ISSUE 14 August 21, 2008
CROP ROTATION FOLLOWING VALOR APPLIED AS A DESICCANT
Valor has received full federal registration for use a desiccant in dry edible beans. Information on application is contained in the label and on page 29 in the ND Weed Control Guide. Valor has performed equal or better than other registered dry bean desiccants. Like other desiccants, Valor requires maximum sunlight and temperatures for maximum activity. Valor is not a panacea for dry bean desiccation and growers should not expect Valor to desiccate dry beans as well under cloudy and cool weather. Valor has provided greater desiccation in these less than optimum conditions than the other products.
Apply Valor at 1.5 to 2 fl oz with an MSO adjuvant. Adjuvants containing MSO provides the greatest enhancement of Valor. If an applicator chooses a petroleum oil adjuvant (COC) instead of an MSO then performance will decrease. Valor will desiccate dry beans but will not desiccate weeds. Valor can be applied with gramoxone for weed desiccation. MSO adjuvant will enhance both Valor and gramoxone.
Earlier this year a grower asked me a question, "What will be the crop rotation restrictions for Valor applied as a dry bean desiccant as compared to a preemergence application applied in the spring?" This is important in that growers want to have flexibility in choosing which crop to plant the next year.
Supplemental Labeling shows that any crop can be planted the following season (>4 calendar months) after Valor applied as a PRE after crop planting or as a desiccant at 2 oz/A or less.
Valent, through research conducted in ND, has found some response from canola in no-till conditions. Valent may increase the restriction for canola on the next label submission. They found no canola response in conventional tillage systems.
WEEDS DIMINISH LIGHT QUALITY TO CROP
It is commonly taught that weeds reduce crop yield by capturing light, moisture, nutrients, and space. Dr. Clarence Swanton, University of Guelph, Ontario has found another way weeds compete with crops - light quality. He found that the quality of light detected by a crop as it emerges and grows during the first few weeks may be a yield-limiting factor. Swanton has studied how crop plants react to having other green plants nearby as they emerge and grow by measuring crop plant reactions to different ratios of red and far red light reaching the plant. The far-red light is the reflected red light and not the optimum light that comes directly from the sun. The larger the red/far red ration the better for crop plants to develop.
Weeds that are near crop plants reflect far red light to crop plants which has a negative affect on growth. Swanson has observed at least three things from this reflected light. One - there is a delay in the rate leaves develop. Two - the total above ground weight of crop plants is less. Three - the total biomass of roots are less. With hours after crop plants emerges, they sense their external environment by sensing light quality.
This and other research confirms the most critical period for weed control in corn, is from the 3-leaf to 8-leaf stage. Weeds that emerge after that period do not compete for yield but may add to harvest problems and to the weed seed bank.
Extension Weed Specialist