Posts Tagged ‘weed control’

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.

A Couple of Yearly Reminders Regarding Herbicides

Thursday, April 5th, 2012

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

Acetochlor
Acetochlor is a preemergence herbicide for corn that controls annual grasses and some broadleaf weeds. It is in the following products: Harness, Harness Extra, Degree, Degree Extra, Topnotch, Fultime, and Keystone. There are use restrictions related to groundwater quality. The restrictions are based on depth of groundwater within one month of planting and the combination of soil type and organic matter. Do not apply acetochlor if the groundwater depth is within 30 feet and you have sands with less than 3% organic matter, loamy sands with less than 2% organic matter, or sandy loam with less than 1% organic matter.

“Activating” Herbicides
Herbicides applied to the soil surface require rainfall or irrigation to move them into the soil where the plants will absorb them; or mechanical incorporation (field cultivator). Some areas have not received much rainfall lately and you need to be aware if your soil-applied herbicides have been activated. If you have irrigation and your herbicides have been applied but you have not received water, you should consider irrigating to activate those herbicides.

Reducing Weed Seed Production in Harvested Fields

Friday, August 19th, 2011

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

Many annual and some perennial weeds are flowering, particularly those that emerged early in the summer. Destroying the plant or seed heads now will prevent most of these plants from producing mature seed. If these plants are mowed off, they are likely to regrow and eventually produce seed, but the quantity of seed produced will be dramatically reduced. Many of these fields will need at least one additional mowing to prevent seed production. Disking or a non-selective herbicide is another option to prevent seed production.

A Few Changes to Rotational Intervals for Herbicides

Friday, April 22nd, 2011

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

Since the Weed Control Manuals were updated last fall, I have been made aware of a few label changes for crop rotations. The label for Raptor now requires a longer interval for barley (9 months); and intervals for alfalfa, lima beans, snap beans, and peas are shorter (no restriction for these crops). Basis rotations also are not correct in the guides, most notably barley has been shortened to 4 months, cucumber 10 months, and tomatoes 1 month; while snap beans and peas have switched from 8 to 10 months and squash is now 18 months. Remember our guides are revised in September and any changes made since then are not updated so it is important that you always refer back to the current label.

 

Inconsistent Control With Burndown Herbicides

Friday, April 22nd, 2011

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

There are a lot of fields that have been sprayed with a burndown and the control was not as good as expected. It is not uncommon for early season burndown applications to be erratic, but this season seems worse than others. The most common complaints have been with grass control, henbit, and chickweed. A few observations from my experiences: glyphosate is good on most of these species, but is not great. Glyphosate often provides good to excellent control of grasses if the rate is adequate (at least 0.75 lbs acid equivalent) and the plants are growing. However, annual ryegrass (aka Italian ryegrass) is hard to kill with glyphosate and requires close to a 2X rate if spraying in early spring. The addition of a triazine will significantly reduce the control of annual ryegrass. I often see only fair control of henbit with glyphosate. The addition of a triazine herbicide like atrazine or simazine will help. That is the tough choice, adding a triazine may help with some species, but can reduce the control of other species. You have to determine what weeds you have and which are going to be the most difficult to control and decide.

As far as paraquat, adding a triazine for the burndown before corn almost always improves control. However, grass control of annual ryegrass or grass cover crops will probably not be acceptable due to significant regrowth.

 

Herbicide Rotation Restrictions

Friday, March 11th, 2011

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

Herbicide rotational restrictions or guidelines are based on two criteria; regulatory and biological. Both of these criteria are equally important to the end user of the commodity and can be justification for rejecting the harvested product. Maximum residue levels are determined based on a range of tests and studies. Residue levels are determined to ensure that they are below a level that could cause an effect. Biological criteria are established to ensure the succeeding crops aren’t adversely impacted. It is critical that the pesticide label is read and understood before application. It does not matter whether the rotational restrictions were determined based on regulatory or biological criteria, the label needs to be followed. Rotational restrictions are often changed on the labels with little to no publicity, so review pesticide labels every year to be sure you are in compliance with the label.

Where we seem to have the biggest issue with rotational crops is with double cropped vegetables. Products used in sweet corn, peas, or other early-season crops can limit what can be planted after harvest.

Palmer Amaranth is in the Area

Friday, September 10th, 2010

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

I have seen a few fields in the area (Delaware and Maryland) with infestations of Palmer amaranth. Palmer amaranth is related to pigweed, and early in the year they look very much alike. However, at this time of the year, the seedheads look very different. Palmer amaranth has been described as pigweeds on steroids because of its ability to grow very rapidly, get very tall, and be very competitive with crops. Palmer amaranth is found throughout the southern US and is moving northward. Palmer amaranth is not as sensitive to Group 2 herbicides as smooth or redroot pigweed (this includes Pursuit, Sandea, Accent, Matrix etc). Furthermore, glyphosate-resistant Palmer amaranth is present in Georgia, North and South Carolina and other southern states. I am not aware of any herbicide-resistant Palmer amaranth in our area.

My article last week was about cleaning equipment before moving to the next field and it certainly pertains to this species. If you suspect you might have Palmer amaranth, do not spread it from field to field.

Characteristics Redroot Pigweed Smooth Pigweed Palmer Amaranth
Stem hairs Hairy Hairy No hairs
Stems Often ridges running length of stem Often ridges running length of stem Mostly smooth
Leaf petioles Petioles no longer than length of the leaf Petioles no longer than length of the leaf Long drooping petioles
Seed head Short, stout, prickly Long, slender, slightly prickly Very long, thick, very prickly

A couple of good publications include:
http://www.extension.iastate.edu/Publications/PM1786.pdf
http://www.ksre.ksu.edu/library/crpsl2/s80.pdf

Smooth pigweed

Palmer amaranth

Cleaning Equipment to Prevent Spreading Weed Problems Around

Friday, September 3rd, 2010

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. 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 would you 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 and leave the seeds where you found them.

Fall Control of Perennial Weeds

Friday, September 3rd, 2010

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

Fall is the best time to treat 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 are 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 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. 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 Banvel application 20 days per pint of Banvel applied. Fall herbicide applications should be made to actively growing plants. Allow plants to recover after harvest before treating them. And with all the drought we have had be sure there is good moisture before you treat the weeds. 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.

The Order Does Matter

Thursday, April 15th, 2010

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

Tank-mixing more than one pesticide is happening more frequently, particularly as we have to deal with herbicide resistant weeds. So I thought it might be time to send out a reminder about the order that the pesticides go into the tank. Putting chemicals in the tank in the wrong order can result in the chemicals forming a “gunky mess” in the bottom of the tank. Sometimes the pesticides will settle out (form gunk) even when the proper order is followed, in which case a compatibility agent is needed. The order of putting pesticides in the tank is based on the formulation. The general order for mixing is as follows:

1. Compatibility agent (if needed)
2. Products in water soluble PVA bags (wait until they fully dissolve before continuing)
3. Wettable powders (first mixed with water in a bucket to form a slurry)
4. Dry flowables or water dispersible granules
5. Liquids (these are the true liquids, they do not turn the solution white when added to water)
6. Emusifiable concentrates (these do turn white when added to water) – this includes crop oil concentrate and methylated seed oil
7. Water-soluble additives (such as dry and liquid fertilizers, i.e. ammonium sulfate or UAN)

Some pesticides may suggest a different order for mixing, so refer to the label. Each type of formulation should be added and allowed to agitate for a few minutes before adding the next formulation. To further reduce chance of incompatibility, mix each pesticide with water prior to adding to the tank.

To check if a compatibility agent is needed prior to adding pesticides in the tank, use a jar test. Use a pint or quart jar and fill half full of the carrier (water or fertilizer). Calculate the proportion of each ingredient (i.e. water, liquid fertilizer, pesticides) to add to the jar. The proportions should be the same as will be added to the spray tank. Assuming spray volume is 25 gallons per acre, a dry formulated pesticide applied to a pint jar at 1½ teaspoons is the same as 1 lb/A. Likewise, a liquid formulation at ½ teaspoon in a pint jar is the same as 1 pint/A. Add the appropriate pesticides separately in the above order and shake the jar gently between pesticides. After all has been added, fill the jar with water, and give a final shaking. Let the jar set for about 10 minutes and look for the formation of large flakes, sludge, gels, or precipitates. This test could be run with two jars, one with a compatibility agent and one without. A compatibility agent added to a pint jar at ¼ teaspoon is the same as 2 pints per 100 gallons of carrier.

If your tank does end up with incompatible pesticides gunking up the bottom, try Dawn dish detergent. I have not done this myself but was told it was effective. Mixing Dawn (Dawn supposedly works better than all other dish detergents) with the water will re-suspend the incompatible pesticides. It is difficult to say how much Dawn to add, but start with a quart and add more if needed.