Diagnosing Plant Diseases and Pests

Diagnosing Plant Diseases and Pests Sherry Curtis

IPM System • The best way to control insects and diseases to prevent them before they get a foot hold in your garden.

Soil Preparation • Most important step in your whole gardening process. • Soil test • PH 6.5 ( for most vegetables) • Maintain adequate fertility • Till soil in Fall to expose pests • Keep garden biologically active • Compost • Aged animal manure

Plant Selection • Only plant plants suited to your climate • Use certified disease free seed • Select for maximum insect and disease resistance • Select sturdy plants with healthy root systems • Buy plants from reputable growers • Plant at proper time and temperature

Cultural Practices • Water in the morning so plants have time to dry before the evening • Space plants properly • Use mulch to reduce soil splash • Rotate crops yearly • Stay out of garden when plants are wet • Remove and dispose of diseased leaves and plants

…Continued • Stake tall plants or put in cages • Time plantings • Inspect plants for insects often • Use approved traps for slugs • Keep down weeds and grass

Biological Controls • Disease resistance plants • Biological pesticides • Mechanical Controls • Plant when soil is workable • Sanitize stakes, cages, and tools with a light bleach solution. • DO NOT use tobacco products ( Mosaic Virus)

Chemical Controls • Each pesticide has a different amount of toxicity. • Spray on calm days early in the morning. • Always read pesticide label thoroughly • Apply at recommended rate • Use pesticides as a LAST resort.

Diagnosing Plant Problems • What is the plant? • Have you sprayed the plant with anything? • Define the problem.. • Look for patterns. • Examine spread of problem • Determine likely cause • Don’t lock on to your 1st impression

Disease • Plant+Pathogen+Environment= DISEASE

Fungi • If caught in phase 1, can be washed off • If caught in phase 2, it has taken control of tissue • If caught in phase 3, take serious control

Powdery Mildew • Most successful and most common • Doesn’t kill plant • Compromises photosynthesis • Stored in roots • Starts in cool wet weather • Shows up in hot weather • Spores can travel 3,000 miles

Signs of problems • Fungi-3 dimensional, produces structures, reproduces on outside of plants, and responsible for 85% of plant diseases • Bacteria-dissolves plant cells, leaves look collapsed ( tomato bacteria can live up to 8 years in soil) • Virus- Cause slow plant growth, flower drop, spread by bugs, no known cure, systemic implant.

Plant Diseases • Fungal pathogens • Over 80,000 known • Cause circular leaf spots • Stem rot • Concentric rings • Wilt • Dis-colorization

… continued • Bacterial Pathogens • Form galls • Irregularly shaped leaf spots • Wet rots • Wilting • Yellowing and drying • Over 8,000 in US

…continued • Viral Pathogens • Inhibit chlorophyll formation • Causes mottling • Stunted growth • Distorted growth • Tip die back • Are parasitic • Usually debilitate not kill

…continued • Nematodes • Microscopic round worms • Cause disease like symptoms • Moisture loss • Wilting • Stunting • Foliar nematodes cause angular leaf spots • Return on 12 year cycle

Beneficial Insects • Everyone recognizes the familiar Ladybug, or ladybird beetle. Many species have an enormous appetite for aphids--one of our most common plant pests. Others prefer scale insects and mites and are very effective in reducing infestations.

… • Ladybug larvae are equally relentless predators. Their colorful, but ferocious appearance often causes unknowing gardeners to assume that they must be harmful. Nothing could be further from the truth.

… • The Praying Mantis is another widely-recognized insect predator. Nymphs and adults alike lie in wait for an unlucky insect which strays too close, then strike out to grab it with their modified front legs.

Ambush bugs use the same lie-in-wait tactic. Notice that their front legs are also enlarged and modified. The bright yellow colors of this species camouflage them in their favorite hideout--goldenrod flower.

The Lacewing Larvae are miniature monsters when viewed at close range. They are deadly enemies of small caterpillars, aphids, and other soft-bodied insects.

In addition to these flies, many Small Wasps are important parasites of other insects. Adult parasites range in size from very small. Most range in size from 2 to 15 mm. Larvae of most parasites develop inside the bodies of their prey, but some feed externally or pupate outside the host's body. These parasites are important in suppressing populations of many insects. They are important for control of loopers, cutworms, and aphids.

Plants that Attract Lacewings

Plants that attract Ladybugs

Pesticides • Is damage caused by a pest or could it be a cultural practice? • What kind of pest is it? • Are there non chemical ways to control it? • Is damage severe enough? • Is pesticide cost effective? • Can pest be controlled at this stage of life cycle? • Do you have the proper equipment and skill?

Which Pesticide will meet your need? • Chemical VS Biological • Choose product labeled for your plants • Never use on food crop unless directed to • Consider the site • What equipment is necessary • Minimize waste • Choose least toxic product • ALWAYS READ DIRECTIONS

Biological Pesticides • Some botanicals are broad-spectrum pesticides. • Botanicals are generally less harmful in the environment than synthetic pesticides because they degrade quickly, but they can be just as deadly to beneficials as synthetic pesticides. • The manufacture of botanicals generally results in fewer toxic by-products.

Microbial Pesticides • Insecticidal Soaps • Horticultural Oils • Diatomaceous Earth • Bacillus Thuringiensis (Bt) • toxin produced to kill caterpillars

Common Garden Pests Spider mites Aphids

… Mealy bugs Thrips

Cabbage Looper Potato Beetle

Tomato Horn Worm Squash Vine Borer

Japanese Beetle Slug

Scale Two Spotted mite

Common Diseases • Powdery Mildew • Anthracnose

Septoria Fusarium

References • www.idlab.ento.vt.edu • www.ppws.vt.edu/~clinic/

Diagnosing Plant Diseases and Pests