Prep Course

Front 1

Weather

(factor that influences effectiveness)

Back 1

• temperature - herbicides more effect when warm because plant is growing (translocated best), heat leading to drought can cause leaf pores to close to preserve moisture (prevents herbicide from entering plant
• rainfall - rainfall soon after foliar application reduces effectiveness (washed off herbicide), if rainfall occurs within 2 wks after application soil-applied pre-emergent work best (herbicide moves to top 3" where seed germination occurs
• humidity - high humidity increases performance, work better when plant is growing, translocated especially effective

Front 2

Ways to Reduce Herbicide Drift

Back 2

• avoid spraying in windy conditions (most are fine if wind is less than 5 mph, some CA labels restrict use if wind is over 10 mph)
• increase droplet size (small drift further, reduce tank pressure by using large nozzles)
• use drift control agents (adjuvant/thickening agents increase spray droplet size)
• be careful during hot, dry weather (small droplets evaporate before hitting target & have greater potential for drift)
• temperature inversions (cold air trapped by warm air, droplets are trapped & can form pesticide cloud which can move off-target)
• buffer zone (area within treatment area remaining untreated to protect sensitive adjacent areas)

Front 3

Soil Conditions Which Effect Herbicide

Back 3

1. Soil Texture - relative amounts of sand, silt & clay. Sand = reduction of effectiveness as herbicide can leach below seed germination zone (top 1"-3"). Clay = reduction of effectiveness as herbicide can be trapped.
2. Organic Matter Content - reduce effectiveness as organic matter binds to herbicide molecules

Front 4

Foliar Characteristics Which Effect Herbicide Performance

Back 4

• leaf shape - large, horizontal leaves are best targets/narrow, vertical leaves shed herbicides
• wax & cuticle - thick leaf wax/thick cuticle can prevent herbicides from penetrating leaf. Young plants have less thick wax & cuticle
• leaf hairs - herbicides bead up on leaf hairs, prevents leave penetration.

Front 5

Surfactants

Back 5

• used to improve performance of pesticide by improving coverage or penetrating through tiny cracks in leaves on target foliage
• non-ionic - no electrical charge & most common (especially translocated)
• anionic - have negative charge, help herbicides remain on leaf (some prevent herbicide from being washed off)
• cationic - have positive charge, not usually used for herbicide surfactants

Front 6

Herbicide Application Methods

Back 6

• Basal Bark Treatment - applied to bottom 12"-18" of the target plant's stem, oil diluent may be used in place of water (helps to penetrate bark)
• Cut Surfaces Treatment - applied to cuts made in stem or trunk, oil diluent may be used in place of water, called "hack & squirt"
• Cut Stump Treatment - herbicide or herbicide/oil mixture applied to freshly cut stumps to target trees or shrubs