They bring additional infections as their honeydew secrete and also transmit viruses from one plant to another over a prolonged period.

Hosts: Aphids has a vast list of plants which it affects. Few of them are Almond, apple, cabbage, cotton, garlic, grape, lettuce, maize, mango, millet etc.

They are very small in size (0.5 mm to 2 mm) and delicate bodied insects with long legs and antennae. They are found in multiple colours like brown, yellow, red or black depending on which species they belong to. They grow underside clusters of young leaves and shoot tips. They suck out fluids from the tissues with the help of their long mouth parts to tender them. 

In late spring or early summer, their invasion slows down as their population diminishes naturally due to climate change and increase in natural enemies. Several other species carry plant viruses which can lead to the development of other forms of diseases.

Biological remedies

Few predators are there which can help in controlling the population of aphids are ladybugs, lacewings, soldier beetles and parasitoid wasps. These natural killers of aphids will take care of the sucking insects in field conditions. You can use soft insecticidal soap solution or solutions depending on plant oils in case of mild infestation. Aphids are very sensitive to fungal diseases when it is humid around them. A simple spray of water can remove them from infected plants.

Black lesions are also present on leaves. Leaves can wither and fall on severe infestation. Minute brown or black spots can appear on immature fruits. The spots are about 3 mm in diameter and are surrounded by a red tint on mature fruits. This infection reduces the quality of the produce. 

The symptoms arise are due to a group of three different fungi of alternaria. During favorable conditions, they come out of hibernation from the soil and produce spores that are carried by the rain or wind. Nutrient deficiency, high humidity, high temperatures, dew formation and sunny days are some of the important factors that are responsible for the development of alternaria. 

Some of the characteristics of alternaria can be confused with that of Botryosphaeria dothidea. Rub the leaves to tell if the late blight is caused by alternaria alternata or not.

Biological Remedies

Apply a paste of garlic on the leaves and fruits for biological control . You can also use solutions based on Bacillus subtilis which is found to be lethal to fungus. One should always start treatment against this disease before the fruits get ripened in the early summer.

Symptoms

Once water soaked-spots appear on leaves, they spread rapidly when conditions get moist and ambient temperature is around 24-28 degree celcius. These spots expands upto a point they fill the area between leaf veins completely, but do not cross each other. Occasionally, older spots dry out and tear apart, leaving a hole at its place.  On fruits, the spots appear as perfectly circular and water soaked and comparatively smaller than those on the leaves. The spots become powdery white and may crack the fruit open once the disease spreads. This contaminates fruits and causes fruit rot.

Biological Remedies

Use garlic solutions and hot water for around 30 minutes on infected seeding material. Use dehumidifiers in greenhouses to control night time humidity. It has also been found out that Pentaphage is lethal to Pseudomonas syringae, and organic copper fnngicides can slow the spread of the disease.