Plant Diseases

Disease fungi take their energy from the plants on which they live. They are responsible for a great deal of damage and are characterized by wilting, scabs, moldy coatings, rusts, blotches and rotted tissue. This page is designed to help identify some of the more common plant diseases and provides earth-friendly solutions (see organic fungicides) for combating them.

Plant disease1; Blossom End Rot

This common garden problem is often caused by a lack of calcium and/or uneven watering.

A serious disorder of tomato, pepper, cucumber and eggplant, blossom end rot is an environmental problem (not fungal) most often caused by uneven watering or by calcium deficiency. (These can be related; uneven watering can interfere with the uptake of calcium.) This common garden “disease” is often brought on by rapid growth from too much fertilizer, high salt levels or drought.

Blossom end rot symptoms occur on both green and ripe fruits and is identified by water-soaked areas that gradually widen and mature into sunken, brown, leathery spots on the bottom end. In many cases, secondary pathogens, which appear as a black, fuzzy-like growth, attack the affected area and cause complete rotting of the fruit. Blossom end rot will not spread from plant to plant.


Since this plant problem is physiological in nature, fungicides will not work as a control measure. We recommend the following:

  • Choose resistant vegetable varieties whenever possible.
  • Prevent problems by keeping soil evenly moist and by foliar spraying plants with a kelp or calcium solution.
  • Adding high levels of calcium — bone meal, oyster shell or gypsum — to the soil at planting time usually prevents this problem from developing.
  • A layer of mulch (straw, compost, grass ) will help conserve soil moisture during the hot, dry days of July and August.
  • Foliar applications of Liquid Calcium 5% (1-2 Tbsp/ gallon of water) can be used to correct or prevent deficiencies of this essential nutrient. For best results, combine with a natural surfactant to increase adhesion and spray leaves to the point of run-off.
  • Mulching plants will help conserve moisture and provide a more uniform water supply.
  • Avoid using high nitrogen fertilizers which accelerate vegetative growth and reduce the uptake of calcium by plants. A large selection of balanced organic fertilizers are available at Planet Natural.

Plant disease2; Early Blight

The plant disease is possible to control early blight using proven, organic and natural methods. Here’s how:

Common on tomato and potato plants, early blight is caused by the fungus Alternaria solani. Symptoms first appear on the lower, older leaves as small brown spots with concentric rings that form a “bull’s eye” pattern. As the disease matures, it spreads outward on the leaf surface causing it to turn yellow, wither and die. Eventually the stem, fruit and upper portion of the plant will become infected. Crops can be severely damaged.

Early blight overwinters on infected plant tissue and is spread by splashing rain, irrigation, insects and garden tools. The disease is also carried on tomato seeds and in potato tubers. In spite of its name, early blight can occur any time throughout the growing season. High temperatures (80-85˚F.) and wet, humid conditions promote its rapid spread. In many cases, poorly nourished or stressed plants are attacked.


  • Prune or stake plants to improve air circulation and reduce fungal problems.
  • Make sure to disinfect your pruning shears (one part bleach to 4 parts water) after each cut.
  • Keep the soil under plants clean and free of garden debris. Add a layer of organic compost to prevent the spores from splashing back up onto vegetation.
  • Drip irrigation and soaker hoses can be used to help keep the foliage dry.
  • For best control, apply copper-based fungicides early, two weeks before disease normally appears or when weather forecasts predict a long period of wet weather. Alternatively, begin treatment when disease first appears, and repeat every 7-10 days for as long as needed.
  • Containing copper and pyrethrins, Bonide® Garden Dust is a safe, one-step control for many insect attacks and fungal problems. For best results, cover both the tops and undersides of leaves with a thin uniform film or dust. Depending on foliage density, 10 oz will cover 625 sq ft. Repeat applications every 7-10 days, as needed.
  • SERENADE Garden is a broad spectrum, preventative bio-fungicide recommended for the control or suppression of many important plant diseases. For best results, treat prior to foliar disease development or at the first sign of infection. Repeat at 7-day intervals or as needed.
  • Remove and destroy all garden debris after harvest and practice crop rotation the following year.
  • Burn or bag infected plant parts. Do NOT compost.

Plant disease3; Downy Mildew

Learn how to identify and control downy mildew naturally — without resorting to toxic sprays!

Downy mildew (Plasmopara viticola) affects many plants and appears as yellow to white patches on the upper surfaces of older leaves. On the undersides, these areas are covered with white to grayish, cotton-like fungi. These “downy” masses are most often noticed after rain or heavy dew and disappear soon after sunny weather resumes. As the disease progresses leaves may eventually turn crisp and brown and fall off even though the plant has ample water.

Downy mildew occurs in cool, moist weather usually in early spring or late fall. Spore production is favored by temperatures cooler than 65˚F. and by relative humidities approaching 100%. This disease overwinters on plant debris and in the soil. Fungal spores can be carried by insects, wind, rain or garden tools.


The best way to prevent downy mildew is to avoid the environmental conditions that favor the disease.

  • Prune or stake plants and remove any weeds to improve air circulation.
  • Water in the early morning hours, or use a soaker hose, to give the plants time to dry out during the day.
  • Keep the ground under infected plants clean during the fall and winter to prevent the disease from spreading.
  • Remove and destroy any plants with serious infection (see Fall Garden Cleanup).
  • Choose resistant varieties whenever possible.
  • Downy mildew is comparatively easy to control on most plants when the foliage and fruit are kept protected by a copper spray. Begin treatments two weeks before disease normally appears or when weather forecasts predict a long period of wet weather. Alternatively, begin treatment when disease first appears, and repeat at 7-10 day intervals for as long as needed.
  • The systemic action moves throughout the entire plant to treat common disease problems. Mix 3/4 tsp per gallon of water and apply to foliage. Spray to run-off, as required for disease control.

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