Posts Tagged ‘vegetable weed control’

Fall Can Be a Good Opportunity for Getting a Jump on Next Year’s Weed Problems

Friday, September 21st, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Fall herbicide treatments have a nice fit for many situations such as small grain weed control, assisting with cover crop management, and reducing the severity of weed infestations for no till corn or soybeans.

Let’s look at each of these situations. Treating small grain fields with a late fall herbicide application has worked well in our trials. As discussed in earlier newsletters there are no herbicides labeled for applications at planting (a preemergence application). As a result we have lots of winter annuals that emerge with or shortly after the crop. Waiting until spring to control these weeds often results in poor control because the weeds are large, and often stressed from the winter weather. On the other hand, an application in the late fall is made while the weeds are relatively small and actively growing. Remember these weeds are winter annual and will continue to grow after a few hard frosts, and the soil temperatures allow for significant growth through the month of November. If there is a lot of spring emergence, then those weeds can be controlled with a herbicide applied in combination with spring nitrogen applications.

Controlling weeds in cover crops that will be used for early-season vegetables can be challenging in some springs (particularly henbit and chickweed). One way around this with a grass cover crop is using a herbicide in the fall to “clean up the cover crop”. Using a broadleaf herbicide such as Harmony Extra or 2,4-D in the fall will control many of the broadleaf weeds and not limit crop rotation in the spring (replant intervals are 1.5 to 3 months). Then when burning down the grass cover crop in the spring, the concern is killing the cover crop, and not worrying about the winter annual broadleaves that can be tough to control that time of year.

Finally, fall treatments for fields that will be planted to no-till corn or soybeans next spring. We have looked at a number of products that could be tankmixed with glyphosate or paraquat with the idea they would provide residual control for spring emerging plants and these fields will not need a burndown herbicide. UD Weed Science Research has not found a consistent herbicide program for this approach. Furthermore, for effective weed control in corn or soybean most fields need a residual herbicide applied prior to or at planting, so a trip across the field for a herbicide application is needed in the spring. Fall herbicide applications of glyphosate or paraquat with 2,4-D are an excellent way to limit the amount of weed biomass in the spring, which in turn allows the soil to warm up faster and possibly conserve moisture. In our experiences, the addition of residual herbicides to the tankmixture of glyphosate, paraquat, and/or 2,4-D has limited utility in most situations.

Cleaning Equipment to Prevent Spreading Weed Problems Around

Thursday, August 2nd, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

This summer has been very challenging for weed control so I want to remind you to not spread the problems around the farm or from farm to farm. I believe that a lot of our new weed infestations are due to transporting seed on equipment, whether the equipment is mowers, combines, or vegetable harvesters. I have seen a number of fields with heavy weed pressure due to escapes. Some of these are suspected to be resistant biotypes, others just hard to control weeds. If a particular weed is giving you headaches, wouldn’t you rather deal with it in only one field rather than all of your fields? Ask yourself, what you would do if you could no longer use the best herbicide for a problem weed. In vegetables, where we only have one or two broadleaf herbicides, what are your options when they are no longer effective?

Granted weeds that get blown around (like marestail or thistle) or spread (by birds like pokeweed) are difficult to prevent. Nevertheless, many of our problems are due to moving seeds from field to field on equipment; pigweed and lambsquarters are two that come to mind. Take the time to clean the equipment in the field before it gets moved and isolate where those infestations are located. This is true for all fields. A new weed or a resistant biotype does not just take over a field in one year. A few plants get started and they produce seeds which next year leads to more plants and more seeds (see where this is going?). Prevent the problems from developing and spreading. Clean the equipment thoroughly, before it leaves the field, and leave the weed seed where you found it.

Weed Control for Succulent Beans

Friday, June 22nd, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

There is some overlap of herbicide options for snap beans and lima beans, but growers need to pay particular attention that a product is labeled for snaps or lima beans and do not assume if it is labeled for one, it is labeled for both. One thing that is consistent for both lima and snap beans is that postemergence herbicides need to be applied to small weed seedlings (3 inches tall or less).

Snap Beans
Weed control in snap beans starts with a good soil-applied program. The regional recommendations include Eptam, Treflan or Prowl, applied pre-plant incorporated; Dual, which can be applied preemergence or pre-plant incorporated; or Command or Sandea applied preemergence. Early postemergence treatments for broadleaf weeds include Basagran, Reflex, or Sandea. Select Max, Targa/Assure II, or Poast are labeled for postemergence grass control. UD research has seen consistent control with Dual used at planting followed by a timely (1 to 2 trifoliate stage of the beans) application of Reflex and Basagran. If there are concerns about timely application of the postemergence herbicides, consider use of a broadleaf weed herbicide at planting.

Lima Beans
The biggest difference from snap bean herbicides is Reflex. Snap beans tolerate Reflex quite well, but lima beans are very sensitive to Reflex. In fact, Reflex applied earlier in the season then lima beans planted as a second crop can also result in lima bean injury. A soil-applied herbicide program for lima beans is very important due to the lack of effective postemergence herbicides. Herbicides listed in the regional vegetable guide for lima beans include:

Pre-plant incorporated: Prowl or Treflan

Pre-plant incorporated or preemergence: Dual or Pursuit

Preemergence only: Sandea or Spartan Charge (only labeled in DE)

Postemergence: Basagran or Raptor for broadleaf weeds; Select Max or Poast for grasses.

Nutsedge and Horsenettle Control

Friday, June 1st, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

This appears to be the year for yellow nutsedge and horsenettle. Only a few products will provide yellow nutsedge control in corn. Glyphosate products are rated as suppressing yellow nutsedge if applied up to 6 inch tall plants. A recently registered product for our region, Permit Plus at 0.75 oz wt/A, is the best product available. Permit Plus contains halosulfuron and thifensulfuron (active ingredients in Sandea and Harmony). Permit Plus can be tankmixed with glyphosate. Basagran will control emerged tissue of yellow nutsedge, but the plants often regrow from the nutlets. Other products list nutsedge suppression but need to be applied to very small nutsedge plants. For soybeans, Basagran and glyphosate are also available, but so is Classic, for nutsedge plants up to 4 inches tall. Classic can be tankmixed with glyphosate.

Nutsedge control in vegetables includes Basagran or Sandea. Later planted vegetables can be treated at planting with Dual and/or Pursuit for control/suppression of yellow nutsedge. Pre-plant incorporated applications of Dual generally provide better yellow nutsedge control than applications to the soil surface.

Horsenettle is a perennial that emerges from creeping rhizomes and is hard to control. Glyphosate is rated as fair for control of horsenettle, but no other soybean herbicide provides control or appears to enhance glyphosate activity. In corn, Callisto provides good horsenettle control. Banvel, or dicamba containing herbicides, provide fair control of horsenettle. Postemergence options in vegetables are very limited; most products will provide some leaf burn but poor control.

Both yellow nutsedge and horsenettle should be treated after harvest with glyphosate. In late summer or fall, these plants are moving sugars to their root systems where the glyphosate can kill the perennial tissue of the plants.

Options for Postemergence Weed Control in Sweet Corn

Friday, June 1st, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Two broad-spectrum herbicides that have exhibited good crop safety to sweet corn are Impact and Laudis. Both products perform better with 0.25 to 0.5 lbs of atrazine. Both will control a broad range of weeds and grasses. It is important to consider crop rotation prior to treating sweet corn fields with a postemergence herbicide. Double-cropped vegetables are very problematic since few products allow such short rotations. Products that will allow double-cropping include Aim, Basagran, and Cadet. But these products only control small (less than 2 to 3 inches tall) plants. Most other herbicides are either not labeled for short rotations, or they have precautions about potential crop injury. Be sure to read and follow herbicide labels.

Pea Herbicides

Friday, March 2nd, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Weed control options remain limited for processing peas. Pursuit, at 1.5 to 2.0 fluid ounces per acre, needs to be used as a pre-plant incorporated or preemergence treatment and is used primarily for broadleaf weeds. Preemergence applications of Command at 8 to 16 fl oz or Dual at 0.5 to 1 pt/A are labeled for control of annual grasses and some broadleaf weeds. Basagran and Thistrol are labeled for postemergence control of broadleaf weeds. Apply Basagran at 1.5 to 2 pints per acre after peas have more than three pairs of leaves. Do not add oil concentrate. Select, Assure II, Targa, or Poast can be used for postemergence grass control.

Cover Crops, Winter Annual Weeds and Spring Vegetables

Friday, September 23rd, 2011

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Using cover crops prior to early-spring vegetables like peas and sweet corn is becoming more common. One issue for growers who want to no-till into that killed cover is managing winter annual weeds, like henbit and chickweed. In this situation, glyphosate is usually used to kill the cover crops (such as barley, wheat, rye). But glyphosate often will not provide the necessary control of henbit or chickweed because the weeds have not started actively growing that time of year. One way around this is using a herbicide in the fall to “clean up the cover crop”. Using a broadleaf herbicide such as Harmony Extra or 2,4-D in the fall will control many of the broadleaf weeds and not limit crop rotation in the spring (replant intervals are 1.5 to 3 months). Then, when burning down the cover crop in the spring, the concern is killing the cover crop, and not worrying about the winter annual broadleaves that can be tough to control that time of year.

Cleaning Equipment to Prevent Spreading Weed Problems Around

Friday, September 9th, 2011

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

This summer has been very challenging for weed control so I want to remind you to not spread the problems around the farm. I have seen a number of fields with heavy weed pressure due to escapes. Some of these are suspected to be resistant biotypes, others just hard to control weeds and others are due to poor herbicide performance as a result of the summer drought. If a particular weed is giving you headaches, wouldn’t you rather deal with it in only one field rather than all of your fields? Ask yourself, what you would do if you could no longer use the best herbicide for a problem weed. In vegetables, where we only have one or two broadleaf herbicides, what are your options when they are no longer effective?

Granted weeds that get blown around (like marestail or thistle) or spread (by birds like pokeweed) are difficult to prevent. Nevertheless, many of our problems are due to moving seeds from field to field on equipment; pigweed and lambsquarters are two that come to mind. Take the time to clean the equipment in the field before it gets moved and isolate where those infestations are located. A new weed species or a resistant biotype does not just take over a field in one year. A few plants get started and they produce seeds which next year leads to more plants and more seeds (see where this is going). Prevent the problems from developing and spreading. Clean the equipment and leave the seeds where you found them.

Fall Control of Perennial Weeds

Friday, September 9th, 2011

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Fall is the best time to treat most perennial weeds because it is the time that plants are best able to move the herbicide to the roots where it will do the most good. When considering fall weed control the emphasis should be on what the patch of weeds will look like next spring or summer not the amount of dead stems this fall. Also, it is important to consider that a fall application will not eradicate a stand of perennial weeds; the fall application will reduce the stand size or the stand vigor. Fall applications of glyphosate is the most flexible treatment for most perennial weeds such as artichoke, bermudagrass, Canada thistle, common milkweed, common pokeweed, dock, hemp dogbane, horsenettle and johnsongrass. Rates of 1 to 1.25 lb acid per acre are consistently the most economical (or about 1.5X the normal use rate for annual weeds). Allow at least 7 days after treatment before tilling, mowing, or planting through the treated area. Dicamba (Banvel) at 2 to 4 pints is also labeled for artichoke, bindweeds, dock, hemp dogbane, horsenettle, milkweeds, pokeweed or Canada thistle. Allow 10 days after treatment before disturbing the treated plants. Planting small grains must be delayed after dicamba application 20 days per pint of dicamba applied. Fall herbicide applications should be made to actively growing plants. Allow plants to recover after harvest before treating them. Consider keeping the combine header as high as possible so the weeds are quicker to recover; or combining around the weed patches and then spraying those patches immediately after harvesting. Weed species differ in their sensitivity to frost; some are easily killed by frost (i.e. horsenettle) others can withstand relatively heavy frosts. Check the weeds prior to application to be sure they are actively growing.

Dual Has a 24c Registration for Spinach in Delaware

Friday, August 19th, 2011

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Delaware has been granted a state registration (24c) for use of Dual Magnum in spinach. Growers in other states need to check with officials to ensure you have this registration. A few reminders: rate is 0.33 to 0.67 pt/A to the soil surface as a preemergence application i.e. prior to crop and weed emergence. Dual will not control emerged weeds. Irrigating spinach within two days of Dual application will ensure it gets moved into the soil. Restrictions: (1) Do not mechanically incorporate. (2) Do not apply this product through any type of irrigation system. (3) Only one application of Dual MAGNUM is permitted per spinach growing season. (4) Do not exceed more than 0.67 pt/A Dual MAGNUM. (5) Do not harvest with 50 days of application. Dual can cause injury to spinach and end user or grower accepts the risk of crop injury.