Soil, Crop and Pest Management

Weed Management Advice

by Richard Bonanno, Frank Mangan and Mary Jane Else

INTRODUCTION:

Weeds influence peppers by competing for water, light and nutrients. Weeds also harbor diseases and insects, interfere with harvesting operations, and produce seeds which cause problems for years to come. Most weeds found in peppers fields are annual broadleaf weeds and grasses.

Whichever strategy you use to control weeds, work to minimize or eliminate weed seed production, especially if the weed in question is not common or not spread throughout the field. Scout fields in late summer or fall to determine problem or uncontrolled weed species and use this information to plan for next year.

STALE SEEDBED TECHNIQUE:

The main idea with this technique is that most weeds that have the potential to germinate, because of their placement in the upper 1" to 2" of the soil, will actually do so within two to four weeks after the soil is prepared. Adequate soil moisture and temperature (at least 50°F at a depth of 2") are necessary. Gramoxone, Roundup or flaming will kill these weeds. By not redistributing the soil any more than is absolutely necessary during the seeding or transplanting process, no new weed seeds will be brought closer to the soil surface.

This technique, because it reduces the number of viable weed seeds near the soil surface after seeding or transplanting, will help residual herbicides, if they are used, to perform better than they normally would. Finally, any cultivation which is performed should be kept extremely shallow (3/4" to 1") so as not to reposition any additional weed seeds.

Here are the steps:

1. Prepare the soil as if you are about to seed or transplant. If a soil-incorporated herbicide is used, it must be applied and incorporated at this time. The soil should have good moisture (irrigate with 1/4" of water if necessary).

2. Wait as long as possible so that the weeds will germinate and emerge. Allow weed seedlings to grow to the third leaf stage, or at least to the first true leaf. On sandy soil, loamy or high organic matter soils, the soil should not crust and modern seeders should still work satisfactorily. On heavy clay soils, crusting could make this technique unusable.

3. When using transplants, flame the soil or make an application of Gramoxone or Roundup to the soil surface before transplanting. Transplant the crop (without dragging any additional soil off the bed) and then apply any preemergence herbicide, which you would normally use, to the soil surface.

HERBICIDES:

Herbicides should be selected based on weeds to be controlled. An herbicide selectivity chart is found on the opposite page of this fact sheet.

Perennial weeds are best controlled by a fall application of Roundup. Cultivation, spring or summer applications of Roundup, and all preemergence herbicides registered for use in peppers are ineffective on all perennial weeds such as bindweed, quackgrass, and dock. After the harvest season has ended, broadleaf perennial weeds must be sprayed before they experience cold weather injury. Quackgrass can be spayed as late as early-mid November.

A common practice for many growers in Massachusetts is to incorporate trifluralin (Treflan) before planting and then to apply either napropamide (Devrinol) or metolachlor (Dual) after planting. If using plastic mulch, the napropamide or metolachlor should be band spayed between the mulch.

HERBICIDES REGISTERED FOR PEPPERS:

Stale Seedbed Technique

(see directions on page 1)

glyphosate (Roundup 4WSL): 1 to 5 qts/A (REI 12h). Do not apply within three days of transplanting.

paraquat (Gramoxone Extra* 2.5S): 2 to 3 pts/A (REI 12h).

Preplant Incorporated/Preemergence

clomazone (Command 4EC): 1-1/2 pt/A (REI 12h). All peppers except banana. Apply to the soil and immediately incorporate to a depth of 1" before transplanting peppers. See label for incorporation equipment description. Place roots of pepper transplants below treated zone. CAUTION: clomazone must be incorporated with appropriate equipment immediately after application. Drift of clomazone before or after application will cause severe injury to adjacent crops. DO NOT exceed labeled rates or severe crop injury will result. See label for replanting restrictions. Excellent for control of velvetleaf.

metolachlor (Dual and Dual 8E): (REI 12h) MASSACHUSETTS ONLY. Transplanted Bell Pepper ONLY. This is a restricted label available only to those Massachusetts growers who apply through the Massachusetts Department of Agriculture. Main target weeds for this registration are galinsoga and yellow nutsedge. All label instructions will be supplied after the application for use is completed. Growers may contact UMass Extension, NEVBGA, or Mass. DFA for an application.

napropamide (Devrinol 50DF): 2 to 4 lb/A (REI 12h).Use lower rate on light soil and higher rate on heavy soil. Incorporate thoroughly to a depth of 1 to 2". May also be applied overtop after transplanting. Shallow cultivation or irrigation will improve control.

trifluralin (Treflan 4E): 1 to 2 pt/A (REI 12h). Incorporate before planting. Disc twice immediately after spraying for satisfactory incorporation. Weak on ragweed. Not effective on excessively wet soil.

Postemergence

paraquat (Gramoxone Extra* 2.5S): 2-1/2 pt/A (REI 12 h). Apply as a directed and shielded spray to emerged weeds between rows of peppers. Crop contact by the spray will cause severe crop injury or death.

sethoxydim (Poast 1.53EC): 1 to 2 pt/A (20 dh, REI 12h) postemergence. Apply with crop oil concentrate at 2 pt/A. Apply to actively growing grasses (see product label for susceptible stage of growth). DO NOT cultivate for five days prior or seven days after Poast application. DO NOT apply more than a total of 4-1/2 pts/A per season. DO NOT apply during periods of high temperature and high humidity.

Table 1. Relative Effectiveness of herbicides on weed species.

CULTIVATION:

Cultivations should be shallow and timely. If weeds are small, cultivation may be used to move some soil into the pepper row to smother weeds. Deep cultivation will injure plant roots, expose moist soil to drying, and reposition weed seeds near the surface for germination. Hand weeding supplements both herbicides and cultivation by controlling escapes as well as new or troublesome weeds.

PLASTIC MULCH:

Plastic mulch can help to reduce herbicide and labor inputs; however effective control of weeds between plastic mulch is essential. In plasticulture, use of a combination of a banded preemergence herbicide application combined with either Gramoxone applied as a shielded spray or cultivation can control weeds between mulches.

USE OF COVER CROPS FOR WEED SUPPRESSION:

Cover crops can be used to suppress weeds, but require more management than more traditional weed control strategies such as herbicides or cultivation. For this reason it is strongly recommended that you start on a small scale and experience all aspects of the system before trying it on a larger scale.

There are two basic ways that cover crops can be used to suppress weeds in peppers:

1. ‘Dead’ mulch system - This is when a cover crop is killed by mowing or herbicides before pepper plants are transplanted into the field. This system has been intensely researched in many parts of the country, in particular with tomatoes.

This is traditionally a no-till system since the soil is not plowed in the spring. Special arrangements will have to be made to transplant the pepper seedlings through the mulch. One way is to till a strip where the pepper seedlings will be transplanted, however this strip will have to be kept free of weeds during the season.

A major concern with this management strategy in New England is the cooler soil temperatures due to the crop residue on the soil surface. Work at the UMass Research Farm has documented delayed maturity and in some instances yield reductions of crops grown in a dead mulch system due to reduced soil temperatures.

Another drawback to this system is that mechanical or hand cultivation is more difficult to implement if the weed suppression given by the residue on top of the soil breaks down.

2. Living mulch system - As the name implies, the cover crops are not killed, but are usually managed in some way to decrease growth and competition. Traditionally this system is used in combination with plastic mulches in order to protect the peppers from direct competition with the living mulch.

Cover crops such as annual ryegrass (30 - 40 lbs/A) or white clover (10 - 15 lbs/A) are seeded in between the plastic after it is laid. These cover crops will establish quicker if the plastic is laid in late April or early May. Cover crops need to be mowed multiple times during the season.

Results from research trials at the UMass Research Farm on this system with peppers have been mixed, ranging from no yield reduction to 60% reductions due to competition from the cover crops.

Recommendations based on this work are to use raised, plastic-covered beds combined with frequent mowing of the cover to reduce the amount of competition from cover crops.

The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in conflict with the label.

University of Massachusetts Extension

VegSF 3-97

Printed May 1997