[tree fruit, IPM]
Passing this on from Mary Concklin at UCONN.
Herbicide Applications this Fall
There are a couple of times during the year when the timing of herbicides will have the largest positive impact on your weed management – fall and spring. Herbicides applied at other times during the season are good for eliminating those few pesky weeds that managed to sneak through, often times because of extended wet periods.
Summer annual weeds: they likely died off with a hard frost earlier this fall. Pre-emergent herbicides applied this fall will help to control new annual weed germination in the spring. It is also easier to apply this time of the year than during the busy wet spring when, in some years, it is difficult to get into the fields before germination occurs.
Fall applications: For all perennial weeds, a combination of pre- and post-emergent materials will provide the best results as long as the application is made while the emerged weeds are still alive. Applications made after they have been hit with a hard frost can be with pre-emergent materials only which aims at moving the herbicide into the root zone and impacting emergence in the spring.
Some materials perform better in the fall because of their mode of action. Glyphosate/Roundup is a systemic that moves into the plant. In late summer and fall, plants are moving food reserves to the roots. Glyphosate applied at this time will also move to the root system and kill the plant. In the spring, movement is upward in plants as they grow, so glyphosate applications made at that time have less of a chance of giving you the results you are looking for.
Organic growers also have organic herbicides available. These are contact not systemic materials and work best when applied to young weeds for knockdown. They will need to be re-applied several times throughout the growing season.
Brad Majek, Rutgers, offers the following about timing:
Apply herbicides to the tree row in established orchards twice annually, in late fall and in late spring. Herbicides applied in late October or early November control winter annuals, certain perennials, and early season summer annuals. Spring herbicide applications extend summer annual weed control through harvest. Advantages of two herbicide applications per year include:
1. Control of winter annual weeds, including camphorweed, wild lettuce and horseweed (marestail) and summer annual weed control for the same cost as most single application weed control programs.
2. Improved spring labor and equipment distribution requirements by controlling early summer annual weeds with residual herbicides applied the previous fall, thus delaying the need to spray in the spring until May or early June.
3. Increased consistency of weed control treatments, especially control of summer annual weeds when dry weather follows the spring herbicide application.
4. Decreased risk of crop injury, since each herbicide application must last less than a full year. Herbicides can be alternated and rates can be reduced or split to improve crop safety.
5. Decreased competition from established winter annual weeds and summer annual weed seedlings in March, April, and May for fertilizer and water when the trees begin to grow.
Late Fall Herbicide Applications should include a translocated post emergence herbicide, and a residual broadleaf herbicide. A residual grass herbicide may also be applied in the fall. Apply 2,4-D to control emerged winter annual broadleaf weeds tank-mixed with Princep for residual control. Consider a labeled glyphosate product if perennial weeds are present and treatment is recommended in the fall. The use of a grass herbicide in the fall depends on the product chosen. Kerb 50WP is the only grass herbicide that must be applied in the fall, if it is used, to control certain cool season perennial grasses. An additional residual annual grass herbicide is needed in the spring to provide full season summer annual grass control following a fall application of Kerb 50WP. Solicam 90DF, Surflan 80WP, Devrinol 50WP and Prowl 4EC (non-bearing only) are annual grass herbicides that should be applied in late fall or as a split application, half in the fall and the second half in the spring. Use the split application when grass pressure is heavy for best results. The use of these herbicides in spring only has resulted in inconsistent weed control when dry weather followed the application.
Information on tree fruit herbicides may be found at: https://netreefruit.org/weeds
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