|
||||||||||
| Department of Agriculture and Aquaculture |
||||||||||
|
||||||||||
|
C4.1.0 Since its registration in 1982, VELPAR (hexazinone) has been the predominant herbicide used in wild blueberry production. It revolutionized the industry by providing a high level of grass, broadleaf and woody weed control, which was previously unattainable.In 1990, a granular formulation of the same chemical found in VELPAR (hexazinone) was also registered and sold under the name PRONONE 10G. PRONONE 10G is essentially the same product as VELPAR but is a granular formulation that requires no mixing with water. Most wild blueberry growers in New Brunswick currently use and depend upon these two herbicides to provide them with weed control over most of their acreage. In order to achieve optimal results and benefits from VELPAR and PRONONE 10G, there are a number of factors to consider: FACTORS WHICH CAN INFLUENCE THE PERFORMANCE OF VELPAR AND PRONONE 10G Soil texture: Soil texture influences the performance of VELPAR and PRONONE 10G. In a range of increasing heaviness of soils from sand to clay, increasing rates of VELPAR and PRONONE 10G will be required to obtain the same degree of control. Soils high in clay tend to bind more Velpar than on sandy soils, thereby making it less available. As a result the higher rates are recommended to make up for the amount that is adsorbed and unavailable. Hexazinone is also highly water soluble and can leach out of the seed and root zone of light textured soils. In seasons of high rainfall hexazinone can therefore disappear, thereby resulting in reduced weed control. On sandy/gravely soils, best results are obtained when VELPAR OR PRONONE 10G is applied as close to blueberry emergence as possible. PRONONE 10G may be more effective than VELPAR on these sandy/gravelly soils, as it can be applied later than VELPAR. Unlike VELPAR, significant injury will not result if PRONONE 10G is applied to emerged blueberry leaves, as no foliar uptake results from the granules which fall to the ground (however, post emergence use is not presently registered in Canada). In addition, it is thought that hexazinone may be released more slowly from the granules of PRONONE 10G than from VELPAR. Organic matter: Like heavy soils, fields that are high in organic matter (greater than 6.0%) will also adsorb more VELPAR and PRONONE 10G, thereby making the chemical less available for weeds to absorb. As a result, reduced weed control can be expected on soils high in organic matter. Higher rates should therefore be used to adjust for this adsorption. Drainage: VELPAR and PRONONE 10G can cause injury to blueberries if applied to poorly-drained areas, particularly in standing water. In addition, weed control in poorly drained or wet areas has often been observed to be poor. Slope: VELPAR and PRONONE 10G can move with surface water and accumulate in low areas. Blueberries are often injured in these areas. In addition, heavy rains may move more VELPAR and PRONONE 10G away from the higher ground, thereby resulting in poor weed control. Frozen ground: Applications should not be made to frozen ground as it will be more difficult for the herbicide to move into the soil where it is required. Furthermore, heavy rains may cause the herbicide to run off the frozen surface. Temperature: Warm temperatures enable weeds to grow more actively. As a result, weeds can pick up and translocate VELPAR and PRONONE 10G more quickly and effectively. Moisture: VELPAR and PRONONE 10G require 0.6 to 1.3 cm (1/4 to 1/2 inch) of rainfall within two weeks of their application. This is necessary in order to move hexazinone into the weed seed and root zones where the herbicide activity is needed. Too much rain may leach the herbicide through the soil past that zone, however. Crop sensitivity: There are differences in the sensitivity of various blueberry clones to VELPAR and PRONONE 10G. It is estimated that 3 to 10% of blueberry clones are sensitive. Blueberry clonal injury should become less evident after a few years of VELPAR and PRONONE 10G use, as sensitive clones are killed out and replaced by tolerant ones. In addition, blueberry plants weakened by heavy weed competition, frost heaving, heavy disease or insect pressure etc.,are more sensitive to herbicide injury than healthy, vigorously growing plants. Weed sensitivity: Some weeds are not susceptible to VELPAR or PRONONE 10G and will therefore not be controlled at any of the recommended rates. In addition, even susceptible weeds vary in their sensitivity to VELPAR and PRONONE 10G and their level of control can be dependent on rate, timing and weather. Some sensitive weeds, like sheep sorrel and grasses may reestablish from seed after PRONONE 10G or VELPAR dissipates (Refer to Pub. No. 1014, - Factsheet C4.2.0 - for a list of sensitive and tolerant weeds). Accuracy of application equipment: The boom sprayer for VELPAR application and the fertilizer spreader for PRONONE 10G application must be properly calibrated to ensure proper delivery of the products. Uniform distribution with proper overlap is critical (foam markers are recommended). Nozzles should be checked to ensure that they are clean and not worn. For the VELPAR, selection of the proper nozzle size for the desired water volume and tractor speed is also very important. The fertilizer spreader opening setting is also very important to ensure the proper application rate for PRONONE 10G. Even and uniform application is more difficult on rough fields. Tractors should therefore travel very slowly to avoid excessive movement of application equipment. Crop injury and variable weed control often result from uneven or improperly calibrated applications. For more information about the calibration of a sprayer or a spreader please refer to factsheet C1.2.0 and C4.4.0. RATES OF VELPAR AND PRONONE 10G TO USE Please consult product labels and the most recent weed control guide (Guide to Weed Control for Lowbush Blueberry Production in Atlantic Canada, Publication No. 1014 - Factsheet C4.2.0) for rate information. Because field conditions vary widely, rates should be adjusted accordingly. In general, on a medium type soil (i.e. loam), annual herbaceous weeds are the easiest to control and therefore require only the lowest recommended rates. Most of the grasses associated with blueberry fields can be reduced to acceptable levels at the low to mid VELPAR or PRONONE 10G rates. Woody weeds are more difficult to control and generally require the highest recommended rate. It is important to remember that the soil type and organic matter levels can dictate herbicide rates as much as the weed species. For example, annual herbaceous weeds growing on a soil high in both clay content and organic matter may require the high recommended rate. In an effort to reduce the herbicide load from an integrated weed management stand point, some growers have been using below labelled rates. Results have been somewhat variable depending upon weed pressure, soil type, organic matter, rainfall amount and application timing. The most consistent and promising results from reduced rates have been obtained from applications made to fields with: (1) a low weed pressure; (2) a medium textured type soil (not too sandy or too much clay); (3) with organic matter levels below 6.0%, and (4) when applied as close to blueberry emergence as possible. Growers will have to experiment on a small scale first to determine whether reduced rates will provide the desired level of weed control. SPECIFICS ON PRONONE 10G Characteristics of PRONONE 10G: Advantages: 1. PRONONE 10G is a ready-to-use granular product, therefore no mixing or water is required. Applicator exposure is less of a concern, and a water source for mixing is not a problem. 2. Drift is less of a concern since granules are used. PRONONE 10G could therefore be applied in stronger winds than liquid VELPAR. 3. There is more flexibility in application timing (since PRONONE 10G can be applied early post emergence without significant injury). This can be beneficial for fields which are wet in the spring, when pre emergence applications are difficult. 4. The product can provide better control of some weeds when applied post emergence, than either VELPAR or PRONONE 10G applied pre emergence. 5. Container disposal is not an issue. 6. PRONONE 10G can be applied with fertilizer spreaders, which are cheaper than sprayers. 7. Fertilizer spreaders are perceived more positively than pesticide sprayers. Disadvantages: 1. Even coverage can be difficult since rough terrain can influence distribution. 2. Proper overlap can be difficult. 3. Product bags are more difficult and cumbersome to move than the liquid containers. POST EMERGENCE APPLICATIONS OF PRONONE 10G: VELPAR and PRONONE 10G are both registered for use as pre emergence herbicides in the sprout year. These herbicides should therefore be applied before the wild blueberry plants emerge and leaf out. Applications of PRONONE 10G applied after the blueberries emerge and leaf out show some tolerance and are also being evaluated, but are not presently registered in Canada. This application timing is not possible with liquid VELPAR since the spray would come in contact with the emerged leaves and cause severe injury. However, the granular PRONONE 10G drops to the soil surface, thereby avoiding any uptake through the leaves. In a post-emergent PRONONE 10G application, blueberry leaves should be dry. Post emergence PRONONE 10G applications could be advantageous on sandy/gravely soils where pre emergence applications may leach away before the weeds start to actively grow. Post emergence applications of PRONONE 10G could also be advantageous on fields which are wet in the spring and inaccessible at the pre emergence timing. Post emergence applications of PRONONE 10G are currently being evaluated but it is important to remember that only the pre emergence application timing is currently registered in Canada. Prepared by : Kevin McCully, P.Ag., Weed Specialist, N.B. Department of Agriculture & Rural Development; Klaus Jensen, research scientist, Agriculture and Agri-food Canada, Kentville Research Station; Glen Sampson, professor-researcher, Nova Scotia Agricultural College, Doug Doohan, Weed specialist, Nova Scotia Department of Agriculture and Marketing. Revised 1996 |