UC Garden Blogs
Hurray for the red, white and blue! One more day until we celebrate the birth of our country, Independence Day, and the patriotic colors will be out in force. Insects, also, can be red, white and blue. Take the red...
"Red" is for the red flameskimmer, Libellula saturata. (Photo by Kathy Keatley Garvey).
"White" is for the cabbage white butterfly, Pieris rapae. It's a pest, but its colors are appropriate on Independence Day. (Photo by Kathy Keatley Garvey)
"Blue" is for Acmon Blue (Plebejus acmon) butterfly. It's as blue as the starry background on the American flag. (Photo by Kathy Keatley Garvey)
They're good bees. You can take that to the bank! The excitement began when Martin Guerena, an integrated pest management (IPM) specialist with the City of Davis, encountered a native bee nesting site Wednesday in front of the U.S. Bank, corner of 3rd...
Sunflower bees, Svastra obliqua expurgata, flying to a nesting area in downtown Davis, Calif. (Photo by Kathy Keatley Garvey)
A sunflower bee delivering pollen to its nest. (Photo by Kathy Keatley Garvey)
A pollen-packing sunflower bee making a deposit near a Davis bank. (Photo by Kathy Keatley Garvey)
Lindsey Hack (left) and Allie Margulies of the Neal Williams lab, UC Davis, photographing the sunflower bees. (Photo by Kathy Keatley Garvey)
People make deposits in this bank, but sunflower bees are making deposits near the bank (left, in the wood chip mulch, circled here by yellow caution tape). (Photo by Kathy Keatley Garvey)
Beekeepers don't like their "girls" foraging in California buckeye (Aesculus californica) It's poisonous to bees. "The signs of poisoning can be as severe as dying adult bees and brood, only dying brood, brood that barely makes it and emerges...
A bee forages on California buckeye in Vacaville, Calif. (Photo by Kathy Keatley Garvey)
California buckeye is poisonous to bees and can result in dying brood, or misshapen brood. (Photo by Kathy Keatley Garvey)
A California buckeye blooming on the UC Davis campus. (Photo by Kathy Keatley Garvey)
When we think about weed control in crops, we often think about 'short-term' results: weed control after 30 days, weed control after 60 days, weed control at harvest, etc. But weeds and weed control efforts in one crop can significantly influence the density and composition of weeds in the following crop. The carryover between commodities and seasons is accomplished via the weed seedbank, which serves, in my opinion, as the memory of crop production practices. Weed control successes and failures are reflected in the changes that occur in this genetic reservoir. In good years, weeds are successfully controlled and few to no seeds enter the seedbank; in bad years, weeds escape management strategies, flower, set seed and the seedbank grows.
Figure 1. The soil seedbank cycle
Why should we worry about the seedbank? It's a numbers game, really. The more seeds that are present, the greater the potential number of germinating seeds/emerging seedlings, the greater the potential for weed control escapes. This would require growers to engage in additional management practices that may have been unplanned and that add to the cost of crop production. NOTE: this isn't to suggest that growers shouldn't diversify with respect to weed management tools (i.e. using crop rotation, cultivation, herbicides, etc...), rather, it it means that these unintended occurrences can place an additional burden on a producer. Increased seedbank/in-field weed densities could also facilitate the development of herbicide resistance. According to Jasieniuk et al. (1996), where weed infestations are heavy, the probability of selecting for resistance can be high, even if the mutation rate is low.
Figure 2. A recreation of some data presented in Jasieniuk, M., A.L. Brule-Babel, and I.N. Morrison. 1996. The Evolution and Genetics of Herbicide Resistance in Weeds. Weed Sci. 44: 176-193
In my opinion, a complete weed management program will target both above-ground weeds and below-ground seeds. The most obvious way to directly impact buried propagules is through soil disturbance, i.e. tillage or cultivation, affect the vertical distribution of seeds in the soil. Soil disturbance can either help or hinder seedbank depletion, depending on its intensity and the biology of the weed species present. While inversion tillage can remove naturally short-lived seeds from the surface seedbank, some seeds may be protected from environmental fluctuations when they are buried more deeply.
Figure 4. Although deep burial can reduce the Palmer amaranth surface seedbank, deeply buried seeds may remain viable for a longer period of time.
If you really want to reduce the seedbank, minimize inputs (i.e. reduce seed set, prevent new seed introductions) and maximize losses (i.e. bury seeds below the optimal germination zone, facilitate predation or pathogenesis)! The following figures provide valuable suggestions. Regardless of your management strategies, vigilance is key! Weeds are especially adaptive and lapses in control can cause significant setbacks. Good luck!
Figure 5. Best Management Products (BMPs) for maximizing seed loss.
Figure 6. Best Management Products (BMPs) for minimizing seed return.
It's sort of like "The Beauty and the Beast." Or "The Pollinator and the Pest." A gorgeous Western Tiger swallowtail (Papilio rutulus), seeking nectar from a butterfly bush, touched down and began to feed. It didn't take long for the butterfly to...
Papilio rutulus, lands on a butterfly bush. Note the stink bug on top. (Photo by Kathy Keatley Garvey)
The Western tiger swallowtail quickly jerks back as it spots the stink bug. (Photo by Kathy Keatley Garvey)
Oops! A sip of a nectar and a view of the stink bug. (Photo by Kathy Keatley Garvey)