Crop Notes September 2004

Desiccate all crops as soon as tubers reach the desired size range for your target market. Late harvest dates increase the risk of mechanical damage, disease infection and slug attack thereby reducing marketable yields. Aim to have all crops desiccated by mid September. Seed growers are reminded that all seed for certification must be desiccated by 4th September.

Split rather than single applications of Reglone give growers flexibility to achieve improved haulm desiccation. Where haulms are of average size 1 litre/ha should be applied initially to open up the crop canopy followed 3-5 days later with 3 litres/ha to complete desiccation. Where tops are large and green it may be beneficial to use two equal applications of 2 litres/ha each. No more than 4 litres/ha of Reglone should be applied in total.

With the high blight pressure of recent weeks there have been twenty three blight outbreaks reported across all counties, it is important to prevent blight spores infecting tubers. Growers are therefore strongly recommended to apply blight fungicides with good performance against tuber blight, such as Shirlan, Ranman or Electis, both prior to desiccation and in tank mix with your desiccant. Further fungicides will be needed if the haulms are still green after desiccation. Given the current high blight pressure conditions these products should be applied at the shortest intervals permitted. A five day local weather forecast can be obtained from the Met Office web site at www.meto.gov.uk/weather/europe/uk/nireland.html.

At the end of the season, if there is blight in the crop, destroy the haulm as soon as possible to reduce the risk of tuber infection. Sulphuric acid gives the quickest haulm kill and is the best product in this situation, but must be applied by a contractor.

Slug control

Slug damage can result in serious losses especially in crops intended for pre-packing. Crops most at risk are maincrops of susceptible varieties such as Maris Piper and Marfona. Most damage occurs from now on as the tubers continue bulking up to harvest. Slug pellets containing methiocarb, thiodicarb or metaldehyde should be applied to susceptible varieties if soil conditions remain damp. For less susceptible crops test baiting should be used to assess the need to apply slug pellets.

Store hygiene

Spores of many storage diseases lie dormant in the dust and debris remaining in stores, boxes and equipment from the previous harvest. Significant reductions in infection can be achieved by thoroughly power-hosing or vacuuming stores and equipment before the new crop is harvested. Effectiveness can be further improved by applying an approved disinfectant after initial washing or vacuuming.

Removing excess surface moisture is of great benefit in reducing the incidence of diseases such as silver scurf and soft rots that thrive in wet conditions. Ventilation systems have been developed which force high volumes of air through boxes or bulk piles for a short period to dry the crop quickly. Dried potatoes are then cured as normal prior to storage.

Wet or damp crops should be dried as soon as possible after harvest. If fungicides are to be applied to the crop, they should be applied prior to drying.

Forced ventilation systems are available to suit most needs including:

drying floors, horizontal ducts, and pedestals for bulk stores, tents, suction walls, posi-vent ducts, and letterbox systems for box storage.

Wound healing

Some damage will occur during harvesting and a short period of wound healing or 'curing' should be allowed. After drying, the crop should be held at ambient temperatures (12-150C) for a period of 7-10 days. It should then be ventilated periodically using dry outside air to remove moisture from the store. Once curing is complete the crop can be brought slowly down to the desired storage temperature.

Destroy the 'green bridge' to reduce BYDV risk

Strategies for Barley Yellow Dwarf Virus (BYDV) prevention should start prior to sowing. Crops following grass, weedy stubbles, and set-aside can be infected by wingless aphids which walk directly from this 'green bridge' onto the emerging cereal crop. This green bridge should be destroyed 7-10 days prior to ploughing, using glyphosate or paraquat. The cereal crop should then be sown no sooner than 14 days after herbicide application.

Carried over winter wheat seed

Some growers may have carried over seed from last year, in particular winter wheat. Many factors could influence the germination of this seed including storage conditions and seed dressings. Seed should have a minimum germination of 85% and preferably over 90%. Less than 85% germination   indicates a seed lot which could perform badly especially under poor conditions. The Plant Testing Station at Crossnacreevy can test seed for germination. This can be arranged through your local Crops Development Adviser.

Soil analysis

Following harvest is an ideal opportunity to carry out soil analysis. With fertiliser accounting for a considerable proportion of cereal variable costs (approximately 35-40% in the case of winter wheat), it is important that this input is used efficiently. In addition, fields with a low pH can be identified and rectified with applications of lime. Your Crops Development Adviser can assist you in arranging soil analysis and in the interpretation of results.