From the Alfalfa & Forage News blog :: Feb. 18, 2013

Dodder is a troublesome annual parasitic weed that infests alfalfa fields. Initial infestations are usually caused by sowing dodder infested seed (a good reason to purchase Certified seed) and by “sheeping off” fields with sheep that came from an infested field. Perhaps no weed problem is worse than an alfalfa field heavily infested with dodder. As a parasite, it lives at the expense of the alfalfa plant and literally sucks the vigor and life out of the plant. If left uncontrolled it can actually kill the alfalfa plant. It emerges as a rootless shoot and must...

Or rather, think about the weed seedbank, which is the reservoir of viable weed seeds held within the soil profile of an ecosystem. These seeds may be recent additions (e.g. seed that was produced on mother plants within the previous year) or else dormant seeds that have persisted in the soil environment across multiple seasons (e.g. seeds that have not germinated despite exposure to optimal environmental conditions). Whether we realize it or not, our ability to manage weeds in agricultural or horticultural settings can be significantly influenced by the density and diversity of the weeds seedbank. Numerous studies have demonstrated that as weed seed numbers increase, so do the numbers of weeds that survive management...

Here's an article from the San Joaquin County Field Notes newsletter (Feb. 2014.)

Dormant Weed Control in Tree Nut Crops 2014

Mick Canevari, Farm Advisor Emeritus
Brent Holtz, Pomology Farm Advisor and UCCE County Director
Brad Hanson, Extension Weed Specialist, UC Davis

Current dry weather has preempted most normal winter weed germination and growth while prolonged periods of dry soil has caused some early weeds to desiccate and die. In most tree and vine herbicide trials conducted so far this winter—the...

Despite the increasing potential for rain this week, California remains poised to experience exceptional drought conditions in 2014. Under prolonged periods of dry weather, weed control is likely to suffer. This is especially troubling for growers as both crops and weeds will be competing to capture limited soil moisture, which could result in significant yield losses.

Although fewer weed seeds may germinate under dry conditions, weeds that do emerge and become established may be more difficult to manage with herbicides. Drought-stressed weeds are likely to have thicker cuticles (which is the waxy coating on the surface of the leaf), which can inhibit the absorption of post-emergence products. Additionally, plant architecture...