Tag: herbicide

Spring Weed Control for Pasture and Hayfields

Dr. Amanda Grev, Pasture & Forage Specialist
University of Maryland Extension

As things are greening up this spring, you may notice a few not-so-friendly plants popping up around your fields, especially given the milder weather this past winter. If you haven’t already done so, now is the time to scout your pastures and hayfields in search of winter annual and biennial weeds. When it comes to weed control, timing of herbicide application is critical and it is important to spray when weeds are most susceptible to achieve maximum effectiveness.

Winter annuals typically germinate in the fall, overwinter, and complete their reproductive cycle in the spring or early summer. Common winter annual species include chickweed, purple deadnettle, field pennycress, henbit, horseweed/marestail, shepherd’s purse, and the mustard species.  Annuals are best controlled during the seedling and early vegetative stage when they are young and actively growing. Herbicide applications will be more effective if made at this stage while they are still vegetative and more susceptible and will prevent them from flowering and producing seed.  At this time of year, these winter annuals are growing rapidly and have already or will soon begin to flower and set seed. If the winter annuals in your fields have moved beyond this stage, an application may offer some control but you may also want to take note of those weedy areas now and target them later this year with a late fall application.

Biennials live for two growing seasons, with the first year consisting of only vegetative growth as a seedling and rosette and the second year consisting of vegetative growth and also reproductive growth in the form of an elongated flower stalk. Common biennial species include burdock, bull thistle, musk thistle, and wild carrot. These weeds are best controlled during the seedling and rosette stage, and should be treated now while they are smaller and more susceptible and before they begin to bolt.

There are a number of herbicides available for control of broadleaf weeds. Herbicide selection should be based on the type of forage and weed species present. The most common herbicides used for control of broadleaf weeds in grass hay or pasture are the plant growth regulator herbicides, which includes products containing 2,4-D, dicamba, triclopyr, aminopyralid, picloram, or a mix of these (see the table below for a list of common products). These products are safe if applied to grass forages at the labeled rates but can kill or injure desirable broadleaf forages (i.e. clover) in grass-legume mixed pastures.

If weedy annual grasses such as crabgrass, foxtail, panicum, and Japanese stiltgrass are problematic, pendimethalin (Prowl H2O) now has a supplemental label that allows for its use on established perennial pastures or hayfields grown for grazing, green chop, silage, or hay production. It may be applied to perennial grass stands or alfalfa-grass mixed stands. Prowl H2O may be applied as a single application in the early spring, or for more complete control it can be applied as a split application with the first application in early spring and the second application after first cutting. Keep in mind, this herbicide is a pre-emergent herbicide, meaning it will only control weeds if applied prior to germination. If soil temperatures in your area are already above 50°F it is likely that crabgrass and stiltgrass has already germinated, but a split application of Prowl H2O now and after first cutting can help control foxtail. There are currently no herbicides labeled to control emerged weedy grasses in grass stands or alfalfa/grass mixes.

Note that if forages were recently seeded and are not yet established many of these herbicides can cause severe crop injury. Most herbicide labels for cool-season perennial grasses state that the grasses should be well established with at least 4-5 inches of growth, although some labels are more restrictive than this. In addition, some of these herbicides have haying or grazing restrictions following application. Always read and follow the guidelines listed on the product label for proper rates, timing, residual effects, and any grazing or harvest restrictions following application.

Lastly, remember that while herbicides can be a useful tool for weed management in pastures and hayfields, they are not the only option for weed control. A program that integrates several different control strategies is generally more successful than relying on a single method. For maximum results, include cultural practices such as selecting adapted species and maintaining optimum soil fertility, mechanical practices such as timely mowing or clipping to suppress weed seed production, and biological practices such as utilizing livestock for controlled grazing or browsing. And remember that weeds are opportunistic; the best method for weed control is competition with a healthy, dense stand of desirable forage species.

Product Active Ingredients Application Rate* General/Restricted Use
2,4-D 2,4-D 1 to 2 qt/A General
Banvel/Clarity dicamba 0.5 to 2 pt/A General
Crossbow 2,4-D + triclopyr 1 to 6 qt/A General
GrazonNext HL 2,4-D + aminopyralid 1.2 to 2.1 pt/A General
Grazon P+D 2,4-D + picloram 2 to 8 pt/A Restricted
Milestone aminopyralid 3 to 7 fl. oz/A General
PastureGard HL triclopyr + fluroxypyr 0.75 to 4 pt/A General
Prowl H2O pendimethalin 1.1 to 4.2 qt/A General
Remedy Ultra 4L triclopyr 0.5 to 4 pt/A General
Stinger clopyralid 0.7 to 1.3 pt/A General
Surmount picloram + fluroxypyr 3 to 6 pt/A Restricted
WeedMaster 2,4-D + dicamba 1 to 4 pt/A General

*For use in established grass pasture or hayfields

 

Pyrethroid insecticide effects on pests and beneficials in field corn

Maria Cramer, Edwin Afful, Galen Dively, and Kelly Hamby
Department of Entomology, University of Maryland

Overview

Background: Due to their low cost, pyrethroid insecticides are often applied when other chemical applications are made. For example, they may be included in tank mixes with herbicides in early whorl corn and with fungicides during tasseling. These pyrethroid sprays often target stink bugs; however, the timing of these treatments is not ideal for stink bug management. Pyrethoid insecticides may harm beneficial insects that help keep pest populations in check and repeated use of pyrethroids can contribute to insecticide resistance.

Methods: In this study, we examined the effect of Bifenture EC® (pyrethroid active ingredient: bifenthrin) applied with herbicides in V6 corn and with fungicides in tasseling corn. We evaluated impacts on pests and beneficials at both application timings. Yield was measured at harvest.

Preliminary Results:  At both application timings, Bifenture EC® did not improve insect pest management because pests were not present at economic levels. We did not find evidence for flare-ups of aphids or spider mites, but a rainy late summer made it unlikely that we would see many of these pests. There were no yield differences between the treatments.

Background

As a result of the low cost of pyrethroid insecticides, preventative applications are common, especially in tank mixes with other routine chemical inputs, such as herbicides and fungicides. However, lower grain prices and low insect pest pressure make it less likely that pyrethroid applications will provide economic returns. Bt hybrids1 and neonicotinoid seed treatments control many of the pests targeted by pyrethroid insecticides. Because they have broad spectrum activity, pyrethroids can negatively impact natural enemies2 which can result in flare-ups of secondary pests3. Tank mix timings may be less effective than applying when insect populations reach threshold. For example, when pyrethroids are combined with herbicide applications, they are too late to control early-season stink bugs and other seedling pests. When pyrethroids are combined with fungicide sprays at tasseling, few insect pests are present at damaging levels. Stink bugs may feed on the developing ear at this time, causing deformed “cowhorned” ears; however, this is rarely a problem in Maryland and stink bug damage is generally not economic throughout a field because feeding is primarily concentrated at the field edge4. Insecticide applications at tasseling have a high potential to affect beneficial insects, especially pollinators and natural enemies that are attracted to corn pollen.

Objectives: Our objectives were to determine the effect of pyrethroids applied preventatively in tank-mixes on corn pests, beneficials, and yield.

Methods: This study was conducted in 2018 and 2019 at the University of Maryland research farm in Beltsville, MD. For each application timing, we planted four replicate plots of a standard Bt field corn hybrid, DeKalb 55-84 RIB (SmartStax RIB complete Bt insect control in addition to fungicide and insecticide seed treatments) at 29,999 seeds per acre. Standard agronomic practices for the region were used.

The herbicide timing compared two treatments:

  1. Herbicide alone (22 oz/acre Roundup WeatherMAX®, 0.5 oz/acre Cadet®, 3 lb/acre ammonium sulfate
  2. Herbicide (same as above) + Insecticide (Bifenture EC® 6.4 oz/acre)

Treatments were applied at V6/V7. We visually surveyed corn plants for pest and beneficial insects before and after application. We also placed sentinel European corn borer (ECB) egg masses in the field to assess predation rates before and after treatment.

The fungicide timing compared two treatments:

  1. Fungicide alone (Trivapro® 13.7 oz/acre)
  2. Fungicide (same as above) + Insecticide (Bifenture EC® 6.4 oz/acre)

Treatments were applied at green silk. We inspected the ear zone and silks for pests and beneficial insects before application. After application, we recorded the number of ears with pest damage and the kernel area damaged. We also counted stink bug adults and cowhorned ears. Six weeks after application, we visually assessed plants for spider mite and aphid colonies.

Sampling for pests and beneficials (left) and; sentinel European corn borer egg mass (right).
Sampling for pests and beneficials (left) and; sentinel European corn borer egg mass (right).

Results

In the herbicide-timing study in 2019 we observed no effect on beneficial insects from the treatments (Figure 1). The most abundant beneficial species were minute pirate bugs and pink spotted lady beetles, which are very mobile and may have recolonized treated plots after treatment. Similarly, treatments did not affect predation on the sentinel egg masses, suggesting that the pyrethroid application may not have affected predators’ ability to locate and consume eggs. Across the treatments, 30-50% of egg masses were consumed by predators.

Minute pirate bug on European corn borer egg mass.
Minute pirate bug on European corn borer egg mass.

The treatments did not impact the number of beneficials at the herbicide timing (N.S.). The pyrethroid insecticide significantly reduced the number of plant hoppers and plant bugs from less than 4 per plant on average to less than 2 per plant (significantly different p<0.05, *), though these insects are not economic pests at this stage. There were never more than 2 stink bugs per 90 plants, well below the treatment threshold of 13 per 100 plants4.

In the fungicide-timing study in 2019, beneficials, especially minute pirate bugs, were abundant at the time of application (3 in every 10 plants), while stink bugs, the presumed target pest, were very rare (1 stink bug in every 68 plants). In 2018, stink bugs were similarly scarce. Overall pest abundance was low (1 in every 35 plants). After application, there was no difference in the incidence or amount of the corn ear damaged by worms, stink bugs, or sap beetles between treatments. Average stink bug and earworm incidence was roughly 1 in 10 ears, while sap beetle was even less frequent. Cowhorned ears and adult stink bugs were almost non-existent in both treatments.

Six weeks after application we found no differences in aphid or spider mite populations between the treatments, suggesting that pyrethroid applications at tasseling did not cause secondary pest outbreaks. We sampled after a period of dry weather; however, the late summer was rainy at Beltsville, which likely suppressed spider mite and aphid populations. Under drought-stress, reductions in the natural enemy population from pyrethroid use might contribute to flare-ups of aphids and spider mites.

Figure 1. Herbicide timing. July 3, 2019, Beltsville MD. Mean number of insects per 10 plants in V7 corn after treatment. N.S.=not significant. H=herbicide; P=pyrethroid.

Yield

For the herbicide timing and fungicide-timing (Figure 2) studies, treatments did not affect yields in either 2018 or 2019.

Conclusions

Figure 2. Herbicide timing (left) and fungicide timing (right), 2018 and 2019, Beltsville MD. Mean yield per acre under two treatments. Yields were not significantly different by treatment in either study. For the fungicide-timing study, 2019 yields were significantly higher than in 2018. N.S.=Not Significant. H=Herbicide; F=Fungicide; P=Pyrethroid.

Results from the 2018 and 2019 studies suggest that pyrethroid applications do not provide yield benefits in corn when tank-mixed with herbicides or fungicides, likely due to the lack of insect pest pressure at these spray timings. Beneficial insects were abundant in the crop at each of these timings and did not appear to be affected by the pyrethroids in the herbicide plots. Repeated preventative use of pyrethroids in the same field could potentially hinder the natural biocontrol of corn pests.

Lady beetle larva (a predatory insect) in silks.
Lady beetle larva (a predatory insect) in silks.

Sources

1 DiFonzo, C. 2017. Handy Bt Trait Table for U.S. Corn Production, http://msuent.com/assets/pdf/BtTraitTable15March2017.pdf

2Croft, B.A., M.E. Whalon. 1982. Selective toxicity of pyrethroid insecticides to arthropod natural enemies and pests of agricultural crops. Entomophaga. 27(1): 3-21.

3Reisig, D.C., J.S. Bacheler, D.A. Herbert, T. Kuhar, S. Malone, C. Philips, R. Weisz. 2012.Efficacy and value of prophylactic vs. integrated pest management approaches for management of cereal leaf beetle (Coleoptera: Chrysomelidae) in wheat and ramifications for adoption by growers. J. Econ. Entomol. 105(5): 1612-1619

4Reisig, D.C. 2018. New stink bug thresholds in corn, https://entomology.ces.ncsu.edu/2018/04/new-stink-bug-thresholds-in-corn/

 

Herbicide Options for Monsoon Season

By Matt Morris, Agriculture Extension Educator
University of Maryland Extension, Frederick County
mjmorris@umd.edu

While I am usually very cautious to complain about the rain, enough is enough! There isn’t one farm in this State that isn’t weeks behind because of our recent weather. Most all the hay is nearing straw quality and there’s still a good amount of corn that is yet to be planted. Not to mention the sheer number of soybean acres that haven’t gone in the ground. One thing this weather has done a good job of is ruining the best laid herbicide plans for corn and soybeans. I’ll outline some scenarios and what post-emergence options you might have.

Let’s say you planted corn May 15th and were planning to spray after you planted, but before the plants emerged. Then it started raining. Now your corn is up and at the V3 or V4 stage (3 or 4 visible leaf collars). Weeds are emerged and racing the corn. The obvious go-to would traditionally have been glyphosate (RoundUp) for tolerant corn varieties. However, in the day and age of herbicide resistance this probably won’t be enough. For tough to control broadleaf weeds I’d suggest throwing a product like Status or Diflexx Duo in with your glyphosate to pick up weeds like marestail, lambsquarter, or pigweeds. These are “safened” dicamba products. The caution is that these products cannot be applied to corn before the V2 stage. Also remember, most herbicides have a maximum height for application ranging anywhere from V2-V8.

You’ll also want to think about throwing a residual product in the tank since we missed that before planting. This is where atrazine or S-metolachlor (Dual) can work well. Atrazine can help control a lot of our broadleaf weeds and works really well on morning glory if you have pressure in your fields. S-metolachlor won’t kill emerged weeds, but will keep any small seeded weeds from germinating for several weeks. A word of caution: atrazine cannot be applied to corn greater than 12” in height. S-metolachlor has a maximum application height of 40”.

Soybeans present a much more challenging problem due to herbicide resistant broadleaf weeds and their widespread prevalence in the area. Here’s our first scenario: You sprayed a combination of burndown and residual herbicides on May 15th with hopes to plant that weekend. Then it started raining. You still can’t get into the field to plant. Whatever you do, resist the temptation to plant without another residual application. If you can’t, the weeds will come up long before your crop can canopy. You may need to go back in with a product like S-metolachlor, metribuzin, or Valor to hold weeds back until the crop canopies. If you need another burndown because weeds are emerged, adding in a product like paraquat with your residual can help. The key is starting clean. A word of caution: most herbicides have a maximum application rate per season so read the label to make sure you don’t exceed that amount.

Here’s the second scenario: you planted soybeans on May15th and planned to come in and spray the next day. Then it started raining. Now your soybeans are up and no burndown or residual herbicides were applied. The first thing to do is remember that most all of our marestail are glyphosate and ALS (Firstrate, Synchrony, Raptor, etc.) resistant so I will not consider them here. That being said there are areas they still may work, but I caution against them being used alone. Post-emergence options are limited and work best on 4” or smaller weeds. The PPO herbicides like Reflex or Blazer can be applied post-emergence for small, annual broadleaf weeds, but can cause minor crop injury. Since there was no opportunity to apply a residual herbicide it may be a good idea to include S-metolachlor or Zidua to try and hold back any weeds yet to germinate. Zidua must be applied by the 3rd trifoliate growth stage.

If you planted dicamba tolerant soybeans or Liberty-Link soybeans they can provide excellent post-emergent weed control. Again, I caution using dicamba or Liberty on weeds greater than 4” or in the tank alone as that is the path to herbicide resistance.

There are a million different scenarios you can be faced with in the field and we’re dealing with Mother Nature. That means we can still get rains delaying us even further. If you have questions about your options don’t hesitate to give your local Extension office a call and one of us can work up something specific for your scenario.

 

Matt Morris
301-600-3578
mjmorris@umd.edu

Proper Stewardship by Growers is Essential to Ensuring Dicamba Tolerant Soybeans Continue to be Available

By Matt Morris, Agriculture Extension Educator
University of Maryland Extension, Frederick County

Dicamba tolerant soybeans, marketed under the trade name Roundup Ready 2 Xtend soybeans, are again available to  Maryland growers for the 2018 growing season. This line of soybeans will combine previous Roundup Ready technology with tolerance to the herbicide dicamba.

While this new dicamba tolerance may be useful in combating certain tough-to-control weeds, including marestail and palmer amaranth, use caution when applying dicamba. Applications of dicamba may cause problems due to the sensitivity of certain crops to the herbicide. Exposure can occur due to drift, volatility, or a non-target application.

Below are some recommendations to consider when using new dicamba-tolerant technologies.

  • Dicamba type:

The only dicamba products that will be approved for in-crop use with Xtend soybeans will be XtendiMax from Monsanto, FeXapan from Dupont, and Engenia from BASF. These are lower volatility formulations than other dicamba products and are designed for dicamba-tolerant soybeans. These products will be classified as restricted-use pesticides for 2018 and all users must take dicamba or synthetic auxin herbicide training prior to purchasing these products.

  • Know the location of sensitive crops:

Talk with your neighbors and know where crops such as tomatoes, grapes, alfalfa, and non-tolerant soybeans are located. Engenia includes woodlands and native vegetation as sensitive crops; any broadleaf cash crop is listed as a sensitive crop in the XtendiMax label. This information will help you decide whether to use dicamba near these crops, especially if a prevailing wind will cause drift in their direction.

In addition, you should maintain buffer zones of 110 feet (220 feet if a 22 oz/ac rate is exceeded), between dicamba application sites and sensitive crops. The two websites below contain a (incomplete) list of some sensitive crops in your area:

http://maryland.maps.arcgis.com/apps/OnePane/basicviewer/index.html?appid=a4e2153518d04317bbac79702aafcd53

www.driftwatch.org

  • Rates:

Engenia – Dicamba tolerant soybeans – maximum of 12.8 fl oz/application and 51.2 oz/season.

FeXapan and XtendiMax – Dicamba tolerant soybeans – maximum of 44 fl oz/pre-plant application, 22 fl oz/post-emergence application, and a maximum of 88 fl oz/season.

  • Nozzle selection:

Engenia – Only TTI11004 and TTI11005 are currently approved.

FeXapan and XtendiMax – Apply large droplets with specific nozzles. Do not use flat fan nozzles that produce driftable fines. Use TTI11004 or nozzles listed on the EPA-mandated product websites.

  • Tank mix partners and water conditioning:

Ammonium sulfate (AMS) CANNOT be mixed with the new dicamba formulations. AMS is commonly used as a water conditioning agent for glyphosate applications. Adding AMS will increase the volatility of dicamba. Also, certain spray adjuvants and herbicide tank mix partners are not compatible with the new dicamba formulations.

Lists of approved tank mix partners can be found at:

http://www.xtendimaxapplicationrequirements.com/Pages/default.aspx

http://agproducts.basf.us/campaigns/engenia/tankmixselector/

http://www.dupont.com/products-and-services/crop-protection/soybean-protection/articles/fexapan-tank-mix-partner.html

  • Recordkeeping:

For the 2018 season, recordkeeping will be mandatory when applying dicamba in-crop on soybeans. Specific recordkeeping requirements will vary between the three approved, in-crop dicamba products, so always consult the label. However, it is recommended you always record wind speed and direction, air temperature, humidity, location of the application, product(s) used, rate, crop being treated, pests being targeted, and total product amounts used, among other information. Proper recordkeeping can provide essential evidence in the event of herbicide damage to a non-target crop.

  • Wind speed, temperature, and temperature inversions:

The optimal wind speed for applying the new dicamba products is 3-5 mph. Applications are prohibited when wind speeds are above 10 mph.

As the temperature increases, so does the volatility of dicamba. Use caution when applying dicamba products in hot, humid weather.

Take caution when wind speeds are below 3 mph, since this could indicate the presence of a temperature inversion. This phenomenon occurs when the temperature, which normally decreases with height in a thin layer of the atmosphere, increases with height. Inversions are another cause of vapor drift. Other indicators of a temperature inversion include low-hanging smoke or dust, morning fog or frost, clear and still nights with little to no cloud cover, and ground temperatures cooler than early morning air temperatures.

  • Multiple applications and weed height:

Multiple herbicide applications with the same mode of action within a single season selects for herbicide resistance. Avoid using dicamba on tolerant soybeans more than once in a season. If possible, a pre-emergence herbicide should be applied before or at planting. It is also important to remember that weeds should be targeted at 4” of height or less for successful control.

  • Application suggestions:

Keep ground speeds below 15 mph and nozzle pressures as low as possible to maintain the desired application rate. Boom height should be no more than 24” above the crop or weed canopy. If a weed is 4” tall, boom height should not exceed 28.”

  • Most importantly:

ALWAYS READ AND FOLLOW PESTICIDE PRODUCT LABELING. It is a violation of Federal and state law to use any pesticide product in a manner inconsistent with its labeling.

Approval of dicamba-tolerant soybeans by the U.S. Environmental Protection Agency will run until the end of 2018. At that point, they will consider whether to renew approval based on the number of problems that occur as a result of this new technology.

If you have questions regarding the use of dicamba tolerant soybean technology or dicamba, please contact Matt Morris @ 301-600-3578 / mjmorris@umd.edu or your local Extension office for more information.

Dicamba Changes for 2018:

  1. Classified as a restricted use pesticide that only certified pesticide applicators can purchase.
  2. Anyone applying these products MUST receive dicamba or auxin-specific training.
  3. Applications can ONLY be made between sunrise and sunset.
  4. Recordkeeping is mandatory. Refer to the individual labels for exact recordkeeping requirements.
  5. All applications cannot be done when wind speeds exceed 10 mph (down from 15 mph).
  6. Record of compliance with spray system cleanout is mandatory.
  7. Labels have enhanced language about susceptible crops. This includes non-dicamba-tolerant soybeans.
Herbicide-damaged soybeans from dicamba drift
Figure 1. Example of damage when a label rate of 1pt/ac of the herbicide Clarity drifted on to non-tolerant soybeans.