The risk from Phoma leaf spot continues to rise in the many rapidly growing oilseed rape crops and, where a fungicide application has already been made earlier in the season, a follow-up second autumn spray may be necessary.
But the choice of this second fungicide should have both disease control as well as the start of crop manipulation in mind, says Jon Williams of BASF. "Combining the benefits of regulating canopy development, promoting root growth and managing key diseases has a significant impact on final yield potential of oilseed rape. Field-based research work by ADAS has demonstrated that small rape canopies with good rooting systems produce the best yields and the autumn is when you need to start this process."
"There has been some debate recently around the effects of triazoles on rooting, based on limited indoor studies. Unlike other materials, Sunorg Pro (metconazole) has been proven in full scale field trials, laboratory studies and commercial usage to give significant positive impact on root development. For example in ADAS trials the use of 0.4 l/ha of Sunorg Pro in the autumn resulted in a 5% yield increase over the untreated in non-drought spring conditions as a consequence of canopy benefits. Under drought conditions, however, the autumn application gave 16% increase in yield over the untreated. This yield benefit arose because of optimal canopy size as well as increase in rooting mass density. Rape plants with a strong rooting system are able to better utilise both water and nutrients. They are also better anchored and the risk of lodging in the spring is reduced," says Jon Williams.
"The positive rooting effects from Sunorg Pro have been observed over several seasons under field conditions. It reflects and supports the general view that Sunorg Pro has always been the best growth regulating fungicide," he says.
Jon also points out that an autumn application of Sunorg Pro encourages a more efficient canopy structure through early initiation of side branches, which will aid ultimately light capture and increase yield. "Side branches of the rape plant are initiated in the autumn and promoting their development encourages more uniform branching and improved seed-fill in the spring. Sunorg Pro also regulates plant height, keeping the canopy closer to the ground and helping the crop through the winter."
"Following excellent planting and growing conditions this autumn, many winter rape crops this year will benefit from combined growth regulation and disease control. A late application of Sunorg Pro will protect the crop by reducing the risk of Phoma directly infecting and girdling the stem as well as enhancing rooting and improving overall hardiness for the on-coming winter."
Jon points out that in the minority of crops this autumn Sunorg Pro usage would not be appropriate. "Where the crop is uniformly small, short of nitrogen or under stress, an alternative fungicide with no regulatory effects should be used."
