Summer weed control

Be careful about spraying weeds in the summer as chemicals can volatilize and damage non-target plants.

The issue: Summer is when weeds are most noticeable, mostly because they are large and that is the time we are out in our yards and fields. Annuals and seedlings are easy to kill. Biennials are usually going to seed during the summer months. Perennials are quite difficult to kill in the summer.

The main object of summer weed control activities should be to keep all weeds from going to seed, whether annual, biennial or perennial.

Integrated control options:

· Prevention: Feed weed-free hay to horses for three days before taking them on a trail ride; feed weed-free hay at home; keep ditch banks free of seed-producing weeds; clean recreational, farming and construction vehicles before moving to a new area or coming home.

· Mechanical: Hoeing, hand-pulling and mowing do well on seedlings and annual weeds; summer cultivation tillage should be shallow to avoid damaging roots of desirable plants; biennials can be lifted with a shovel, be sure to remove 2-3 inches of root below the crown and destroy any open flowers.

· Cultural: Solarization during hot summer months for four to six weeks by covering the ground with clear plastic is very effective on seedlings and annual weeds; promote competition from desirable plants — nature hates bare ground; apply 3 to 6 inches of organic mulch in shrubs and flower beds.

· Biological: Release weed-specific biocontrol agents.

· Chemical: Be very careful about spraying herbicides in the summer. High temperatures (above 85 F during the three days following application) can cause many herbicides to volatilize and drift to non-target plants — a common complaint I receive every year. Burn-down products such as pelargonic acid may be quite effective on small annuals and seedlings. Carefully read and follow the label.

Combine them:

Combine several of these weed control activities to achieve better overall control.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County.