Parasite

Parasites have many different ways of using host plants to survive that ultimately result in the plant's death or illness:

• Parasites can infect the fruits, roots, plant tissues, and vascular systems.
• Some insects use the grapes to hatch their eggs, when the grape breaks open it makes the cluster vulnerable to disease, rot and viruses that could affect the surrounding insect-free grapes.
• Some nematodes (or worm) parasites live in the soil and target the root systems inhibiting development and yields, resulting in irregular growth patterns across the vineyard.

Not all parasites have negative consequences for grapevines, as some are parasites to other pests, which provides protection against insects while leaving the vine unharmed. Vineyard managers must be able to determine which fungi, mildews or insects are parasitic or symbiotic and be careful not to eradicate parasites that are cooperative.

It is more difficult to eliminate parasites than pests from vineyards, as they can infest the crops sporadically and may contain viruses/diseases. One practice involves abstaining from planting new grapes for a period of time until the numbers of parasites in the soil decrease and the rootstock decomposes. Chemical intervention may include manures, fertilizer, or soil fumigation, which if applied correctly, have shown to decrease or eliminate parasites in vineyards.

Specific parasites that harm grapevines and other fruit bearing plants include:

• Aphelinid wasps
• Tachinid flies
• Trichogramma wasps
• Powdery mildew fungi
• Butterfly/moth larvae
• Roundworms
• Dagger nematodes
• Citrus nematodes
• Ring nematodes
• Root knot nematodes