Diseases of Horticultural Crops Shubin K. Saha D.P.M., Ph.D., Extension Vegetable Specialist Department of Horticulture University of Kentucky
A disease can be Non-infectious (abiotic) P deficiency Infectious (biotic) Pythium aphanidermatum (Edson) Fitzpatrick
Non-Infectious Often too much or too little problems Factors include- water heat fertilizer/nutrients pesticides Leaves of a pepper plant affected by a somatic mutation are an example of a non-infectious problem.
Boron deficiency-muskmelon Non-infectious
Hollow Heart - Watermelon Non-infectious
Lightening strike
Ethylene damage Notice the epinasty (down turned leaf petioles)
INFECTIOUS DISEASES Living agent Biotic (parasites)
Susceptible Host Conducive Environment Pathogen
Susceptible Host Disease Conducive Environment Pathogen
Parasites-any organism that obtains nourishment at the expense of another living organism. Plant Pathogen-biotic agents such as fungi, bacteria or viruses that cause plant disease. Plant disease-interaction between host and the environment that results in an abnormal condition.
Infectious agents include: Fungi Bacteria Virus Nematodes Higher plants
Parasitic fungi Saprophytic fungi
Examples of fungal pathogens
Damping-off Infection versus infestation-seedling above is infected soilless mix above is infested.
Greenhouse sanitation-transplant trays Used unwashed Transplant tray Used washed Transplant tray
Downy Mildew Pseudoperonospora cubensis (Berkeley & Curtis) Rostovtsev
Downy Mildew on cucumbers
Late blight of tomato (and potato)
Late blight of tomato
hyphae spores Fungus that causes late blight of tomato
mycelia White mold of tomato
bacterium
Examples of bacterial pathogens
Bacterial Wilt Cucumbers
bacterial spot of tomato
Sanitation-bacterial canker
Virus particles
Examples of viral pathogens
Aphid vector Zucchini yellow mosaic virus pumpkin
Zucchini yellow mosaic virus pumpkin
Zucchini yellow mosaic virus pumpkin
Examples of nematode pathogens
A nematode has: Digestive organs Reproductive organs Excretory structures Muscles Nerves Tough skin or Cuticle
Root knot nematode muskmelon
Examples of parasitic higher plant
Dodder muskmelon Mistletoe
Integrated Pest Management (IPM) A multi-tactic approach to mitigate a crop disorder in the most economical manner using pesticides as a last option. Examples of IPM Scouting for pests Insect thresholds Weather based disease forecasting Variety Selection (Host Resistance) Planting Densities (air movement and leaf wetness) All of the above
Calendar-based schedule: every 7 days. 8 fungicide applications per year. Weather-based disease forecaster-apply fungicides according to weather conditions. 6 fungicide applications per year.
Insect thresholds-only apply insecticides when a the number of pests/damage reaches a specific number. Corn earworm larvae on sweet corn Example-apply treatment for corn earworm when more than 10/moths caught per night.
Disease management strategies using the disease triangle
Manage the host-disease resistance Watermelon hybrids vary in host resistance to Fusarium wilt
Manage the pathogen- Sanitation Clean propagation materials quarantines Seeds may harbor plant pathogens
Manage the environment- Fall tillage Crop rotation Planting date Rotate to an agronomic crop like field corn between horticultural crops.
Questions to ask. What is the crop and production system? Plasticulture? High Tunnel? What is the size of the planting? What is the age of the crop? What are the signs/symptoms?
Questions to ask. What percentage of the planting is showing symptoms/signs? What portion of the individual plant is affected? Fruit? Foliage? Roots? Have any fungicides already been used? If so, when and what? What kind of sprayer is available and what is max pressure (PSI)?
Questions? Contact: Shubin K. Saha Shubin.saha@uky.edu 859-257-3374