mar-apr-2020

Weed Control Summer weed control in mature and young orchards is challenging given the growing number of glyphosate (Roundup ® , etc.) resistant weeds, increasing labor costs for repeated “burndown” sprays, and risk of herbicide damage to trunks in young orchards. Late spring application of surflan or pendimethalin is an effective approach for summer grass (jungle rice, 3-spiked goosegrass, sprangletop, etc.) control in almond orchards, but it’s limited to sprinkler irrigated orchards. Use of one quart surflan per acre across the orchard floor in late April/ early May in a sprinkler irrigated orchard gave good summer grass control from trunk to trunk in research by Joe Connell, retired UCCE Farm Advisor in Butte County. Reduced tractor trips for mowing and herbicide spraying were measured with this practice compared to mowing and strip spraying with glyphosate. Effective weed control in young orchards is challenging given label limitations on many preemergent materials. Trellis ® , surflan and pendimethalin are safe preemergent herbicide for young trees, but other popular materials specify postplanting limitations. Repeated postemergent (burndown) herbicide applications can be expensive, depending on the target weeds and herbicides used. In addition, tree damage can result from use of postemergent herbicides in young orchards. It can be difficult to keep herbicides off young trees. Don’t expect white paint to protect young tree trunks from all herbicide rates and combos. In UC research last summer, a 1:1 white latex paint/water mixture painted on trunks did not protect second leaf almond trees from trunk damage when maximum rates of glyphosate and glufosinate were applied together. Damage was similar whether applied trunks were painted two days or nine weeks before spraying. New trunk cartons provided the best trunk protection, followed by bare, unpainted trunks hardened off by nine weeks without any carton with the painted trunks showing the worst damage (see photo). See study details at ucanr.edu/blogs/blogcore/postdetail. cfm ? postnum=38701. This work will be repeated to confirm the results, but this work shows 1) tree protection cartons are the best protection for young trees and 2) trunk paint can provide excellent sunburn protection but may not keep out damaging herbicides. Replacement cartons are expensive in time and labor, but that cost should be weighed against possible tree losses/trunk damage and the time and money spent pulling out and replanting what were established trees. Finally, when selecting and timing any pesticide application, always read the label carefully and consult with an experienced PCA. This year looks like it will be interesting and demanding in many ways: weather, water, world markets and Covid19 pandemic. All the best to all readers and their families. Franz Niederholzer, UCCE Farm Advisor, Colusa & Sutter/Yuba Counties Vulnerable green tissue is just behind paper-thin painted bark on this 2nd leaf Nonpareil tree. Any micro cracks in the paint could allow herbicide to reach that vulnerable tissue. Photo credit: Franz Niederholzer. IN YOUR ORCHARD 4 0 A L M O N D F A C T S