DARD Management Notes: Horticulture

Canker stems
Canker stems

TOP FRUIT: Autumn spray options

A very variable Bramley crop this year has left some orchards with heavy extension growth and numerous water shots. If you are concerned about the lack of fruit bud initiated for blossom next spring it isn’t too late to apply a spray of the growth regulator ‘Cerone’ (a.i. 2-chloroethylphosphonic acid). This is a recent addition to growth regulators allowed on apple trees, having proved its worth on cereal crops previously. When sprayed onto trees after fruit picking, ‘Cerone’ closes down any late season vigour. There is also strong evidence that if applied before leaf fall starts, it can change terminal bud into fruit bud, even on Bramley. The maximum dose in any year is only 0.75 litres per hectare (0.5 pints per acre). It should be effective if applied as a single spray treatment at this rate. There is an argument for better effect by applying it as two half-rate sprays, ten to 14 days apart’ although weather or surface conditions may not permit two treatments in November. Another benefit of this product is that it provides some plant defence to stressed trees, because it’s active ingredient is converted into a form of systemic fungicide (similar to ‘Alliette’) on absorption.

Where an orchard has shown significant canker (Neonectria) infection on stems and fruit, it will benefit from a late season fungicide treatment to dry up live lesions, suppress further spore production and reduce the number of new infections. Active ingredients available for this purpose include copper oxychloride (sold as ‘Cuprokylt’) and tebuconazole (sold as for example ‘Fathom’, ‘Folicur’, ‘Orius 20EW’). Applied at 5 per cent and 50 per cent leaf fall, any of these products will help protect scars and wounds from fresh canker attack. Remember that Neonectria sporing can occur in any wet weather where temperatures are 6 degrees centigrade or higher.

Biological control of spider mite

Over the past number of years there has been an increase in spider mites (two-spotted mite, red or glasshouse mite and fruit spider mite) in a range of crops in protected and nursery stock plant species. Biological control is the main control in many situations following mites developing resistance to a range of pesticides.

At the Horticulture Centre, Greenmount, we use biological control agents for spider mite in a range of crops. We have identified a number of factors which need to be considered specifically in the use of biological control in spider mite control. These are as follows:

Crop surface area - as the crop grows over the season the leaf cover surface area also increases, therefore you may need to increase the volume of biological predators to give better coverage especially in high density cropping.

Limitations of the predator species - of the biological predators available for spider mite control specific species are more effective at different stages of the spider mite population and population density.

Temperature - one of the most voiced concerns of using biological control is temperature. However when you look at the temperature requirements of most biological control predators, including those which can be used for spider mite, they are able to cope with temperatures between 8 and 30 degrees.

Relative humidity - some predator species, for example Phytoseiulus persimilis, find it difficult to work in very dry warm conditions and need a relative humidity of at least 60 per cent while the other species used as a control, Amblyseius californicus, can tolerate a lower humidity.

Over-winter - spider mites have a great capacity to over-winter within a structure and crop. They go through a dormant-like period (diapauses) of not eating and reproducing (survival instincts) making them a serious threat from early in the season. On-going vigilance is important especially with reducing egg numbers before the main cropping periods.