PLANT HEIGHT AS A FACTOR IN COMPETITION BETWEEN BLACK NIGHTSHADE AND 2 HORTICULTURAL CROPS (TOMATO AND PEPPER)

In a glasshouse experiment the differential competitive relationship b etween black nightshade, tomato and pepper was investigated at four ti mes of weed emergence. Thus, the weed emerged at the six, four and two -leaf stages of both crops and simultaneously with them. Black nightsh ade competed for light and nutrients with tomato only when the weed he ight exceeded that of the crop from the beginning of tomato flowering onward, as it was the simultaneous emergence that reduced tomato fruit yield (36.5%), number of fruits and N, P and K uptake. Competition be tween the weed and pepper for light and nutrients was more severe, eve n when weed emergence was delayed until the six-leaf stage of the crop which reduced fruit yield, number of fruits and N, P and K uptake. Th e earlier the weed emerged relative to the pepper, the les's the crop height and yield. Pepper yield was reduced by 29, 44 and 62% when the weed emerged at the six, four and two-leaf stages respectively. Black nightshade that emerged simultaneously with the crop reduced pepper yi eld by 93% and fruit weight by 74%.