may-jun-2020

Almond orchards in the Central Valley of California sown with PAm Mustard Mix between rows to provide supplemental bee forage. Photo Credit: Project Apis m. Left: A forager has her head covered in pollen while seeking nectar from deep within a mustard flower. Right: A forager shows that the pollen color for mustard is a slightly darker yellow than the petals. Photo Credit: Dan Wyns The most common mustard variety, white mustard ( Sinapis alba ), originated in the Mediterranean and has spread to its current global distribution. It is cultivated as a cover crop and is also harvested for human consumption, including prepared mustards (from seeds) and young greens. White mustard also grows in a wide variety of environmental conditions including roadsides and disturbed soils leading many locations to classify it as an invasive species. In a cultivated context the crop will bloom six to eight weeks after planting, while wild plants typically bloom in the spring into the early summer with bloom lasting about a month. When it is sown in agricultural fields it is typically done so as a fall crop to be incorporated into the soil as a green manure. As far as a resource for honey bees, mustard is always a very welcome sight to beekeepers and its attractive and easily accessible nectar can provide significant resources to honey bees when soil moisture is adequate. White mustard pollen is abundant and foraging bees often have much of their heads and bodies covered by the golden dust. The nutritional content of the pollen is moderate, but it is of great value to colonies when the availability of other blooms is limited. As a natural bloom it can be an important nutritional component for spring buildup, and when cultivated, it is often among the last available pollen sources available to honey bees prior to winter. Both Dr. Sagili from Oregon State University and Dr. Niño from UC Davis have reported interesting preliminary results regarding the benefits of mustard plantings in and around almond orchards. Dr. Sagili’s group has observed significantly higher hypopharyngeal gland protein content in bees — a nutritional health indicator — from colonies placed in orchards with rapini mustard compared to colonies in orchards with no supplemental forage. The brood area was also significantly greater in colonies placed in orchards with rapini mustard. More specifically, Dr. Niño’s group at UC Davis observed an average increase of three full frames of bees in colonies near mustard plots. There is a great deal of research aimed at developing cover crop seed mixes to supplement honey bee forage before and after almond bloom. Many of these seed mixes contain a high proportion of mustard, including the mustard mix from Project Apis m. In addition to providing forage and habitat for pollinators and other beneficial insects, cover crops can increase soil organic matter, breakup compacted soil, improve water retention, limit erosion, all without increasing frost damage. It is not just almond growers that are adding cover crops between their rows; mustard blooming throughout California Central Valley vineyards and walnut groves has become an increasingly common sight in early spring. While some growers may express concern about the potential for these additional plant species to compete for pollination services and reduce almond pollination success, growers’ observations and study results on this topic reveal increased nut yield per acre in orchards with supplemental forage compared to those with bare orchard floors and higher Nitrogen content and soil surface temperature during bloom. 31 M A Y – J U N E 2 0 2 0