Strawberry Tip Runners

The long term future of methyl bromide for weed and pest control in strawberries is limited, and there does not appear to be any suitable substitute is on the horizon. In Australia there is considerable interest in the development of chloropicrin as the basis for the control of soil borne weeds and pathogens for strawberry runner and also for cropping beds, but the importance of having good weed control is paramount, as is the need to ensure that there is not the danger of nematode build up. Methyl bromide appears to be unique not only in terms of effectiveness but also price.

Clearly however there is no going back—methyl bromide is out. The risk of damaging the fragile ozone layer (particularly for Australia and New Zealand) and the increased dangers from melanoma are too high, and far outweigh the importance of making strawberry growing easier.

In the long term it would appear that the use of any chemical fumigant, which eventually, inevitably, finds it’s way into the atmosphere will have a limited life, because public opinion (in spite a of any assurances to the contrary) will limit (or even eliminate) its use and availability. The effect of the chloropicrin escape in Hawkes Bay late last year clearly demonstrates the public’s view on the use of such materials.

In any case, no one has yet come up with a satisfactory alternative to methyl bromide, so I guess the question is really academic at this point in time.

At Massey University we are developing hydroponic systems for producing strawberries year round, and this has raised a number of problems, one of which is what is the best planting date. In order to resolve this question we need a supply of runners year round, something that traditional runner production is unable to provide, as all runner production is targeted to autumn or early winter planting.

The idea of tip runners came from a small comment by Geoff Langford and Cath Snelling of HortResearch in the NZ Commercial Grower in the middle of last year, and resulted in my visit to a most impressive strawberry operation in England (Mockbeggar Farm) where most of the plants are produced by tip runners.

As a result of this visit we are now producing all the runners for our hydroponic studies using this method.

Essentially we are growing the mother plants in a greenhouse using an NFT system in “high gulleys,” so that the runners hang down, have no contact with the ground and can be harvested easily. The nutrient solution is regularly supplied with a systemic insecticide so that there is little risk of any virus due to aphid transmission. Ideally this part of the operation would be undertaken in a screen house. Every month the mature plantlets are removed (well before they have developed any roots), and are trimmed and then pegged into pots in a sterile medium (we are using vermiculite), and placed under mist propagation.

In a week the plants have developed roots, and the pots can be removed from the mist. After a week or two in the greenhouse bench they can then be planted in the hydroponic system, where they soon develop roots.

Inevitably with a new technique we still have a lot of questions to resolve, in order to make the system work efficiently, but the system may have potential for field grown plants for example where size of planting material or date of planting can be shown to have a major influence on yield. Because the plants can be easily grown on in a greenhouse, or put into cool storage, the potential to manipulate crop productivity with such plants would appear to considerable. Of course there is a cost. Our current production systems essentially revolve around relatively cheap field grown runners planted at high density. Perhaps we can achieve an improved productivity by planting well grown plants at a lower density? Producing runners in this manner opens up the potential to provide the plants with the optimum pre-plant environment, so that they are able to perform at a very high level in the field.

There are a large number of questions that need answering, if we are to achieve the best from the system.

These include:

1) What is the best harvesting strategy? Currently we harvest every four weeks, and take everything except for those runners which are too small.

2) Will the mother plants continue to produce runners indefinitely (we remove all the flowers), or will they need some daylength or temperature treatment to ensure continuity of runner production?

3) What is the best time to plant runners in the field or in a greenhouse for fruit production?