSNT) to fall back on in this type of situation. This test can be used to give us an indication of the N availability status of our corn fields just before the peak N demand by the corn crop. For optimum N nutrition for corn, the soil nitrate-N level in the PSNT should be above 21 ppm when the corn is 12 inches tall or around leaf stage 6. If it is above this level, there is adequate N in the soil to meet the needs of the crop. However, if it is below this critical level then sidedressing additional N is recommended, even if adequate N was applied earlier.

Agronomy Fact # 17, “Pre-sidedress Soil Nitrate Test for Corn“ provides all of the details on the PSNT including the sampling procedures and how to make recommendations based on the results. A couple of important points to keep in mind when using the PSNT:

(Note: Because of the narrow window for sidedressing, most soil testing labs including the Penn State Ag Analytical Services Lab will provide 1 day turn-around once they receive the samples for the PSNT)

Sampling several fields that are representative of different N management strategies on your farm this spring can be very helpful in making a decision about whether additional sidedress N is needed. N is too expensive to just put some extra on just in case. Sidedress N recommendations based on the PSNT are, on average, twice as accurate as recommendations made without the PSNT.

Agronomy Facts #17 and soil sample kits for the PSNT are available from your local Penn State Cooperative Extension office.

If less than 15 lb of fertilizer N was applied around planting time, the chlorophyll meter can be used to test the N status of the crop. This is especially helpful if you are counting on manure to meet most or all of the crop N needs. A new factsheet on using the chlorophyll meter is available on the Crop Management Extension Group (CMEG) website. (http://cmeg.psu.edu/). There is also a video demonstrating how to use the chlorophyll meter at that same website.

Chlorophyll Meter N Test Resources — Douglas Beegle

The chlorophyll meter is a tool that can be used in some situations just before sidedressing to significantly improve N sidedress recommendations. The recommended procedures for using the chlorophyll meter must be strictly followed if the results and recommendations are to be valid. Some key instructions include:

All of the details for using this test are available in a new revised factsheet on using the chlorophyll meter, Agronomy Facts #53 (Revised) The Early—season Chlorophyll Meter Test for Corn, which is available on the Crop Management Extension Group (CMEG) website. (http://cmeg.psu.edu/). This factsheet updates the procedure for testing fields with a high N reference area and includes the new two—step procedure for fields with recent manure or a forage legume without a high N reference area. There is also a video demonstrating how to use the chlorophyll meter at that same website.

Corn Club Deadline Approaching — Del Voight and Dr. Greg Roth

Another corn crop is underway, with many stands are looking good and some potential for great yields again this year. Its time now to consider entering the PA Five Acre Corn Club, a joint effort between Penn State Cooperative Extension and the Pennsylvania Corn Growers Association. Each year approximately 100 corn producers across the state participate in this program to share knowledge and experiences in growing high yields of corn. Over the years Five Acre Corn Club members have documented considerable changes in corn production including narrower rows, higher plant populations and use of transgenic hybrids. These have contributed to consistent and significant improvements in yield.

To participate in the Corn Club program, complete the entry form by July 1, 2008 and return it to us at: 5–Acre Corn Club, Department of Crop and Soil Sciences, 116 ASI Bldg., University Park, PA 16802. Registration fee is $20. Awards are made for highest yields in both tilled and a no-till/strip till class and for three year participants in each class. Each participant in the program receives a summary of all of the entered fields, including hybrids used, inputs and yield data from each. Rules and entry forms are available online at http://cornandsoybeans.psu.edu/corncl.html.

Consider enrolling in the club this year. It’s a great way to share information with other top growers in the state. We will have an awards program this year at the Professional Crop Producers Conference on February 17th and 18th, 2009.

Upcoming Events — use the link to Calendar of Events (below) for contact information

June 24 – No—till Field Crop Walk 10 am–12 p.m. at Richard, Jr. and Nelson Troutman, Richland, PA To access program highlights and directions, go to: http://berks.extension.psu.edu/Agriculture/crop_walk6_08.html 610-378-1327
June 26 – Leguminous Cover Crop Twilight Meeting 7–8 pm, PSU Agronomy Farm Contact Beth Futrick at 814–355–6817 for more information.
July 1 – Weed Twilight Tour—Landisville
July 2 – No—tilling for Success Field Day—Landisville
July 10 – Rock Springs Agronomy Weed Tour
July 22 – and 23 Agronomic Field Diagnostic Clinics — Rock Springs Agronomy Farm

Contributors: Susan Alexander (Jefferson), Andrew Frankenfield (Montgomery), Kevin Fry (Armstrong), Jeff Graybill (Lancaster), Mena Hautau (Berks), Mark Madden (Sullivan), Dana Rizzo (West Moreland), Jonathon Rotz (Cumberland), John Rowehl (York), Grant Troop (Lebanon), Craig Williams (Tioga), University Park: Doug Beegle, Bill Curran, Sjoerd Duiker, Greg Roth, Ron Hoover, John Tooker, Del Voight

Editor: Joel Hunter (Crawford)

Upcoming Events

Real time pest and heat unit activity: http://psu.zedxinc.com/cgi-bin/site.cgi?location=2&user=psu#

Calendar of Events: http://www.events.psu.edu/cgi-bin/cal/webevent.cgi?cmd=opencal&cal=cal209&

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