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Consider herbicide selectivity and carryover if you want successful fall

cover crops

Bill Curran, Penn State University ([email protected])

Crop Management 1+1 WebinarFebruary 18, 2013

Copyright 2013, The Pennsylvania State University

Diverse Crop Rotations Can Provide Many Benefits and Cover Crops Can

Be Part of This

• Additional sources of feed or forage

• Improved nutrient cycling• Opportunities to cover the soil

and improvements in soil quality

• Integrated pest management and other ecosystems services

• Economic stability or greater market opportunities

But……• Greater complexity requires

more management• Herbicide selection and

rotation flexibility are an important consideration in diverse rotations

Diversity can provide



Hairy Vetch Cereal Rye Oats

Red Clover Winter WheatForage Radish

Cover crops – can be a valuable part of the cropping system



Residual Herbicides• Used in many of our major crops• Usually soil applied – not always• Generally provide 8 to 12 weeks of weed

control• Half‐life too short ‐ lack of residual weed

control (performance reduced)• Half life too long ‐ carryover to following crop

– Very important consideration for some crops and especially those established in late summer



Herbicide carryover to wheat



Carryover Injury to Subsequent Crops Depends On:

• Herbicide persistence in soil– How long does it last?– Herbicide half‐life gives us some indication

• Rotational crop susceptibility– How sensitive are rotational crops ‐ legumes, other broadleaves, grasses

• As long as cover crops are not harvested for animal consumption (but they often are), illegal residues not a concern, but injury risk remains with the grower



Dissipation or Degradation rate

• Half-life: the amount of time needed to degrade half of the herbicide present



Herbicide half‐life

• Short ‐ < 30 days• Intermediate ‐ 30 –120 days• Long ‐ > 120 days



Herbicide carryover potential based on half lives and soil availabilityHerbicide Strengths Half life (days) Carryover potential

2,4‐D amine broadleaves 7 NoneAccent brdlfs+grass 21 LowAssure/Targa grass 60 LowAtrazine brdlfs+grass 60 Moderate

Authority broadleaves 32‐302 ModerateBalance Pro brdlfs+grass 50‐120 Moderate

Callisto broadleaves 5‐32 Moderate

Clarity/Banvel broadleaves 5‐14 NoneClassic broadleaves 40 Moderate

Dual II Mag brdlfs+grass 15‐50 LowFirstRate broadleaves 8‐33 LowGlyphosate brdlfs+grass 47 NoneGramoxone brdlfs+grass 1000 NoneHarmony broadleaves 12 LowHarness brdlfs+grass 10‐20 LowIgnite brdlfs+grass 7 NoneImpact brdlfs+grass 14 LowLaudis brdlfs+grass 14 LowOutlook brdlfs+grass 20 LowPeak broadleaves 9‐152 ModeratePermit broadleaves 9‐27 LowProwl H2O brdlfs+grass 44 LowPursuit brdlfs+grass 60‐90 ModerateRaptor brdlfs+grass 20‐30 LowReflex broadleaves 100 ModerateResolve brdlfs+grass 2‐4 LowSelect grass 3 d NoneSencor brdlfs+grass 14‐60 LowSharpen broadleaves 7‐35 LowSimazine brdlfs+grass 60 d ModerateStinger broadleaves 40 ModerateValor broadleaves 12‐20 low

Herbicide half‐life estimates derived from the WSSA Herbicide Handbook, 2007 or other scientific literature.



Herbicide carryover potential based on half lives and soil availabilityHerbicide Strengths Half life (days) Carryover potential

2,4‐D amine broadleaves 7 NoneAccent brdlfs+grass 21 LowAssure/Targa grass 60 LowAtrazine brdlfs+grass 60 Moderate

Authority broadleaves 32‐302 ModerateBalance Pro brdlfs+grass 50‐120 Moderate

Callisto broadleaves 5‐32 Moderate

Clarity/Banvel broadleaves 5‐14 NoneClassic broadleaves 40 Moderate

Dual II Mag brdlfs+grass 15‐50 LowFirstRate broadleaves 8‐33 LowGlyphosate brdlfs+grass 47 NoneGramoxone brdlfs+grass 1000 NoneHarmony broadleaves 12 LowHarness brdlfs+grass 10‐20 LowIgnite brdlfs+grass 7 NoneImpact brdlfs+grass 14 LowLaudis brdlfs+grass 14 LowOutlook brdlfs+grass 20 LowPeak broadleaves 9‐152 ModeratePermit broadleaves 9‐27 LowProwl H2O brdlfs+grass 44 LowPursuit brdlfs+grass 60‐90 ModerateRaptor brdlfs+grass 20‐30 LowReflex broadleaves 100 ModerateResolve brdlfs+grass 2‐4 LowSelect grass 3 d NoneSencor brdlfs+grass 14‐60 LowSharpen broadleaves 7‐35 LowSimazine brdlfs+grass 60 d ModerateStinger broadleaves 40 ModerateValor broadleaves 12‐20 low

Herbicide Strengths Half life (days) Carryover potential

2,4‐D amine broadleaves 7 None

Atrazine brdlfs+grass 60 Moderate

Dual II Mag brdlfs+grass 15‐50 Low

Glyphosate brdlfs+grass 47 None

Herbicide half‐life estimates derived from the WSSA Herbicide Handbook, 2007 or other scientific literature.



Recrop Restriction Information

• Current Herbicide Labels• University Agronomy Guides ‐http://agguide.agronomy.psu.edu/

• University Commercial Vegetable Production Recommendations (extension.psu.edu/vegetable‐fruit/production‐guides/2011‐comercial)



Penn State Agronomy Guide ‐ Table 2.2‐17. Example corn herbicide rotational restrictions (months after application).

Herbicide Alfalfa Clover Grain sorghum

Soybeans Spring Oats

Winter Barley

Winter rye

Winter Wheat

Long‐est

Accent 10 19 10 0.5 8 4 4 4 10

Atrazine SY SY NR NY SY NY NY NY SY

Balance 10 18 6 6 18 6 18 4 18

Callisto 10 18 NR 10 NR 4 4 4 18

Dual 4 9 NR NR 4.5 4.5 4.5 4.5 12

Hornet 10.5 26 12 10.5 4 4 4 4 26

Permit 9 9 2 9 2 2 2 2 SY

Prowl NY NY NY NR NY 4 NY 4 NY

Sharpen ‐1 oz

4 4 NR 0 NR NR NR NR 4

*Lumax 18 18 NY NY NY 4.5 4.5 4.5 NY

* Mixture of Atrazine + Callisto + Dual



Recrop Interval Information

• Determine which products have ≤4 month rotation restriction for potential rotation crops or their relatives.

• Alfalfa, clover, pea, sorghum, oats, wheat, barley, and are included in the PSU Agronomy Guide.

• Hairy vetch and more obscure legumes are not listed.– Examine alfalfa or clover restrictions to get a good idea of which

herbicides may cause potential injury to other legumes.

• Crops such as canola, forage radish, and buckwheat can be difficult to determine as they are usually never listed.

• Small seeded species generally most sensitive.



General guidelines• Corn herbicides

– In general, atrazine or simazine applied PRE at less than 1 lb/A can allow cereal grain establishment; less than 0.75 lb/A may allow for most legume cover crops, mustards, and annual ryegrass.

– Mesotrione (Callisto and a component of Lumax/Lexar, Halex GT and others) is problematic for legumes and mustards like canola and forage radish. Additional products containing this active are forthcoming.

– Clopyralid (Stinger and a component of Hornet and SureStart) could also affect these small seeded broadleaves.

• Soybean herbicides– Chlorimuron (Canopy, Classic, Envive, Synchrony, etc.), Pursuit or

Extreme (imazethapyr), and Prefix or Reflex/Flexstar (fomesafen) could be a problem for fall seeded legume or mustard cover crops, but cereal grains should be OK.



General guidelines (cont.)

• Other corn and soybean herbicides and their impact on legumes or mustard species in particular is less clear.

• Wheat herbicides– Generally not a problem, except for companion or relay cropping ‐ If you can double‐crop soybean, should be OK

• Until more research is conducted assessing specific herbicide‐cover crop interactions, the general guidelines provided in Agronomy Guide Tables 2.2‐17and 2.4‐15 can be helpful.



Corn Herbicide Safety Study – 2010 & 2011

Silt‐loam soils, 1‐3% OM, pH = 6.5, precip. = 45 inHerbicide treatments – 25 to 27 corn herbicides applied pre and some postCover crop treatments planted at inter‐seeding (after POST) and after silage harvestVisual evaluation in fall and spring (0‐100% scale)

• Inter‐seeder – ryegrass, red and white clover, and mixture

• Fall – rye, wheat, oats, ryegrass, clovers, hairy vetch, canola, forage radish

InterInter‐‐seederseeder

Fall seededFall seeded



Results• Had a number of challenges – slugs, compaction, drought, too

many plots (1200 ‐ 1500)– Clovers, forage radish, and canola data mostly lost and hairy vetch

variable

• Inter‐seeder – metolachlor, nicosulfuron, (atrazine?) reduced ryegrass

• Fall ‐ did not observe problems for establishment of cereals ‐oats, wheat, and rye

• Concerned about translating results to the farming public (small inference space) – need more locations and years to be confident

• Other ways to study or demonstrate this more easily?



Effect of PRE herbicides on annual ryegrass establishment with inter‐seeder (2010)

Treatment Rate (lb ai/acre) % Reduction

11‐11‐10 5‐5‐111Untreated 0 02 Atrazine 1 0 23 Atrazine 1.5 7 74 Atrazine 2 11 205 Simazine 1 12 206 Simazine 2 17 227Mesotrione (Callisto) 0.188 15 278 Isoxaflutole (Balance) 0.094 14 129 Flumetsulam (Python) 0.0575 2 510 Rimsulfuron (Resolve) 0.0313 10 511 Clopyralid (Stinger) 0.188 2 512 Saflufenacil (Sharpen) 0.067 10 713 Pendimethalin (Prowl) 1.43 31 1514 s‐metolachlor (Dual) 1.6 57 6215 Isoxaflutole + Atrazine 0.094 + 1 22 2716Mesotrione + Atrazine 0.188 + 1 11 17

LSD (0.05) 22 23



Dual (metolachlor) injury on inter‐seeded ryegrass

Callisto (mesotrione) injury on fall seeded forage radish



Predicting Herbicide Half Life• If it’s short, it’s always short, but……• For intermediate or long, it can be a moving target• Factors:

– Application timing, rate, and frequency– Dry vs. wet weather– Soil clay and organic matter content and soil pH

• Heavy soils more problematic• High and low pH more problematic (<5 and >7)

– Herbicide history• Just because you get away with it once, doesn’t mean you won’t have a problem another time

• Half‐life doesn’t demonstrate selectivity/susceptibility



Herbicide persistence and selectivity demonstration

Seeded crimson clover, alfalfa, annual ryegrass, forage radish, sorghum sudangrass, hairy vetch, oats, and cereal rye and applied herbicides PRE (18 different treatments) using a log sprayer

1 & 2 L bottles –Weed Systems(weedsystems.com)



Herbicides included in DemoTrt Treatment Form Form Rate Other Other Estimated

No. Name Conc. Type Rate Unit Rate Rate Unit Half‐life1

1. Untreated2. Dual II Magnum 7.62 EC 1.59 lb ai/a 1.67 pt/a 15‐50 (35)

3. Harness 7 EC 1.75 lb ai/a 2 pt/a 10‐20 (15)

4. Prowl H2O 3.8 CS 1.42 lb ai/a 3 pt/a 44

5. Atrazine 4 L 1.5 lb ai/a 3 pt/a 60

6. Callisto 4 SC 0.188 lb ai/a 6 fl oz/a 20

7. Classic 25 DF 0.0313 lb ai/a 2 oz/a 40

8. Valor 51 WDG 0.08 lb ai/a 2.5 oz/a 12‐20 (16)

9. Pursuit 70 DG 0.063 lb ai/a 1.44 oz/a 60‐90 (75)

10. Raptor 1 SC 0.039 lb ai/a 5 fl oz/a 20‐30 (25)

11. Resolve 25 DF 0.0156 lb ai/a 1 oz/a 2‐4 (3)

12. Sharpen 2.85 SC 0.067 lb ai/a 3 fl oz/a 7‐35 (21)

13. Bicep II Mag 5.5 L 2.9 lb ai/a 2.1 qt/a 60

14. Lumax 3.95 L 2.47 lb ai/a 2.5 qt/a 60

15. Callisto 4 SC 0.094 lb ai/a 3 fl oz/a 5‐32 (20)

Atrazine 4 L 0.75 lb ai/a 1.5 pt/a 6016. Impact 2.8 SC 0.0164 lb ai/a .75 fl oz/a 14

17. Permit 75 DF 0.031 lb ai/a .66 oz/a 9‐27 (18)

18. Accent 75 DF 0.031 lb ai/a .66 oz/a 21



Herbicide DemoHalf‐life

0 1 2 3 4Rate reduction

Tradename Rate/A Common name 1X 1/2X 1/4X 1/8X 1/16Xlb ai/acre and days to reach rate

1. Dual II Magnum 1.67 pt metolachlor 1.60 0.80 0.40 0.20 0.100 35 70 105 140

2. Atrazine 4L 3 pt atrazine 1.50 0.75 0.38 0.19 0.090 60 120 180 240

3. Callisto 4SC 6 oz mesotrione 0.19 0.09 0.05 0.02 0.010 20 40 60 80

4. Lumax 3.95L 2.5 qt metolachlor 1.67 0.84 0.42 0.21 0.100 35 70 105 140

atrazine 0.63 0.31 0.16 0.08 0.040 60 120 180 240

mesotrione 0.17 0.08 0.04 0.02 0.010 20 40 60 80



Evaluated Plots and Conducted a Field Day



Effect of Dual II Mag on crop growth [X rate = 1.6 lb ai or 1.67 pt]

0 35 70 105 140Days (half life)

PSU demo 2012



Effect of Atrazine 4L on crop growth [X rate = 1.5 lb ai or 3 pt]

0 60 120 180 240Days (half life)

PSU demo 2012



Effect of herbicides on diakon or forage crop growth

Days (half life) PSU demo 2012



Common corn and soybean herbicides, estimated half‐lives, cash crop restrictions and their potential to injure fall cover crops.

Herbicide Active ingredient

NormalRate/acre

Half life (days) 1

Cash crop restrictions

Fall cover crops Other

OK to plant Concern for2,4‐D 4S 2,4‐D 1‐2 pt 7 Plant anything 30

days after applicationAll grasses Wait 30 days

before planting sensitive broadleaves

Amine formulations more water soluble and can leach into seed zone

Atrazine 4L atrazine 1‐2 qt 60 Can plant corn, sorghum, and soybean the following year (some products allow others)

Sorghum species Cereals, ryegrass, legumes, and mustards

More persistent in high pH soils(> 7). Rates < 1 lb/acre can allow more flexibility

Callisto(includes Lumax, Lexar, Halex GT)

mesotrione 3‐6 fl. oz 5‐32 10 to 18 months for legumes and vegetables

All grasses Small seeded legumes, mustards

Sequential applications (PRE fb POST) increase the potential for injury

Dual II Mag 7.62E/Cinch

metolachlor 1.67 pt 15‐50 Labeled for use on many crops

Almost anything Annual ryegrass or other small seeded grasses

Higher rates and later applications more of a potential problem

Impact 2.8SC topromesone 0.75 fl. oz 14 Alfalfa, canola, soybean and sunflower have a 9 mo. restriction

Wheat, barley, oats, and rye are allowed after 3 mo. Ryegrass should also be OK

Although many broadleaves are restricted, Impact does not have much soil activity

We have not seen this herbicide carryover in PA.

http://extension.psu.edu/cover‐crops/fact‐sheets/herbicide‐persistence



Planning Ahead –know your herbicide residual

• Check a current University Agronomy Guide – recrop tables• Check label for use restrictions – recrop tables• For species not listed, use related species (e.g. other small

seeded legumes or grasses)• Replicated small plot research has not been very successful –

difficult to draw recommendations and lots of work• Demonstration trials using reduced rates and half‐life

comparison:– Very useful for demonstrating medium to longer residual herbicide activity on sensitive crops and herbicides with little soil activity (e.g. atrazine and topromezone)



Thank you…Any QUESTIONS?



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