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

June 1, 2020

Residual Weed Control in Cabbage and Other Cole Crops

Good weed control in transplanted and seeded cole crops requires planning and the use of pretransplant or preemergence herbicide applications.

Cabbage treated pretransplant with Goal and never cultivated.

Cabbage treated pretransplant with Goal.  The crop was never cultivated.

Preplant incorporate Treflan HFP at 1 to 1.5 pt/A for seeded and up to 2 pt/A for transplanted, or apply Dacthal 6F at 6 to 14 pt/A or Prefar 4E at 4 to 9 qt/A preemergence or post-transplant to control annual grasses and certain broadleaf weeds. Choose Dacthal or Prefar in early spring when soils are cold and wet when Treflan may cause temporary stunting. Please make sure to check the label before mixing as these herbicides are registered for use only on certain cole crops.

Goal 2XL and GoalTender 4F are labeled for transplanting ONLY!.  Goal 2XL can ONLY be used pretransplant whereas GoalTender 4F can be used pre-transplant or post-emergence with a 24(c) Special Local Needs label on broccoli, cabbage and cauliflower in New Jersey (NJ 24(c) SLN GoalTender 4F). Build beds, spray, and transplant through the herbicide barrier. Use Prefar or Dacthal post-transplant for grass control. Treflan or Dual Magnum applied preplant incorporated may increase the risk Goal injury. Do NOT cultivate unless weeds appear. Incorporation of Goal reduces or eliminates the effectiveness of the product for weed control. Goal and GoalTender are registered for use only on certain transplanted cole crops.

Dual Magnum 7.62E has a 24 (c) Special Local Needs label for use on cabbage in New Jersey. Use Dual Magnum at the rate of 0.5 to 1.33 pt/A  depending on soil type. Use the lower rate on soils that are relatively coarse-textured or low in organic matter; use the higher rate on soils that are relatively fine-textured or high in organic matter. Apply to weed free soil in transplanted cabbage after transplanting, or to direct seeded cabbage when the seedlings have developed 3 to 4 true leaves. The delayed use in directed seeded cabbage reduces the risk of slight temporary stunting of the crop. Dual Magnum controls annual grasses, nightshade species, and galinsoga. Yellow nutsedge will be suppressed or controlled at the rates and use patterns on the Dual Magnum label for cabbage. To obtain a label, an indemnification agreement must be filled out on line agreeing not to hold the manufacturer responsible for crop damage. Obtain a copy of the label and complete the indemnification agreement on the Syngenta website. Register or sign in, select state and product, and submit. You will then be asked to select your crop before accepting or not the waiver of liability and indemnification agreement. You must have a copy of this 24(c) label if you want to use Dual Magnum on cabbage!

Consult the 2020/2001 Mid-Atlantic Commercial Vegetable Production Recommendations for rates and additional information.

 

Filed Under: Vegetable Crops Tagged With: , , , ,
May 30, 2020

Specialty Crops Injury Caused by Dicamba Herbicide Drift

Figure 1. Non-tolerant soybean foliage when exposed to a sublethal rate of dicamba 2 weeks after treatment. Leaves are cupped with the bottom edges curved towards the top surface of the leaves.

By Maggie Wasacz1 and Thierry Besancon2

1 Rutgers Weed Science Graduate Student; 2 Rutgers Weed Science Extension Specialist for Specialty Crops

Glyphosate-tolerant soybeans were first commercialized in 1996 in the United States. By 2006, almost 9 out of every 10 soybean acres were planted with glyphosate-tolerant cultivars. However, reliance on glyphosate alone for soybean weed control stimulates the selection of weed biotypes naturally resistant to glyphosate. By 2019, there were 43 weed species known to be resistant to glyphosate, including species such as Palmer amaranth or waterhemp that can easily out-compete soybean and reduce yield by more than 50% if left uncontrolled.

What is Dicamba Herbicide?

One way to control glyphosate-resistant weeds is to treat them with herbicides other than glyphosate, such as dicamba. Dicamba is a synthetic auxin herbicide that has been used to control broadleaf weeds for over 50 years. Chemical and seed companies have recently developed new soybean varieties that are tolerant to dicamba and that started to be commercialized in 2016. With the development of genetically modified dicamba-tolerant soybeans, dicamba may be sprayed more frequently during the growing season. Additionally, dicamba is regularly applied in corn, for right-of-way applications, and in the early fall for perennial weeds control.

Dicamba can injure sensitive broadleaf plants through tank incorrectly rinsed after spraying dicamba, particle drift during the dicamba application, and vaporization after dicamba has been applied . Particle drift refers to the herbicide being carried off-target by the wind during the application. Wind speed, particle droplet size, nozzle type, carrier volume, application method, and application speed will affect the extent of particle drift. Vaporization, on the other hand, occurs when the herbicide evaporates from the target plant and these vapors travel off-target.  For more information on herbicide drift, please refer to the following PPA post 10-best-management-practices-to-avoid-herbicide-drift.

If some of the dicamba sprayed onto a soybean field moves off-target and lands on a nearby field planted with a sensitive crop, the results can be very harmful. This injury could potentially cause aesthetic damage as well as reduce yield reduction.  Potential for yield loss is influenced by amount of dicamba as well as when the injury occurs. Small volumes of dicamba products can cause leaf cupping and deformation, plant twisting, and in extreme cases, plant death of sensitive crops.

Screening Vegetables for Dicamba Sensitivity

Greenhouse studies conducted at Rutgers University in 2019-2020 screened economically important vegetable crops from the mid-Atlantic region for sensitivity to sublethal doses of dicamba. These micro-rates of dicamba simulated varying levels of drift conditions in the field. To put the rates into perspective, the highest dose in this study was equivalent to about one drop of product per quart of water. The goals of this study are to develop recommendations that can help growers design their planting strategies around dicamba-treated fields as well as to use this data to help refine recommendations to maximize protection of sensitive crops.

Crop-Specific Reactions to Simulated Dicamba Drift

The most sensitive crops in this study were the leguminous crops, including non-tolerant soybean, lima bean, and snap bean, as well as solanaceous crops, such as tomato, eggplant and pepper. These crops demonstrated severe injury.

Soybean injury is characterized by the underside edges of the leaves curling upward toward the top surface of the leaves (Figure 1). Lima bean and snap bean have similar injury symptoms, both exhibiting injury in several ways. Higher rates caused some leaves to not emerge at all, while lower rates caused leaf cupping injury that caused the top edges of the leaves to curve downward towards the ground. Other symptoms included a bubble-like texture on the top sides of the leaves, as well as leaf crinkling.

Figure 2. Eggplant 2 weeks after treatment. The undersides of affected leaves are curled upward toward the top surfaces of the leaves.

Figure 3. Bell pepper 2 weeks after treatment. The leaves are cupped with a bubble-like texture on the top surface.

 

 

 

 

 

 

Figure 4. Tomato 2 weeks after treatment. Leaflets are curled, reduced in size, and deformed.

For eggplant and bell pepper, injury was expressed as the undersides of the leaves curling upward toward the top surface (Figures 2 and 3). Additionally, leaf crinkling is seen in bell pepper foliage (Figure 3). Finally, tomato plants express dicamba injury with leaf twisting, cupping, stunting, and crinkling. At higher rates, these leaflets will be extremely stunted and deformed (Figure 4). Lower rates will show slight cupping, leaf crinkling and a change in leaf surface texture. Among the most tolerant crops from this study were basil, pumpkin, lettuce, and kale. These plants incurred the lowest amount of damage. The moderately sensitive crops included watermelon, cucumber, and summer squash. Watermelon foliage exhibits injury differently than many of the other crops tested in the study. Rather than leaf cupping, watermelon leaf texture appears shriveled and more deeply lobed with small bubbles on the top leaf surface (Figure 5).

 

 

Figure 5. Watermelon 2 weeks after treatment. Leaves are deeply lobed with a puckering, bubble-like texture.

Figure 6. Summer squash 2 weeks after treatment. Leaf edges are curved downward toward the ground.

Figure 7. Cucumber 2 weeks after treatment. Leaf is cupped and the bottom edges of the leaf are curved upward towards the top leaf surface.

 

Summer squash and cucumber, however, show leaf cupping when injured. In summer squash, the top edges of the leaf curve downward towards the ground (Figure 6).  The foliage of cucumber tends to curve the bottom edges upward toward the top surface of the leaf, although both directions of cupping were observed. (Figure 7).

On-Going Research at Rutgers

This summer, Rutgers researchers will select a few of these crops to take yield in a field-based dicamba drift study that tests different drift rates and application timings. Although this study gives some preliminary information, more detailed studies are necessary to confirm these findings. However, in the meantime, this greenhouse work gives us a brief snapshot of which species to be most concerned with when working near dicamba treated fields and provides help with field identification of these injury symptoms.

If you suspect that dicamba drift may have injured your crops, please contact you local county extension agent or Rutgers weed science specialist (Dr. Thierry Besançon) as soon as possible, and take detailed pictures of the observed damages.

 

 

Filed Under: Blueberry, Commercial Ag Updates, Fruit, Organic Production, Tree Fruit, Vegetable Crops, Wine Grape Tagged With: , , , , , ,
May 22, 2020

10 Best Management Practices to Avoid Herbicide Drift 

The last few weeks have been very windy, and we already received numerous calls from specialty crops growers inquiring about the risk of herbicide drift or investigating if observed crop damages may be the result of herbicide drift.

Fig.1 Paraquat drift on blueberry flowers

Why does it seem like crops are more affected by herbicide drift in the spring? Well, mostly because this is the time when newly planted crops develop new shoots or reproductive structures that may be very sensitive to herbicide drift (Figure 1). This is also the time of the year when most postemergence herbicide are applied to control emerged weeds and subsequent new flushes. When both events coincide and if weather conditions favor herbicide drift, this could lead to disastrous injury on sensitive non target crops!

Drift is defined as physical movement of an herbicide through air, at the time of application or soon thereafter, to any site other than that intended. It can be particle drift from fine herbicide spray droplets that can travel over long distances during period of high wind. High wind speed, low relative humidity, high temperatures, small droplet size, and spray boom maintained high above the ground are factors that increase the risk of particle drift. Depending on the herbicide, application and weather conditions, fine droplets can travel up to several miles! It can also be vapor drift which results from the ability of an herbicide to vaporize and mix freely with air. Volatility of any herbicidal substance is characterized by its vapor pressure. The higher the vapor pressure of a substance, the greater its tendency to volatilize (Table 1). However, other factors such as herbicide formulation and weather conditions will influence volatility. Some herbicides classified as growth regulators (2,4-D, dicamba, triclopyr or clopyralid) are well known for the higher risk of vapor drift associated with their use when herbicide formulation and/or weather conditions increase volatility (Figure 3).

Herbicide Vapor Pressure (mmHg)
Glyphosate IPA 1.58 x 10-8
Glyphosate Ammonium Salt 6.75 x 10-8
2,4-D DMA <1.0 x 10-7
2,4-D Acid 1.4 x 10-7
Atrazine 2.9 x 10-7
2,4-D BEE 2.4 x 10-6
2,4-D EHE 3.6 x 10-6
Trifluralin 1.1 x 10-4
Clomazone 1.4 x 10-4
Table 1 Vapor Pressures for 2,4-D Formulations and Several Commonly Used Herbicides. Abbreviations: IPA, isopropylamine; DMA, dimethylamine; BEE, butoxyethyl ester; EHE, 2-ethylhexyl ester.

So, there are a few things that you need to consider reducing the risk of potentially expansive damages to sensitive crops:

  1. Select nonvolatile or low volatility herbicides to minimize the risk of vapor drift. Growth regulator herbicides such as 2,4-D, MCPA or triclopyr can be formulated as ester or amine salt. The ester formulation is notorious for its volatility; therefore, always use these herbicides formulated as amine salt to reduce the risk of vapor drift. Other herbicides than growth regulators have high vapor pressure that makes them prone to vapor drift (clomazone, trifluralin, EPTC), but either should be soil incorporated or are formulated in a way (micro-encapsulation) that will limit the risk of vapor drift.

    Fig. 2 New growth chlorosis on beet. A WSSA group 27 herbicide (“bleacher”) was applied preemergence at planting in a neighboring corn field and drifted to the beet field because of high wind.

  2. Carefully read the herbicide label. The product label will provide information regarding when it is not safe to apply the product based on various parameters such as wind speed, temperature, humidity. You may also find information buffer requirement when spraying near sensitive downwind plants or information on the type of nozzle you must use for a specific herbicide.
  3. Select nozzles that produce the large size droplets while providing adequate coverage at the intended application rate and pressure. You can also select specifically designed drift-reduction nozzles (for example, drift-guard or air induction types) operate at lower pressure (15 to 30 psi) and produce large droplets that will have less potential for drift. A good source of information on droplet characteristics and operating pressure for various nozzle types is the TeeJet nozzle catalog (https://www.teejet.com/CMSImages/TEEJET/documents/catalogs/cat51a_us.pdf).
  4. Use low application pressure and drive at low speed when applying herbicides. Herbicide drift will increase with application pressure and speed…
  5. Keep the boom stable and the nozzles close to the soil as this will minimize herbicide drift but also potential injury to the crop on which herbicide is applied. You may want to consider using a shielded boom when spraying herbicide that are prone to drift or may injure your crop. Keep in mind that postemergence herbicide will provide optimal weed control when applied timely with regards to weed development. If the weeds are too tall (see the maximum weed size for each weed species on the label), then it’s too late to spray!

    Fig. 3 Damages to pepper (left), cucumber (center), and eggplant (right) caused by dicamba herbicide applied at 1/1000 of the labeled rate on soybean.

  6. Mix spray additives recommended by the label to reduce the production of fine spray droplets. Avoid tank mix ammonium sulfate with volatile herbicides as ammonium sulfate increases volatility. You can also consider the use of drift retardants that reduce drift by increasing the viscosity or surface tension of a spray solution. However, research shows that while some drift retardants may help under some conditions, the prevention of herbicide drift should primarily rely on nozzle selection, boom height, application pressure, and environmental conditions.
  7. Do not apply herbicides when wind is blowing toward sensitive plants or when wind speed exceeds 10 mph. Ideal spray conditions are when wind speed is between 3 and 10 mph. Low winds (< 3 mph) tend to be unpredictable and variable in direction and may indicate conditions that help the development of a temperature inversion. Applying any herbicide when wind speed exceeds 10 mph may result in catastrophic consequences for neighboring sensitive vegetable or horticultural crops (Figure 2).
  8. Do not apply herbicides when temperature inversion occurs. Inversions occur when warm light air rises upward into the atmosphere and heavy cool air settles near the ground, preventing the mixing of air layers. Temperature inversion will cause small-suspended droplets to form a concentrated cloud that can move long distances (up to several miles). Typically, temperature inversions start at dusk and break up with the sunrise because of vertical air mixing. To confirm the presence of an inversion, air temperature should be measured carefully at two heights out of the direct sun: 6 to 12 inches above the ground or the top of a nearly closed-crop canopy, and at a height of 8 to10 feet above the surface to be sprayed. When the temperature at the higher level is greater than the temperature at the lower level, an inversion exists. The greater the temperature difference between the two levels, the more intense the inversion, and the more stable the lower atmosphere. To test for sure, you can use smoke by burning a small amount of dry vegetation to see if the smoke dissipates or hangs low to the ground. If the smoke hangs in the air together then moves off slowly without dissipating, it indicates that a temperature inversion exists and that you do not want to spray as  long as the temperature inversion persists. Usually, temperature inversion will dissipate when temperature rises 3 degrees or more above the morning low, or when the wind speed increases to more than 3 mph.
  9. Spray when temperatures remain below 80°F to minimize vaporization and droplet evaporation. This will minimize vapor drift but also help with weed control by avoiding that spray droplets evaporate before reaching the target…
  10. Leave a buffer zone between treated fields and sensitive plants. Herbicide labels may specify the width of the buffer zone. The buffer zone will allow larger droplets to settle before reaching sensitive plants. The buffer zone may not be effective in settling small droplets.

Remember that all herbicides are capable of drift, no exception.

When spraying a pesticide, you have a moral and legal responsibility to prevent it from drifting and contaminating or damaging neighboring crops and sensitive areas. Always monitor weather conditions and their evolution carefully when spraying an herbicide. Overall, do not spray if all conditions are not suitable, and stop spraying if conditions change and become unsuitable.

Filed Under: Blueberry, Cranberry, Field, Forage & Livestock, Fruit, Landscape, Nursery, & Turf, Nursery, Strawberry, Tree Fruit, Vegetable Crops, Wine Grape Tagged With: ,
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

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

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: , , ,