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.

 

Identifying and controlling common leaf spot in strawberry

Strawberry leaf spot, caused by the soil-borne fungal pathogen, Mycosphaerella fragariae, has been found in some strawberry fields on some cultivars this past week in southern New Jersey. Leaf spot can infect leaves, petioles, runners, fruit stalks (pedicels), and berry caps or calyxes. Small, dark purple to reddish-purple, round spots, 1/8 to 1/4 inch in diameter (3 to 6 millimeters), appear on the upper leaf surfaces. The center of the spots soon become tan or gray and eventually almost white, while the broad margins remain dark purple. Later in the season, dark specks (sclerotia and/or perithecia) may be seen in the older lesions. Tannish areas form on the underleaf surface. The symptoms on the other plant parts, except the fruit, are almost identical to those that develop on the upper leaf surface.

Strawberry leaf spot on infected leaves

Strawberry leaf spot on infected leaves.

Symptoms of strawberry leaf spot on infected leaf petioles

Symptoms of strawberry leaf spot on infected leaf petioles.

Microsclerotia and conidia from infected leaves that survive the winter can lead to infections of new growth in the spring. The period between infection and the appearance of lesions on the upper leaf surface can range from 10 to 14 days depending on weather conditions. Large numbers of conidia can cause secondary infections during prolonged periods of damp to wet, moderately warm weather. Temperatures between 65 and 75 F (18 to 24 C) are optimal for the growth of fungus and for lesion development. Infections can continue to occur throughout the growing season. Young, expanding leaves are much more susceptible to infection than mature leaves. If frequent rains occur during early- and mid-spring, a few infection sites can start an epidemic.

 

Control of strawberry leaf spot begins with recognizing symptoms and preventative fungicide applications. All strawberry fields need to be scouted on a regular basis. Especially, during periods of wet weather or during heavy use of overhead irrigation. Weekly applications rotating the following should be done as long as symptoms are present and weather conducive for disease development persists. For more information please see the 2020/2021 Mid-Atlantic Commercial Vegetable Recommendations Guide. Fungicide applications for strawberry leaf spot will be effective for strawberry leaf scrorch and strawberry leaf blight.

Code Product Name Product Rate Active Ingredient(s)

(*=Restricted Use)

PHI

(d)

REI

(h)

Bee

TR

M04 Captan 50W 6.0 lb/A captan 0 24 N
M04 Captan 80WDG 3.7 lb/A captan 0 24 N
M04 Captan 4L 3.0 qt/A captan 0 24 N
M04+17 Captevate 68WDG1 3.5 to 5.25 lb/A captan + fenhexamid 0 24 N
Do not apply the same FRAC code more than twice in a row or in a season.
1 Topsin M 1.0 lb/A thiophanate-methyl 1 24 N
2 Meteor2 1.5 to 2.0 pt/A iprodione n/a 24 N
2 Nevado 4F2 1.5 to 2.0 pt/A iprodione n/a 24 N
2 Rovral 4F2 1.5 to 2.0 pt/A iprodione n/a 24 N
3 Rally 40WSP 2.5 to 5.0 oz/A myclobutanil 0 24 N
11 Cabrio 20EG 12 to 14 oz/A pyraclostrobin 0 12 N
3 + 11 Quadris Top 1.67SC 12 to 14 fl oz/A difenoconazole + azoxystrobin 0 12
3 + 11 Quilt Xcel 2.2SE 14 fl oz/A propiconazole + azoxystrobin 0 12 N
7 + 11 Merivon 2.09SC 4 to 7 fl oz/A fluxapyroxad + pyraclostrobin 0 12 N
7 + 11 Pristine 38WG 18.5 to 23.0 oz/A boscalid + pyraclostrobin 0 12

 

For organic strawberry growers, weekly applications of an OMRI-approved copper or potassium bicarbonate have been shown to be effective in mitigating strawberry leaf spot. Please see link to MSU’s fungicide efficacy table for organic and conventional fungicide use.

For information on controlling angular leaf spot in strawberry please click here.

For information on controlling fruit rots in strawberry please click here.

For more information on strawberry leaf spot please see the following:

University of Illinois – http://ipm.illinois.edu/diseases/series700/rpd702/index.html

University of Wisconsin – https://hort.extension.wisc.edu/articles/common-leaf-spot-of-strawberry/

Michigan State University, 2015 – Information on diseases and fungicide efficacy – https://www.canr.msu.edu/news/protect_strawberries_from_foliar_diseases_after_renovation

Cornell University, 2013 – Information on diseases and fungicide efficacy – https://cpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/0/7265/files/2017/01/strleafdisidmgmt-yjcu5n.pdf

Please remember, the label is the law!

Understanding and controlling angular leaf spot in strawberries

Often considered a minor pathogen, angular leaf spot caused by the bacterium, Xanthomonas fragariae, can cause serious leaf and calyx infections ruining the marketability of fruit if left uncontrolled. Like all bacterium, the pathogen will infect leaves and the calyx through natural openings or wounds. Primary infections of new growth in the spring originate from systemically infected overwintered plants and dead leaves in which the bacterium survives the winter; or from infested transplants. The pathogen is very resistant to desiccation and can survive in old, dried leaves or infected plant debris buried in the soil. The pathogen will not survive free in the soil so it originates primarily from infected leaf debris and infected crowns.

Fig. 1. Water-soaked lesions caused by angular leaf spot on infect strawberry leaf. Photo by P. Nitzsche

Infections can often start in production operations and come in on infected bare root transplants or cuttings. Symptoms on leaves include initial small, irregular water-soaked lesions (Fig. 1). Young, actively growing leaves are most susceptible, especially on vigorously growing plants. Disease development is favored by moderate to low daytime temperatures, low night time temperatures – near or below freezing, and high relative humidity. Long periods of precipitation, overhead irrigation used to establish plantings or protect plantings from freezing, and heavy dews favor disease development.
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Controlling Strawberry Fruit Rots – 2017

Anthracnose fruit rot of strawberry

Anthracnose Fruit Rot of Strawberry

Fruit rots in strawberry can cause significant losses if not recognized early and controlled. The use of good cultural practices such as keeping fields weed-free and promoting good drainage, long crop rotations, and preventative fungicide applications are critical.

Pathogens such as anthracnose, gray mold (Botrytis), and leather rot (Phytophthora) can become systemic problems in strawberry plantings once established. All three fungal diseases are soil-borne and once in fields can be difficult to manage over the lifetime of the planting.

The use of mulch (matted rows) to prevent/reduce soil splashing and keeping fruit from coming into direct contact with the soil surface can be beneficial in organic production systems where conventional fungicides cannot be used. Use of long crop rotations and staying away from areas of the farm with known instances of any of these pathogens is also important. Remember that same species of Colletotrichum that causes fruit rot in pepper and other crops can also infect strawberry.

[Read more…]

The National Strawberry Sustainability Initiative

If you’re a strawberry grower, nurseryman, or Extension Educator or advisor to strawberry growers – WE NEED YOUR INPUT!

The National Strawberry Sustainability Initiative (NSSI) is leading efforts to identify the critical research and outreach needs of the strawberry industry and to develop a project around these issues through the support of the USDA Specialty Crop Research Initiative. The NSSI is a collaboration among universities, USDA-ARS, strawberry growers and the strawberry industry, across 13 states, with the goal to support and expand sustainable strawberry production.  Please contribute to this national strawberry industry needs assessment by taking this survey. It should take 10-15 minutes and your answers will remain anonymous.  The survey can be accessed through a link on our NSSI website, http://strawberry.uark.edu.

For questions about the project or the survey, please contact Heather Friedrich at heatherf@uark.edu or 479-575-2798.

Ultra-Niche Crop Educational Sessions Offered

County Agent Peter Nitzsche displays strawberry crop.

County Agent Peter Nitzsche displays strawberry crop.

Rutgers Cooperative Extension is offering a series of workshops for new and beginning farmers. The series, sponsored by a grant from the USDA-NIFA Beginning Farmer and Rancher Development Program, is part of the Rutgers Ultra-Niche Crops Project. Ultra-Niche Crops are exceptionally high value crops that can be grown on small acreage. The program is geared towards anyone who is interested in making more money off less land. If you are a new or beginning farmer, or an experienced farmer interested in learning about niche crops, then join the mailing list for more information.

The first class on growing and marketing Plasticulture Strawberries will be held on September 28th. More details and registration are now available. To speak with the project director, contact County Agricultural and Resource Management Agent Jenny Carleo by email (ko at rutgers dot edu) or by phone at 609-465-5115 x607.