CMEG Crop Management Extension Group

Field Crop News

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

April 28, 2009    Vol. 09:08

IN THIS ISSUE:

Weather Outlook — Paul Knight, Pennsylvania State Climatologist

The early season heat wave will come to an end as a cold front slowly pushes to the southeast. The cooler, drier air will take hold in the northern half of Pennsylvania on Wednesday with readings closer to seasonal levels (though still a bit above average). In the southern counties, clouds and patches of morning showers will provide a marked change with maximum readings at least 20 degrees lower than recent days. A return flow of warm, humid air during Thursday will be accompanied by widespread clouds and patchy showers (mainly in the central and west) and some drizzle. A return of very warm and noticeably more humid air is expected on Friday along with intervals of sunshine and balmy, gusty winds. A more significant cold front will cross the state Friday night and Saturday morning with some rain for most (>.10") and a few heavy thunderstorms in the northwest third of the Commonwealth. Much of Saturday will be bright and pleasantly cool. A series of rapidly moving disturbances will then effect the state from Sunday into next Wednesday with periods of clouds and showers separated by a dry day, but the timing is difficult to determine.

The risk of a cool snap just after mid-month in May is still likely. Rainfall which has been much closer to average during April is expected to remain near normal until mid-May and then become less frequent. Odds favor above average temperatures for the June through August period with a notable wet period in the latter half of July or August. The hurricane season should have a late start with notably fewer storms than recent years.

Are Preemergent Herbicides in Soybeans Needed? — Bill Curran, Penn State Weed Specialist

This is an article I should have written a few weeks back, but better late than never. We have seen a significant influx of new soil applied soybean herbicide products in the last few years with relatively little adoption in Pennsylvania. Keep in mind that thus far these are not NEW herbicide modes of action, but rather new mixtures of active ingredients found in other products. In general, when starting clean with a burndown or tillage, glyphosate applied once or maybe twice postemergence in soybean has been sufficient for most Pennsylvania soybean growers. Unlike some areas of the US, most PA farmers that grow soybeans have fortunately had fairly diverse rotations that include corn, small grains, Roundup Ready and conventional crops, maybe alfalfa and probably some tillage helping to diversify the weed management program. However, some northeastern farmers certainly do and would benefit from residual herbicide programs in soybean, so where do they make the most sense?

To start the list, long-term continuous no-till where reliance on herbicides is greater than where tillage is used is a prime candidate. Secondly, this becomes even more important in continuous Roundup Ready soybeans and corn which often depend heavily on glyphosate for weed control. Third, wide-row soybeans can benefit from a residual herbicide in combination with a single well-timed post application. This helps suppress the weeds early in the summer and the post application cleans things up. Fourth, if you battle problem perennials like Canada thistle, pokeweed, hemp dogbane, or others, glyphosate applied to the perennial weeds at the bud to bloom stage will have the biggest bang for the buck. Control the annual weeds with the soil-applied residual program to allow for the slightly later more optimum post application targeting the perennials. Fifth, if you routinely have problems controlling annual weeds because of high severity, prolonged germination pattern, or other reasons with a single in-crop application, then a soil applied program can make sense. Sixth, if you are unfortunate enough to be dealing with glyphosate resistant or tolerant weeds like horseweed (marestail), ragweed, or lambsquarters, then a soil residual program will help this effort. This can also be true for ALS-resistant weeds like shattercane, pigweed, and foxtail. Finally, a soil residual program can definitely provide some insurance and lessen the workload when weather and tight spray schedules are frequently a problem in making a well timed application. So, as you prepare to plant that soybean crop over the next few weeks, consider where residual programs make the most sense and choose the program for good reason(s). Here is a summary list:

Including Insecticides as Part of a Preemergent Burndown Treatment — John Tooker, Penn State Entomology Specialist

We have had a couple questions from the western part of Pennsylvania on the advantages of adding a broad-spectrum insecticide to the tank when conducting spring burn down treatments of winter annuals and/or cover crops. This appears to be a fairly popular practice with folks hoping that the insecticide will kill any potential pests that are present in fields, and we have heard mention of cutworms, wireworms, and grubs as potential victims.

This tactic would definitely be considered an ‘insurance’ spray, many of which have not been closely evaluated and their economic value might be minimal. Economically sound integrated pest management (IPM) practices are based on applying control treatments only when necessary. This means scouting for insect pest species and their damage and applying a control when damage thresholds are exceeded. Insurance sprays in the absence pest pressure, and this spring insurance spray in particular, may be dubious for a few reasons. First, the insecticide (and its cost) could be wasted because a) pests are not present is significant numbers, b) potential pests like wireworms or grubs, are not accessible by the insecticide because they spend the great majority of time in soil, and c) the residual is not long enough to provide any significant control. Second, indiscriminant use of insecticides in absence of pest pressure can hasten development of insecticide resistance. Third, the tank-mixed insecticide might be redundant if insecticide-treated seeds will be planted—remember each insect can be killed only once! Fourth, the broad-spectrum insecticides that are typically used will kill insect predators and parasitoids potentially leading to outbreaks of secondary pests, which natural enemies often control.

So while mixing in an insecticide might be a usual practice, perhaps it is time to consider if any return is actually coming from that investment. If you want to test the efficacy of the tactic yourself, perhaps consider leaving a test strip where you do not apply the insecticide and see if you see any differences as the crop develops.

Killing Rye Stubble After Rye Silage Harvest — Bill Curran and Dwight Lingenfelter, Penn State Weed Science

Producers wishing to no-till corn into rye harvested for silage are sometimes concerned with rye regrowth. How long must you delay a burndown herbicide application after chopping rye to effectively prevent regrowth? A few years ago, we conducted a small experiment at our Rock Springs Agronomy Farm examining several herbicide treatments. The rye was chopped to about a 2-inch stubble height on May 5, while in the early head stage of development. Glyphosate was applied at 0.75 lb ae/acre (32 fl oz glyphosate 4L product) and Gramoxone was applied at 0.5 lb ai/acre (equivalent to 2 pt Gramoxone Inteon) to the rye stubble at three different times following harvest. Glyphosate or Gramoxone were also applied with 1.1 lb/acre atrazine 90DF. The herbicides were applied the same day (0 day), 3 days, and 7 days following rye harvest. Rye regrowth was visually evaluated in each herbicide treatment/timing and also harvested approximately 6 weeks after the burndown herbicides were applied. No crop was planted in this experiment.

No rainfall was received until about 15 days after harvest which likely impacted our results. Glyphosate alone and with atrazine effectively killed the rye regardless of timing. Apparently, an adequate amount of green leaf tissue was present at the base of the plants to absorb the systemic herbicide. The addition of atrazine did not improve or reduce control with glyphosate. For the most part, Gramoxone was less effective for control of rye than glyphosate. Gramoxone applied the day of planting and 7 days after planting was sometimes better than the 3 day after harvest treatment, probably because of subsequent plant stress that developed following the mowing. Adding atrazine to Gramoxone either improved or did not affect rye control. With more timely rainfall following the herbicide applications, the addition of atrazine should have greatly improved control with Gramoxone. Also, a higher rate of Gramoxone Inteon (3 to 4 pt/acre) should improve performance. On a side-note: atrazine (alone or in typical premix residual products) will usually not be adequate to control rye in the spring. The key to controlling rye is to include either glyphosate or Gramoxone in the spray mixture.

This study demonstrates the superior performance of a systemic herbicide (glyphosate) compared to a contact herbicide (Gramoxone) in this type of application. Delaying application following harvest may not be a concern if cutting height and the presence of healthy basal leaves at application time ensures adequate control with glyphosate.

Timothy Mite Alert — Del Voight, Interim Grain Crop Specialist

Reports from across the state and first hand observations in many timothy stands in Armstrong County indicate that Timothy mite levels are extremely high and damage is evident this spring. You will recall that the timothy mite, actually the Cereal Rust Mite, develops from December until June. Our weather this past January to present has been ideal for rapid build up of these mites. Typically signs of mite infestation are the appearance of droughty or curled leaves. This is most commonly found in late April or early May after mite populations have reached high levels. This year those signs can be seen already.

Timothy mites

Growers are counciled to visit their timothy stands now to look for signs of mites. You will not be able to see the mites without the use of a 20 power hand lens. Look at the base of the tillers or in the sheltered parts of the plants on cooler days. On warmer days the mites will travel out the leaf surfaces and will be more easy to find. Look for curling of the leaves as another sure sign of infestations.

Typical control materials, 3 pints of Sevin, are recommended to be applied around the 25th of April. This timing provides high levels of control and will minimize the build up of any mite populations that survive treatments and provide a 30 day harvest delay interval. This year with extremely high levels of mites at this time, most growers will want to apply controls soon. Be sure to apply with sufficient carrier levels, 20 to 25 gallons/acre to ensure coverage of the timothy leaves. Recall that Sevin is a short residual, contact type insecticide that needs to reach the mites for effective controls. Failures occur when the timothy leaves are wrapped so tight that the pesticide is unable to come in contact with the mites.

Horseweed ID and Burndown Considerations — Bill Curran and Dwight Lingenfelter, Penn State Weed Science

Images of horseweed and fleabane

Horseweed and various fleabane species can be difficult to identify when they are in the seedling or early immature stages. Not only have we noticed this while walking fields but others have called inquiring about the appropriate identification of these various species.

Both horseweed and fleabane are part of the aster family and once mature have numerous, small daisy-like flowers and other features to distinguish them. However, in the rosette and early bolting stages, those differences are not so apparent. Despite the fact that there are numerous images of weeds in books and on the web, there are very few that show the differences between the immature fleabane species common to our area namely daisy fleabane (Erigeron annuus), rough fleabane (E. strigosus), and common or Philadelphia fleabane (E. philadelphicus). (For some images of horseweed and fleabane see the following Web sites: http://weeds.cropsci.uiuc.edu/extension/factsheets/Horseweed.pdf and http://www.wssa.net/Weeds/ID/PhotoGallery.htm

As weed scientists, we generally lump these annual fleabanes together and provide a herbicide control rating as a group. In most cases, this is adequate when they are small. However, as they mature (i.e., 4 to 6 inches or taller), higher herbicide rates are generally necessary to control them. Glyphosate product labels have a table that lists some fleabane species along with height and rate information. Other labels such as, 2,4-D and Clarity, are not as specific. But if the confusion occurs between horseweed and fleabane how will this impact burndown herbicide selection? With the concern for glyphosate resistant horseweed, the need for tank mixtures becomes more critical. However, annual fleabanes can also be difficult to control and may also require the use of tank mixtures to improve control. Keep in mind that these herbicides will provide better control when the weeds are small (i.e., 2-3 inches tall) and applied in combination with a crop oil concentrate and/or N-fertilizer solution. However, the inclusion of 2,4-D to a soybean burndown program does provide some planting challenges; so remember to wait at least 7 days before planting, when using 1 pt/A or less.

Horseweed management recommendations: The majority of horseweed usually emerges in the fall, it can also emerge in spring and early summer. Horseweed is more easily controlled when small in late fall or early spring. As it matures and bolts in the spring and early summer, herbicides become less effective at killing this weed. In addition to glyphosate resistance, populations in Ohio and Indiana are also resistant to the ALS inhibitors (Classic FirstRate, etc.). At this point in time, the most economical treatments for control include 2,4-D ester at 1 to 2 pints/acre probably in combination with glyphosate or possibly Gramoxone. Even 2,4-D ester should be applied to small plants (less than 2 inch rosettes) to ensure effective control. Delaware, Maryland, and New Jersey weed scientists are also recommending dicamba (Banvel or Clarity at 6 to 8 oz/acre) at least 30 days in front of soybean planting (see recommendations below). A primary goal for horseweed management in soybean (or corn) should be effective control of emerged plants prior to planting. Here are some important principles for horseweed control outlined by weed scientists:

Final Management Tips for 2009 Barley Production — John Bray, CCA, S.E. Agronomy Extension Team

With the growing season for barley coming to a close there are still some management decisions that can be made for a successful high yielding crop of barley. First, evaluate your fields and determine the nitrogen level available to the crop. Applied fertilizer nitrogen, nitrogen applied from manure, and residual nitrogen left from previous manure applications should all be considered. If higher levels of nitrogen exist the consideration of applying a plant growth regulator (PGR) might be advisable. A PGR can keep barley standing and make harvest easier as well as provide a better quality grain. Cerone, from Bayer can aid in preventing lodging. This application should be made when the barley is in the Feekes Scale between stages 8 and 10. This is the period when the flag leaf just becomes visible. Rates of 1 to 2 pints should be considered, but usually 1 pint is adequate. (Consult label for your particular situation) Some of the considerations to watch are;

Contributors: State Specialists: Marvin Hall, Doug Beegle, John Tooker, Sjoerd Duiker, Greg Roth, Bill Curran, and Dwight Lingenfelter. Extension Educators: Paul Craig (Dauphin), Del Voight (Lebanon) Kevin Fry (Armstrong), Andrew Frankenfield (Montgomery), Mena Hautau (Berks), Joel Hunter (Crawford), Jeff Graybill (Lancaster), Dave Messersmith (Wayne), and John Bray.

Editor: Mark Madden

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