Weeds and Pests

Our goal as humans, is to OPTIMIZE the growth of our plants.
This requires just the right amount of each of several factors:

One more factor is:

Competition for Environmental Factors (above)

AKA: Plant Spacing

Too Close:

Competition increasedYield decreased
Higher humidityYield increased
Fungal GrowthYield decreased

Too Distant:

Increased heatYield decreased
Increased airflowYield increased
Less fungiYield increased
More water neededYield decreased
Wasted spaceYield decreased
Weeds invadeYield decreased
Erosion increasedYield decreased

Two important spacing considerations:

1. Thin Seedlings - story about Mrs. Fulton's Tomato Seedlings

2. Plan for mature size of trees and shrubs

Foundation Plantings -- windows

Sidewalk and Driveway proximity

Overhead Wires

Weeds = Plant out of Place = Competitor

Tomato seedlings = weeds
Goldenrod = garden flower in Europe
Weed is in the mind of the gardener!

Weedy Characteristics:

1. Rapid Growth

2. Mature Young

3. Many Seeds

4. Vegetative spread

5. Stress Tolerant

Biological Stress (few pests, competitive)

Environmental Stress (deep roots, efficient biochem.)

6. Longevity in Soil "Seed Bank" (100+ years)

How to Control Weeds

1. Mechanical Elimination
a. Pulling out by hand (ouch my aching back)

b. Hoeing (too much energy needed)

c. Wheel Hoe (better but many trips down each row)

d. Garden Rake (so that's what it is for!)

2. Mulching
a. Deep Enough

b. Apply when plants are tall enough, pile it deep (6")

c. Remove when needed
(for thermal insulation: apply anytime AFTER ground is frozen, remove EARLY spring)

d. Water Use Benefits! Soil Conditioning Benefits!

e. Types

1. Inorganic = rocks, plastic, etc. - personal favorite: old carpet strips

2. Organic = newspapers, dead leaves, grass clippings, straw, salt marsh hay (NOT HAY)

3. Chemical Controls
a. Vegetation Killers = Non-selective Herbicide
1. arsenic = heavy metal toxin

2. glyphosate = Roundup = Kleenup = fairly "safe" = plants only

3. boiling water

4. torch

b. Selective Herbicides
1. 2,4-Dichlorophenoxyacetic acid kills broadleaf in grass (suspected carcinogen)

2. Eptam kills grass seedlings in broadleaf crops

3. Trifluralin = Treflan kills seedlings (Pre-emergence)

Considerations before using any chemical pesticide:

1. Application: am I using it for the right crop?

2. Concentration: do I need to dilute this stuff? how much?

3. Frequency: how often should I use it?

4. Conditions: when and in what weather do I apply it?
(don't spit into the wind! be ready to drink what you spill!)

5. Residue: how long will the plant be poisonous? when can I harvest? can it be washed off?

6. Uptake: is this chemical taken into the plant, making it toxic? (Systemic)

7. Duration: how long before my environment is pesticide free?
Can I grow a different crop here next year?

8. Biological Magnification: effect on "food chain" = DDT

Do I really want a weed-free lawn?

Monocultural disadvantage - lost disease/pest resistance
Maintenance hassle
Fertilizer costs
Pest control costs
Mowing costs


Disease/Pathogen (altered physiology or development)

Parasite on Host (decreased vigor)

Herbivore/Omnivore (plant parts missing)

General Ideas for Avoiding Pests

1. Buy resistant Varieties (T V F N Tomatoes)

2. Completely remove diseased/infested plants or limbs

3. Increase air movement and decrease humidity (Pruning!)

4. Optimize Growth: ALL FACTORS!

How to tell if plants are attacked by pests: Symptoms

-Parts missing = chewing insect (bagworms, beetles, borers, cut worms, hornworms) or snail/slug

-Yellow/deformed leaves esp at top = sucking insect (aphids, nematodes, mealy bugs, spider mites, white flies, etc.)

-Discolored Leaves = fertilizer (maybe fungi NOT insects)

-Spotted Leaf/Fruit = bacterial, fungal, viral infection...maybe mites

-Collapse when watering is normal = fungi

Pests Classified into different levels (Kingdoms)

Viruses-Tobacco Mosaic Virus - tobacco, tomato, potato, pepper, eggplant, petunia

-no cures
-buy resistant varieties (T Tomatoes)
-keep smokers out of your garden, greenhouse
Bacteria-Tumors (Agrobacterium tumefaciens), Galls, Witches Brooms (Corynebacterium), fruit and blossom rots
-antibiotics too expensive


-keep plants in drier atmosphere

-avoid over-watering

Fungi-molds, mildews, blight (mushrooms)
-fungicides work, but toxic to humans (Captan)
Bordeaux Mixture story = Copper Sulfate + Lime
Sulfur Powder = Dust
Irish Potato Famine = thank a New World Plant and a fungus for the fact you are here
Dogwood Anthracnose!
-open plant to better air circulation
-buy resistant varieties (Korean Dogwood, VF Tomatoes)
-Parasites = Mistletoe, Dodder

-Weeds = Competitors (already discussed)



Animals-(Herbivores, Omnivores, etc)
Invertebrates (no backbone)
Nematodes - nematicide (repel with marigolds?)
-buy resistant varieties (N Tomatoes)

Molluscs - snails and slugs - moluscicide

Arthropods - mites - miticide (Lindane, Kelthane)

- insecticide - insecticide
contact: Malathion
systemic: Isotox, Temik)

-disease BT = Bacillus thuringiensis

-sticky boards = yellow + grease +- pheromone

-predators "not all insects bad!"
(wasps, mantis, ladybug)

-pick off yourself (alcohol swab or squash)

-water spray under leaves (eggs explode via osmosis)

-soap improves it!

-smother with oil spray (be careful timing, etc. TOXIC TO PLANT)

-diatomaceous earth (bleed to death!)

Vertebrates - (backbones)
birds - puke spray for scout birds
- shiny ribbon, tinsel

mammals - rabbits, ground hogs, mice, deer, birds, (moles), humans!

-fences make good neighbors (10' for deer!)

-traps (dead or alive? where to release?)

-poisons (pets, humans, beware!)


This page © Ross E. Koning 1994.



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