Several types of pests lay red eggs on leaves, including spider mites, gouty pitch midges and others. These insects may cause damage to trees, so it is important to control them before they hatch and begin to wreak havoc. Once these tiny creatures hatch, they are much harder to control.
Southern Red Mite
The most likely culprit of red eggs on oak tree leaves is the southern red mite, or Oligonychus ilicis. These mites feed on more than 30 different species of plants, and may cause damage to leaves and herbaceous stems. The eggs of the southern red mite are very tiny, sphere shaped and a deep red or reddish-brown in colour. They hatch into red-brown nymphs that are egg-shaped. Eventually, they look similar to minute ticks. The adults lay their eggs on the underside of leaves, where the eggs stay for the winter. They may also lay darker eggs in summer. The southern red mite is most active during the milder temperatures of spring and fall, going dormant in summer and winter. Most standard insecticides won't kill mites, so you must purchase a miticide. Dicofol is the most effective miticide, however it is not widely available. Other insecticides may not be as effective, but there are several registered for use as a miticide, including acephate, dimethoate, diazinon and malathion.
Lecanium scales resemble pollen, and they are usually almost white in colour. However, the female insects are reddish brown or brown and may appear in clusters like eggs. They typically infest dogwoods, but may also infest oak and other trees. Control lecanium scales with pesticides such as Orthenex, Orthene, Sevin or malathion.
Galls are growths that develop on plants that may appear to be insect eggs. They are actually cause by enzymes given off by insects that grow within plant tissue. These galls may be caused by gall mites, gall wasps or gall midges. Unfortunately, by the time galls are noticed, it is usually too late to control infestation. Sprays may work, but they will often be ineffective until the pests emerge from the galls. Fortunately, galls are not usually damaging to the tree itself. Although the galls are unsightly, they will not cause the tree to die.
Gouty Pitch Midge
Another possibility is the gouty pitch midge, also known as Cecidomyia piniinopsis. This pest typically inhabits the Ponderosa pine, laying eggs on new shoots; however, insects will often lay their eggs on other species in desperation. It can cause severe damage.
Predatory insects are highly effective for control of pests such as spider mites. Lacewings and lady beetles both feed on spider mites, and predatory mite species such as Phytoseiulus spp. and Metaseiulus spp. are also extremely effective.
Physical Pest Removal
Since these pests are so tiny, shooting them with water will knock them off leaves. Use a water hose to spray a strong stream of water directly onto infested leaves. This technique is known as syringing. It will remove large numbers of pests from leaves, while not usually harming beneficial predatory species.