Mike Basedow, Janet van Zoeren, and Lynn Sosnoskie

During the weed management session of the 2021 Cornell Tree Fruit Conference, we asked attendees to type in their most problematic weed species.  We tallied up the responses, and below are the most commonly named weeds that received more than one mention:

 

Weed	Number of people who mentioned it as being a problem
Canada thistle	32
Field bindweed	25
Quackgrass	11
Poison Ivy	8
Horsenettle	7
Yellow nutsedge	6
Rootsuckers	3
Wild Buckwheat	2
Horseweed	4
Milkweed	2

 

Figure 1. List of problematic weeds from our winter tree fruit conference.

This informal survey suggests Canada thistle, field bindweed, and quackgrass present the strongest management challenges for those that responded. With this in mind, we will discuss management strategies for these three species.

 

Canada Thistle

Canada thistle (Cirsium arvense) is a common broadleaf perennial weed. It produces an extensive root system, which can spread up to 17 feet across and reach 20 feet deep. It forms a rosette of spiny, lobed leaves (Figure 2A), which will emerge from its roots (vegetative reproduction, leading to large stands dense with thistle) during both a spring and fall flush of growth. Canada thistle can also spread through seed dispersal. Seeds germinate about the same time as the spring flush.  A single large seed head can produce up to 5000 seeds (Figure 2B), and a new plant can sprout from as little as a single inch of root segment.

 

 

 

 

 

Figure 2. Canada thistle rosette of spiny lobed leaves (A), flowers, and seed head (B). Photos courtesy Dr. James Altland, Oregon State University.

Management

• Dichlobenil (Casoron, WSSA Group 20) provides control of some perennial weeds, including Canada thistle. Casoron 4G (granular formulation) must be applied between November 15 and February 15, which is not always practical in our region. The CS formulation provides somewhat more flexibility, as it must be applied when air temperatures are less than 70°F and before seedlings are two inches tall in the early spring.
• Rimsulfuron (Matrix, WSSA Group 2) can provide partial control of Canada thistle. Matrix should be applied to small actively growing Canada thistle only once it has emerged.
• Clopyralid (Stinger, WSSA Group 4) is another post-emergent material for the control of thistle. It should be applied to Canada thistle from the rosette to the bud stage to keep plants from setting seed. It cannot be applied during apple bloom. Clopyralid can also be applied to thistle postharvest, but should go on prior to the first frost while the plant is still actively growing and healthy.
• 2,4-D (another WSSA Group 4) will also provide partial control when used at similar timings as clopyralid.
• Contact products such as glufosinate (Rely, WSSA Group 10), paraquat (Gramoxone, group 22) and group 14 products like pyraflufen-ethyl (Venue) and saflufenacil (Treevix) will also burn down emerged foliage.
• Mowing while the plant is flowering will keep Canada thistle from setting new seeds, but no mowing should be done for at least ten days following a systemic herbicide application to ensure chemical movement out of the treated tissues.
• Multiple seasons of good management practices will be necessary to gain control of this difficult weed.

 

Field Bindweed

Field bindweed (Convolvulus arvensis) is a perennial broadleaf that spreads by seed and through its large, creeping root system (Figure 3A). Bindweed’s tap roots, which can grow to more than 30 feet long below ground, facilitates its persistence and tolerance of environmental stress and most weed control tactics. Bindweed has arrowhead-shaped leaves that are simple and alternate with a flattened base and a rounded tip (Figure 3B). It has white or pink, funnel-shaped flowers that are one to two inches across (Figure 3C). The species can be confused with another perennial bindweed, Calystegia sepium (hedge bindweed), which produces larger leaves (with a deeply lobed base and pointed tips) and flowers.

Figure 3. Field bindweed has a creeping root system (A), produces arrowhead-shaped leaves that are simple and alternate (B) and has white or pink, funnel shaped leaves (C). Photos by Dr. Lynn Sosnoskie.

 

 

Management

Field bindweed is best controlled prior to planting, through frequent cultivations and systemic herbicide applications.

• Once the orchard is planted, late fall/early spring applications of dichlobenil (Casoron, WSSA Group 20) can provide control when seedlings are small. Be mindful of the timing limitations associated with these products, as spring applications must be made between Nov 15 and Feb 15 for the 4G formulation, and when air temperatures are less than 70°F and before seedlings are two inches tall for the CS formulation.
• applications should be followed up with spot treatments of a systemic product. Remember that some formulations of 2,4-D, an auxinic herbicide, cannot be applied at apple bloom.
• Contact products like glufosinate (Rely, WSSA Group 10), paraquat (Gramoxone, Group 22) and group 14 chemistries such as carfentrazone-ethyl (Aim) and pyraflufen-ethyl (Venue) may also be used to burn back foliage.
• Mowing is rarely an effective strategy for controlling field bindweed as the prostrate vines often grow under the height of a mower deck.

 

Quackgrass

Quackgrass (Elymus repens) is a perennial grass that reproduces by seed and through underground stems. The plant reaches 20 to 40 inches tall, with leaves 2 to 13 inches long and 1/8 to ¾ inches wide. It is found in most cultivated fields, and is very difficult to eradicate once it becomes established (figure 4).

 

 

 

 

 

 

 

 

 

Figure 4. Established quackgrass in an orchard row middle spreads both by seed and through underground stems. 

Management

• Dichlobenil (Casoron, WSSA Group 20) is labelled for controlling quackgrass. The CS formulation lists quackgrass as moderately susceptible.  Again, note the 4G formulation must be applied between Nov 15 and Feb 15 and the CS should be applied early spring when air temperatures are less than 70°F and before seedlings are two inches tall.
• Rimsulfuron (Matrix, WSSA Group 2) will provide postemergence quackgrass control when applied to plants that are 4 to 8” tall. Quackgrass not emerged at the time of application will not be controlled or suppressed, and would require a second postemergent application for acceptable control.
• Terbacil (Sinbar, WSSA Group 5) usually provides partial control of quackgrass.
• Sethoxydim (Poast, WSSA Group 1) can provide control of quackgrass. It should be applied to quackgrass in the spring before the grass reaches a height of 8 inches. Up to 7 applications can be made per season, with at least 14 days between each application.
• Glufosinate (Rely, WSSA Group 10) can also provide burndown control of quackgrass.
• Pronamide (Kerb W and Kerb SC, WSSA Group 3) will provide some pre and post emergent control of quackgrass, but applications must be in the fall, after the fruit is harvested and prior to soil freeze-up.
• Mowing can also be used to help suppress quackgrass. It should be mowed as close to the ground as possible to deplete the reserve of carbohydrates within the rhizomes. Wait to mow following any systemic application, to allow the product to fully move out of the treated tissues.

 

A note on glyphosate use for perennial weed management

Glyphosate can be an important tool in a perennial weed management program, as it is both non-selective and systemic, allowing it to be translocated from the foliage down into the storage tissues.  There are a few key points to keep in mind if you plan to use glyphosate.

• Due to glyphosate’s broad spectrum and systemic properties, it must be used with caution to prevent injury to the apple trees. It should only be used in the spring, not beyond early July. Later applications risk uptake by the trees, increasing the potential for sub-lethal damage and winter injury. Every measure should be taken to keep the herbicide from contacting the tree foliage, root suckers, and trunks.
• To get the most out of glyphosate’s systemic properties, timing is critical. For many weeds, it is best to apply in the spring prior to bud formation up through the flowering period, as this is the period when plants are actively growing and when phloem-mobile products are most likely to be translocated to the roots. Check the label for specific use instructions for the weed species you are looking to treat so that you are treating at the optimum timing.
• Pay close attention to the weed’s growth status, and to any adjuvant recommendations. Stressed plants do not uptake systemic products as readily as rapidly growing plants. In hot, dry conditions, control will likely be more limited than in years where there is a healthy flush of weed growth.
• Look closely at the recommended adjuvants. Pay close attention to adjuvant recommendations for the particular weed species you are looking to control with glyphosate. Many species require the addition of ammonium sulfate to the mix to optimize weed control.

For a full review of the effects glyphosate can have on the apple orchard, we recommend the following Fruit Quarterly article from 2013: http://nyshs.org/wp-content/uploads/2016/10/Pages-23-28-from-NYFQ-Winter-12-12-2013.cmc_.pdf

Always read the label before choosing a product and making an application. Each product has specific product use and tree age restrictions that are pertinent to your operation. Many herbicides can cause damage to trees if they come into contact with sensitive tissues; check labels regarding safe spraying requirements. While some pre-emergence herbicides can control small, emerged, annual weeds, a burn-down herbicide may be required to achieve complete vegetation control. Active ingredients vary with respect to their spectrums of control; reference product labels regarding tank-mixing recommendations. While we make every effort to provide up to date information, remember that ultimately the label is the law.