1. Herbicide Carryover Katie Jennings, David Monks, and Steve Meyers NCSU
Department of Horticultural Science

2. Sandea herbicide label Rotational restrictions
The information printed on the top of this label page provides rotational restrictions with the use of Sandea herbicide. ROTATIONAL CROP INFORMATION
Gowan Company recommends the following recropping intervals for crop safety. Planting prior to the intervals shown below may result in crop injury when using Sandea herbicide. Rotation intervals below may need to be extended if drought or cool conditions prevail. Rotation intervals may need to be extended in drip irrigation crops in Arizona and California. Gowan recommends that the end user test this product in order to determine its suitability for such intended uses. It may be appropriate to use shorter intervals in areas where local experience has demonstrated safety. In the event of crop failure, labeled crops may be planted back into the treated area at the user’s risk for potential phytotoxicity to the subsequent crop.
Many herbicide labels do not address rotational restrictions for specific vegetable crops. Instead there is a statement referring to “all other crops not listed’, or “Crops not specifically Listed.”

3. Rotation Restrictions with Herbicides Registered in Other Crops
Vegetables
Atrazine
> 1 year
Valor
8 to 18 months
Envoke
210 to 540 days
Sandea
2 to 12 months
Classic
9 to 30 months
Harmony GT XP
45 days
Callisto
18 months
Sencor
4 to 18 months
Staple
10 to 12 months
Cotoran
8 to 9 months

4. What is a Residual Herbicide?
A herbicide that provides extended weed control.
Preemergence or Postemergence
Herbicide activity is only beneficial for the time it is needed; longer activity can cause injury to subsequent crops.

5. Herbicide Persistence
The amount of time that a herbicide or a metabolite remains active (present and available) in the soil.
Varies with environmental conditions, soil type and soil characteristics, and cultural practices.
Half-life of a herbicide is the amount of time it takes to decompose 50% of the herbicide to an inactive form.
Determined under standard conditions in the lab.
Half-life in field will vary depending on environmental and soil conditions.

6. Herbicide Half-Life Herbicide Days Atrazine 60 Reflex 120-240 Stinger
Sandea
25-30
Pursuit
60 to 120
EPTC
7-14

7. Factors Affecting Herbicide Carryover Environment
Increased rainfall tends to reduce the likelihood of carryover to another crop.
Irrigated crop
Under flooded soil conditions less microbial activity occurs.
If rainfall is low then there is an increased chance of carryover to a follow-crop.
Less microbial degradation occurs under limited moisture conditions.

8. Factors Affecting Herbicide Carryover Soil Characteristics
Soil pH
High pH may decrease herbicide degradation. (sulfonylureas)
Chemical degradation slows and less tightly adsorbed to soil particles making more available for plant uptake.
Soil organic matter – tends to increase adsorption.
Soil type.

9. Factors Affecting Herbicide Carryover Herbicidal Characteristics
Herbicide rate
Herbicide persistence
Varies by herbicide and can range from a few days to a few years.
Influenced by soil type, soil pH, climatic conditions, and cropping systems.

10. Factors Affecting Herbicide Persistence
Plant uptake
Detoxification
Harvest removal
photodecomposition
volatilization
Surface runoff
leaching
Soil adsorption
Microbial degregation
Chemical decomposition

11. Herbicide Bioassay
Collect field soil from the top 2 to 3 inches and mix thoroughly (sample various places).
Plant several crop seeds that are known to be highly susceptible to the herbicide of concern.
Thin to 1 plant per pot after emergence.
Place pots in natural light if possible.
Evaluate for herbicide injury symptoms.

12. Herbicide Bioassay Field
Some labels require a field bioassay.
Crop must be grown to a specific growth stage, some to maturity.
Herbicide specific.

13. ACCase Inhibitors Graminicides (Poast, Select, Select Max)
Persistence is short to moderate.
Rotation restriction is often 120 days or less.
Adsorption is low to moderate.
Leaching is low.
Microbial degradation is high.
Chemical decomposition is low to moderate.
Photodecomposition is low to high.

14. ALS Inhibitors Sulfonylureas
Persistence is short to long.
High pH – sulfonylurea rotation restriction is long.
Low pH – imidazolinone rotation restriction is long.
Adsorption is low.
Leaching is low to moderate.
Microbial degradation is moderate to high.
Chemical decomposition is very high (decreases as soil pH increases).
Photodecomposition is low.

15. Dinitroanilines (Prowl, Sonalan, Treflan, Curbit)
Persistence is moderate.
Adsorption is high (increases with increasing om).
Leaching is low.
Microbial degradation is moderate to high.
Chemical decomposition is low.
Photodecomposition is moderate to high.

16. Photosystem I Inhibitors Bipyridyliums (Paraquat and diquat)
Persistence is very long.
Inactivated.
Adsorption is very high .
Leaching is low.
Microbial degradation is low.
Chemical decomposition is low.
Photodecomposition is moderate.
Minimal risk.

17. Photosystem II Inhibitors Triazines, Uracils (Atrazine, Sencor, Sinbar)
Persistence is moderate to long.
Adsorption is low to high.
Leaching is moderate to high.
Microbial degradation is moderate to high.
Chemical decomposition is low to moderate (> at low pH).
Photodecomposition is low.
Rotational restrictions can be greater than 2 yr in some cases; often greater at high soil pH.

18. PPO Inhibitors Triazilone(Sulfentrazone, Carfentrazone, Flumioxazin)
Persistence is short to long (sulfentrazone).
Adsorption is moderate (sulfentrazone) to high.
Leaching is low to moderate (sulfentrazone).
Microbial degradation is moderate to high.
Chemical decomposition is low.
Photodecomposition is low to high.

19. Sulfentrazone Injury to Vegetable Crops
Rates (oz/A)
Bell Pepper
6 WATr1
Onion
12 WATr
Snap bean
4 WAP1
Tomato
6 WATr
Watermelon 4 WAP
Squash
4 WAP 6
1 b
3 b
1 c
0 c 12
9 a
4 b
2 b
8 b
20 b 24
10 a
13 a
15 a
5 a
18 a
36 a
This slide illustrates results from research conducted in North Carolina to determine the carryover potential of sulfentrazone when applied in soybean/tobacco to vegetable follow-crops. The rates of 6, 12, and 24 oz/A correspond to 1, 2, and 4 times the labeled rate of sulfentrazone in soybean and tobacco on this particular soil (loamy sand). Visual injury increased for bell pepper, onion, snap bean, tomato, watermelon, and squash as sulfentrazone rate increased. Injury in bell pepper, onion, snap bean, tomato, and watermelon was 20% or less from all rates. Injury from the 1x rate of sulfentrazone in all crops was 3% or less. No injury was observed with sulfentrazone at 6 oz/A in squash. However, injury from 12 and 24 oz/A was 20 and 36%, respectively.
1WATr = weeks after transplanting and WAP = weeks after planting.
Pekarek, Monks, Garvey, Jennings, and MacRae Weed Tech. 24:20-24.

20. Synthetic Auxins (Banvel, 2,4-D, Stinger, Tordon, )
Persistence is very short to short with exception of some (moderate to long).
Adsorption is low.
Leaching is low to high.
Microbial degradation is high (soil moisture and temperature are important).
Chemical decomposition is low.
Photodecomposition is low.
Rotation restrictions fairly short with exception of Stinger and Tordon.

21. Herbicide Carryover Growth regulator type herbicides
Aminopyralid, clopyralid, fluroxypyr, picloram, triclopyr
Crop residue
Mulch – grass clippings
Manure

22. To Minimize Carryover Potential in Manure, Clippings and Compost
Check with source of manure, clippings, and compost.
IF you can’t determine whether these herbicides were applied do not use manure, compost, or clippings near sensitive crops including tomato unless you conduct a bioassay.
A bioassy involves potting up suspected material

23. Herbicide Carryover to Vegetables is a Great Concern for Growers
‘Athena’ cantaloupe
‘Heritage’ bell pepper
‘Amelia’ tomato
Several studies were conducted to determine the carryover potential of Stinger when applied in strawberry to follow-crops (bell pepper, cantaloupe, and tomato). After final strawberry harvest paraquat was sprayed to burndown the foliage. Follow-crops were planted.

24. Stinger Carryover to Vegetable Crops
Tomato and pepper
Crop injury on foliage.
Misshapen fruit.
Reduction in yield.
Stinger carryover caused damage to tomato and pepper foliage. Tomato fruit was deformed.
Nontreated
Stinger

25. Risk Points Previous herbicide history. e.g., rental property
Overlap of herbicide spray at the ends of the rows.
Misapplication. e.g., miss target rate
Late applications
Sprayer contamination.
Read label.
Keep historic records for each field.
Crop failure.

26. Off Target Movement of Herbicides

27. Off Target Movement of Herbicides
Growth regulator type herbicides
Dicamba and 2,4-D
Herbicides that cause chlorosis (yellowing) of foliage
Glyphosate (Roundup)

28. Growth Regulator Type Herbicides
Twisting of stems.
Cupping and twisting of leaves.
Leaves can become thick and leathery.
Distorted fruit.

29. Glyphosate Injury
White/yellow discoloration at the base of new leaflet.
Cupping and twisting of leaves.
Photos Courtesy of Virginia Polytechnic Institute.

30. Questions??
Contact Information
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