University of Vermont Extension System
Department of Plant and Soil Science

Dr. Leonard P. Perry, Extension Professor

Insects

Perspectives

• often tolerable, especially at low levels, determine "threshold" before control
• much aesthetic damage is just that, may only be a nuisance
• most damage is specific to few species, even cultivars
• most insects are beneficial, controlling bad may control the good too

• general: aphids, Japanese beetle (midsummer) and grubs (early summer), caterpillars? (many desirable moths and butterflies)
• specific: lacebug (aster), mites (phlox, hollyhock), plant bugs (coreopsis, daisy), iris borer (bearded iris), slugs (hosta), leaf miners (columbine)

• indirect suppression: redesign landscape, modify habitat, modify cultural practices
• direct suppression: physical, biological, insecticides, least toxic chemicals:
• inorganic (sulfur, copper)
• botanicals (pyrethrum, rotenone, nicotene)--may be quite toxic to humans
• other (horticultural oils)
• microbials (living eg. BT)
• phermones (Japanese beetle traps)
• Insect Growth Regulators (IGRs)

Perspectives

• many of the same IPM (Integrated Pest Management) practices as for weeds, insects
• often unsightly but no long term injury to plant
• best defense: good culture, plant health, and environment (just as with people)

• Gray mold (botrytis): gray mold on leaves and flowers, stems soft and rotten; remove affected parts, space properly, water only in mornings and not on plants, destroy severely infected plants
• Leafspots: often fungal, brown or black, circular or irregular; control as for gray mold
• Powdery mildew: whitish growth on leaves, mid to late summer, often on undersides and bottom leaves first, when severe causes total leaf drop; choose resistant varieties, trim off leaves, hort. oils, tolerate
• Rusts: rusty colored spots starting on lower leaves, when severe causes leaf drop; as for gray mold and powdery mildew, only use wettable sulfur instead of oil
• Wilts: often bacterial, rapid wilt and sudden death of whole plant, may be from root rots, distinguish from other root damage by blackened roots and stems; often no cure, improve drainage, replant elsewhere (rotation)
• Viruses: irregular mottled or circular patterns in leaves, transmitted by insects; control leafhoppers and other insects, healthy plants usually outgrow, tolerate high levels, destroy severely infected

Physiological

• Drought: slow growth, warped, yellow leaves, brown tips
• Poor drainage: slow growth, yellowish, wilted (often think dry and add more water!)
• Sunscald: too much sun with too little moisture, or shade plants misplaced; papery or translucent patches and irregular burns
• Inadequate light: sickly pale, spindly and stretched
• Transplant shock: long term wilt, leaves begin browning and dropping
• Salts: near ocean or road or walks where deicing salts used; like dessication browning
• Freeze damage: blacken or kill outright quickly, perennials hopefully recover
• Fertilizer deficiency: chlorosis (yellowing) and discoloration, often specific, rare
• Fertilizer burn: scorched brown, dessicated leaves, fairly quick death in extremes, less common
• Chemical damage: either from air pollution or in soil, includes herbicides as in lawn fertilizers or drift, swimming pool chemicals, pesticide overuse or misuse

Slugs, snails

• large patches of foliage disappear overnight, heavy feeders, nocturnal
• leave silvery slime trails
• controls: change habitat (they prefer dark and moist, as under leaves), create more air circulation, trap with beer or boards or moist rolled paper, exclude with copper strips, repel with moth flakes or other; poison with baits

• microscopic worms, affect mainly roots but sometime stems, feed in intercellular spaces
• cause abnormal swellings, root galls (not to confuse with legume plant galls), irregular branching, deformed leaves, bud blast; not too common with perennials
• controls: nematicides, crop rotation

Weeds

Perspectives

• often defined subjectively as a plant in a place where it is not wanted, one person's weed may be another person's wildflower or even perennial
• weeds are weak in the long run, in natural succession gone in a few years, in ecological succession weeds are the first conservationists, goal same as gardener--stabilize a disturbed site
• weeds are indicators of poor or improper soil, insufficient planting to cover earth

• cultural: closer plant spacing, limit area you can keep weeded, keep annuals from reseeding
• physical: weed barriers, mulches
• mechanical: hoe, pull, whack
• biological: diseases that attack, insect feeding
• chemical: limits since many are same as perennials, pre vs post emergence, selective (eg grasses) vs broad spectrum (all green), systemic (translocated in plant, eg Roundup) vs contact (only kill part hit)

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture.University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.

Version 3.01