Abnormal Color Response of Turf Ryegrass to Top-Dressed Isobutylidene Diurea
1976
Volk, G. M. | Dudeck, A. E.
Isobutylidene diurea (IBDU) is an excellent source of controlled-release N for turfgrasses, but certain reports imply a generally low toxic potential not completely supported by recent Florida work. To evaluate toxicity, IBDU (0.7 to 1.4 mm diam. pellets) was used in single applications at 1 to 7.3 kg N/are rates on winter ryegrass (Lolium perenne L.) and at 1.5 to 5.9 kg N/are on bermudagrass (Cynodon sp.), the latter in all combinations with 0, 0.25, and 0.50 kg urea-N/are every week, and of 0 and 2.4 kg Ca(OH)₂/are at initiation of tests. A 2.2 kg N/are rate of IBDU resulted in chartreuse green ryegrass when soil pH was above 7.0. At 3.3 to 7.3 kg IBDU-N/are the ryegrass was chartreuse-yellow at 1 month after application, regardless of soil pH. Tissue analysis showed an excellent inverse correlation with Mn content. There was no off-color response to sulfur-coated urea or ureaform applied at N rates equivalent to those above. Color assessment by chlorophyll extraction with methanol supported visual observations. There was no toxic response of bermudagrass to IBDU at soil pH 5.1 to 7.3 or at any combination of IBDU with Ca(OH)₂ and/or urea. Application of IBDU “fine” to ryegrass apparently should not exceed 2.0 kg of N/are if visual toxicity symptoms are to be avoided.
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