Seasonal Trends of Total Nonstructural Carbohydrates in Lindheimer Pricklypear (Opuntia lindheimeri)

Pricklypear (Opuntia spp.) is a major constraint to rangeland livestock production in several resource areas of Texas. The phenological and physiological stages of pricklypear have heretofore been ignored in relation to timing of herbicide applications. The phenology, percent total nonstructural carbohydrates (TNC), and water content in Lindheimer pricklypear (Opuntia lindheimeri Engelm. # OPULI) were monitored biweekly for 2 yr in the southern Rolling Plains of Texas. TNC in cladophylls, crowns, and roots declined sharply from bud break (late March to late April) through the period of rapid development of new cladophylls and fruits, with minimum levels occurring during mid-July to early August. This depletion period coincides with the period when control has traditionally been attempted with broadcast applications of translocated herbicides with erratic results. Replenishment of TNC in cladophylls and basal crowns occurred during August through March or mid-April; major increases in root TNC occurred from early autumn through midwinter. Application of herbicide in late summer, autumn, or winter when TNC is being replenished in organs bearing meristematic tissue may be more effective for pricklypear control if the herbicide is translocated with photosynthates.