Improving Production Practices of Alabama Christmas Trees

Abstract

A series of trials were conducted to provide updated recommendations regarding cultural practices for fertility and weed control for Alabama Christmas tree growers. Three trials were conducted to determine the effects of nitrogen (N) rate on newly planted Leyland cypress (x Cuprocyparis leylandii). The rates of N differed between trials due to the production practices associated with collaborating farms. Two trials were also conducted to evaluate plant safety in response to four popular preemergent herbicides. In Trial 1 the high N rate, 135 kg N ha-1 in year 1 and 67 kg N ha-1 in year 2 (135Y1/67Y2) had 25% greater growth when compared to the 0Y1/34Y2 kg N ha-1 rate; however, the 67Y1/34Y2 rate was similar to both 135Y1/67Y2 and 0Y1/34Y2. In Trial 2 the lowest rate of N (90 kg N ha-1) produced the greatest increase in plant height when compared to the medium (135 kg N ha-1) and high rate (180 kg N ha-1) representing an increase of 14% and 5%, respectively. Similar to Trial 2, Trial 3 did not show growth benefit when applying N over 90 kg N ha-1, when compared to the low rate. Soil type likely impacted the utilization of N as Trial 1 was conducted on a sandy soil and Trials 2 and 3 took place in a location with a higher CEC. Trial 4 and 5 were conducted to evaluate plant safety in response to four preemergent herbicides on Leyland cypress and Green Giant Arborvitae (Thuja plicata) with over-the-top applications. These included indaziflam, dimenthenamid-P, flumioxazin and a combination product of prodiamine and isoxaben all of which were compared to an untreated control. Trial 4 evaluated rates of 1x and 2x the label rate for each product and Trial 5 focused on the amount of time before a rain/irrigation event (1 hr. and 24 hr. post treatment for each product). Very little damage and reduction in growth was seen across both trials. Rate was not significant in Trial 4 and irrigation delay was not significant in Trial 5. Generally, across both studies, indaziflam had the greatest level of phytotoxicity and impact on growth; however, the damage was not extensive enough to be of horticultural significance.