J. Michael Moore
Weeds reduce tobacco plant growth by competing with the crop for light, nutrients and water. Weeds also serve as a host for diseases and insects that attack tobacco. Since the climate in Georgia is ideal for weed growth, tobacco producers must use many tools to control and/or suppress weed infestations. Weed management includes knowledge of the pest, crop rotation and other control methods.
KNOWLEDGE OF THE PEST: Before a control measure is implemented in a tobacco field, knowledge of the pest is required. Producers must be aware of the weed species that infest an area in order to decide upon the proper control measures. Correct identification of a weed species can be obtained through the county agent. Weed maps and other documentation that are gathered over several years will help in avoiding weeds that are impossible to control in tobacco.
CROP ROTATION PRACTICES: Crop rotation practices will directly influence the weed species and pressure to expect. Rotations that include corn, cotton, sorghum or soybeans will help reduce the weed pressure in tobacco fields. IMPORTANT: Herbicides that are used in row-crop production can sometimes persist and injure tobacco planted the next season. Growers should be aware of the crop rotational restrictions BEFORE using any herbicide in a crop preceding tobacco.
CONTROL METHODS: The most effective weed control is obtained through the use of several methods:
TILLAGE AND CULTIVATION: Tillage should be used prior to transplanting tobacco to remove existing weed growth. There are no herbicides available that will kill emerged weeds without severely injuring tobacco. After transplanting, cultivation can be used to remove small weeds as they emerge. Cultivation should be shallow and should not disturb the established plants.
CHEMICAL: Herbicides are an effective tool for controlling weeds in tobacco. However, there are no herbicides labeled for use in tobacco that will control all weeds encountered in Georgia. Herbicide(s) applied before transplanting should be incorporated to control weeds before they emerge. Other herbicides are available that can be applied after transplanting. Recommendations for controlling weeds in tobacco can be found in the most current "Georgia Pest Control Handbook". The following "rules of thumb" should be used when applying herbicides: a) always calibrate the sprayer and recheck every few hours; b) check the effectiveness of the incorporation equipment; c) be familiar with the rotational restrictions and other instructions on the manufacturer's label; d) follow the safety guidelines listed by the manufacturer; e) never use a herbicide that is not specifically labeled for use on tobacco.
| Table 1. Tobacco Weed Control Alternatives (multiple pages) | ||||
| BROADCAST RATE/ACRE | ||||
TIMING |
HERBICIDE FORMULATION |
AMOUNT OF FORMULATION |
POUNDS ACTIVE INGREDIENT/A |
REMARKS AND PRECAUTIONS |
| PLANT BED (for control of soil fungi, bacteria, nematodes, insects and weeds) |
Methyl Bromide 98%
Methyl Bromide 68.6% |
9 lb/100 sq yd 10-12 lb/100 sq yd |
8.82/sq yd 6.8 - 8.2/sq yd |
Apply methyl bromide when soil temperature is above 50oF. Cans: Release gas under plastic covering. Plastic should be sealed around the edges with soil. Leave covered for 24 hours. Seed bed after 72 hours of aeration.
Cylinders: Inject into well prepared soil with chisel applicators. Cover immediately with plastic and seal all edges. Leave covered for 48 hours. Remove cover to provide sufficient aeration 72 hours prior to seeding. |
| dazomet (Basamid) |
7.5 lb/100 sq yd |
Apply granules to moist soil. Proper calibration of the spreader to be used is important. Incorporate thoroughly 4 to 8 inches deep. Cover with plastic for 7 to 10 days when soil temperatures are at least 50oF. Activity and effectiveness are reduced at low temperatures and at low soil moisture levels. Aerate treated soil for 5 to 10 days depending on soil temperature. Soil must be tilled to insure adequate aeration after removing the plastic cover and prior to seeding. Inadequate aeration will result in a lack of germination. A germination test may be performed on representative soil with a glass jar and lettuce seed. | ||
| metham-sodium (Vapam) |
1 - 1.5 gal/100 sq yd |
Spray onto moist soil in a minimum of 40 gal of water/A. Incorporate thoroughly three to four inches deep. Cover with plastic for 1 to 2 days when soil temperatures are at least 50oF. Aerate soil prior to seeding. | ||
| (for post emergence control of grasses) |
sethoxydim (Poast) 1.5 lb/gal |
1.0 pt (0.33 fl oz per 100 sq yd) |
0.19 | For use in tobacco seedbeds only. Do not use in the field. Addition of a non-phytotoxic oil concentrate at 1 qt/A (0.67 floz per 100 sq yd) is required. Allow plants to completely dry before covering, especially with plastic. |
| PREPLANT | clomazone (Command) 3ME 3 lb/gal |
2.0 to 2.66 pt/A or |
0.75-1.0 | Apply Command as a broadcast spray at low pressure and large droplet size. Incorporate
to a depth not to exceed one inch prior to transplanting. Transplant roots should be
placed below the treated area. Off-site movement of spray drift or vapors of Command can cause foliar whitening or yellowing of some plants (fruit and nut trees, berries, roses, other landscape plants and greenhouse plants). Temporary whitening and/or yellowing of the treated crop and rotational crops may occur. The crop should grow through this with no adverse impact. The introduction of the 3ME formulation should reduce the potential for off-site movement and injury to sensitive plants. Do not plant small grain for grain less than 12 months after application of Command. Do not graze treated areas for 9 months. |
| isopropalin (Paarlan) 6E 6 lb/gal pendimethalin (Prowl) 4E 4 lb/gal (Prowl) 3.3E 3.3 lb/gal napropamide (Devrinol) 50W (Devrinol) 2E |
1 qt
1.5 - 2 pt
1.8 - 2.4 pt
2 - 4 lb 2 - 4 qt |
1.5 0.75 - 1.0
1.0 - 2.0 |
Apply and soil incorporate within 14 days prior to transplanting. Prior to bedding,
apply and soil incorporate either Paarlan, Prowl or Devrinol with a power-driven rotary
tiller set to cut 4 inches deep or incorporate by disking and cross disking with a disk
harrow set to cut 4 to 6 inches deep. If applied to preformed beds, "board off"
to planting level and incorporate with a power-driven rotary tiller set to cut 4 inches
deep. Devrinol is for field use only. Not labeled for tobacco seedbeds due to plant injury. |
|
| pebulate (Tillam) 6E 6 lb/gal (Tillam) 10G |
5 pt 5 fl oz 40 lb |
4.0 | Tillam should be used if nutsedge is a problem in the field. Apply and incorporate immediately either before or after bedding as discussed above. If possible, apply Tillam at least 2 days before transplanting. | |
| PREPLANT (continued) |
pebulate (Tillam) 6E 6 lb/gal + napropamide (Devrinol) 50W (Devrinol) 2E |
5 pt 5 fl oz +
2 lb 2 qt |
4.0 +
1.0 1.0 |
Tillam and Devrinol may be tank-mixed to provide control of nut-sedge and many annual grasses and some broadleaf weeds. Apply and incorporate immediately either before or after bedding as discussed above. If possible, apply this combination at least 2 days before transplanting. |
| PRETRANS-PLANT (surface application only) |
sulfentrazone (Spartan DF) 0.75 lb ai/lb |
5.3 oz |
0.25 | DO NOT INCORPORATE !! CALIBRATION IS IMPORTANT !! Application rate should be limited to 0.25 lb ai per acre (5.3 oz Spartan DF) for most tobacco soils in Georgia. Excessive application rates or poor calibration may result in injury to tobacco. Do not apply to soils classified as Sand with less than 1% Organic Matter and shallow groundwater. Application methods should be directed toward applying and maintaining Spartan DF at the soil surface. Spartan DF may be surface applied up to 14 days prior to transplanting after all other soil incorporation practices have been performed where transplanting occurs without bedding. If beds are formed prior to transplanting, the top of the beds should be dragged or knocked off prior to application. Transplant into the treated bed without pushing additional soil from the bed. Spartan DF should not be incorporated into the bed greater than 2 inches. Do Not apply post-transplant over the top of tobacco as crop injury may occur. Rotational Guidelines limit recropping treated soil to: wheat - 4 months, field corn - 10 months, cotton - 18 months, canola - 24 months. Although recropping to vegetables is not mentioned on the label, the limited information available would discourage recropping treated soil to most vegetables in less than 12 months after treatment. Accuracy of measurement of Spartan can be improved by using a set of scales rather than using a volumetric measuring cup. |
| POST TRANSPLANTING | ||||
| napropamide (Devrinol) 50W
clomazone (Command)3ME 3 lb/gal |
2 - 4 lb 2.0 to 2.66 pt/A |
1.0 - 2.0 0.75-1.0 |
Apply directly over the top of tobacco immediately after trans-planting to control
weeds before they emerge. Irrigate with 1/2 inch of water if no rainfall occurs within 3 to 4 days. Refer to Remarks for Command under the Preplant section for comments on application, off-site movement and rotation. Tender plant bed plants and particularly greenhouse plants have been shown to be very sensitive to Command and some leaves may turn white for a short period of time. This does not usually cause a reduction in yield and has not been widely observed in Georgia. |
|
| LAYBY | napropamide (Devrinol) 50W pendimethalin (Prowl) 4E 4 lb/gal (Prowl) 3.3E 3.3 lb/gal |
2 lb
1 - 1.5 pt
1.2 - 1.8 pt |
1.0 - 2.0 0.5 - 0.75
0.5 - 0.75 |
These herbicides are applied following the last cultivation (usually 4 to 6 weeks after transplanting). Spray equipment should be set up with drop nozzles to direct the herbicide spray to the shoulders of the tobacco beds and middles. These herbicides will not control established weeds; therefore, middles should be free of any existing weeds prior to herbicide application. Irrigate with 1/2 inch water if no rain on Prowl occurs within 3 to 4 days. Do not spray in the buds of tobacco as plant injury may occur. |
| TOBACCO WEED RESPONSE TO
HERBICIDES J. Michael Moore |
|||||||||||
| PLANT BED | FIELD APPLICATION | ||||||||||
| PRETRANSPLANT | POST TRANSPLANT |
LAYBY |
|||||||||
| SURFACE APPLIED | INCORPORATED | ||||||||||
Poast |
Spartan1 |
Command |
Prowl |
Dev-rinol | Tillam |
Devrinol + Tillam |
Dev-rinol | Command |
Dev-rinol | Prowl |
|
| PERENNIAL WEEDS | |||||||||||
| purple nutsedge | P | G | P | P | P | P | P | P | P | P | P |
| yellow nutsedge | P | G-E | P | P | P | F | F | P | P | P | P |
| ANNUAL GRASSES | |||||||||||
| crabgrass | G-E | G-E | E | E | G | G | G | G | E | G | E |
| crowfootgrass | E | --- | G | E | P | G | G | E | G | E | E |
| goosegrass | F-G | E | G | E | P | G | G | P | G | P | E |
| fall panicum | E | F | G | G | G | G | G | G | G | G | G |
| johnsongrass (seedling) | E | F-G | F | E | G | G | G | G | F | G | G |
| sandbur | E | P-F | F | F | F | F | F | F | F | F | F |
| Texas panicum | E | G-E | G | G | F | F | F | F | G | F | F-G |
| BROADLEAFS | |||||||||||
| bristly starbur | P | F-G | P | P | P | G | G | G | P | G | P |
| Florida beggarweed | P | G-E | F-G | P | P | P | P | P-F | F-G | P-F | P |
| Florida pusley | P | F-G | F-G | E | G | E | E | E | F-G | E | G |
| lambsquarters | P | G-E | F-G | E | E | E | E | E | F-G | E | G |
| pigweeds | P | G-E | P | E | G | G | G | G | P | G | G |
| prickly sida | P | G-E | G | P | F | F | F | F | G | F | P |
| purslane | P | F-G | F-G | E | E | E | E | E | F-G | E | F |
| ragweed | P | G-E | F | P | G | G | G | G | F | G | P |
| morningglory sp. | P | G-E | |||||||||
Key to response symbols: E = Excellent control, weed kill 90% or above. G = Good control, weed kill 80% or above. F = Fair control, weed kill 70% or above. P = Poor control, less than 70% control. If no symbol is given, weed response is unknown.
Ratings are based on average to good soil and weather conditions for herbicide performance. |
|||||||||||
| Bermudagrass and rhizome johnsongrass cannot be controlled with presently labeled tobacco herbicides in the same growing season. However, control can be achieved with Roundup in the season prior to transplanting tobacco (check label for rates and application). | |||||||||||
| 1 Transplant into the Spartan DF treated bed surface without pushing additional soil from the bed. Spartan DF should not be incorporated into the bed greater than 2 inches. Do Not apply Spartan DF post-transplant over the top of tobacco as crop injury may occur. | |||||||||||
Spartan Combinations And Application Methods Test
J. Michael Moore, Extension Agronomist
Ed Troxell, Ag. Extension Technician
Ben Tucker, Cook County Extension Coordinator
Nutsedge is a major weed affecting a major portion of the tobacco production area of Georgia. Chemical controls for nutsedge in tobacco production have been very limited. Spartan 75DF received a label during the 1998 tobacco transplanting season. Growers in Cook County have had little experience with the application and results of this material. A large demonstration plot was developed to observe the recommended rate and application methods for Spartan 75DF. The demonstration plot was included on the 1998 Georgia Tobacco Tour. Local growers were invited to attend and observe the results of the demonstration.
The Spartan 75DF application and methods demonstration was conducted to evaluate nutsedge control on the Tommy Daughtrey Farm in Cook County in 1998. The predominant species of nutsedge in the particular field was Purple Nutsedge. Spartan 75DF was evaluated as a PPI treatment, Pre-transplant treatment, and post-transplant treatment in an attempt to determine the best method of application. Spartan was also used in combinations with Command and Prowl herbicides. Phytotoxic injury to the foliage of the tobacco was also observed and rated.
All plots were arranged in a randomized complete block design. Plots were two 46-inch rows approximately 1000' long for each treatment with 2 replications. Two ratings were made within each replication. Application techniques included pre-transplant incorporation (PPI), pre-transplant surface application (Pre-T) and a shielded spray application after transplanting (Post-T). The PPI treatments were incorporated with a tillovator after spray application to top of beds. Beds were left raised, but flat for pre-transplant applications. Pre-transplant treatments were applied at 25 gallons of solution per acre at 22 psi.
Post-T applications were directed using a shielded sprayer. Treatments were applied using two 8001.5 tips, 20 PSI, and 30 gallons per acre. The spray solution was applied in eight inch bands on the shoulders of the bed using sliding shields to protect the transplants from the spray solution.
PPI and Pre-T plots were rated on 4/30/98, two weeks after transplanting, but before tobacco was cultivated. Post-T treatments were rated on 5/21/98, two weeks after the first cultivation.
Treatments and results of the demonstration are included in Table 1. Nutsedge, texas panicum, and common bermudagrass were the major weed and grass species present in the demonstration site. Spartan 75DF was good to extremely effective with nutsedge control ranging from 75 to 95 percent control depending upon the application method. The pre-transplant application method was the most effective. However, it resulted in moderate injury to the tobacco foliage. Very little injury was observed later in the growing season and tobacco growth seemed to be unaffected. Spartan was observed to continue to kill nutsedge well into the production season on all treatments. Application following transplanting, using sliding shields to prevent the herbicide from contacting the plant appeared to be a successful alternative, and may better fit the routine soil preparation and transplanting operations of the typical tobacco grower. Using this approach, no spray was allowed to contact the plants and only a small strip of soil in the drill was untreated. This area received treated soil as soon as the first cultivation moved the soil up around the transplants.
Based on the results of the demonstration, Spartan 75DF provides the growers an excellent way to control both purple and yellow nutsedge in tobacco.
| Table 1. Nutsedge Control with Various Spartan Combinations And Application Methods, Tommy and Bem Daughtrey, Cook County, 1998. | |||||
Trt |
Chemical Name |
Rate (lb ai/A) |
Growth Stage |
Nutsedge Control (%) | Percent Phytotoxicity |
| A. | Spartan 75 DF | 0.25 | PPI | 76 | 0 |
| B. | Spartan 75 DF | 0.25 | PRE-T | 93 | 15 |
| C. | Spartan 75 DF | 0.25 | POST-T | 90 | 0 |
| D. | Spartan 75 DF Command 3 ME |
0.25 0.5 |
PPI PPI |
78 | 0 |
| E. | Spartan 75 DF Command 3 ME |
0.25 0.5 |
PRE-T PRE-T |
91 | 15 |
| F. | Spartan 75 DF Command 3 ME |
0.25 0.5 |
POST-T POST-T |
92 | 0 |
| G. | Spartan 75 DF Prowl 3.3 EC |
0.25 0.75 |
PPI PPI |
75 | 0 |
| H. | Spartan 75 DF Prowl 3.3 EC |
0.25 0.75 |
PRE-T PRE-T |
95 | 13 |
| I. | Spartan 75 DF Prowl 3.3 EC |
0.25 0.75 |
POST-T PPI |
95 | 0 |
| J. | UNTREATED CHECK | 0 | 0 | ||
| PRE-T = PreTransplant Surface Application PPI = PrePlant Incorporated POST-T = Post Transplant Application W/SHIELD = Applied with two 8001.5 tips, 20 psi, 30 gpa, 8" bands on either side of sliding shields. No spray was allowed to contact the plants and a six inch strip of soil along the top of the row. Later cultivations moved the treated soil up around the transplants. PPI & PRE-T trts rated 4/30/98. POST-T rated 5/21/98 |
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