What is in this article?:
- Arizona Veg IPM: vegetable pest control, lettuce drop, weed seeds
- Lettuce drop: aerial infection
- Weed seeds and pre-emergent herbicides
- Updated best management practices for insect control in vegetables focus on shifting pest spectrums, selective pesticide technologies, resistance management, maximum residue levels, and other issues.
- For lettuce, the initial application of fungicides during the rosette stage, about 30 to 40 days before harvest, has been shown to significantly reduce the incidence of lettuce drop caused by airborne infections of Sclerotinia sclerotiorum.
- Most pre-emergent herbicides do not kill dormant weed seeds – in most cases the seeds must first germinate and contact the herbicide before the seeds are killed.
Weed seeds and pre-emergent herbicides
By Barry Tickes, UA Area Agriculture Agent
Most pre-emergent herbicides do not kill dormant weed seeds. In most cases, the seeds must first germinate and contact the herbicide before they are killed. Some pre-emergent herbicides are absorbed only by the roots, some by shoots only (at the hypocotyl in broadleaves and at the coleoptile in grasses), and some by roots and shoots.
Weed seedlings sometimes emerge and grow for awhile before dying or becoming uncompetitive with the crop.
Some fumigants kill weed seeds including metam sodium (Vapam), clorpicrin (Telone), dazomet (Basamid), methyl bromide, methyl iodide, and calcium cyanamide.
Flooding and solarization also can kill weed seeds. Fumigants, flooding, and solarization are often used primarily to control diseases and have the added benefit of controlling some weeds.
Contact Tickes: (928) 580-9902 or firstname.lastname@example.org.