EAST LANSING, Mich. — April is an important time to apply pre-emergent herbicides. Weeds are beginning to emerge and most pre-emergent materials should be applied either before weed emergence or when weeds are just small. In most southern Michigan locations, mid-April is a good time.
There are quite a few materials to choose from. Choose herbicides based on the age of the plants (young plants are less tolerant than older plants), weeds present and soil type. Some pre-emergent herbicides are stronger on grasses or broadleaf weeds, so use combinations that control a broad range of weeds. Also, consider using herbicides with different modes of action (see table below) so that there is less chance weeds will develop resistance to a particular mode of action.
Michigan State University Extension suggests the following spring treatments based on plant age. Rates are in pounds active ingredient (a.i.) per acre.
For new plants, choose herbicides based on efficacy on weeds and crop safety. The following combinations provide good grass control (Surflan, Prowl, Devrinol, Dual Magnum) and broadleaf suppression (Trellis). These materials need to be applied before weeds emerge. They do not affect emerged weeds. They may need to be followed later in the season with post-emergent grass killers such as Fusilade, Poast or SelectMax.
- Surflan (2-4 pounds) + Trellis (0.5-1.0 pound)
- Prowl +Trellis (0.5-1.0 pound)
- Devrinol (4 pounds) + Trellis (0.5-1.0 pound)
- Dual Magnum (0.6-1.3 pounds) + Trellis (0.5-1.0 pound) *If nutsedge is present
In addition to the first year options, consider the following programs. Matrix, Solicam and Princep are stronger materials and should be used at their lower labelled rates here. Callisto, Casoron, Dual, Sandea and Sinbar are also labeled for second year plants.
- Solicam (2 pounds) + Trellis (0.6-1.0 pound)
- Solicam (2 pounds) + Princep (2 pounds)
- Matrix (0.063 pound)
Plantings older than two years
There are many combinations that can be used on established blueberries. Consider combinations of products that differ in mode of action and the types of weeds they control.
- Chateau (0.19-0.38 pound)
- Chateau (0.19-0.38 pound) + Rely (0.9-1.5 pounds) *If marestail is a problem
- Solicam (2-4 pounds) + Princep (2 pounds) or Karmex (1.8-3.6 pounds)
- Matrix (0.063 pound) + Sinbar (1 pound) or Princep (2 pounds) or Karmex (1.8-3.6 pounds)
- Zeus (0.25-0.38 pound) + Rely (0.9-1.5 pounds)
- Sandea (0.023 – 0.047 pound) + Solicam (2 pounds) or Sinbar (1 pounds)
- Velpar (1-2 pounds) + Solicam (2 pounds) or Surflan (2-4 pounds) *If brambles are present
Application times specified on labels are summarized in the chart below. Some labels are very specific; others are not. Velpar and Casoron need to be applied earliest (by early April). Herbicides that do not control emerged weeds need to be applied before weed seeds germinate (Devrinol, Prowl, Surflan, Trellis). Others have some post-emergent activity and can be applied after some weeds begin to emerge (Chateau, Diuron, Matrix, Princep, Sandea, Sinbar).
Herbicides kill weeds by disrupting specific processes, and they are classified based on these modes of action. Repeated use of herbicides with the same mode of action will become less effective because tolerant weed species will become established and populations of some species may develop resistance. Blueberry herbicides are grouped below by mode of action. Alternate or combine herbicides with different modes of action.
|Modes of action of blueberry herbicides|
|Herbicide||Mode of action|
|Karmex, Princep, Sinbar, Velpar||Inhibit photosystem II|
|Casoron, Trellis||Inhibit cellulose synthesis|
|Sandea, Matrix||ALS inhibitor|
|Solicam||Disrupt carotenoid synthesis|
|Stinger||Synthetic Auxin growth regulator|
|Surflan, Prowl||Inhibit microtubules (cell division)|
|Devrinol, Dual Magnum, Kerb||Inhibit VLCFAs (cell division)|
|Callisto||HPPD inhibitor (pigments)|
|Aim, Chateau, Zeus||PPO inhibitor (disrupts membranes)|
|Poast, SelectMax||Lipid synthesis inhibitors|
|Gramoxone||Photosystem I electron diverters|
Drs. Hanson and Zandstra’s work is funded in part by MSU‘s AgBioResearch.