Growth and yield response to simulated hail damage in guar

Hail damage can result in substantial economic loss to annual spring and summer crops. Crop insurance guidelines to assess hail damage on major crops are readily available to adjusters. However, research and guidelines to assess hail damage on minor crops is lacking and may limit their expansion. A dryland field study with guar [Cyamopsis tetragonoloba (L.) Taub.] was designed to determine the effect of simulated hail damage at two growth stages and three levels of defoliation on plant regrowth and bean yield. Experiments were conducted on a Miles fine sandy loam (fine-loamy, mixed, superactive, thermic Typic Paleustalfs) near Vernon, TX, from 2001 through 2003. A commercial grass trimmer was used to simulate hail damage by flailing plants to targeted defoliations levels of 33, 66, and 90% at 6 and 12 wk after emergence (WAE). Both final plant height and yield were reduced to a greater extent when plants were damaged at 12 WAE (grain-fill period) than at 6 WAE (early flowering). Regression analysis from data combined over years showed that guar yields were reduced 50% with a 66% defoliation level at 6 WAE, but required only 42% defoliation to reduce yield levels 50% with late-season defoliation. This is the first report of using a grass trimmer to simulate hail damage by shredding plant material rather than manually removing plants and plant parts. Results from this study also provide a basis for producers and insurance adjusters to quantify and estimate economic losses in guar due to hail damage at two growth stages.