A basis for controlling herb growth.

Excessive growth in crops leads to management problems and reduces yield and quality of produce. Synthetic growth retardants can be used to reduce these problems. In some crops, however, it is not common practice to apply growth retardants because either: there are no approved active substances; the retardants available are expensive; or application of synthetic active substances may not be permitted in the retailer produce specifications. There is thus scope for lower-cost growth retardants that are acceptable to retailers. Basic research into the control of leaf growth has shown acid pH in the cell walls is necessary for cell expansion, and in some species, retardation of leaf growth during drought may result from alkaline sap moving from the roots to the leaves, neutralising the normal acidity. Exploiting this knowledge may enable a cheaper growth retardant to be used based on food ingredients or on commodity substances already approved for other uses. Research at Harper Adams has focused on arable crops. Experiments with detached shoots of oilseed rape and barley have shown that both species respond to artificial alkaline xylem sap with reduced leaf expansion. Spray applications of alkaline pH buffers to intact plants of oilseed rape have, however, been variable in effects on leaf expansion. This was thought to possibly be a result of difficulty in penetrating the thick layer of epicuticular wax. Application of either alkaline pH buffers, or of solid calcium carbonate (lime), to field-grown barley has retarded leaf canopy expansion, but only for a short period. Thus the greatest commercial potential for alkalizing growth retardants may be with short duration crops, and possibly with crops that also do not have a thick layer of epicuticular wax. Herbs may present the best opportunity, and recent experiments indicate that coriander is sensitive to reduced growth from alkaline bicarbonate applications. HDC Project PE 005 aims to discover whether this effect is commercially useful on coriander, basil, mint and flat leaf parsley