Apr 3, 2020MSU stresses importance of spring herbicide application in fruit trees
Effectively managing weeds is critical and one of the most important steps in the production of fruit trees. Weeds can directly impact fruit yield and quality by competing with trees for water, nutrients and light. Weeds can also serve as alternative hosts for insects and pathogens and interfere with crop management and harvest processes. Therefore, effective weed management programs should be developed based on orchard monitoring, correct weed identification and using multiple chemical and non-chemical tools.
There are several herbicides registered for use in fruit orchards. Timely application of herbicides in fall, spring and during the growing season is key to achieving optimum weed control. In general, most of the long-residual herbicides labeled for fruit trees may be applied in spring or fall. Weed suppression after spring preemergence application is effective for six to eight weeks, after which another application of residual and/or postemergence herbicides is needed to keep weed growth under control. At least three residual herbicides with different mechanism of action may be needed each year to provide appropriate weed management. Tank mixing a foliar-active herbicide with residual herbicides will greatly improve control of emerged weeds.
Fall is a perfect time to apply residual and foliar-active herbicides in established tree fruit, especially to manage hard-to-control perennials such as Canada thistle, dandelion and quackgrass, and winter annuals such as horseweed or marestail, white campion and yellow rocket. The benefits of fall application in tree fruits have been previously discussed by Bernard Zandstra in the Michigan State University Extension article, “Fall weed control in established fruit crops.”
While fall applied herbicides are a common practice throughout the state, many growers were not able to make this application in 2019 due to a late harvest and unfavorable fall weather. Therefore, it is important that this spring’s herbicide is applied on time, before weeds start growing and get a foothold in the orchard. Due to a mild winter and early spring, growers may consider starting spring applications in early April if weather is favorable.
Temperature and soil moisture can greatly influence the efficacy of herbicides. Ideally, postemergence herbicides should be applied at temperatures between 65 and 80󠇨 degrees Fahrenheit; however, that range is not always practical with early spring application. Herbicides can be applied at temperatures from 40 to 60 F, but you may observe slower death of weeds. The activation of preemergence herbicides are mainly influenced by soil moisture since uptake into germinating weeds occurs from the soil solution. Lower level of weed control may be observed under both extremely dry and wet conditions due to herbicide inactivation and potential leaching issues, respectively.
To achieve optimum weed control, avoid herbicide application under unfavorable weather conditions such as forecasted temperatures below 40 F for an extended period of time after postemergence application, cloudy days followed by an extended period of below 40 F temperatures, and continuous rainy days in the forecast. It is important to check the pesticide labels for specific instructions on application timings to optimize efficacy.
Several residual herbicides, representing multiple herbicide mechanism of action, are available for use in spring in tree fruit systems (Table 1). Spring application should be made before trees bud break or emergence of new growth to avoid crop injury. Selecting herbicide depends on several factors including weed type and species, tree age, soil type and vegetation or crop residue. It is important to select herbicides based on the type of weeds present in the orchard since not all herbicides are equally effective for all weed species. For example, Alion can provide excellent to good level of control for annual grasses such as crabgrass, fall panicum, foxtail, etc., and several annual broadleaves such as common chickweed, pigweed spp., mustards, nightshade and velvetleaf, but provides fair to poor level of activity for sandbur, common lambsquarters and smartweeds.
Zeus Prime, effective to control sandbur, common lambsquarters and smartweeds might be an effective tank-mix with Alion to ensure the entire weed spectrum is effectively targeted. If orchard soil is light sandy in texture, then it is wise to use a lower application rate of herbicides such as Princep, Sinbar or Surflan to avoid crop injury.
It is also very critical to select herbicides based on tree age because some herbicides might cause a significant amount of injury if applied on younger trees than recommended. Herbicides such as Sinbar, Alion and Zeus Prime should be used on established trees, which are at least 3 years old. The efficacy of residual preemergence herbicide may be reduced in the presence of actively growing vegetation, such as winter annual weeds, and crop residue, such as leaf litter, on the soil surface. Therefore, it is suggested to use postemergence herbicides such as paraquat (Gramoxone*), carfentrazone (Aim) or glufosinate (Rely, Lifeline, Reckon) to kill emerged weeds. Inclusion of pyraflufen-ethyl (Venue) with these post-emergence applications improves burndown and broadens the weed control spectrum.
An effective spring weed control treatment plan might include one of the following combinations: Chateau plus Karmex, Alion plus Princep, Matrix plus Zeus Prime, Prowl H2O plus Trellis, Alion plus Surflan, Karmex plus Prowl H2O, Chateau plus Surflan, or Goal plus Prowl H2O. Include Gramoxone*, Aim or Rely if seedlings of new emerging weeds are observed at the time of application. Always be cautious to alternate or tank-mix herbicides with different mechanism of action to avoid evolution of resistant weed biotypes.
*Please note that there are new label and training requirements associated with paraquat dichloride containing products like Gramoxone. More information is available on the EPA’s Pesticide Worker Safety website.
|Table 1. Selection of preemergence herbicides for spring application in fruit trees including apple and cherries (tart, sweet), peach, pear and plum. Source: 2020 Michigan Fruit Management Guide|
Common name1 (trade name)
Mechanism of action
|Registered crops (crop age)|
|Diuron (Karmex, Direx)||7||B||B||B|
|Pendimethalin (Prowl H2O)3||3||B,N||B,N||B,N||B,N||B,N|
1Always check the most recent herbicide label to ensure application rates and other restrictions and to make sure that all applications are safe and legal.
2Abbreviations: B, bearing; N, nonbearing
3Solicam (only in apple), Surflan, Prowl H2O, and Trellis can be applied to newly planted trees once the soil has settled.