Non-chemical Weed Control
Non-chemical methods of weed control have not generally been used alone but are often used prior to or following other treatments to further enhance control.
One common production practice utilized by blueberry producers is pruning by fire or mowing. Although the main purpose of pruning is to rejuvenate blueberry plants, it also aids in weed control. Burning will control coniferous species and some shallow rooted grasses. The top growth of many deciduous saplings are generally killed by burning but underground parts may resprout, indicating the need for additional control measures. Burning also helps prevent the return of many weed seeds from mature plants to the soil, and will kill many of the weed seeds present near the soil surface. Frequently however, only partial or erratic control results. Burning or mowing alone may promote growth of many perennial weeds with extensive underground root system.
Mowing and cutting are useful, particularly on weeds higher than the blueberries. Weeds must be mowed or cut several times during the season to ensure suppression. Species such as maple, birch and willow should be cut back to ground level. Regrowth from the roots usually results and should therefore be cut again. Species cut in June, July and August for a few seasons will help ensure weed control. Cutting weeds every mid-summer has also been found to help control bracken fern, sweet fern, bayberry, Prunus spp., lambkill, wild rose and others. Bracken fern should be cut just as the fronds unfold, at least two times, at four to six week intervals. Cutting the tops off weeds can also prevent seed production which could reduce future weed problems. This must be done before seeds ripen. Cutting is, however, labour intensive, and does not generally result in permanent control. Other practices which may help to control weeds include the use of mulches. Wood chips, sawdust or bark mulch could be used to reduce weed problems, particularly on bare spots within the fields. Planting blueberry plants in bare spots throughout the field help bare spots to fill in more rapidly.
Preventative methods such as cleaning field equipment (mowers, harvesters, tractors, winnow machines and boxes) also help prevent the spread of undesirable weeds into previously uninfested fields. The use of biological control agents such as Chrysolina beetle on St. John's wort can also help suppress weeds although the use of this method is not compatible with most insecticides.