Pests - Insects & Weeds PLS 386 August 31, 2005 Outline of topics: (pp in text) I. Insect lifecycles II. Feeding habits III. Other crop pests (animals) IV. Weeds as pests V. Weed characteristics

Pests - Insects & Weeds PLS 386 p. 2 About 80% of all animals are insects. Damage can be from direct feeding or from vectoring pathogens. ~600 species of insects are crop pests. 8 orders of insects are important to crop production.

Pests - Insects & Weeds PLS 386 p. 3 Important Insect Orders: Lepidoptera - leaf miners, stem borers, caterpillars, loopers Coleoptera - beetles Hymenoptera - sawflies, ants Diptera - flies, fruit flies Thysanoptera - thrips Aphididae - aphids Orthoptera - grasshoppers Cicadellidae - cicadas

Pests - Insects & Weeds PLS 386 p. 4 Insects can be classified based on their lifecycle: 1. No metamorphosis - thrips egg > young > adult 2. Gradual metamorphosis - grasshoppers, aphids egg > nymph > adult 3. Incomplete metamorphosis egg > naiad > adult 4. Complete metamorphosis - butterfly, fly, bee egg > larva > pupa > adult

Pests - Insects & Weeds PLS 386 p. 5 Insects can be classified based on feeding habits: 1. Chewing insects - cause defoliation, boring, root feeding. 2. Sucking and piercing insects - scales, aphids, mealybugs, thrips, leaf hoppers Damage to plants is mainly physical, and occurs at all plant growth stages.

Pests - Insects & Weeds PLS 386 p. 6 Other crop animal pests: 1.Mites - spidermites (order of Acarina) 2.Mollusks – snails and slugs 3. Vertebrates - birds, rodents, etc. These can cause severe losses at harvest or in storage.

Pests - Insects & Weeds PLS 386 p. 7 Weeds have different lifecycles: 1. Annuals - complete their lifecycle in one growing season. Summer annuals vs. Winter annuals. 2. Biennials - grow one season, flower anddie the next season (thistles, mullein). 3. Perennials - live many years (bindweed, trumpet creeper, dandelions, johnsongrass)_

Pests - Insects & Weeds PLS 386 p. 8 Why are weeds a problem? 1. Weed seed have dormancy mechanisms. 2. Weeds are more stress-tolerant than crops. 3. Some weeds have similarities to crop plants (similar seed size, growing requirements) 4. Weeds are competitive and spread quickly. 5. Many weeds persist in the soil (rhizomes and stolons)

Pests - Insects & Weeds PLS 386 p. 9 Growth strategies of weeds: Reproductive versus growth Some weeds produce huge numbers of seeds These tend to be annuals (‘r=selected’) Other weeds grow for long periods, producing fewer seeds, but more rhizomes, stolons, etc. (‘K-selected’)

Pests - Insects & Weeds PLS 386 p. 10 Growth strategies of weeds: Reproductive versus growth Logistic growth model: dN/dt=rN[(K-N)/K] =rN(1-N/K) Where N=population size, r=intrinsic rate of increase and K=carrying capacity.

Pests - Insects & Weeds PLS 386 p. 11 Weed control measures: traditional 1. Physical methods - hands, hoes, cultivation, mowing. 2. Mulching - also helps with water conservation. 3. Fire

Pests - Insects & Weeds PLS 386 p. 12 Weed control measures: modern 1. Preventive - keep weeds from reseeding. 2. Crop competition - reduce time to canopy closure. 3. Biological control - insect or fungi. 4. Chemical control - main way in field crop production.