Agronomic cover crop management supports weed suppression and competition in California orchards

Abstract

Cover crops enhance the biodiversity of cropping systems and can support a variety of useful ecosystem services including weed suppression. In California orchards, cover crops are typically implemented as annual plants that can replace resident vegetation in orchard alleyways during the rainy winter season. Our research objective was to evaluate cover crop management factors that support a competitive, weed-suppressing cover crop in the unique orchard systems of Central California. We conducted two experiments, which included an experiment evaluating cover crop management intensification in walnuts and an experiment evaluating multispecies cover crop mixes and planting date in almonds. These experiments demonstrate that timely cover crop planting is important for producing an abundant cover crop, and a variety of cover crop management programs can produce weed-suppressing cover crops. However, cover crops do not result in weed-free orchards and should be considered within the context of integrated management programs. The apparent flexibility of orchard cover crop management provides opportunity to promote other agroecosystem services, with vegetation management and weed suppression as complementary management goals.

Developing cover crop systems for California almonds: Current knowledge and uncertainties

“…In a study in California wine grapes, cover crop competition generally decreased weed biomass in alleys without impairing other aspects of vineyard management (Baumgartner et al 2008). In recent orchard research, management practices that influenced cover crop establishment had a larger impact on weed competition than the specific cover crop mix (Haring and Hanson 2022). Cover crops are not likely to fully control weeds in orchard alleys but direct competition with weeds and the weed control benefits of cover crop termination will contribute to weed control goals over the multiyear lifespan of an almond orchard.…”

The Potential of Cover Crops for Weed Management: A Sole Tool or Component of an Integrated Weed Management System?

“…As mentioned above, cover crops are usually planted in the fall, early or late winter, or summer depending on the type of cash crop to be planted after cover crop termination in annual cropping systems [ 7 , 27 , 28 , 29 ]. In orchards and vineyards, cover crops are usually planted in fall or early winter [ 8 , 26 , 30 ]. The cover crops are generally terminated before the planting of the cash crop in annual cropping systems or before the orchard crops or grapevines resume active growth after dormancy [ 30 ] because the termination date can negatively affect the emergence of cash crops [ 31 ] and result in crop yield losses [ 9 , 18 ].…”

“…In orchards and vineyards, cover crops are usually planted in fall or early winter [ 8 , 26 , 30 ]. The cover crops are generally terminated before the planting of the cash crop in annual cropping systems or before the orchard crops or grapevines resume active growth after dormancy [ 30 ] because the termination date can negatively affect the emergence of cash crops [ 31 ] and result in crop yield losses [ 9 , 18 ]. As a general rule, under north American conditions, specifically in the southeast, it was suggested that cover crops should be terminated two to four weeks prior to cash crop planting [ 32 ].…”

“…Timing of cover crop planting can have direct implications for the growth rate and amount of biomass accumulation by the cover crop because of a longer growing season, amount of nitrogen fixed in the case of legumes [ 33 ], and amount of weed suppression [ 29 , 30 , 34 ]. For example, it was reported that cover crops produced 40% less biomass, and less nitrogen production by the legumes, when they were planted in mid-October compared to early-September [ 33 ].…”

“…For example, it was reported that cover crops produced 40% less biomass, and less nitrogen production by the legumes, when they were planted in mid-October compared to early-September [ 33 ]. Haring and Hanson [ 30 ] attributed some suppression of weed biomass by cover crops to early planting compared to late planting. However, a longer growing season may also mean more biomass accumulation in both the cover crop and the weeds [ 28 , 29 ].…”