Horticulture notes April 2007

Your annual apple scab control programme should now be underway.  It is important to monitor leaf quality regularly in the expanding bud clusters.  Early applications of protectant sprays should have given you satisfactory control, if growth is slow and weather has been fine.  But remember that newly expanded tissue has no protection until the next spray date so keep your intervals short - certainly no longer than 10 days especially during periods of rapid growth.

Where spore release periods (Mills’ periods) have occurred and conditions remained mild, you should consider your next tank mixture to include ingredients with curative potential. These will provide some degree of ‘kickback’, although any delay more than 48 hours after an infection period means scab symptoms are very likely to develop.

It pays to plan ahead with your spray programme to avoid disease resistance developing in the longer term.  For example, those products incorporating a strobilurin (QoI) fungicide should not be used more than 4 times in a scab control programme.  In addition, best practice advises you not to apply strobilurin (QoI) fungicides more than 2 times consecutively in any programme.

Why not draw up a scab spray programme for the rest of the season, if you have not already done so?  It can always be altered to suit any change in conditions, but will still give you a sound basis for effective disease control.

Slugs can be a serious problem in ornamental crops at this time of year. David Kerr, Ornamental Crops Development Adviser is highlighting the need for control of this pest. ‘New foliage on a range of herbaceous plants is particularly prone to damage, while the garden centre market requires plants to be completely free from pests or blemishes’ explained David.  

Slugs tend to lay more eggs and feed more actively in damp, mild conditions that have occurred recently.  One of the most damaging species is the field slug, a small cream or grey slug which can be difficult to detect in the early stages of infestation and feeds voraciously at night.

A new slug pellet is now available to commercial growers based on the compound iron (ferric) phosphate.  It is sold as ‘Ferramol’ and is more environmentally safe than many other slug control pellets.  You can apply it to field and container crops where animals or birds are present.  Also, the active ingredient breaks down to a plant nutrient, leaving no residue. It gradually degrades to release iron and phosphorus into the soil.  These are then both available for plant uptake as nutrients.  

‘Ferramol’ is available in pellet form.  These should be applied evenly over the surface at the recommended rate(s) for the crop and growing system.

If you are intending to grow cut flowers in tunnels or glasshouses this season there is still time to take a horticultural soil sample to test for N, P, K, Mg, pH levels and salt content (Conductivity). You must carry out a soil analysis to justify application of phosphorus prior to any base fertiliser being applied for a soil grown cut flower crop.  A soil analysis will

Consult David Davidson (david.davidson@dardni.gov.uk), Cut Flower Development Adviser to help with interpretation of your soil sample results.

Weed control in soil grown cut flowers is also important to avoid excess labour required to hand weed cut flower crops.  A relatively effective method to reduce hand weeding is to apply a chemical sterilant such as ‘Basamid’ with the active ingredient 97 percent w/w dazomet.  This chemical if applied in accordance with the manufacturer’s recommendations should significantly reduce the level of weeds in tunnel and glasshouse soils to manageable levels.  To ensure the effectiveness of dazomet, apply evenly to a moist, warm soil.  Work the chemical into the required cropping depth and cover with heavy gauge polythene sealing the sides to prevent leakage of the gas. The process should take 3 weeks to complete, soil covered for 2 weeks followed by one week to allow aeration of soil.

Your questions and comments are very welcome so that we can address the issues that are important to you. Please email the author directly at graeme.cross@dardni.gov.uk