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Strawberry spraying with TWIN

11 August 2006

Strawberries have to be protected against diseases and pests with a level of care and efficiency that exceeds many other crops. In the past, growers would use high water volumes and/or e.g. use equipment to turn the leaves to try and get more PPP where it is most needed; within the crops’ canopy. These traditional approaches cause difficulties - high water volumes do not efficiently deposit the spray on delicate plant structures such as the flowers petals and more of the pesticide is wasted on the ground. Using mechanical equipment to turn the leaves are also increasingly non-acceptable; they slow down the spraying speed, waste much time and can delay critical timings.

Not surprisingly, TWIN spraying in strawberries has dramatically increased to a point where we have now made commitments to give proven, well based advice. HARDI have examined the key application settings that will optimise TWIN use in this highly valued crop; settings that identify how to gain optimal deposits and penetration within the crops’ canopy - applying more spray to more critical points where other methods fail.

 

Making every droplet count
Two water quantities were sprayed: 150 l/ha and 300 l/ha. This lower rate is one that TWIN users can safely apply - without fear of drift or spray coverage loss - and the higher one is at the lower limit of conventional practice. The TWIN sprayer was adjusted to apply both these water volumes in three air quantities which were directed at three angles. Deposits on leaves and stems were graded on a scale from 1 that was no spray to 5 where spray coverage was optimised using a special UV tracer.

Result
Lower water volume use of finer sprays is as critical to strawberry growers as it is to the arable farmers. Traditional spraying applies - at 150 l/ha - almost all the spray to upper leaf surfaces; there is no enhancement to under surface deposits despite use of finer sprays. All TWIN settings increased underside leaf deposits. Optimal upper leaf deposits were best gained with forward angling at all air speeds whilst high vertically directed air is best for lower leaves within the canopy.

Table 1: TWIN air assistance will always increase spray deposits in strawberries at 150 l/ha but the scale of that benefit is dependent on how that air is applied. Speed 5 km/h. ISO nozzle 110-FF02 @ 2 bar.

Angle (°) Position Air quantity Upperleaf Topside Upperleaf Underside Lower leaf
Conventional 5 1 2
30 Backwards Low 4 4 3
30 Backwards Medium 4 5 3
30 Backwards Max 4 4 4
0 Vertical Low 4 2 2
0 Vertical Medium 4 3 4
0 Vertical Max 4 3 5
30 Forwards Low 4 5 2
30 Forwards Medium 4 5 3
30 Forwards Max 4 5 3


TWIN summary

  • Deposit on the top side of the upper leaves always adequate at all air settings
  • Under surfaces of the upper leaves enhanced when angled either forward or backwards.
  • Lower leaf deposits enhanced at higher air speeds – especially when angled vertically. 

Higher water volumes traditionally applied - do increase canopy penetration. However, the difficulties and costs of carrying water for spraying are expensive, waste time and may lessen product efficacy. TWIN air assistance allows for safe applications at 150 l/ha; the critical lower leaves and stems are protected more effectively that traditional means despite using half the amount of water.

Table 2: TWIN air assistance overcomes the traditional need to use high water volumes to gain acceptable canopy penetration. For 150 l/ha the speed was 5 km/h and for 300 l/ha the speed was 2,5 km/h. ISO nozzle 110-FF02 @ 2 bar. TWIN air used at highest speed.

Angle (°) Position Volume (l/h) Upper leaf Lower leaf Main stems
Conventional 300 5 4 2
30 Vertical 150 4 5 4
30 Vertical 300 4
3
0 Backwards 150 4 4 2
0 Backwards 300 4
3
0 Backwards 150 4
4
30 Backwards 300 4
5


TWIN Summary

TWIN air assistance permits reduced water volume use of 150 l/ha and will deposit as much spray or more as that from the traditional 300 l/ha application.Air assistance may optimise stem deposits when angled 15° backwards.

Conclusion
Strawberry spraying efficiency can be enhanced with TWIN air assistance; big benefits in deposits being gained at the lower water volumes now demanded by growers. Optimised use of this air assistance follows simple rules. Underside surfaces of the upper leaves benefit from angling; which direction is used - is not so important. Leaves are twisted and turned by the air to expose the under surfaces and leaves further within the canopy. If infestations of disease or pest are more within the canopy then consider full vertical air assistance.

Agronomist Dorthe Kappel

 
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