Weed suppression by grasses for orchard floor management

Authors: Tworkoski, Thomas; Glenn, David

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2012
Publication Date: 8/15/2012
Citation: Tworkoski, T., Glenn, D.M. 2012. Weed suppression by grasses for orchard floor management. Weed Technology. 26(3):559-565.

Interpretive Summary: Orchard floor management in recent decades has relied on herbicides to maintain tree rows without weeds, but there are concerns among growers that this practice can cause environmental degradation, decline in soil physical properties, and development of herbicide-resistant weeds. In addition, organic fruit production is increasing, but the lack of effective weed management is a significant limitation. The current research compared five grasses with one another and with three other weed management systems to determine if one grass was better at suppressing weeds and if so, if it also suppressed apple and peach growth and yield. In the field, the combination of grass and mowing generally increased weed suppression with time, and grass was more effective than mowing alone and provided suppression of broadleaf weeds similar to herbicide treatments. Although all grasses reduced average fruit size, yield loss was not significant, and fruit reduction may be acceptable when balanced with environmental and some economic benefits. Although none of the grasses was clearly superior, perennial ryegrass appeared most suitable as a weed suppressor within tree rows and least reduction of yield.

Technical Abstract: Fruit trees in orchards of the mid-Atlantic region of the U.S. are often planted in vegetation-free rows alternating with grass travel alleys. The tree rows can be maintained vegetation-free by herbicides or tillage, but soil degradation or tree injury can result. Grass that is managed to suppress weeds but compete minimally with fruit trees may be an alternative to herbicide and tillage. This research was conducted in the greenhouse and field to assess five different grasses (rough stalk bluegrass, Poa trivialis; Chewings red fescue, Festuca rubra; creeping red fescue, Festuca rubra; Fawn tall fescue, Festuca arundinaceae; perennial ryegrass, Lolium perenne) that may suppress weeds without reducing yield of fruit trees. In pot trials using different seeding rates in the greenhouse, creeping red fescue competed most effectively while rough stalk bluegrass competed least effectively with three weeds (dame's rocket, Hesperis matronalis; cornflower, Centaurea cyanus; Chicory, Cichorium intybus). However, with reduced seeding rates, grass competitiveness with weeds was similar between Chewings red fescue, creeping red fescue, Fawn tall fescue, and perennial ryegrass. Similar results were obtained over a 4-year field experiment. Rough stalk bluegrass competed least effectively with weeds, but the other four grasses provided similar weed suppression; generally, providing as much weed suppression as traditional herbicides. None of the candidate grasses significantly reduced yields of 10-year-old apple and peach trees, although, fruit size was affected by some grasses. The grass that was least suppressive of yield, rough stalk bluegrass, was the least effective in controlling weeds. Mowing in combination with four of the grasses tested is one option to manage the orchard floor with reduced herbicides, but fruit size may decrease.