0330 NowTime

3/30/2013 7:00 AM

To Control Winter <\n>Annual Weeds in Alfalfa

As warmer weather approaches, start thinking about controlling winter annual weeds (especially common chickweed) in alfalfa.

Extension agronomist Bill Curran reminds us that once the temperature rises and alfalfa starts breaking dormancy, it can quickly grow beyond the growth stage to safely spray some of these products. In most cases, 2 inches of alfalfa regrowth is the maximum height listed.

Spraying beyond this stage may cause stand or yield reductions. Keep in mind all of these herbicides are labeled for use in pure-stand alfalfa. However, only Metribuzin and Pursuit can be applied to established alfalfa-grass mixes. Here are a few guidelines about available products:

Your best bet when controlling chickweed is Gramoxone SL, Pursuit, Raptor or Metribuzin (if chickweed is ALS-resistant, Pursuit and Raptor will not control it.).

For annual bluegrass, your best option is Gramoxone SL. For henbit/deadnettle, use Gramoxone SL or Metribuzin. For yellow rocket, use Pursuit, Raptor or Metribuzin.

Here are some additional details on use of these products: Gramoxone SL 2L (paraquat) may be applied at one to two pints per acre to established “dormant” stands before 2 inches of spring regrowth. The weeds must be actively growing at the time of application. Gramoxone is also labeled at one to two pints per acre for dormant application on new fall seeded stands.

One pint per acre can be applied between cuttings, but no more than five days after harvest and before 2 inches of regrowth. Gramoxone will desiccate any green tissue, including actively growing alfalfa and possibly cause stand or yield reductions. However, if chickweed infestations are thick, this may be a necessary option to help suppress it.

Be especially cautious with new fall seedings. Do not tank-mix with Metribuzin on newly seeded (less than 1 year old) alfalfa. Gramoxone is effective on low to moderate infestations of winter annuals including chickweed, henbit, deadnettle and mustard species. Do not use on mixed stands.

Pursuit 70DG (imazethapyr) may be used for weed control in seedling (two trifoliates or larger) or established alfalfa. Apply Pursuit at 1.08 to 2.16 fluid ounces per acre plus adjuvants to actively growing weeds 1 to 3 inches in height.

Pursuit performance improves with warmer temperatures. If spraying during extended cold periods, expect weeds to respond more slowly or the herbicide can have reduced activity. Pursuit is effective on many winter annual broadleaves including small chickweed. Pursuit may be used on established alfalfa-grass mixtures.

Raptor 1AS (imazamox) may be used for weed control in seedling or established alfalfa. Apply Raptor at four to six fluid ounces per acre plus adjuvants to small, actively growing weeds and to established alfalfa in the fall or in the spring.

Any application should be made before significant alfalfa growth or regrowth (3 inches) to allow Raptor to reach the target weeds.

Like Pursuit, Raptor performance is influenced by temperature. Therefore, try to apply the herbicide on warmer days and when weeds are actively growing. Raptor has a similar spectrum of winter annual weed control as Pursuit. Do not use on mixed stands.

Metribuzin 75DF (Dimetric, Glory, TriCor) may be used on established alfalfa. Apply 0.5 to 1 pound per acre before spring regrowth. Impregnation on dry fertilizer can improve crop safety and allow for slightly later applications (up to 3 inches spring regrowth).

Metribuzin controls winter annual broadleaves and grasses (higher rates for grass control) and may be used on mixed alfalfa-grass stands. Higher rates can potentially cause a reduction in grass stand.

To Review Fruit <\n>Educational Talks Online

If you wish to review recommendations provided at your local winter tree fruit educational meeting, you may now find the speakers’ slides online.

You can now go to the Penn State Tree Fruit Production website under Presentations — http://extension.psu.edu/fruit-production/presentations — to find this material.

To Attend a <\n>Cover Crop Field Walk

Make plans now to come out to one of Penn State Extension’s 10 cover crop field walks in April.

Penn State’s Crop Management Team has established cover crop trials on dairy farms across Pennsylvania since 2009. At these walks, we will review results from the first two years, and you will have the opportunity to observe the performance of various cover crop mixtures, and interact with peers and specialists.

Mixtures of several different cover crops will be highlighted. Walks are planned for 10 a.m.-noon for these dates and locations — April 5 in Delta, York County (contact John Rowehl at 717-840-7408); April 9 in Elverson, Berks County (Mena Hautau at 610-378-1327); April 10 in Waynesboro, Franklin County (Jennifer Bratthauar at 717-263-9226); April 11 in Lancaster County (Jeff Graybill at 717-394-6851); April 12 in Beaver Springs, Snyder County (Dave Hartman at 570-784-6660); April 15 in Doylestown, Bucks County (Andrew Frankenfield at 610-489-4315); April 19 in Allensville, Mifflin/Huntingdon counties (Ron Hoover at 814-865-6672); April 22 in Rome, Bradford County (Mark Madden at 570-928-8941); April 22 in Butler, Butler County (Alicia Spangler at 724-548-3447); and April 30 in Harrison Valley, Potter County (Nicole Santangelo at 814-274-8540).

Quote of the Week

“Easter says you can put truth in a grave, but it won’t stay there.”

— Clarence W. Hall

Leon Ressler is district director of Penn State Cooperative Extension for Chester, Lancaster and Lebanon counties.

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