Suppression of spininess in M.26 and P.22 apple rootstocks.

These studies were conducted in three separate expe riments including rootstock production (mound layering) and rootstock liners (tree product ion prior to budding) using M.26 and/or P.22 plant materials. To counteract spininess in examine d plants dinitroaniline compounds: butralin, butralin + fatty alcohols (BFA), and pendimethalin were applied. In a preliminary study late summer sprays of butralin at 4000 mg l -1 reduced spininess in stool beds of excessive spiny hybrids of Malus robusta 5 x M 9 but caused premature plant defoliation with no bark injury. In stool beds with M.26 plants two applications of 1500 mg l -1 did not affect spininess. In M.26 and P.22 rootsto ck liners two sprays of either butralin, BFA or pendimethalin at 1000, 2000 or 3000 mg l -1 (for butralin and BFA), or 1500, 2500 or 3500 mg l -1 (for pendimethalin) significantly reduced spinines s as compared with intact plants but no differences in this respect am ong the chemicals and rates were found. Two manual operations were somewhat more efficient in s p e removal than chemical treatments but no practical differences between them in the field wer e observed. There were no adverse residual effects of chemical treatments on nursery tree performance (Jacyna et al., 2002).