Rutgers University | New Jersey Agricultural Experiment Station | Pesticide User Responsibility

May 7, 2020

Weather Conditions and Herbicide Performances

Temperature and Herbicide Performance

With air temperatures remaining relatively low this spring, growers have asked about how temperature may affect the efficacy of herbicide applications. The effect of cool temperatures on weed control efficacy will depend on the type of herbicide application, the rate applied, and the physiological status of the target weed.

Summer annual weeds such as lambsquarters or crabgrass require good soil moisture and soil temperatures between 60 and 70F to start the germination process. It is important for preemergence applications to be effective that residual herbicides are applied before soil reaches this optimum temperature range. Of course, herbicides should never be applied on frozen ground. However, cool and wet weather can increase the potential for crop injury with preemergence herbicides because of slower herbicide metabolization by the crop.

Grass and broadleaf weeds are controlled more effectively when plants are actively growing. The ideal air temperature for applying most post-emergence herbicides is between 65°F and 85°F. At lower temperature, weed control will be slower, especially with systemic herbicides such as glyphosate, Poast, Select, or Sandea that are more slowly absorbed and translocated by the weeds compared to applications at higher temperatures. Also, slower herbicide uptake by the weeds will increase the required rainfast period and slows the development of herbicide symptoms on the plants. Weeds that have been damaged (by mechanical equipment for example) or that are under stress (drought, water excess) at the time of herbicide application or before herbicide has properly translocated will not be properly controlled. Reduced herbicide rate treatments are less likely to provide acceptable control under adverse conditions than when plants are actively growing. Thus, it is best to avoid applications of postemergence herbicides during periods of cool temperatures (<40°F at night; <55°F during the day).

High temperatures increase the loss of volatile herbicides. 2,4-D ester or dicamba will rapidly evaporate at temperatures above 80°F, causing. The use of such ester formulations should be restricted to fall, winter, and early spring because sensitive plants are not present and lower temperatures reduce vapor drift hazard.

Adjuvants may also affect crop safety and weed control. Oil additives may increase risk of crop injury but may be necessary for greatest weed control. Refer to each herbicide label for specific information on adjuvant use during stress conditions. Use an oil additive if risk of crop injury is acceptable for those herbicides that allow use.

Ideally, you should be waiting for the right conditions to apply the herbicide. However, if weeds are at growth stage that require a rapid intervention, select a herbicide with excellent efficacy for controlling your target weeds. Remember that the efficacy pf postemergence applications is mainly dictated by weed size… spraying weeds beyond the size range recommended on the label will result in porr weed control.

Rainfast Period

The rainfast period is the minimal period of time that must elapse between herbicide application and subsequent rainfall to ensure good postemergence herbicide performance. Generally, herbicide rainfast ratings are based on good growing conditions (table 1). Poor conditions may require a longer interval between application and any rainfall to ensure adequate herbicide translocation within the weed before the herbicide is washed off. For many herbicides, any amount of rainfall soon after spraying has the potential to reduce absorption, translocation, and subsequent weed control. If you apply herbicide and it rains before it’s rainfast, herbicide performance will be reduced.

Table 1. Rainfast time for postemergence herbicides commonly used in New Jersey Specialty Crops.

*Rainfall will improve control from root uptake.

**Rainfall within 6 hr. after application may reduce effectiveness. Heavy rainfall within 2 hours after application may wash the chemical off foliage and a repeat treatment may be required.

Filed Under: Blueberry, Fruit, Tree Fruit, Uncategorized, Vegetable Crops, Wine Grape Tagged With: ,
April 24, 2020

Chemical Alternative Options to Paraquat for Weed Control in Vegetable Crops

Spraying for pests in a field Paraquat is an herbicide labeled on various crops species for row middles applications. However, with new paraquat use restrictions in place, vegetable growers may be interested by other herbicide options available for controlling emerged weed seedlings. Paraquat controls numerous annual grasses and broadleaf weeds seedlings by inhibiting plant photosynthesis. Its acts quickly by contact when absorbed by plant foliage and has no soil activity due to complete soil adsorption. Because of poor translocation, it is essential to have complete foliar coverage to achieve good weed control. Hence, the need for a non-ionic surfactant and the importance of making sure that weeds are not taller than 6” when direct-spraying paraquat in row middles. Paraquat offers relatively good crop safety because it does not translocate and will control a wide range of annual weeds at the seedling stage, which makes it the herbicide of choice for postemergence row middles weed control in labeled crops.

However, paraquat high toxicity to humans either through ingestion, breathing, or simple dermal contact justifies its “Restricted Use Pesticide” classification and the implementation of new EPA regulations since November 2019 (https://plant-pest-advisory.rutgers.edu/gramoxone-paraquat-mandatory-training-required-before-use/)

Chemical alternatives to paraquat are available for vegetable growers but may not provide a similar level of weed control or can have more detrimental effects when contacting the crop because of their systemic activity. All the alternative options presented in this post are classified by WSSA Group Numbers which are based on herbicide site of actions within the plants. All recommendations provided here are strictly limited to shielded row middle applications. Consult label for approved surfactants, application restrictions, pre-harvest intervals, and crop rotation restrictions. The mention of trade names and rates is for educational purposes and does not imply endorsement by the author or the New Jersey Agricultural Experiment Station. Always defer to the product label for instructions on properly applying an herbicide.

 Labeled Crops for Postemergence Row Middles Herbicides

WSSA Group Product Name Asparagus Strawberry Cucumbers Pumkin, winter, and summer squash Cantaloupe Watermelon Eggplant Pepper Tomato
2 League – – – – YES YES – YES YES
Sandea 75 DF YES – YES YES YES YES – YES YES
Solida 25DF – – – – – – – – YES
4 Spur / Stinger 3A YES1 YES2 – – – – – – –
Weedar 64 YES YES – – – – – – –
5 Metribuzin 75DF – – – – – – – – YES
7 Lorox 50DF YES – – – – – – – –
14 Aim EC YES YES YES YES YES YES YES YES YES
Reflex 2SL – – – YES3,4 – YES3 – – –
22 Reglone – – – – – – – – YES5
27 Callisto YES – – – – – – – –

1 Only Spur is labeled for use on asparagus

2 Only Stinger is labeled for use on strawberry

3 Special Local Need label approved for New Jersey and expiring on Dec. 21, 2022

4 Labeled only for straight neck yellow, crooked neck yellow, and zucchini summer squash types

5 Special Local Need label approved for New Jersey and expiring on Dec. 31, 2021

Group 2 – Inhibition of amino acids biosythesis

Sandea (halosulfuron), League (imazosulfuron), and Solida (rimsulfuron) have both preemergence and postemergence activity. These herbicides will control emerged seedlings of galinsoga, pigweeds, and ragweed, and suppress yellow nutsedge. League has shown good suppressive activity of common purslane. However, they are weak on common groundsel, common lambsquarters, eastern black nightshade. Sandea and League have little to no activity on grasses whereas Solida will have fair activity on crabgrass, barnyardgrass, and foxtail, but not on goosegrass or fall panicum. Thus, these herbicides should always be tank mixed with an herbicide partner for broadening their weed control spectrum. These herbicides have systemic activity and contact with the planted crop should always be avoided. Postemergence activity will be achieved if targeted weeds are no taller than 3” tall and if the appropriate surfactant is added to the spray solution.

Group 4 – Plant growth regulators

Spur/Stinger (clopyralid) is a soil residual and postemergence herbicide that received a 24(c) Special Local Need label for use on strawberry in New Jersey. Label allows spring and post-harvest applications to control composites (thistle, ragweed, dandelion, groundsel, galinsoga) and leguminous (clover, vetch, mugwort) weeds. It has very little to no activity on other broadleaf weed as well as on grasses. Stinger should not be tank-mixed with any other herbicide or with a surfactant. Weedar 64 (2,4-D) is strictly a postemergence herbicide only labeled for use on asparagus and strawberry. Weedar is active on many annual and perennial broadleaf weeds but is weak on galinsoga and has no activity on grasses. Because of the risk of physical or volatility drift associated with growth regulator herbicides, Stinger, Spur or Weedar should never be applied if sensitive crops (cucurbits, eggplant, pepper, tomato) are planted nearby or if conditions (wind, inversion temperature, topography) favor drift.

Group 5 and 7 – Photosynthesis inhibitors

Metribuzin (metribuzin) is a soil residual and postemergence herbicide labeled for use on tomato that will primarily control broadleaf weeds no taller than 1”. Metribuzin provides good control of young seedlings of most broadleaf weeds, except for morningglories and nightshades. Metribuzin can be applied postemergence as a directed spray at least 2 weeks after transplanting and when tomato plants have reached the 5-leaf stage. injury. Lorox (linuron) is labeled for use on asparagus as a postemergence spray before the cutting season or immediately after cutting. Lorox will provide similar control to metribuzin on weeds no taller than 4”. Both Metribuzin and Lorox are providing poor control of grasses and should therefore be tank mixed with a graminicide if grass seedlings have already emerged. Contact with the planted crop should always be avoided to reduce the risk of herbicide injury.

Group 14 – Cell membrane disrupters

Aim (carfentrazone) is strictly a postemergence herbicides that acts by contact on many annual broadleaf weeds no taller than 3-4”. It has no activity on grasses and only poor to fair efficacy on cocklebur, jimsonweed, and common purslane. Complete foliar coverage is essential to achieve good weed control and will require mixing COC, MSO or a non-ionic surfactant. Reflex (fomesafen) received a 24(c) Special Local Need label for use on pumphin, watermelon, winter and summer squash. Reflex has both soil residual and postemergence activity. It will provide fair to good control of various broadleaf weeds, including galinsoga, pigweeds, jimsonweed, nightshads, ragweed, carpetweed and shepherd’s purse, but is weak on grasses. Row middle applications should be made prior to emergence or transplanting for pumpkin and squashes, but are allowed post-transplant for watermelon. Applications should always be made with a shielded sprayer to avoid crop injury.

Group 22 – Cell membrane disrupters

Reglone (diquat) is a postemergence non selective herbicides that belongs to paraquat herbicidal family but has a lower toxicity. Reglone received a 24(c) Special Local Need label for shielded applications in tomato row middles. Spray coverage is essential for optimum effectiveness and can be achieved by mixing a non-ionic surfactant to the spray solution. Reglone is expected to have a similar weed control spectrum than paraquat but local data are needed to confirm its efficacy, especially on grasses.

Group 27 – Pigment inhibitors

Callisto (mesotrione) has both soil residual and postemergence activity and is labeled on asparagus for banded application prior to soear emergence or after harvest. Callisto applied postemergence will provide excellent control of annual broadleaf weeds such as galinsoga, lambsquarters, morningglories, pigweeds, nightshades, or velvetleaf. Callisto is not effective for controlling grasses and only provide limited control of common purslane and common ragweed. Callisto can also help suppressing yellow nutsedge. Applications for controlling targeted weed seedlings should always include COC or a non-ionic surfactant in addition to ammonium sulfate for improving Callisto burndown effectiveness. Weeds should not be taller than 5″ for optimal control.

 

In summary, there are other chemical options that can replace paraquat for control of emerged weeds in row middles in vegetables. However, most of them will have a more restricted spectrum of weed control than paraquat and will require the growers to properly identify the weed species before deciding which postemergence herbicide they want to use. Most of these herbicides have little to no control of grasses and will therefore require mixing a postemergence grass herbicide such as clethodim or sethoxydim for controlling emerged grass seedlings. Finally, timing of application with regard to weed growth stage is more critical with alternative options than with paraquat, since most of these herbicides require weeds no taller than 3 to 4″, or even 1″ for some herbicides, for achieving proper control.

 

Filed Under: Vegetable Crops Tagged With: , , , , ,
April 20, 2020

Safely Using Herbicides in Re-Used Plastic Mulch

Crops covered with plastic protection

Plastic mulch and trickle irrigation are expensive. Re-using the mulch for a second crop after the first can be an effective way to spread the cost.

Plastic mulch and trickle irrigation are expensive. Re-using the mulch for a second crop after the first can be an effective way to spread the cost. When the cost of supplies and labor are evaluated, re-using a field with trickle irrigation and black plastic mulch is an attractive idea, but weed control can be a problem.

The herbicides used under the plastic and between the rows of mulch for the first crop must be safe and labeled for use in the second crop. Prefar applied at 6 quarts per acre in a band when the mulch is laid is a good choice for under the plastic. Prefar is labeled for many vegetable crops but ALWAYS check the label to see if the crop you plan to plant is listed on it. Prefar and Gramoxone plus NIS (nonionic surfactant), applied as a shielded banded spray between the rows of mulch, are also labeled for a wide range of vegetable crops. Be sure post plant applications of Gramoxone plus NIS are shielded, applied at low pressure, and a low drift agent is used.

Often the greatest challenge is eliminating the first crop and any weeds in the field prior to planting the second crop in the mulch. No herbicide should be sprayed broadcast over the mulch except Gramoxone, which is quickly broken down by sunlight.

Roundup and other glyphosate products should NEVER be used on plastic mulch. Gyphosate has no residual activity due to strong and immediate adsorption by the soil where it is slowly broken down by soil microorganisms as a food source. On plastic mulch without contact with the soil, glyphosate does not easily wash off the plastic with rain or irrigation. The simple act of letting the root ball in contact with the plastic during transplanting can expose the crops roots to enough glyphosate to cause lasting injury and crop loss!

Residual herbicides must be banded between the rows of plastic mulch, NEVER sprayed broadcast over the mulch. Broadcasting residual herbicides over plastic mulch can increase the risk of washing the herbicide from the plastic into the planting hole when it rains or if you irrigate overhead. Herbicide concentration in the planting hole will be way higher than the safety threshold for any crop! If the herbicide from 1 square foot of plastic washes into the 3 square inch planting hole, that will increase increase 48 times the intended herbicide rate in the planting hole!!! You can certainly not expect good crop safety from any herbicide at 48 times the intended rate! Keep all residual herbicides off the plastic mulch.

In summary, the greatest weed control challenge in re-used plastic is weeds growing under and through holes in the mulch. Gramoxone is broken down by sunlight, so it can be used to kill the first crop and emerged weeds. Consider fumigating under the mulch with a water soluble fumigant injected through the trickle irrigation to provide weed control in the second crop. Disease control may be another added benefit. Remember to wait until the fumigant has dissipated before planting.

Filed Under: Vegetable Crops Tagged With: , , ,
March 16, 2020

2020 Recommendations for Preemergence Weed Control in Established Blueberry

With T3 stage scheduled for late March, it’s really time now to apply your preemergence herbicides before blueberry bud break!

Preemergence herbicides should be applied prior to weed seed germination. If applied to weeds that are already out of the ground, most of these products will not control them. Keep also in mind that these herbicides should receive at least ½” rainfall or irrigation one to seven days after application (depending on herbicides) to incorporate the herbicide in the soil

In order to reduce the potential of selecting for herbicide-resistant weeds, it is highly recommended mixing two residual herbicides with different MOA whenever you apply preemergence herbicides. Make sure the herbicides you plan to apply will be effective at controlling the weed species in your field by checking the herbicide label. Usually, residual herbicides will suppress weed for 6 to 8 weeks depending on irrigation as well as soil and weather conditions. After this period, another residual herbicide can be needed to control weeds through harvest and could be mixed with a postemergence herbicides to control emerged weeds. Roundup (glyphosate), Rely 280 (glufosinate,) and Gramoxone (paraquat) are postemergence herbicides that may be applied with preemergence herbicides before bud break with little risk for crop injury.

  •  MOA 2: Solida (rimsulfuron) and Sandea (halosulfuron) are ALS inhibitors that have both preemergence and postemergence activity. They control most annual broadleaves but are weak on common groundsel, common lambsquarters and eastern black nightshade. Sandea is ONLY recommended for postemergence control of yellow nutsedge. However, these two herbicides will not control ALS resistant weeds (horseweed, ragweed…) already widespread in New Jersey. Thus, these herbicides should always be tank mixed with a partner effective at controlling these weeds
  • MOA 3: Kerb (pronamide) and Surflan (oryzalin) are mitosis inhibitor that will be effective at controlling many annual grass species for 4 to 6 weeks after application. Kerb also help controlling perennial quackgrass. If applied to warm soils (> 55°F), Kerb persistence (and weed control) is much reduced; therefore, reserve Kerb for fall/winter application. Do not use Kerb on blueberries that have not been established for about a year.
  • MOA 5 and 7: The photosynthesis inhibitors (PS II inhibitors) have a broad spectrum of control and will be effective against many broadleaves and annual grasses when applied in spring. Karmex (diuron) and Princep (simazine) have relatively low solubility and have been very safe on blueberries. Sinbar (terbacil) has a longer residual life in the soil and also is more soluble, so it should be used infrequently on light, wet soils. Velpar (hexazinone) is very soluble and should not be used on New Jersey sandy soils. These herbicides are effective on a many broadleaf weed species, including common chickweed, common lambsquarters, common groundsel, henbit, nightshade, redroot pigweed, pineappleweed, shepherd’s-purse, smartweed, and some mustards. Sinbar and Princep will also control most of the annual grasses and help suppressing quackgrass.
  • MOA 12: Solicam (norflurazon) is a pigment inhibitor that may be applied in fall or early spring primarily for annual grass control and quackgrass suppression. Solicam may also provide partial control of many broadleaf weeds as well as of yellow nutsedge. Do not use Solicam on blueberries that have not been established for about a year.
  • MOA 14: Chateau (flumioxazin), Zeus XC (sulfentrazone), and Zeus Prime XC (sulfentrazone plus carfentrazone) are PPO inhibitors with activity against many broadleaves (including redroot pigweed, catchweed bedstraw, common mallow, common lambsquarters, ladysthumb, wild mustard, and shepherd’s-purse) when applied preemergence in spring. Chateau and Zeus Prime XC also have some postemergence activity on newly emerged seedlings of annual weeds. Zeus products may also provide some suppression of yellow nutsedge. Chateau has a 7 day preharvest interval (PHI) and Zeus Prime XC have 3 day PHI, and can therefore be applied later in the season to extend preemergence broadleaves control into late summer. Blueberry plants must have been established at least two years prior to use of these herbicides.
  • MOA 15: Devrinol (napropamide) and Dual Magnum (s-metolachlor) are long chain fatty acid inhibitor. Devrinol will provide good control of annual grasses and should therefore be tank mixed with a PSII or a PPO inhibitor for controlling broadleaf weeds. Devrinol is rapidly degraded if left exposed on the soil surface, so it should be applied less than 24 hours before a rain event to incorporate the herbicide in the soil. Dual Magnum has a 24c Special Local Need label for blueberry in New Jersey. This herbicide controls many annual grasses and some small-seeded broadleaf annual weeds such as redroot pigweed, nightshade and common purslane. Dual Magnum also suppresses emergence of yellow nutsedge. Use Dual Magnum only on plants established for more than one year, and lower rates are suggested on 2- to 3-year-old plantings.
  • MOA 20: Casoron (dichlobenil) is a cellulose synthesis inhibitor recommended for fall application to control many annual and perennial broadleaves, grasses and yellow nutsedge. If left on the soil surface or if applied to warm soil (> 55°F or 70°F depending on dichlobenil formulation), Casoron can lose much of its activity. So, reserve this herbicide ONLY for fall/winter applications. Plants must be at least one year old before Casoron should be used.
  • MOA 21: Trellis SC (isoxaben) is a cell wall synthesis inhibitor currently currently registered for bearing and non-bearing blueberry. Trellis SC primarily controls annual broadleaf weeds, such as horseweed, common lambsquarters, wild mustards, shepherd’s- purse, purslane, and common chickweed; higher rates may also suppress field bindweed and curly dock. However, Trellis SC will have to be mixed with a Group 3, 12, or 15 residual herbicide for controlling annual grasses.
  • MOA 27: Callisto (mesotrione) is an HPPD inhibitor recommended for spring application to control many annual broadleaf weeds as well as annual sedges. It controls large crabgrass but no other grasses, such as goosegrass. Callisto may be used as a broadcast spray between rows to control broadleaves and crabgrass without injuring the fescue sod. Callisto has both preemergence and postemergence activity, and can therefore be used in spring to control ALS-resistant horseweed at the rosette stage.

Consult the 2020 Commercial Blueberry Pest Control Recommendations for New Jersey available on https://njaes.rutgers.edu for rates and additional information. The information above is correct to the best of our knowledge. Other formulations with the same active ingredient as some of the products listed above may exist that may or not may be labeled for the same uses. Always consult the label before making pesticide applications. Information was current as of February 25, 2020.

Filed Under: Blueberry, Uncategorized Tagged With: , ,
July 7, 2017

Getting the Upper Hand on Virginia creeper

Picture 1 – Virginia creeper vine

Virginia creeper (Parthenocissus quinquefolia) is a perennial woody vine that climbs on other objects or trails along the ground.  It is a common weed of orchards, vineyards and blueberry plantation. It is best identified by the typical palmate leaf with 5 leaflets that originate from the same point (picture 1).  Virginia creeper will produce many tendrils with adhesive disks at their tips that will allow the vine to climb upward and to attach to any support. It can grow under a wide range of conditions including dry sandy or moist organic soils, sunny or shady sites, and is tolerant to high salinity.  Plants will often establish through seeds dropped by birds who consumed the small blue berries in fall, but also by the spread of crawling stems that will produce new roots in contact with soil (picture 2). Virginia creeper is often confused with Poison-Ivy (Toxicodendron radicans). However, poison-ivy has 3 leaflets instead of 5 for Virginia creeper and lacks the tendrils and adhesive disks.

As a perennial weed, Virginia creeper will be tough to control as it can easily regrow after foliar injury from its extensive underground root system. When established, Virginia creeper will most often not be controlled with a single herbicide application, and multiple applications will be necessary to achieve acceptable control. Only nonselective postemergence herbicide (glyphosate) must be used to suppress or control this weed. In order to increase the efficiency of postemergence applications during the growing season, remove the vine from their support during winter pruning and lay it on the ground or plan a “cut stump” treatment during the growing season. Do NOT “prune out” the vine during the dormant season.

Picture 2 – Virginia creeper rooting stem

Spot treatment.  Glyphosate may be applied in mid- to late summer after vine flowers in early July until the first signs of fall color appear in the foliage. Good growth and maximum leaf area is needed at the time of herbicide application during the summer.  Wet a minimum of 50 percent of the weed foliage with a 1% glyphosate solution (1.25 oz of 4.5lb acid material per gallon of water) for effective control. For best control, don’t apply on stressed/wilted weeds.

Cut stump treatment. Best results are often obtained in late summer and early fall, but before fall color is observed in the foliage. Apply a 1% glyphosate solution to the cambial areas (inner bark area) of the stump of woody plants IMMEDIATELY after cutting. Cut and treat stumps only when the Virginia creeper is actively growing and not under stress.

WARNING. Injury due to root grafting may occur in adjacent plants. Do not treat cut stumps if there is a possibility of root grafting to desirable vegetation. Do NOT allow contact with green bark, trunk wounds, leaves, or root suckers of blueberry bushes.

The mention of trade names and rates is for educational purposes and does not imply endorsement by the author or the New Jersey Agricultural Experiment Station. Always defer to the product label for instructions on properly applying an herbicide.

Filed Under: Blueberry, Cranberry, Fruit, Strawberry, Tree Fruit, Vegetable Crops, Wine Grape Tagged With: , , , ,
April 20, 2017

Update on Use of Chateau for Weed Control in Potato

Chateau herbicide has a supplemental label for application to potatoes after hilling for preemergence suppression of various broadleaf weed species. This supplemental label will expire on June 30, 2017 and Chateau must not be used on potato after this date.

This supplemental label will not be renewed by Valent as the company is in the process of putting this supplemental label on the federal label. However, this use for potatoes will show up on the revised federal label when it reissues from the EPA.

We currently do not have a time frame for that but it probably will not before June 30. We are expecting that the revised federal label will be issued prior to the use season next year.

Filed Under: Vegetable Crops Tagged With: , ,