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Spray Pointers for Pulse Crops JUN 8 2016 | Producers | Blog Post

by Tom Wolf, Agrimetrix Research & Training

Spray season is in full swing and it’s time to review the application needs of pulse crops.

Most pulse crops start off relatively slowly with comparatively low plant populations. As a result, good herbicide efficacy is needed to make up for the lack of crop competition.

Early weed removal protects yield potential, but it can mean spraying weeds that are fairly small and therefore difficult to hit. Pre-emergent products like Edge and Authority have a great fit for that reason. For post-emergent products, a coarse spray will mean lower droplet numbers, and that can mean misses. The best way to boost droplet density is to either increase water volumes or to decrease droplet sizes.  I always favour the increased water volume option because it gives two important advantages:

  • For some pulse herbicides, greater volumes improve crop safety.
  • For all pulse herbicides, greater volumes make it possible to take advantage of low-drift sprays. Low-drift spray, in turn, make it easier to apply the spray on time because of less sensitivity to windier conditions.

Try to apply herbicides using Coarse to Very Coarse sprays, in at least 8 to 10 US gpa, to get good coverage. The higher volumes will improve the performance of contact products such as the bentazon (Group 6) in Basagran, or as a component in Viper.

With the timely rains and warm temperatures that many areas received at the end of seeding, we’re expecting good conditions for disease development. This is where it gets challenging, because pulses quickly form very dense and complex canopies that are notoriously difficult for sprays to penetrate.  A few rules for fungicides (thanks to Dr Sabine Banniza of the U of S Crop Development Centre for helpful discussions on these points):

  • Understand the disease in your crop. Do you need to protect stems (anthracnose), leaves and stems (ascochyta complex, mycosphaerella), or senescing leaves or flowers (sclerotinia)? This is where the spray needs to go.
  • Understand the time of disease development.
    • Trash-borne diseases like anthracnose and ascochyta will start at the bottom of a lentil canopy, and early treatment before canopy closure will be important to arrest or at least delay disease development as long as possible.
    • Late season diseases like sclerotinia and botrytis push the application timing towards a closing or closed canopy. Success of such sprays is more elusive because of the rapid development of new biomass.
  • Regardless of the timing of the spray, take a bird’s eye view of the canopy.
    • If you can see the target you need to spray, the job is pretty straightforward and conventional water volumes and nozzles will work.
    • If the targets are hidden from view, it will take more water, slower travel speeds, and perhaps finer sprays to get the required coverage. Consider the higher end of the recommended water volumes (15 gpa in most cases), slower travel speeds (10 mph) and higher pressures (to generate the finer sprays).
  • Look at the size of the plant part you need to target. Large targets like leaves can capture almost any droplet size, but small targets like petioles or vertical targets such as stems may benefit from finer sprays, especially if they’re hidden in the canopy.
  • Focus on scouting and application timing. An excellent spray at the wrong time has less value than a mediocre spray at the right time. Again, low-drift nozzles can help with the timing. If it’s breezy, you can still spray safely and research has shown that the coarser sprays typically don’t hurt product performance.

Later in the year, you may consider desiccating your pulse crop. Whenever we have high biomass crops, higher water volumes are our most effective coverage tool. The top third of the canopy usually captures the majority of the spray, and the bottom third may get less than 10%.  By adding more water, the droplet density at the bottom of the canopy increases, boosting herbicide-induced drydown.