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Choosing the right response

Date Added: 07/04/2016

Blog: By Richard Elsdon, Technical Consultant, United Oilseeds

I think Victor Frankl – the Austrian neurologist and psychiatrist (who was a Holocaust survivor) - said it best when he offered the suggestion that “Between stimulus and response there is a space. In that space is our power to choose our response. In our response lies our growth and our freedom.” Yes, that may be a little heavy for an agronomy blog, but it encapsulates my advice to always think and ponder a little before making any knee-jerk reaction.

The knee-jerk reaction I have in mind this week, is the desire to control pollen beetle as soon as they are seen. If temperatures keep rising, that day may not be too far away. The AHDB (formerly HGCA) have been updating their thoughts and advice on the subject and I have to say that, at first sight, some of it did seem a little odd. However, after a moment’s mental digestion, the fog cleared.

But before going onto to look at their advice on control, there are couple of points to mention. First, the need for control is all about timing. When the oilseed rape crop is in the green to yellow bud stage the Pollen Beetle is a pest and this is when you would look at threshold levels and plant populations. However, once the crop has developed to 10% flowering, the beetle is no longer a pest but rather becomes beneficial as it helps pollination. Timing!

The second point to consider, is that for almost every insect there is a parasitic wasp. Now, these tiny fellows are the unsung heroes of agriculture and should be encouraged. In brief, they lay their eggs on developing pest larvae and then their young emerge and gradually eat the pest larvae as sustenance. Once they have achieved the required size to go to the next stage, the host larvae is either dead or incapable of living much longer. By not spraying, you enable more of the parasitic wasps to live and reduce the ability of the pollen beetle to reproduce.

That is fine I hear you say, but what about the thresholds? The science and experience in the field is now saying that before reaching for the insecticide, go out and check the crop stage. Then count beetles per plant. Then count plant numbers. The logic is that while the oilseed rape plant invariably produces excess flower numbers, it is the lower populations which produce the most excess flowers, because they will produce more branches as they have more space available to them. (Keep with me we are nearly there!)

Pulling all of this together, AHDB have produced a chart of pollen beetle contol threshold levels. This chart, produced by AHDB, shows where we are with present control threshold levels.

     if there are less than 30 plants/m2 -
the threshold is 25 pollen beetles per plant

     if there are 30-50 plants/m2 - the threshold is 18 pollen beetles per plant

     if there are 50 plants/m2 - the threshold is 11 pollen beetles per plant

     if there are more than 70 plants/m2 - the threshold is 7 pollen beetles per plant

These threshold levels have been used in Denmark where pollen beetles are more of a problem than in the UK and have been found to work.

By acting in this way we can make the correct response and secure the optimum economic return. In addition, we are being environmentally responsible and are helping to give the parasitic wasps the best chance to do what they do best and benefit the grower.

Victor Frankl probably had no idea his philosophical thought about the nature of response would be so helpful to agriculture.

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