SIZE CONTROL OF CARROTS AND PARSNIPS FOR THE PREPACKED MARKET

Carrots (Daucus carota) in the size grade 25 to 44mm diameter and parsnips (Pastinaca sativa) in the size grade 40 to 60mm diameter can gain a premium on the market when presented as prepared and over-wrapped whole vegetables. Whole roots larger than the maximum sizes stated are of a much lower value, if they obtain a market at all, and if not saleable they add greatly to the packhouse waste problem. This experiment sought to hold a crop that had reached its optimum prepacking size root yield in that state for as long as possible using growth suppressing techniques. The methods comprised mowing off the foliage, spray application of a contact herbicide to damage the foliage or covering with straw to smother the foliage. The latter technique, although most expensive, could also be used as a field storage system. The Chantenay and Nantes type carrots were drilled on 27 April to 1 May and the bulk of their roots were in the prepacking size grades by early-mid September. All of the foliar treatments reduced total yield compared with untreated carrots when assessed later in the season in all three years. The most immediate and effective suppression of further growth was achieved with a covering of straw on 7 or 21 August. Other partially effective growth suppressing techniques were mowing to 25mm above the crown and an application of a high rate of chemical desiccant, but these tended to reduce rather than to suppress further growth. When applied in September, the three foliar treatment techniques gave a more similar degree of growth suppression. The yield of over-large carrots was considerably reduced using these techniques. No foliar treatment caused an increase in yield of prepacking sized carrots but all increased the proportion of these 25 to 44mm diameter roots within each crop.

For the parsnips, cv Alba and Albino drilled from 27 April to 1 May, the foliar treatments were effective in temporarily suppressing the growth of each crop, with the straw being the most effective. Most of the parsnip yield was in the under 60mm size grade suitable for prepacking throughout the autumn harvest period, and thus the foliar treatments were of less value in preventing the formation of over-large parsnips.