Factors Affecting Budbreak in Honey Mesquite in West Texas

Abstract

Budbreak in honey mesquite in west Texas rarely occurs prior to the last spring frost. We monitored many trees from 1970 to 1980 attempting to better correlate mesquite mortality from herbicides to growth stage. In doing so, we found clues to the probable conditions triggering budbreak. Budbreak was closely correlated to daily minimum winter temperatures but totally unrelated to winter maximum, mean, or soil temperatures. Our data showed that the higher the number of consecutive days with minimums below -1°C during January 15 to February 14, the earlier spring budbreak would occur. Once chilling requirements were met, date of budburst then became a function of relatively warmer daily minimum temperatures from February 15 to March 15. Being able to predict budbreak (from equations developed herein) as early as February 15 and/or March 15 should give ranchers and herbicide applicators 4 to 6 weeks lead time in planning mesquite control programs. West Texas notoriously has spring “cold spells” sufficiently severe to freeze foliage and the young fruit of trees that have leafed out and blossomed from late winterbr early spring warm periods. Particularly vulnerable are exotic fruit trees, such as peach (Prunus persica) and apricot (Prunus armeniaca). Honey mesquite (Prosopis glandulosa var. glandulosa), the major endemic woody plant in the area, seemingly oblivious to even prolonged warm weather in February and early March, usually waits until danger of freezing weather is past, then it leafs out. Some believe that once honey mesquite breaks bud, the danger no longer exists for a late spring frost. From 1970 to 1973, we monitored many honey mesquite trees attempting to better correlate their response to herbicides. In doing so, we found clues to the probable conditions triggering budbreak (Goen 1975). For more than 50 years, observers have reported that trees and shrubs of cold climates kept continuously warm during the winter start growth much later in the spring than those subjected to a period of chilling (Coville 1920). Chandler et al. ( 1937) also noticed that warm winters delayed budbreak of most deciduous trees, and trees or shrubs growing in shade had their chilling requirement satisfied better than those growing in the sun. Further, budbreak started on shaded parts of the same tree earlier than on those parts exposed to the sun all day. McGee (1976) also noticed this effect of shade on budbreak of young oak trees (Quercus sp.). Others have