Evidence of plant diseases exists in fossils found from 250 million years ago. Big outspreads of plant diseases have been the reason for famines and other changes in the economy of nations throughout the history of mankind. Plant diseases can cause big losses, resulting in a reduction in income for growers and higher prices for consumers.
Fungal Diseases
Anthracnose
This disease is caused by a fungus. Infected plants will develop dark, water-soaked lesions on the stems, leaves, or the fruit. The centers of these lesions often become covered with pink masses of spores. Anthracnose can cause the death of your plants in just a few days. The spores causing Anthracnose to thrive in moist, warm weather and are spread by wind, rain, insects, and garden tools. To remove Anthracnose it is important to remove and destroy any infected plants or trees, disinfect garden tools, and keep picking up and disposing of any diseased or dead plant parts, from the plants and the ground around the plants.
Grey Mold (or Bud Rot)
Grey Mold is caused by a fungus called Botrytis. It is mostly found on plant buds in the late stage of flowering. Grey Mold is easily visible to the naked eye and action should be taken immediately since it can destroy an entire crop in just a few days. The first sign of Grey Mold infection can be seen in the color and texture of the plant when leaves appear dry and the stem becomes soft and brown. Grey Mold also presents itself as a powdery white substance that turns grey over time (and sometimes black or purple). Once Grey Mold has appeared, it is often too late to save the plant, and affected plants should be removed immediately to prevent contamination of other plants. A sanitary grow area with good airflow and drainage, low humidity, and sufficient spacing between plants will do a lot to prevent Grey Mold.
Powdery Mildew
Powdery Mildew is a fungal disease that will steal your plant’s nutrients, so the plant gets weaker and weaker. Powdery Mildew thrives in warm, dry climates, and does require fairly high humidity to spread. Once one plant is infected, the fungus spores will spread among other plants. Powdery Mildew usually starts as circular white spots and looks white and powdery. It usually covers the upper part of the leaves but can grow on the undersides as well. Younger plants are usually more susceptible. To remove Powdery Mildew it is necessary to remove the affected plant immediately and destroy it. Pruning the plant can help since it will make the air circulate better and reduce humidity.
Pests
Aphids
Aphids are small insects that suck the nutrient-rich liquid out of plants. They can weaken plants and harm flowers and fruit. These insects multiply quickly, so it is important to get them under control early. Aphids move fairly slow and controlling them is relatively easy. Aphids are nearly invisible to the naked eye and come in various colors, most species can develop wings when the population becomes overcrowded. Aphids generally feed on a wide variety of plants, but can also be specific to certain plants (such as the potato or cabbage aphids). Plant symptoms of aphid damage include stunted, misshapen or yellowing leaves, a sticky substance on leaves or stems (so-called “honeydew”), distorted or deformed flowers or fruits, gall-forming on roots and leaves, and other insects or plant viruses may appear. To remove aphids cold water can be sprayed on the leaves (the water can be mixed* with natural soap, cayenne pepper, or alcohol), plants can be dusted with flour which constipates the pests, neem oil or other organic sprays are also effective against aphids. To prevent further aphid infestation you can buy beneficial insects that eat them (such as ladybugs), catnip can be grown as a natural aphid repellent, mustard and nasturtium attract aphids and can be used to create aphids traps, garlic and chives also repel aphids. *Be cautious when mixing anything to your water and always first try out the mixture on a small part of your plants before treating the whole plant.
Red Spider Mite
The tiny red spider mites can be found on the undersides of leaves (which will look dusty) and leave bite marks on the plant. Leaves will turn yellow and webs may appear. It is very hard to get rid of these insects, so prevention may be better. Spider mites thrive in dry, hot environments, so controlling the temperature, humidity, and air circulation is a good way to prevent infestation. Lacewings and ladybugs are a natural predator and will eat the mites. Also make sure your plants have enough water, as the red spider mites prefer dry areas.
Whitefly
Whiteflies are little white flying bugs that are also known as Aleyrodidae. They are closely related to aphids. These creatures are usually found on the undersides of the leaves. Whiteflies suck the nutrient-rich plant juices and produce a sticky substance known as honeydew. This honeydew can cause fungal disease. Whiteflies can weaken plants, turn leaves pale or yellow, make leaves wilt, and stunt plant growth. Adult females can lay up to 400 eggs, making quick control of the infestation necessary. To treat a whitefly infection a watering hose can be used to blast them off the plants, natural predators, such as ladybugs and spiders will eat the insects, nasturtiums and zinnias can be planted to attract whiteflies and their natural predators, or yellow sticky paper can be used to attract whiteflies and trap them.
Other Problems
Damping Off
Damping Off is a condition caused by several different pathogens that attack, weaken or kill seeds or seedlings before or after germination. This is especially prevalent in wet and cool environments. Damping Off is a sort of reaction that your plant has to a disease. Nutrients are stopped from moving up the plant, resulting in parts of the stem becoming soft and mushy, making the young plant topple over and die. Damping Off typically starts right under the soil line. You may notice yellow or brownish discoloration of the stalks closest to the base. You may notice lesions between the nodes, which will darken into red-brown cankers. After a while, the entire stem will become soft and brown and the plant will collapse. It may first resemble an overwatering problem because of wilting. Control moisture levels of your soil and make sure you have proper drainage. You can spray your soil with a garlic oil or chamomile tea to reduce fungus in the soil. Sterilize your tools after each use. When seedlings are exhibiting signs of damping off, you probably won’t be able to save them. Try removing the parts of the plants that have been affected. The best way to avoid Damping Off is dedicating the time and effort to giving your plants a strong basis for healthy growth. High humidity levels, planting seeds too deep in the soil where there is more water and not enough oxygen for the roots. Damping Off is hard to stop, affected seedlings will almost always die. Make sure to prevent damping off. Good air circulation can help.